- Email: [email protected]
Effect of salicylic acid treatment on sensory quality, flavor-related chemicals and gene expression in peach fruit after cold storage
Postharvest Biology and Technology 161 (2020) 111089
Contents lists available at ScienceDirect
Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Effect of salicylic acid treatment on sensory quality, flavor-related chemicals and gene expression in peach fruit after cold storage
T
Can Yang, Wenyi Duan, Kaili Xie, Chuanhong Ren, Changqing Zhu, Kunsong Chen, Bo Zhang* Laboratory of Fruit Quality Biology/Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Zhejiang University, Zijingang Campus, Hangzhou 310058, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Chilling injury Esters Lactones Lipoxygenase Organic acids Sugars
Salicylic acid (SA) has been used in reducing chilling injury of horticultural crops caused by postharvest cold storage. However, effect of SA on fruit flavor quality in response to chilling need to be further investigated. In the present study, SA treated peach fruit (Prunus persica L. Batsch., cv. Hujingmilu) were stored at 0 °C for 7, 14, 21 and 28 d followed by a subsequent shelf-life at 20 °C, respectively. SA treatment (1 mM) alleviated development of flesh browning and maintained softening ability of peach fruit after cold storage. Electronic nose (e-nose) and electronic tongue (e-tongue) analysis showed separation of SA treated fruit and controls based on discriminant factor analysis (DFA) plots, particular for peaches during 3 d shelf-life after 28 d cold storage (C28dS3). Reduced content of fruity note volatile esters and lactones was observed for peach fruit with extended cold storage, SA treatment maintained significant higher volatiles than controls. Transcript levels of genes derived from volatile ester biosynthesis pathway, including lipoxygenase PpLOX1, hyperoxide lyase PpHPL1, alcohol dehydrase PpADH1 and alcohol acyltransferase PpAAT1, were analyzed using real-time quantitative PCR. For SA-treated peach fruit after cold storage, significant higher transcript levels was detected for the PpLOX1 which encodes the first enzymatic step of the pathway. Regrading to soluble sugars, high sucrose content and low content of fructose and glucose was observed for SA-treated peach fruit. Gene expression analysis revealed higher transcript abundance of sucrose synthase PpSUS4, neutral invertase PpNINV8 and tonoplastic monosaccharide transporter PpTMT2 in peach fruit treated with SA. No significant difference in contents were observed for citric acid, malic acid and quinic acid between SA-treated samples and controls. This study showed that SA treatment alleviated the cold storage-induced reduction of a number of volatiles and sugars, and thereby maintained flavor quality of peach fruit during shelf-life after cold storage.
1. Introduction Cold storage has been widely used to prolong postharvest life of horticultural crops. However, some fruit are sensitive to low temperature and develop physiological disorders with extended cold storage period. Chilling injury symptoms, flesh browning, loss of softening capacity and flavor quality, were observed for peach fruit after cold storage when transfer to shelf-life at room temperature (Lurie and Crisosto, 2005; Zhang et al., 2011; Wang et al., 2017). In general, the firmness below 10 N is a normal feature of ripening in melting peach types (Wang et al., 2017). Various postharvest treatments have been applied to reduce development of chilling injury and to maintain flavor quality of peach fruit, including different low temperature regimes (Zhang et al., 2011; Brizzolara et al., 2018), intermittent warming (Xi et al., 2012), low temperature conditioning (Wang et al., 2017), 1-
⁎
methylcyclopropene (Cai et al., 2018), nitric oxide (Zhu et al., 2010), ultrasound (Yang et al., 2012), controlled atmosphere (Sanhueza et al., 2015), melatonin (Cao et al., 2016) and methyl jasmonate (Yu et al., 2016). Salicylic acid (SA) enhanced plant tolerance to low temperature during growth (Kim et al., 2017). Moreover, SA treatment has been applied to reduce chilling induced disorders of postharvest horticultural crops, including watermelon (Yang et al., 2008), sweet basil (Damalas, 2019), strawberry (Asghari and Hasanlooe, 2015), banana (Khademi et al., 2019), winter pineapple (Lu et al., 2011) and peach fruit (Cao et al., 2010; Yang et al., 2012). For peach fruit, postharvest SA treatment increased enzyme activities such as ascorbate peroxidase and glutathione reductase, thereby improving plant antioxidant capacity and alleviating chilling injury during cold storage (Wang et al., 2006; Tareen et al., 2012; Razavi et al., 2014). Chilling-induced flavor loss was observed for postharvest fruit (Xi et al., 2012; Zhang et al., 2016),
Corresponding author. E-mail address: [email protected] (B. Zhang).
https://doi.org/10.1016/j.postharvbio.2019.111089 Received 5 August 2019; Received in revised form 9 November 2019; Accepted 3 December 2019 Available online 12 December 2019 0925-5214/ © 2019 Elsevier B.V. All rights reserved.
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
methyl salicylate treatment maintained contents of flavor-related volatiles of tomato fruit after cold storage (Wang et al., 2015). However, effect of SA on peach fruit flavor quality after postharvest cold storage remains unclear. Fruit flavor quality is determined by a complex mixture of soluble sugars, organic acids and volatiles. Soluble sugars in peach fruit are mainly consist of sucrose, glucose, fructose and sorbitol (Aubert et al., 2014). For peach fruit, sucrose accounted for approximately 40–85 % of the total soluble sugar content, followed by glucose and fructose, together representing approximately 10–25% (Cirilli et al., 2016). Content of sucrose slightly decreased during postharvest storage at room temperature (Borsani et al., 2009; Lombardo et al., 2011). For peach fruit during cold storage, content of sucrose decreased and content of reducing sugars such as glucose and fructose tended to increase (Wang et al., 2013; He et al., 2018). Significant higher content of sucrose observed in peach fruit treated with hot air and methyl jasmonate was considered to be associated with enhanced chilling tolerance during postharvest cold storage (Yu et al., 2016). The predominant organic acids in ripe peach fruit are malic acid, citric acid and quinic acid, which contribute to flavor quality and are used as substrates for respiration (Borsani et al., 2009). Content of organic acids tended to decrease during postharvest cold storage of peach fruit (Brizzolara et al., 2018; Zhou et al., 2019). Postharvest cold storage also affected one of the most important flavor quality parameters of fruit represented by the volatiles (Zhang et al., 2016; Brizzolara et al., 2018). Peach fruit with chilling injury symptom produced significant low contents of volatiles derived from fatty acid pathway, including hexyl acetate, (E)-2hexenyl acetate and (Z)-3-hexenyl acetate (Xi et al., 2012). Sensory analysis coupled with gas chromatography-mass spectrometry (GC-MS) indicated that volatile (Z)-3-hexenyl acetate was positively correlated with consumer liking (Kakiuchi and Ohmiya, 1991). Therefore, changes in contents of flavor related chemicals may be an important factor causing consumer dissatisfaction of peach fruit after cold storage. Sugar metabolism is regulated by a complex network involving various enzymes. Sucrose is cleaved to glucose and fructose by sucrose synthase (SUS) and neutral invertase (NINV) enzymes. SUS catalyzed production of reducing sugars could be reverted for sucrose biosynthesis, whereas NINV converts sucrose irreversibly into glucose and fructose (Cirilli et al., 2016). Meanwhile, sucrose phosphate synthase (SPS) plays a key role for sucrose resynthesis. Tonoplastic monosaccharide transporter (TMT) acts as sugar transporter to transport cytosolic sucrose into the vacuole (Vimolmangkang et al., 2016). Based on peach genome database and gene expression results, PpSUS4, PpNINV8, PpSPS3 and PpTMT2 were important genes associated with peach fruit sugar accumulation (Vimolmangkang et al., 2016). Volatile esters could be formed using fatty acids as precursors through lipoxygenase (LOX) pathway. LOX and hydroperoxide lyase (HPL) convert linoleic and linolenic acids to C6 aldehydes, which are further reduced to the corresponding C6 alcohols by alcohol dehydrogenase (ADH). Volatile esters are synthesized by alcohol acyltransferase (AAT), which catalyzes the final linkage of an acyl moiety and an alcohol acceptor (D’Auria, 2006). Specific gene family member, PpLOX1, PpHPL1, PpADH1 and PpAAT1, whose expression levels were associated with volatile formation and were affected by ripening and cold storage of peach fruit have been identified (Zhang et al., 2010). To link flavor quality with human perception, a full sensory analysis includes chemical determination and sensory panel evaluation. However, panel test is expensive, time consuming and somewhat subjective. Therefore, electronic nose (e-nose) and electronic tongue (etongue) technology has been developed to provide an overview of sensory properties of many fruit. E-nose has an array of nonspecific sensors that interact with volatile molecules to give unique signal patterns or fingerprints, and have been applied in blackberry, apple and peach (Baldwin et al., 2011). E-tongue is designed to mimic the taste perception mechanism in humans. The taste buds on the tongue are replaced by an array of nonspecific sensors equipped by a e-tongue. E-
tongue has been successfully applied in wine, tea, cocoa beans and fruit juice (Raithore et al., 2015). A complex set of multidimensional information generated by e-nose and e-tongue is usually simplified and classified using multivariate statistical analysis such as discriminant factorial analysis (DFA). As mentioned above, SA treatment enhanced enzyme activities of antioxidant system and delayed the development of peach fruit chilling injury caused by postharvest cold storage. Changes in contents of flavor-related chemicals and expression profiles of genes associated with sugar and volatile metabolism were analyzed in peach fruit after harvest. These results provided a frame work for us to further investigate the effect of postharvest SA treatment on changes in fruit flavor quality of peach fruit after cold storage. In the present study, an e-nose and e-tongue were applied to explore difference in flavor quality between SA-treated peach fruit and controls. Fruit quality indicators, flesh browning, firmness, contents of soluble sugars, organic acids and flavor-related volatiles, were measured during shelf-life after cold storage. Expression profiles of genes related to flavor quality formation were analyzed using real-time quantitative PCR. Together, the data support that SA treatment has a role in alleviating loss of peach fruit flavor quality caused by cold storage. 2. Materials and methods 2.1. Plant materials and sampling Melting flesh peach (Prunus persica L. Batsch., cv. Hujingmilu) fruit were harvested at commercial maturity from an orchard in Jiaxing, Zhejiang Province, China. Hujingmilu is one of the main varieties of melting peach type in south part of China. Peach fruit were transported to the laboratory on the day of harvest. Fruit were harvested at commercial maturity with an average total soluble solids concentration (SSC) concentration of 12.29 ± 0.70 % and firmness of 32.10 ± 3.58 N, and then were divided into four groups. One group was treated with 0.5 mM SA solution containing 0.1 % Triton for 10 min. The second group was treated with 1.0 mM SA solution containing 0.1 % Triton for 10 min. The third group was treated with 2.0 mM SA solution containing 0.1 % Triton for 10 min. The fourth group was soaked in tap water containing 0.1 % Triton for 10 min as control. After SA treatment, peach fruit were stored at 0 ± 0.5 °C and 85–90% relative humidity for 7, 14, 21 and 28 d, and then transferred to shelf life at 20 ± 0.5 °C for 3 d. These peach fruit samples during shelf-life after cold storage were named as C7dS3, C14dS3, C21dS3 and C28dS3, respectively. For each sampling point, three biological replicates with five fruit each were used for analysis. After measurement of firmness and internal browning index, fruit slices of mesocarp without skin from same batch of fruit were frozen in liquid nitrogen and stored at −80 °C until further chemical analysis. 2.2. Measurement of firmness and flesh browning According to Zhang et al. (2010), firmness was measured on opposite sides at the equator of each intact fruit using a texture analyzer (TA‐XT2i Plus, Stable Micro System Ltd., Surrey, UK) fitted with a 7.5‐mm‐diameter probe. The rate of penetration was 1 mm s−1 with a final penetration depth of 10 mm and data was expressed in newtons (N). The firmness value of each fruit was taken as the average value of the two vertical interfaces. Internal browning (IB) index was used to evaluate development of chilling injury according to Zhang et al. (2011). The extent of internal browning was calculated using the following formula: IB index = 100 % × Σ[(internal browning scale) × (number of fruit with that internal browning scale)]/[4 × total number of fruit evaluated]. The rating scale was 0 = 0 % flesh surface area affected, 1 = 1–25 % area affected, 2 = 26–50 % area affected, 3 = 51–70 % area affected and 4 = 76–100 % area affected. 2
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
each sample, and the clean phase was 240 s. For each sample, three biological replicates and two technical replicates were applied for enose analysis. An α-Astree II (Alpha MOS, France) e-tongue was employed to analyze taste of peach fruit. The e-tongue is composed of an automatic sampler, seven potentiometric chemical sensors (AHS, SCS, ANS, CPS, NMS, CTS, PKS), a reference electrode of Ag/AgCl, data acquisition system. The cross-sensitivity and selectivity of the sensor array contribute to the detection of most substances found in the liquid matrix, providing a global liquid and taste perception. The form of sample was homogenate and the amount was 80 mL to ensure the sensors could be fully immersed in the liquid. The measurement time was 120 s for each sample, and the sensors were rinsed for 60 s using deionized water. All the samples were detected at 20 ± 0.5 °C. For each sample, three biological replicates and there technical replicates were applied for etongue analysis.
2.3. Volatiles analysis Volatiles were collected and analyzed according to Cao et al. (2019). Frozen peach fruit (5 g) were ground and transferred to 20 mL vials containing 3 mL 200 mM ethylenediaminetetraacetic acid (EDTA) and 3 mL 20 % CaCl2. Before the vials were sealed, 30 μL of 2-octanol (0.8 g L−1) was added as an internal standard. The vials were placed in the tray of a solid-phase micro extraction (SPME) autosampler (Combi PAL, CTC Analytics, Agilent Technologies, USA), coupled to an Agilent 7890A gas chromatograph and an Agilent 5975C mass spectrometer. Volatiles were collected using fibers coated with 65 μm of polydimethylsiloxane and divinylbenzene (PDMS–DVB) (Supelco Co., Bellefonte, PA, USA). The extraction probe was desorbed at the GC-MS inlet (Agilent 7890-5975, Palo Alto, CA, USA) for 5 min and then separated by DB-WAX capillary column (30 m × 0.25 mm i.d. × 0.25 μm film thickness; J&W Scientific, Folsom, CA). The inlet temperature is 240 °C. The temperature program was increased from 40 °C to 100 °C with 0.05 °C s−1 and then to 245 °C at 0.083 °C·s−1. Helium was used as carrier gas at 0.017 mL s−1. MS ion source temperature was 230 °C, the electron energy was 70 eV, and the scanning range of mass spectrometry was from 35 to 350 mZ−1. The mass spectrometry library NIST08 (NIST/EPA/NIH, USA) and Retention Index (RI) were used for volatiles identification. Quantification of compounds was performed using the peak area of the internal standard as a reference based on total ion chromatogram (TIC).
2.6. Real-time quantitative PCR analysis Total RNA from peach samples was extracted according to Zhang et al.(2010). Genomic DNA contamination was eliminated, and 1 μg of RNA was used to obtain cDNA using an PrimeScriptTM RT reagent Kit (TaKaRa, Dalian, China). The synthesized cDNA was diluted with water (1:10), and 2 μL of diluted cDNA was used as the template for qPCR. Reactions were performed in a total volume of 20 μL, consisting of 10 μL of SYBR PCR supermix (Bio-Rad), 1 μL of each primer (10 μm), 6 μL of diethyl pyrocarbonate-water, and 2 μL of diluted cDNA on a CFX96 instrument (Bio-Rad, CA, USA). PpTEF2 was used as an internal control to normalized relative expression levels (Tong et al., 2009). Primers used for gene expression analysis were listed in Supplementary Table S1. The specificity of primers used for qPCR analysis was confirmed by product sequencing. The temperature program for qPCR was as follows: 95 °C for 3 min, 45 cycles of 95 °C for 10 s and 60 °C for 30 s, with a final melting curve step from 65 °C to 95 °C. No-template controls were included in each run. At least three different RNA isolations and cDNA syntheses were used as templates for qPCR analysis.
2.4. Sugars and organic acids analysis Sugars and organic acids content were detected according to method described by Lisec et al. (2006) with some modifications. After grounding into powder under liquid nitrogen, 0.1 g sample was extracted with 1.4 mL of methanol at 70 °C for 15 min, and then centrifuged at 11,000 g. Ribitol (10 μL, 2 g L−1) was added into each 100 μL upper phase as an internal standard. Fresh 60 μL methoxylamine hydrochloride (20 g L−1, dissolved in pyridine) was added to the mixture, and oscillated at 70 °C for 1.5 h. Then, 40 μL Bis(trimethylsilyl) tri fluoroacetamide+1 % Trimethylchlorosilane was added and incubated for 30 min. Transfer aliquot to GC-MS glass vials, and these vials were placed in the autosampler (Combi PAL, CTC Analytics, Agilent Technologies, USA). One microliter sample was injected into an Agilent 6890 N gas chromatograph (Agilent, Palo Alto, CA, USA) in split mode with the split ratio 10:1. The Agilent 6890 N was fitted with a HP5 column (30 m × 0.25 mm i.d. × 0.25 μm film thickness; J&W Scientific, Folsom, CA). The oven, inlet and detector temperatures were 100, 250 and 280 °C, respectively. The column temperature was held at 100 °C for 1 min, increased to 185 °C with a rate of 0.04 °C s-1, increased to 190 °C with a rate of 0.005 °C s-1, increased to 250 °C with a rate of 0.13 °C s-1, then increased to 280 °C with a rate of 0.083 °C s-1 and held for 3 min. Standard curves were developed to calculate contents of sugars and organic acids.
2.7. Statistical analysis A completely randomized design was used in the experiments. Standard errors (SE) were calculated by WPS 2019 (Kingsoft Office Corporation, China), and figures were made by OriginPro 9 (Microcal Software Inc., Northampton, MA, USA). DFA was carried out using AlphaSoft (Version 11.0) for electronic tongue and nose detection data. 3. Results 3.1. Effect of SA treatment on flesh browning and softening of peach fruit after cold storage To test the effect of SA treatment on chilling injury of peach fruit after cold storage, different SA concentrations were applied. Our experiments showed that 2 mM SA treatment caused development of water strains on peach fruit skin, and 0.5 mM SA had no effect on alleviating flesh browning (IB index) and maintaining fruit softening ability (Supplementary Fig. S1). Low levels of IB and normal softening capacity were observed for peach fruit treated with 1.0 mM SA. Therefore, 1 mM SA concentration was chosen as optimal for further analysis in the present study. After treatment with SA, peach fruit had significant higher content of SA than controls throughout experimental periods (Supplementary Fig. S2). IB index, one of the most visible chilling injury symptom, was not detected during 3 d of shelf-life at 20 °C after 7 d of cold storage (C7dS3, Fig. 1A), but appeared with extended cold storage period. Significant lower IB index was observed for SA-treated peach fruit when compared to controls after 21 and 28 d of storage followed by shelf-life
2.5. Electronic nose and electronic tongue analysis The volatiles produced by peach fruit were evaluated using e-nose according to Xin et al. (2018). The FOX4000 (Alpha-MOS, France) enose consists of 18 sensors belong to three sensor types. P & T sensors are metal oxide sensors based on tin dioxide (SnO2). Type T has the sensitive layer placed on a tube of aluminum, while the sensitive layer of type P is placed on a plain substrate. The LY2 sensors are metal oxide sensors based on chromium titanium oxide and on tungsten oxide (WO3). Frozen flesh tissues were ground into powder and transferred 1 g to a cold 10 mL tube containing 5 mL saturated sodium chloride solution, and then 2 mL of homogenate were transferred into a crimp-top vial. Crimp-vial were sealed and warmed in a 40 °C metal bath for 30 min. Headspace gas was injected into the e-nose and pumped into the sensors with rate of 2.5 mL s−1. The data acquisition time was 120 s for 3
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 1. Effect of postharvest SA treatment on fresh browning and softening of peach fruit after cold storage. A, changes in IB index and transcript levels of genes related to fresh browning. B, changes in fruit firmness and transcript levels of genes related to softening. Solid black square/column represents controls, empty square/column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
(C21dS3 and C28dS3, respectively). Peach fruit firmness were approximately 32 N at harvest day, and then softened to approximately 3 N during 3 d of shelf-life after 7 d of storage (C7dS3, Fig. 1B). After 14 d of storage followed by shelf-life at room temperature, significant difference in firmness was observed between SA-treated peach fruit and controls. For the firmness of SA-treated peach fruit decreased to below 10 N, a normal feature of ripening in melting peach types, in contrast to the value of around 20 N for controls after 28 d storage followed by shelf-life (C28dS3). These data showed that SA treatment was effective in alleviating the development of chilling injury while permitting normal softening ability of peach fruit after long-term cold storage. Polyphenol oxidase (PPO) and peroxidase (POD) are two major enzymes involved flesh browning (Lin et al., 2016). Transcript levels of PpPPO1 and PpPOD1 were low after 7 d of storage (C7dS3), and then increased with prolonged cold storage time (Fig. 1A). Significant lower expression were observed for PpPPO1 and PpPOD1 in SA-treated fruit than controls after 28 d of cold storage followed by shelf-life at room temperature (C28dS3), in agreement with lower IB index in SA-treated peach fruit (Fig. 1A). In addition, we analyzed expression levels of genes encoding enzymes involved in fruit softening, including polygalacturonase (PG) and pectate lyase (PL) Transcript levels of PpPG1 and PpPL1 tended to decrease for peach fruit after extended storage. Expression of PpPG1 in SA treated peach fruit was higher than that in controls at C21dS3 and C28dS3 (Fig. 1B). No significant difference in transcript levels were observed for PpPL1 between SA treated peach fruit and controls throughout the experimental period (Fig. 1B). These data indicated that PpPG1 was one of genes likely to be associated with peach fruit softening after cold storage.
3.2. Changes in sensory quality of peach fruit based on e-tongue and e-nose analysis To provide an overview of peach fruit flavor quality, e-nose and etongue were applied in the present study. DFA analysis of e-nose showed that SA-time treatments were distributed from the negative to the positive side on the discriminant factor 1 (DF1) according to days of ripening at shelf-life (Fig. 2A). After 28 d of storage and subsequent shelf-life (C28dS3), peach fruit with chilling injury symptoms were distributed on the positive side of the DF1, while fruit without chilling injury were clustered on the negative side. Peach fruit treated with SA were separated to controls from the same time point (Fig. 2A). These results suggested that volatiles are markedly changed of peach fruit treated SA followed by cold storage and subsequent shelf-life. For e-tongue data, the total explained variance rate was 94.72 % for the first two DFs, which showed that most of the information was included in the plot (Fig. 2B). Values with positive score on DF1 were found for samples from C7dS3, C14dS3 and C21dS3, while samples from C28dS3 had values with negative score on DF1. Compared to SAtreated peach fruit, separation was observed for control samples from C28dS3 (Fig. 2B). Samples from SA-treated fruit and controls were overlapped at C7dS3, C14dS3 and C21dS3.
3.3. SA affected contents of volatile esters and lactones E-nose results revealed difference in volatile profiles of peach fruit treated with SA, therefore, changes in main volatile chemicals were analyzed using GC-MS (Supplementary Table S2). Decrease in content of fruity note volatile esters were observed for peach fruit with prolonged storage time (Fig. 3A). Among the volatile esters, content of (Z)4
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 2. DFA score plot of e-nose (A) and e-tongue (B) data for peach fruit treated with SA after cold storage. C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C). For e-nose analysis, results were from three replicates with two technical replicates each. For e-tongue analysis, results were from three replicates with three technical replicates each.
3-hexenyl acetate at C28dS3 (9.71 μg kg−1) was approximately 8.5 % of peach fruit at C7dS3 (113.51 μg kg−1) (Fig. 3A). Total volatile ester content decreased by approximately 2-fold at C28dS3 relative to C7dS3. Meanwhile, significant difference in content of volatile esters was observed between SA-treated peach fruit and controls. For peach fruit treated with SA at C28dS3, content of (Z)-3-hexenyl acetate was approximately 2.3 fold-higher than controls. Similar greater amount of SA-treated samples was observed for (E)-2-hexenyl acetate during peach fruit postharvest storage. In addition to HJML peach fruit, another melting peach cultivar JX treated with SA also produced significant higher content of volatile esters during shelf-life after cold storage (Supplementary Fig. S3). Similar to changes in volatile esters, decreased contents of lactones were also observed for peach fruit with prolonged storage time (Fig. 3B). Total volatile lactone content decreased by more than 2-fold at C28dS3 relative to C7dS3. Peach fruit treated with SA had significant higher content of total volatile lactones than controls. Content of γdecalactone in SA treated fruit was approximately 2 fold-higher than controls at C28dS3 (Fig. 3B). For another lactone γ-hexalactone, significant higher contents were detected for peach fruit treated with SA throughout the experimental period. To further test the effect of SA treatment on lactones in peach fruit, another melting peach cultivar Jingxiu (JX) was used for analysis. As we expected, significant higher content of total volatile lactones was observed in SA treated JX peach fruit than controls (Supplementary Fig. S3).
3.4. SA affected transcript levels of genes related to ester formation In order to further investigate how SA affects peach fruit volatiles, changes in expression of genes derived from LOX pathway were analyzed. In agreement with decline in volatile esters during peach fruit postharvest storage (Fig. 4), transcript levels of PpLOX1 tended to decline over experimental period (Fig. 4). For peach fruit treated with SA, transcript levels of PpLOX1 were significant higher than controls during shelf-life after cold storage, being approximately 2.5–4.3 fold (Fig. 4). Transcript levels of PpHPL1 in SA-treated peach fruit were significant higher than controls at C7dS3, C14dS3 and C21dS3 (Fig. 4). Similar decreased expression pattern was also observed for PpADH1, however, no significant difference was observed for peach fruit between SA treatment and controls. A decreased expression pattern was detected for PpAAT1 throughout experimental period. Generally, PpAAT1 transcript levels were higher in peach fruit treated with SA than controls (Fig. 4). Gene expression analysis mentioned above showed that SA treated peach had significant higher transcript levels of PpLOX1 throughout the experimental period, therefore, changes in LOX enzyme activity were investigated. In agreement with decreased pattern of volatile esters and PpLOX1, LOX enzyme activity tended to decline in the present study (Supplementary Fig. S4). Moreover, significant higher LOX enzyme activity was observed for peach fruit treated with SA at C28dS3, consistent with high content of volatile esters and transcript levels of PpLOX1 (Figs.3A and 4).
5
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 3. Effect of postharvest SA treatment on contents of volatile esters, lactones. A, changes in contents of volatile esters. B, changes in contents of volatile lactones. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
Fig. 4. Effect of postharvest SA treatment on transcript levels of genes related to ester formation. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
6
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 5. Effect of postharvest SA treatment on contents of sugars and transcript levels of genes related to sugar metabolism of peach fruit after cold storage. A, changes in contents of sugars. B, changes in transcript levels of genes related to sugar metabolism. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
3.5. Effect of SA treatment on content of sugars and expression of genes related to sucrose metabolism
3.6. Effect of SA treatment on organic acid content of peach fruit after cold storage
Different location of peach fruit treated with SA was observed based on the e-tongue plot, therefore, contents of flavor-related soluble sugars were investigated. Sucrose content declined gradually during the whole experiment period, and no significant difference was observed between SA treated and control samples (Fig. 5A). In contrast to the sucrose results, content of glucose and fructose, increased with the prolonged storage time. For glucose, SA treated peach fruit produced low contents than controls, and significant lower production was observed at C28dS3 (Fig. 5A). Significant lower content of fructose were also observed for peach fruit treated with SA at C28dS3 than controls. For content of total sugars, there was no significant difference between SA treated and controls. These results indicated that great difference in sugar contents at C28dS3 may contribute to taste difference based on DFA plot using the e-tongue. To determine the effect of SA on sugar contents, we examined expression level of genes related to sugar metabolism. PpSUS4 showed a decreased expression pattern during shelf life after extended cold storage time, similar pattern was observed for PpSPS3 and PpTMT2 (Fig. 5B). For PpSPS3, transcript levels of control fruit at C28dS3 were approximately 40 % of C7dS3. In contrast, an increased expression was observed for peach fruit treated with SA. Postharvest SA-treated peach fruit had significantly higher transcript levels of PpSUS4, PpNINV8 and PpTMT2 than controls at C21dS3 and 28dS3, while no significant difference was observed for PpSPS3 (Fig. 5B). These results indicated that SA treatment affected expression genes related to sugar metabolism during peach fruit shelf-life after cold storage.
Sensory difference observed by the e-tongue prompted us to further test changes in organic acids caused by SA treatment. Citric acid, malic acid and quinic acid were major organic acids of peach fruit. Content of citric acid tended to decrease with extended storage time, while malic acid and quinic acid maintained constant (Fig. 6). No significant difference in content of organic acids were observed between SA treated peach fruit and controls throughout the experiment period. Therefore, expression of genes associated with organic acid metabolism was not performed. 4. Discussion Dissatisfaction with fruit flavor has existed for decades, and postharvest cold storage can negatively impact flavor quality (Zhang et al., 2011; Xi et al., 2012; Zhang et al., 2016; Meethaworn et al., 2019). Although SA treatment could reduce oxidative stress and alleviate chilling injury of peach fruit during cold storage, the effect of SA on flavor quality after storage need to be investigated. In the present study, we showed that postharvest SA treatment could reduce internal browning, maintain fruit softening ability and alleviate chilling injury. These results were consistent with previous studies on other horticultural crops, including sweet basil (Damalas, 2019), strawberry (Asghari and Hasanlooe, 2015), banana (Khademi et al., 2019), winter pineapple (Lu et al., 2011) and peach fruit (Cao et al., 2010; Yang et al., 2012). SA has been shown to stimulate activities of pectinase and cellulase that are related to cell wall degradation in pathogen systems (Wu et al., 2008). Our present study indicated that SA treated peach fruit had higher transcript levels of PpPG1, which may contribute to 7
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 6. Effect of postharvest SA treatment on peach fruit organic acids after cold storage. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (* P < 0.05 and ** P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
suggested that the first enzymatic step of the ester biosynthetic pathway, PpLOX1, is an important transcriptional point for volatile ester production in SA-treated peach fruit after cold storage. Similar to difference observed from e-nose data, e-tongue results also showed different flavor quality of SA-treated peach fruit at C28dS3 when compare to controls having severe chilling injury. Sugars and acids belong to non-volatile chemicals that affect fruit flavor quality, therefore, we measured the sugar contents to clarify the results of etongue. In the preset study, there was no significant difference either for total sugars or for total acids between SA treated peach fruit and controls after cold storage. However, significant difference was observed for contents of individual sugar, not for individual acids. These results suggested that changes in sugar profile contribute to flavor quality difference of peach fruit caused by SA treatment after cold storage. SA treated peach fruit had marked higher sucrose contents than controls after cold storage, accompanying with significant lower contents of glucose and fructose. In agreement with previous study in ripening peach fruit (Borsani et al., 2009), degradation of sucrose and increase of glucose and fructose were also observed in peach fruit during shelf-life after cold storage. Changes in metabolites of peach fruit after cold storage were analyzed, where higher contents of sucrose were observed for chilling injury resistant peach cultivar Elegant Lady after 21 d cold storage followed by shelf-life at 20 °C (Bustamante et al., 2016). Compared to other two cultivars, peach fruit Red Haven had a marked lower incidence of chilling injury, representing with higher levels of sucrose during shelf-life after cold storage (Brizzolara et al., 2016). These results suggested that changes in contents of sucrose, glucose and fructose contributed to taste quality difference of peach fruit after cold storage. Besides to be involved in taste quality, soluble sugars also played important roles in response to chilling during cold storage (Wang et al., 2019; Yu et al., 2016). Negative correlation was observed between content of sucrose and development of chilling injury of peach fruit during cold storage, indicating that sucrose metabolism was associated with cold tolerance (Wang et al., 2013; He et al., 2018). In the present study, we also observed a reversed pattern between sucrose content and IB index, where peach fruit sucrose tended to decline with extended cold storage time, accompanying with the development of chilling injury. Genes related to sucrose accumulation have been identified in peach fruit, where PpSUS4, PpNINV8, PpSPS3 and PpTMT2 were mainly expressed in mature fruit (Vimolmangkang et al., 2016). Transcript levels
maintain softening ability after cold storage. Previous study in tomato fruit showed that methyl salicylate (MeSA) treatment alleviated chilling induced loss of key aroma volatiles such as geranial and geranylacetone (Wang et al., 2015). In the present study, the DFA plot based on e-nose analysis showed sensory difference of peach fruit treated with SA. Difference in volatile profiles was then revealed by GC-MS analysis. Our dataset in peach fruit showed that SA treatment maintained significant higher contents of fruity note volatile esters than controls during shelf-life after cold storage. These fruity esters are mainly consisted of (E)-2-hexenyl acetate, (Z)-3-hexenyl acetate and hexyl acetate, which are positively correlated with consumer liking and are biosynthesized from the LOX-mediated fatty acid oxidation pathway (Kakiuchi and Ohmiya, 1991; Zhang et al., 2010). Besides the volatile esters, the lactones are characteristic components of peach aroma. Their trend in this experiment is interesting, especially after 21 and 28 d storage, where SA treated fruit show a good retention in comparison to control ones. To study the effects of SA on maintaining volatile ester levels, expression of genes derived from the LOX pathway were analyzed during shelf-life after cold storage. Similar to our previous studies (Zhang et al., 2011), decreased expression patterns were observed for PpLOX1, PpHPL1, PpADH1 and PpAAT1 with extended cold storage time. Although there was no chilling injury at C7dS3 (three days at shelf-life after seven days of cold storage), peach fruit treated with SA produced significant higher content of volatile esters, accompanying greater amount of PpLOX1, PpHPL1 and PpAAT1 transcripts. When chilling injury was developed at C28dS3, significant higher volatile ester levels were observed, accompanying with significant higher expression level of PpLOX1. There was no significant difference in transcript levels of PpAAT1 between SA-treated fruit and controls at C28dS3. These results showed that higher emission of volatile esters by SA-treated samples was concomitant with higher levels of PpLOX1 transcript. For apple fruit after cold storage under ultra-low oxygen storage, LOX was suggested to be a key control point for successful recovery of fruit ability for volatile ester production (Altisent et al., 2009), the importance of LOX and HPL in volatile ester production could also been found in banana fruit (Zhu et al., 2018). In the present study, significant higher LOX activity were observed in SA-treated peach fruit than controls at C28dS3. Similar results were also reported for pear fruit, where decreased LOX activity possibly leading to shortage of lipid precursors for volatile ester production (Lara et al., 2003). Results mentioned above 8
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
of two sucrose-cleaving enzyme genes, PpSUS4 and PpNINV8, were significant higher in SA treated peach fruit at C28dS3 than controls. As a vacuolar monosaccharide importer, TMT could transport sucrose and is responsible for sucrose accumulation (Jung et al., 2015). Similar to high content of sucrose in SA treated peach fruit after cold storage, significant higher transcript levels of PpTMT2 was also observed in fruit treated with SA. For transcript levels of PpSPS3 associated with sucrose resynthesis, no significant difference was observed between SA treated fruit and controls. It has been reported that regulation of sucrose metabolism is complex for postharvest peach fruit (Yu et al., 2016; He et al., 2018). In the present study, our results suggested that sucrose metabolism and accumulation were possibly related to the coordinate interaction between PpSUS4/PpNINV8 and PpTMT2, although further studies are required in future. Transcript levels of gene family members encoding for enzymes involved in sucrose metabolism could be analyzed using RNA-sequencing to screen candidate genes for further function analysis. Therefore, mechanism for sugar metabolism need to be further investigated in peach fruit during shelf-life after cold storage.
Borsani, J., Budde, C.O., Porrini, L., Lauxmann, M.A., Lombardo, V.A., Murray, R., Andreo, C.S., Drincovich, M.F., Lara, M.V., 2009. Carbon metabolism of peach fruit after harvest: changes in enzymes involved in organic acid and sugar level modifications. J. Exp. Bot. 60, 1823–1837. https://doi.org/10.1093/jxb/erp055. Brizzolara, S., Hertog, M., Tosetti, R., Nicolai, B., Tonutti, P., 2018. Metabolic responses to low temperature of three peach fruit cultivars differently sensitive to cold storage. Front. Plant Sci. 9, 706. https://doi.org/10.3389/fpls.2018.00706. Bustamante, C.A., Monti, L.L., Gabilondo, J., Scossa, F., Valentini, G., Budde, C.O., Lara, M.V., Fernie, A.R., Drincovich, M.F., 2016. Differential metabolic rearrangements after cold storage are correlated with chilling injury resistance of peach fruits. Front. Plant Sci. 7, 1478. https://doi.org/10.3389/fpls.2016.01478. Cai, H., An, X., Han, S., Jiang, L., Yu, M., Ma, R., Yu, Z., 2018. Effect of 1-MCP on the production of volatiles and biosynthesis-related gene expression in peach fruit during cold storage. Postharvest Biol. Technol. 141, 50–57. https://doi.org/10.1016/j. postharvbio.2018.03.003. Cao, S., Hu, Z., Zheng, Y., Lu, B., 2010. Synergistic effect of heat treatment and salicylic acid on alleviating internal browning in cold-stored peach fruit. Postharvest Biol. Technol. 58, 93–97. https://doi.org/10.1016/j.postharvbio.2010.05.010. Cao, S., Song, C., Shao, J., Bian, K., Chen, W., Yang, Z., 2016. Exogenous melatonin treatment increases chilling tolerance and induces defense response in harvested peach fruit during cold storage. J. Agric. Food Chem. 64, 5215–5222. https://doi. org/10.1021/acs.jafc.6b01118. Cao, X., Xie, K., Duan, W., Zhu, Y., Liu, M., Chen, K., Klee, H.J., Zhang, B., 2019. Peach carboxylesterase PpCXE1 is associated with catabolism of volatile esters. J. Agric. Food Chem. 67, 5189–5196. https://doi.org/10.1021/acs.jafc.9b01166. Cirilli, M., Bassi, D., Ciacciulli, A., 2016. Sugars in peach fruit: a breeding perspective. Hortic. Res. 3, 15067. https://doi.org/10.1038/hortres.2015.67. Damalas, C.A., 2019. Improving drought tolerance in sweet basil (Ocimum basilicum) with salicylic acid. Sci. Hortic. 246, 360–365. https://doi.org/10.1016/j.scienta.2018.11. 005. D’Auria, J.C., 2006. Acyltransferases in plants: a good time to be BAHD. Curr. Opin. Plant Biol. 9, 331–340. https://doi.org/10.1016/j.pbi.2006.03.016. He, X., Wei, Y., Kou, J., Xu, F., Chen, Z., Shao, X., 2018. PpVIN2, an acid invertase gene family member, is sensitive to chilling temperature and affects sucrose metabolism in postharvest peach fruit. Plant Growth Regul. 86, 169–180. https://doi.org/10.1007/ s10725-018-0419-z. Jung, B., Ludewig, F., Schulz, A., Meissner, G., Wostefeld, N., Flugge, U.I., Pommerrenig, B., Wirsching, P., Sauer, N., Koch, W., Sommer, F., Muhlhaus, T., Schroda, M., Cuin, T.A., Graus, D., Marten, I., Hedrich, R., Neuhaus, H.E., 2015. Identification of the transporter responsible for sucrose accumulation in sugar beet taproots. Nat. Plants 1, 14001. https://doi.org/10.1038/nplants.2014.1. Kakiuchi, N., Ohmiya, A., 1991. Changes in the composition and content of volatile constituents in peach fruits in relation to maturity at harvest and artificial ripening. Journal of the Japanese Society for Horticultural Science 60, 209–216. https://doi. org/10.2503/jjshs.60.209. Khademi, O., Ashtari, M., Razavi, F., 2019. Effects of salicylic acid and ultrasound treatments on chilling injury control and quality preservation in banana fruit during cold storage. Sci. Hortic. 249, 334–339. https://doi.org/10.1016/j.scienta.2019.02. 018. Kim, Y.S., An, C., Park, S., Gilmour, S.J., Wang, L., Renna, L., Brandizzi, F., Grumet, R., Thomashow, M.F., 2017. CAMTA-mediated regulation of salicylic acid immunity pathway genes in Arabidopsis exposed to low temperature and pathogen infection. Plant Cell 29, 2465–2477. https://doi.org/10.1105/tpc.16.00865. Lara, I., Miró, R.M., Fuentes, T., Sayez, G., Graell, J., López, M.L., 2003. Biosynthesis of volatile aroma compounds in pear fruit stored under long-term controlled-atmosphere conditions. Postharvest Biol. Technol. 29, 29–39. https://doi.org/10.1016/j. plantsci.2014.04.014. Lin, Y., Lin, H., Lin, Y., Zhang, S., Chen, Y., Jiang, X., 2016. The roles of metabolism of membrane lipids and phenolics in hydrogen peroxide-induced pericarp browning of harvested longan fruit. Postharvest Biol. Technol. 111, 53–61. https://doi.org/10. 1016/j.postharvbio.2015.07.030. Lisec, J., Schauer, N., Kopka, J., Willmitzer, L., Fernie, A.R., 2006. Gas chromatography mass spectrometry-based metabolite profiling in plants. Nat. Protoc. 1, 387–396. https://doi.org/10.1038/nprot.2006.59. Lombardo, V.A., Osorio, S., Borsani, J., Lauxmann, M.A., Bustamante, C.A., Budde, C.O., Andreo, C.S., Lara, M.V., Fernie, A.R., Drincovich, M.F., 2011. Metabolic profiling during peach fruit development and ripening reveals the metabolic networks that underpin each developmental stage. Plant Physiol. 157, 1696–1710. https://doi.org/ 10.1104/pp.111.186064. Lu, X., Sun, D., Li, Y., Shi, W., Sun, G., 2011. Pre- and post-harvest salicylic acid treatments alleviate internal browning and maintain quality of winter pineapple fruit. Sci. Hortic. 130, 97–101. https://doi.org/10.1016/j.scienta.2011.06.017. Lurie, S., Crisosto, C.H., 2005. Chilling injury in peach and nectarine. Postharvest Biol. Technol. 37, 195–208. https://doi.org/10.1016/j.postharvbio.2005.04.012. Meethaworn, K., Luckanatinwong, V., Zhang, B., Chen, K., Siriphanich, J., 2019. Offflavor caused by cold storage is related to induced activity of LOX and HPL in young coconut fruit. LWT - Food Sci. Technol. 114, 108329. https://doi.org/10.1016/j.lwt. 2019.108329. Raithore, S., Bai, J., Plotto, A., Manthey, J., Irey, M., Baldwin, E., 2015. Electronic tongue response to chemicals in orange juice that change concentration in relation to harvest maturity and citrus greening or huanglongbing (HLB) disease. Sensors Basel (Basel) 15, 30062–30075. https://doi.org/10.3390/s151229787. Razavi, F., Hajilou, J., Dehgan, G., Nagshi, R., Turchi, M., 2014. Enhancement of postharvest quality of peach fruit by salicylic acid treatment. Int. J. Biosci. 4, 177–184. https://doi.org/10.12692/ijb/4.1.177-184. Sanhueza, D., Vizoso, P., Balic, I., Campos-Vargas, R., Meneses, C., 2015. Transcriptomic
5. Conclusion In conclusion, our results showed that SA treatment alleviated the development of chilling injury and maintained flavor quality of peach fruit during shelf-life after cold storage. Peach fruit treated with SA had lower flesh browning than controls, and maintained fruit softening capacity with lower firmness. Difference in flavor quality between SAtreated samples and controls could be recognized by the e-tongue and enose. Significant difference were observed for content of a number of fruity note volatile esters, lactones and soluble sugars in peach fruit treated with SA when compared to controls, but not for content of organic acids. The first enzymatic step of the ester biosynthetic pathway, PpLOX1, is an important transcriptional point for volatile ester production in SA-treated peach fruit after cold storage. Declaration of Competing Interest The authors declare no conflict of interest. Acknowledgements This research was supported by National Key R&D Program of China (2016YFD0400101), the National Natural Science Foundation of China (31672100), Fundamental Research Funds for the Central Universities (2019FZA6010) and Zhejiang Provincial Science and Technology Project (2016C04001). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.postharvbio.2019. 111089. References Altisent, R., Echeverria, G., Graell, J., Lopez, L., Lara, I., 2009. Lipoxygenase activity is involved in the regeneration of volatile ester-synthesizing capacity after ultra-low oxygen storage of’ Fuji’ apple. J. Agric. Food Chem. 57, 4305–4312. https://doi.org/ 10.1021/jf803930j. Asghari, M., Hasanlooe, A.R., 2015. Interaction effects of salicylic acid and methyl jasmonate on total antioxidant content, catalase and peroxidase enzymes activity in “Sabrosa” strawberry fruit during storage. Sci. Hortic. 197, 490–495. https://doi.org/ 10.1016/j.scienta.2015.10.009. Aubert, C., Bony, P., Chalot, G., Landry, P., Lurol, S., 2014. Effects of storage temperature, storage duration, and subsequent ripening on the physicochemical characteristics, volatile compounds, and phytochemicals of Western Red nectarine (Prunus persica L. Batsch). J. Agric. Food Chem. 62, 4707–4724. https://doi.org/10.1021/jf4057555. Baldwin, E.A., Bai, J., Plotto, A., Dea, S., 2011. Electronic noses and tongues: applications for the food and pharmaceutical industries. Sensors Basel (Basel) 11, 4744–4766. https://doi.org/10.3390/s110504744.
9
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
postharvbio.2012.07.003. Xin, R., Liu, X., Wei, C., Yang, C., Liu, H., Cao, X., Wu, D., Zhang, B., Chen, K., 2018. ENose and GC-MS reveal a difference in the volatile profiles of white-and red-fleshed peach fruit. Sensors 18, 765. https://doi.org/10.3390/s18030765. Yang, J., Gao, Y., Li, Y., Qi, X., Zhang, M., 2008. Salicylic acid-induced enhancement of cold tolerance through activation of antioxidative capacity in watermelon. Sci. Hortic. 118, 200–205. https://doi.org/10.1016/j.scienta.2008.06.015. Yang, Z., Cao, S., Zheng, Y., Jiang, Y., 2012. Combined salicylic acid and ultrasound treatments for reducing the chilling injury on peach fruit. J. Agric. Food Chem. 60, 1209–1212. https://doi.org/10.1021/jf2041164. Yu, L., Liu, H., Shao, X., Yu, F., Wei, Y., Ni, Z., Xu, F., Wang, H., 2016. Effects of hot air and methyl jasmonate treatment on the metabolism of soluble sugars in peach fruit during cold storage. Postharvest Biol. Technol. 113, 8–16. https://doi.org/10.1016/j. postharvbio.2015.10.013. Zhang, B., Shen, J., Wei, W., Xi, W., Xu, C., Ferguson, I., Chen, K., 2010. Expression of genes associated with aroma formation derived from the fatty acid pathway during peach fruit ripening. J. Agric. Food Chem. 58, 6157–6165. https://doi.org/10.1021/ jf100172e. Zhang, B., Tieman, D.M., Jiao, C., Xu, Y., Chen, K., Fei, Z., Giovannoni, J.J., Klee, H.J., 2016. Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation. Proc. Natl. Acad. Sci. 113, 12580–12585. https://doi.org/10.1073/pnas.1613910113. Zhang, B., Xi, W., Wei, W., Shen, J., Ferguson, I., Chen, K., 2011. Changes in aromarelated volatiles and gene expression during low temperature storage and subsequent shelf-life of peach fruit. Postharvest Biol. Technol. 60, 7–16. https://doi.org/10. 1016/j.postharvbio.2010.09.012. Zhou, D., Chen, S., Xu, R., Tu, S., Tu, K., 2019. Interactions among chilling tolerance, sucrose degradation and organic acid metabolism in UV-C-irradiated peach fruit during postharvest cold storage. Acta Physiol. Plant. 41, 79. https://doi.org/10. 1007/s11738-019-2871-4. Zhu, L., Zhou, J., Zhu, S., 2010. Effect of a combination of nitric oxide treatment and intermittent warming on prevention of chilling injury of ‘Feicheng’ peach fruit during storage. Food Chem. 121, 165–170. https://doi.org/10.1016/j.foodchem.2009.12. 025. Zhu, X., Luo, J., Li, Q., Li, J., Liu, T., Wang, R., Chen, W., Li, X., 2018. Low temperature storage reduces aroma-related volatiles production during shelf-life of banana fruit mainly by regulating key genes involved in volatile biosynthetic pathways. Postharvest Biol. Technol. 146, 68–78. https://doi.org/10.1016/j.postharvbio.2018. 08.015.
analysis of fruit stored under cold conditions using controlled atmosphere in Prunus persica cv. “Red Pearl”. Front. Plant Sci. 6, 788. https://doi.org/10.3389/fpls.2015. 00788. Tareen, M.J., Abbasi, N.A., Hafiz, I.A., 2012. Postharvest application of salicylic acid enhanced antioxidant enzyme activity and maintained quality of peach cv. ‘Flordaking’ fruit during storage. Sci. Hortic. 142, 221–228. https://doi.org/10.1016/ j.scienta.2012.04.027. Tong, Z., Gao, Z., Wang, F., Zhou, J., Zhang, Z., 2009. Selection of reliable reference genes for gene expression studies in peach using real-time PCR. BMC Mol. Biol. 10, 71. https://doi.org/10.1186/1471-2199-10-71. Vimolmangkang, S., Zheng, H., Peng, Q., Jiang, Q., Wang, H., Fang, T., Liao, L., Wang, L., He, H., Han, Y., 2016. Assessment of sugar components and genes involved in the regulation of sucrose accumulation in peach fruit. J. Agric. Food Chem. 64, 6723–6729. https://doi.org/10.1021/acs.jafc.6b02159. Wang, K., Shao, X., Gong, Y., Zhu, Y., Wang, H., Zhang, X., Yu, D., Yu, F., Qiu, Z., Lu, H., 2013. The metabolism of soluble carbohydrates related to chilling injury in peach fruit exposed to cold stress. Postharvest Biol. Technol. 86, 53–61. https://doi.org/10. 1016/j.postharvbio.2013.06.020. Wang, K., Yin, X.R., Zhang, B., Grierson, D., Xu, C.J., Chen, K.S., 2017. Transcriptomic and metabolic analyses provide new insights into chilling injury in peach fruit. Plant Cell Environ. 40, 1531–1551. https://doi.org/10.1111/pce.12951. Wang, L., Baldwin, E.A., Plotto, A., Luo, W., Raithore, S., Yu, Z., Bai, J., 2015. Effect of methyl salicylate and methyl jasmonate pre-treatment on the volatile profile in tomato fruit subjected to chilling temperature. Postharvest Biol. Technol. 108, 28–38. https://doi.org/10.1016/j.postharvbio.2015.05.005. Wang, L., Chen, S., Kong, W., Li, S., Archbold, D.D., 2006. Salicylic acid pretreatment alleviates chilling injury and affects the antioxidant system and heat shock proteins of peaches during cold storage. Postharvest Biol. Technol. 41, 244–251. https://doi.org/ 10.1016/j.postharvbio.2006.04.010. Wang, L., Shan, T., Xie, B., Ling, C., Shao, S., Jin, P., Zheng, Y., 2019. Glycine betaine reduces chilling injury in peach fruit by enhancing phenolic and sugar metabolisms. Food Chem. 272, 530–538. https://doi.org/10.1016/j.foodchem.2018.08.085. Wu, H.S., Raza, W., Fan, J.Q., Sun, Y.G., Bao, W., Liu, D.Y., Huang, Q.W., Mao, Z.S., Shen, Q.R., Miao, W.G., 2008. Antibiotic effect of exogenously applied salicylic acid on in vitro soilborne pathogen, Fusarium oxysporum f.sp.nIveum. Chemosphere 74, 45–50. https://doi.org/10.1016/j.chemosphere.2008.09.027. Xi, W., Zhang, B., Shen, J., Sun, C., Xu, C., Chen, K., 2012. Intermittent warming alleviated the loss of peach fruit aroma-related esters by regulation of AAT during cold storage. Postharvest Biol. Technol. 74, 42–48. https://doi.org/10.1016/j.
10
Contents lists available at ScienceDirect
Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
Effect of salicylic acid treatment on sensory quality, flavor-related chemicals and gene expression in peach fruit after cold storage
T
Can Yang, Wenyi Duan, Kaili Xie, Chuanhong Ren, Changqing Zhu, Kunsong Chen, Bo Zhang* Laboratory of Fruit Quality Biology/Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Zhejiang University, Zijingang Campus, Hangzhou 310058, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Chilling injury Esters Lactones Lipoxygenase Organic acids Sugars
Salicylic acid (SA) has been used in reducing chilling injury of horticultural crops caused by postharvest cold storage. However, effect of SA on fruit flavor quality in response to chilling need to be further investigated. In the present study, SA treated peach fruit (Prunus persica L. Batsch., cv. Hujingmilu) were stored at 0 °C for 7, 14, 21 and 28 d followed by a subsequent shelf-life at 20 °C, respectively. SA treatment (1 mM) alleviated development of flesh browning and maintained softening ability of peach fruit after cold storage. Electronic nose (e-nose) and electronic tongue (e-tongue) analysis showed separation of SA treated fruit and controls based on discriminant factor analysis (DFA) plots, particular for peaches during 3 d shelf-life after 28 d cold storage (C28dS3). Reduced content of fruity note volatile esters and lactones was observed for peach fruit with extended cold storage, SA treatment maintained significant higher volatiles than controls. Transcript levels of genes derived from volatile ester biosynthesis pathway, including lipoxygenase PpLOX1, hyperoxide lyase PpHPL1, alcohol dehydrase PpADH1 and alcohol acyltransferase PpAAT1, were analyzed using real-time quantitative PCR. For SA-treated peach fruit after cold storage, significant higher transcript levels was detected for the PpLOX1 which encodes the first enzymatic step of the pathway. Regrading to soluble sugars, high sucrose content and low content of fructose and glucose was observed for SA-treated peach fruit. Gene expression analysis revealed higher transcript abundance of sucrose synthase PpSUS4, neutral invertase PpNINV8 and tonoplastic monosaccharide transporter PpTMT2 in peach fruit treated with SA. No significant difference in contents were observed for citric acid, malic acid and quinic acid between SA-treated samples and controls. This study showed that SA treatment alleviated the cold storage-induced reduction of a number of volatiles and sugars, and thereby maintained flavor quality of peach fruit during shelf-life after cold storage.
1. Introduction Cold storage has been widely used to prolong postharvest life of horticultural crops. However, some fruit are sensitive to low temperature and develop physiological disorders with extended cold storage period. Chilling injury symptoms, flesh browning, loss of softening capacity and flavor quality, were observed for peach fruit after cold storage when transfer to shelf-life at room temperature (Lurie and Crisosto, 2005; Zhang et al., 2011; Wang et al., 2017). In general, the firmness below 10 N is a normal feature of ripening in melting peach types (Wang et al., 2017). Various postharvest treatments have been applied to reduce development of chilling injury and to maintain flavor quality of peach fruit, including different low temperature regimes (Zhang et al., 2011; Brizzolara et al., 2018), intermittent warming (Xi et al., 2012), low temperature conditioning (Wang et al., 2017), 1-
⁎
methylcyclopropene (Cai et al., 2018), nitric oxide (Zhu et al., 2010), ultrasound (Yang et al., 2012), controlled atmosphere (Sanhueza et al., 2015), melatonin (Cao et al., 2016) and methyl jasmonate (Yu et al., 2016). Salicylic acid (SA) enhanced plant tolerance to low temperature during growth (Kim et al., 2017). Moreover, SA treatment has been applied to reduce chilling induced disorders of postharvest horticultural crops, including watermelon (Yang et al., 2008), sweet basil (Damalas, 2019), strawberry (Asghari and Hasanlooe, 2015), banana (Khademi et al., 2019), winter pineapple (Lu et al., 2011) and peach fruit (Cao et al., 2010; Yang et al., 2012). For peach fruit, postharvest SA treatment increased enzyme activities such as ascorbate peroxidase and glutathione reductase, thereby improving plant antioxidant capacity and alleviating chilling injury during cold storage (Wang et al., 2006; Tareen et al., 2012; Razavi et al., 2014). Chilling-induced flavor loss was observed for postharvest fruit (Xi et al., 2012; Zhang et al., 2016),
Corresponding author. E-mail address: [email protected] (B. Zhang).
https://doi.org/10.1016/j.postharvbio.2019.111089 Received 5 August 2019; Received in revised form 9 November 2019; Accepted 3 December 2019 Available online 12 December 2019 0925-5214/ © 2019 Elsevier B.V. All rights reserved.
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
methyl salicylate treatment maintained contents of flavor-related volatiles of tomato fruit after cold storage (Wang et al., 2015). However, effect of SA on peach fruit flavor quality after postharvest cold storage remains unclear. Fruit flavor quality is determined by a complex mixture of soluble sugars, organic acids and volatiles. Soluble sugars in peach fruit are mainly consist of sucrose, glucose, fructose and sorbitol (Aubert et al., 2014). For peach fruit, sucrose accounted for approximately 40–85 % of the total soluble sugar content, followed by glucose and fructose, together representing approximately 10–25% (Cirilli et al., 2016). Content of sucrose slightly decreased during postharvest storage at room temperature (Borsani et al., 2009; Lombardo et al., 2011). For peach fruit during cold storage, content of sucrose decreased and content of reducing sugars such as glucose and fructose tended to increase (Wang et al., 2013; He et al., 2018). Significant higher content of sucrose observed in peach fruit treated with hot air and methyl jasmonate was considered to be associated with enhanced chilling tolerance during postharvest cold storage (Yu et al., 2016). The predominant organic acids in ripe peach fruit are malic acid, citric acid and quinic acid, which contribute to flavor quality and are used as substrates for respiration (Borsani et al., 2009). Content of organic acids tended to decrease during postharvest cold storage of peach fruit (Brizzolara et al., 2018; Zhou et al., 2019). Postharvest cold storage also affected one of the most important flavor quality parameters of fruit represented by the volatiles (Zhang et al., 2016; Brizzolara et al., 2018). Peach fruit with chilling injury symptom produced significant low contents of volatiles derived from fatty acid pathway, including hexyl acetate, (E)-2hexenyl acetate and (Z)-3-hexenyl acetate (Xi et al., 2012). Sensory analysis coupled with gas chromatography-mass spectrometry (GC-MS) indicated that volatile (Z)-3-hexenyl acetate was positively correlated with consumer liking (Kakiuchi and Ohmiya, 1991). Therefore, changes in contents of flavor related chemicals may be an important factor causing consumer dissatisfaction of peach fruit after cold storage. Sugar metabolism is regulated by a complex network involving various enzymes. Sucrose is cleaved to glucose and fructose by sucrose synthase (SUS) and neutral invertase (NINV) enzymes. SUS catalyzed production of reducing sugars could be reverted for sucrose biosynthesis, whereas NINV converts sucrose irreversibly into glucose and fructose (Cirilli et al., 2016). Meanwhile, sucrose phosphate synthase (SPS) plays a key role for sucrose resynthesis. Tonoplastic monosaccharide transporter (TMT) acts as sugar transporter to transport cytosolic sucrose into the vacuole (Vimolmangkang et al., 2016). Based on peach genome database and gene expression results, PpSUS4, PpNINV8, PpSPS3 and PpTMT2 were important genes associated with peach fruit sugar accumulation (Vimolmangkang et al., 2016). Volatile esters could be formed using fatty acids as precursors through lipoxygenase (LOX) pathway. LOX and hydroperoxide lyase (HPL) convert linoleic and linolenic acids to C6 aldehydes, which are further reduced to the corresponding C6 alcohols by alcohol dehydrogenase (ADH). Volatile esters are synthesized by alcohol acyltransferase (AAT), which catalyzes the final linkage of an acyl moiety and an alcohol acceptor (D’Auria, 2006). Specific gene family member, PpLOX1, PpHPL1, PpADH1 and PpAAT1, whose expression levels were associated with volatile formation and were affected by ripening and cold storage of peach fruit have been identified (Zhang et al., 2010). To link flavor quality with human perception, a full sensory analysis includes chemical determination and sensory panel evaluation. However, panel test is expensive, time consuming and somewhat subjective. Therefore, electronic nose (e-nose) and electronic tongue (etongue) technology has been developed to provide an overview of sensory properties of many fruit. E-nose has an array of nonspecific sensors that interact with volatile molecules to give unique signal patterns or fingerprints, and have been applied in blackberry, apple and peach (Baldwin et al., 2011). E-tongue is designed to mimic the taste perception mechanism in humans. The taste buds on the tongue are replaced by an array of nonspecific sensors equipped by a e-tongue. E-
tongue has been successfully applied in wine, tea, cocoa beans and fruit juice (Raithore et al., 2015). A complex set of multidimensional information generated by e-nose and e-tongue is usually simplified and classified using multivariate statistical analysis such as discriminant factorial analysis (DFA). As mentioned above, SA treatment enhanced enzyme activities of antioxidant system and delayed the development of peach fruit chilling injury caused by postharvest cold storage. Changes in contents of flavor-related chemicals and expression profiles of genes associated with sugar and volatile metabolism were analyzed in peach fruit after harvest. These results provided a frame work for us to further investigate the effect of postharvest SA treatment on changes in fruit flavor quality of peach fruit after cold storage. In the present study, an e-nose and e-tongue were applied to explore difference in flavor quality between SA-treated peach fruit and controls. Fruit quality indicators, flesh browning, firmness, contents of soluble sugars, organic acids and flavor-related volatiles, were measured during shelf-life after cold storage. Expression profiles of genes related to flavor quality formation were analyzed using real-time quantitative PCR. Together, the data support that SA treatment has a role in alleviating loss of peach fruit flavor quality caused by cold storage. 2. Materials and methods 2.1. Plant materials and sampling Melting flesh peach (Prunus persica L. Batsch., cv. Hujingmilu) fruit were harvested at commercial maturity from an orchard in Jiaxing, Zhejiang Province, China. Hujingmilu is one of the main varieties of melting peach type in south part of China. Peach fruit were transported to the laboratory on the day of harvest. Fruit were harvested at commercial maturity with an average total soluble solids concentration (SSC) concentration of 12.29 ± 0.70 % and firmness of 32.10 ± 3.58 N, and then were divided into four groups. One group was treated with 0.5 mM SA solution containing 0.1 % Triton for 10 min. The second group was treated with 1.0 mM SA solution containing 0.1 % Triton for 10 min. The third group was treated with 2.0 mM SA solution containing 0.1 % Triton for 10 min. The fourth group was soaked in tap water containing 0.1 % Triton for 10 min as control. After SA treatment, peach fruit were stored at 0 ± 0.5 °C and 85–90% relative humidity for 7, 14, 21 and 28 d, and then transferred to shelf life at 20 ± 0.5 °C for 3 d. These peach fruit samples during shelf-life after cold storage were named as C7dS3, C14dS3, C21dS3 and C28dS3, respectively. For each sampling point, three biological replicates with five fruit each were used for analysis. After measurement of firmness and internal browning index, fruit slices of mesocarp without skin from same batch of fruit were frozen in liquid nitrogen and stored at −80 °C until further chemical analysis. 2.2. Measurement of firmness and flesh browning According to Zhang et al. (2010), firmness was measured on opposite sides at the equator of each intact fruit using a texture analyzer (TA‐XT2i Plus, Stable Micro System Ltd., Surrey, UK) fitted with a 7.5‐mm‐diameter probe. The rate of penetration was 1 mm s−1 with a final penetration depth of 10 mm and data was expressed in newtons (N). The firmness value of each fruit was taken as the average value of the two vertical interfaces. Internal browning (IB) index was used to evaluate development of chilling injury according to Zhang et al. (2011). The extent of internal browning was calculated using the following formula: IB index = 100 % × Σ[(internal browning scale) × (number of fruit with that internal browning scale)]/[4 × total number of fruit evaluated]. The rating scale was 0 = 0 % flesh surface area affected, 1 = 1–25 % area affected, 2 = 26–50 % area affected, 3 = 51–70 % area affected and 4 = 76–100 % area affected. 2
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
each sample, and the clean phase was 240 s. For each sample, three biological replicates and two technical replicates were applied for enose analysis. An α-Astree II (Alpha MOS, France) e-tongue was employed to analyze taste of peach fruit. The e-tongue is composed of an automatic sampler, seven potentiometric chemical sensors (AHS, SCS, ANS, CPS, NMS, CTS, PKS), a reference electrode of Ag/AgCl, data acquisition system. The cross-sensitivity and selectivity of the sensor array contribute to the detection of most substances found in the liquid matrix, providing a global liquid and taste perception. The form of sample was homogenate and the amount was 80 mL to ensure the sensors could be fully immersed in the liquid. The measurement time was 120 s for each sample, and the sensors were rinsed for 60 s using deionized water. All the samples were detected at 20 ± 0.5 °C. For each sample, three biological replicates and there technical replicates were applied for etongue analysis.
2.3. Volatiles analysis Volatiles were collected and analyzed according to Cao et al. (2019). Frozen peach fruit (5 g) were ground and transferred to 20 mL vials containing 3 mL 200 mM ethylenediaminetetraacetic acid (EDTA) and 3 mL 20 % CaCl2. Before the vials were sealed, 30 μL of 2-octanol (0.8 g L−1) was added as an internal standard. The vials were placed in the tray of a solid-phase micro extraction (SPME) autosampler (Combi PAL, CTC Analytics, Agilent Technologies, USA), coupled to an Agilent 7890A gas chromatograph and an Agilent 5975C mass spectrometer. Volatiles were collected using fibers coated with 65 μm of polydimethylsiloxane and divinylbenzene (PDMS–DVB) (Supelco Co., Bellefonte, PA, USA). The extraction probe was desorbed at the GC-MS inlet (Agilent 7890-5975, Palo Alto, CA, USA) for 5 min and then separated by DB-WAX capillary column (30 m × 0.25 mm i.d. × 0.25 μm film thickness; J&W Scientific, Folsom, CA). The inlet temperature is 240 °C. The temperature program was increased from 40 °C to 100 °C with 0.05 °C s−1 and then to 245 °C at 0.083 °C·s−1. Helium was used as carrier gas at 0.017 mL s−1. MS ion source temperature was 230 °C, the electron energy was 70 eV, and the scanning range of mass spectrometry was from 35 to 350 mZ−1. The mass spectrometry library NIST08 (NIST/EPA/NIH, USA) and Retention Index (RI) were used for volatiles identification. Quantification of compounds was performed using the peak area of the internal standard as a reference based on total ion chromatogram (TIC).
2.6. Real-time quantitative PCR analysis Total RNA from peach samples was extracted according to Zhang et al.(2010). Genomic DNA contamination was eliminated, and 1 μg of RNA was used to obtain cDNA using an PrimeScriptTM RT reagent Kit (TaKaRa, Dalian, China). The synthesized cDNA was diluted with water (1:10), and 2 μL of diluted cDNA was used as the template for qPCR. Reactions were performed in a total volume of 20 μL, consisting of 10 μL of SYBR PCR supermix (Bio-Rad), 1 μL of each primer (10 μm), 6 μL of diethyl pyrocarbonate-water, and 2 μL of diluted cDNA on a CFX96 instrument (Bio-Rad, CA, USA). PpTEF2 was used as an internal control to normalized relative expression levels (Tong et al., 2009). Primers used for gene expression analysis were listed in Supplementary Table S1. The specificity of primers used for qPCR analysis was confirmed by product sequencing. The temperature program for qPCR was as follows: 95 °C for 3 min, 45 cycles of 95 °C for 10 s and 60 °C for 30 s, with a final melting curve step from 65 °C to 95 °C. No-template controls were included in each run. At least three different RNA isolations and cDNA syntheses were used as templates for qPCR analysis.
2.4. Sugars and organic acids analysis Sugars and organic acids content were detected according to method described by Lisec et al. (2006) with some modifications. After grounding into powder under liquid nitrogen, 0.1 g sample was extracted with 1.4 mL of methanol at 70 °C for 15 min, and then centrifuged at 11,000 g. Ribitol (10 μL, 2 g L−1) was added into each 100 μL upper phase as an internal standard. Fresh 60 μL methoxylamine hydrochloride (20 g L−1, dissolved in pyridine) was added to the mixture, and oscillated at 70 °C for 1.5 h. Then, 40 μL Bis(trimethylsilyl) tri fluoroacetamide+1 % Trimethylchlorosilane was added and incubated for 30 min. Transfer aliquot to GC-MS glass vials, and these vials were placed in the autosampler (Combi PAL, CTC Analytics, Agilent Technologies, USA). One microliter sample was injected into an Agilent 6890 N gas chromatograph (Agilent, Palo Alto, CA, USA) in split mode with the split ratio 10:1. The Agilent 6890 N was fitted with a HP5 column (30 m × 0.25 mm i.d. × 0.25 μm film thickness; J&W Scientific, Folsom, CA). The oven, inlet and detector temperatures were 100, 250 and 280 °C, respectively. The column temperature was held at 100 °C for 1 min, increased to 185 °C with a rate of 0.04 °C s-1, increased to 190 °C with a rate of 0.005 °C s-1, increased to 250 °C with a rate of 0.13 °C s-1, then increased to 280 °C with a rate of 0.083 °C s-1 and held for 3 min. Standard curves were developed to calculate contents of sugars and organic acids.
2.7. Statistical analysis A completely randomized design was used in the experiments. Standard errors (SE) were calculated by WPS 2019 (Kingsoft Office Corporation, China), and figures were made by OriginPro 9 (Microcal Software Inc., Northampton, MA, USA). DFA was carried out using AlphaSoft (Version 11.0) for electronic tongue and nose detection data. 3. Results 3.1. Effect of SA treatment on flesh browning and softening of peach fruit after cold storage To test the effect of SA treatment on chilling injury of peach fruit after cold storage, different SA concentrations were applied. Our experiments showed that 2 mM SA treatment caused development of water strains on peach fruit skin, and 0.5 mM SA had no effect on alleviating flesh browning (IB index) and maintaining fruit softening ability (Supplementary Fig. S1). Low levels of IB and normal softening capacity were observed for peach fruit treated with 1.0 mM SA. Therefore, 1 mM SA concentration was chosen as optimal for further analysis in the present study. After treatment with SA, peach fruit had significant higher content of SA than controls throughout experimental periods (Supplementary Fig. S2). IB index, one of the most visible chilling injury symptom, was not detected during 3 d of shelf-life at 20 °C after 7 d of cold storage (C7dS3, Fig. 1A), but appeared with extended cold storage period. Significant lower IB index was observed for SA-treated peach fruit when compared to controls after 21 and 28 d of storage followed by shelf-life
2.5. Electronic nose and electronic tongue analysis The volatiles produced by peach fruit were evaluated using e-nose according to Xin et al. (2018). The FOX4000 (Alpha-MOS, France) enose consists of 18 sensors belong to three sensor types. P & T sensors are metal oxide sensors based on tin dioxide (SnO2). Type T has the sensitive layer placed on a tube of aluminum, while the sensitive layer of type P is placed on a plain substrate. The LY2 sensors are metal oxide sensors based on chromium titanium oxide and on tungsten oxide (WO3). Frozen flesh tissues were ground into powder and transferred 1 g to a cold 10 mL tube containing 5 mL saturated sodium chloride solution, and then 2 mL of homogenate were transferred into a crimp-top vial. Crimp-vial were sealed and warmed in a 40 °C metal bath for 30 min. Headspace gas was injected into the e-nose and pumped into the sensors with rate of 2.5 mL s−1. The data acquisition time was 120 s for 3
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 1. Effect of postharvest SA treatment on fresh browning and softening of peach fruit after cold storage. A, changes in IB index and transcript levels of genes related to fresh browning. B, changes in fruit firmness and transcript levels of genes related to softening. Solid black square/column represents controls, empty square/column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
(C21dS3 and C28dS3, respectively). Peach fruit firmness were approximately 32 N at harvest day, and then softened to approximately 3 N during 3 d of shelf-life after 7 d of storage (C7dS3, Fig. 1B). After 14 d of storage followed by shelf-life at room temperature, significant difference in firmness was observed between SA-treated peach fruit and controls. For the firmness of SA-treated peach fruit decreased to below 10 N, a normal feature of ripening in melting peach types, in contrast to the value of around 20 N for controls after 28 d storage followed by shelf-life (C28dS3). These data showed that SA treatment was effective in alleviating the development of chilling injury while permitting normal softening ability of peach fruit after long-term cold storage. Polyphenol oxidase (PPO) and peroxidase (POD) are two major enzymes involved flesh browning (Lin et al., 2016). Transcript levels of PpPPO1 and PpPOD1 were low after 7 d of storage (C7dS3), and then increased with prolonged cold storage time (Fig. 1A). Significant lower expression were observed for PpPPO1 and PpPOD1 in SA-treated fruit than controls after 28 d of cold storage followed by shelf-life at room temperature (C28dS3), in agreement with lower IB index in SA-treated peach fruit (Fig. 1A). In addition, we analyzed expression levels of genes encoding enzymes involved in fruit softening, including polygalacturonase (PG) and pectate lyase (PL) Transcript levels of PpPG1 and PpPL1 tended to decrease for peach fruit after extended storage. Expression of PpPG1 in SA treated peach fruit was higher than that in controls at C21dS3 and C28dS3 (Fig. 1B). No significant difference in transcript levels were observed for PpPL1 between SA treated peach fruit and controls throughout the experimental period (Fig. 1B). These data indicated that PpPG1 was one of genes likely to be associated with peach fruit softening after cold storage.
3.2. Changes in sensory quality of peach fruit based on e-tongue and e-nose analysis To provide an overview of peach fruit flavor quality, e-nose and etongue were applied in the present study. DFA analysis of e-nose showed that SA-time treatments were distributed from the negative to the positive side on the discriminant factor 1 (DF1) according to days of ripening at shelf-life (Fig. 2A). After 28 d of storage and subsequent shelf-life (C28dS3), peach fruit with chilling injury symptoms were distributed on the positive side of the DF1, while fruit without chilling injury were clustered on the negative side. Peach fruit treated with SA were separated to controls from the same time point (Fig. 2A). These results suggested that volatiles are markedly changed of peach fruit treated SA followed by cold storage and subsequent shelf-life. For e-tongue data, the total explained variance rate was 94.72 % for the first two DFs, which showed that most of the information was included in the plot (Fig. 2B). Values with positive score on DF1 were found for samples from C7dS3, C14dS3 and C21dS3, while samples from C28dS3 had values with negative score on DF1. Compared to SAtreated peach fruit, separation was observed for control samples from C28dS3 (Fig. 2B). Samples from SA-treated fruit and controls were overlapped at C7dS3, C14dS3 and C21dS3.
3.3. SA affected contents of volatile esters and lactones E-nose results revealed difference in volatile profiles of peach fruit treated with SA, therefore, changes in main volatile chemicals were analyzed using GC-MS (Supplementary Table S2). Decrease in content of fruity note volatile esters were observed for peach fruit with prolonged storage time (Fig. 3A). Among the volatile esters, content of (Z)4
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 2. DFA score plot of e-nose (A) and e-tongue (B) data for peach fruit treated with SA after cold storage. C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C). For e-nose analysis, results were from three replicates with two technical replicates each. For e-tongue analysis, results were from three replicates with three technical replicates each.
3-hexenyl acetate at C28dS3 (9.71 μg kg−1) was approximately 8.5 % of peach fruit at C7dS3 (113.51 μg kg−1) (Fig. 3A). Total volatile ester content decreased by approximately 2-fold at C28dS3 relative to C7dS3. Meanwhile, significant difference in content of volatile esters was observed between SA-treated peach fruit and controls. For peach fruit treated with SA at C28dS3, content of (Z)-3-hexenyl acetate was approximately 2.3 fold-higher than controls. Similar greater amount of SA-treated samples was observed for (E)-2-hexenyl acetate during peach fruit postharvest storage. In addition to HJML peach fruit, another melting peach cultivar JX treated with SA also produced significant higher content of volatile esters during shelf-life after cold storage (Supplementary Fig. S3). Similar to changes in volatile esters, decreased contents of lactones were also observed for peach fruit with prolonged storage time (Fig. 3B). Total volatile lactone content decreased by more than 2-fold at C28dS3 relative to C7dS3. Peach fruit treated with SA had significant higher content of total volatile lactones than controls. Content of γdecalactone in SA treated fruit was approximately 2 fold-higher than controls at C28dS3 (Fig. 3B). For another lactone γ-hexalactone, significant higher contents were detected for peach fruit treated with SA throughout the experimental period. To further test the effect of SA treatment on lactones in peach fruit, another melting peach cultivar Jingxiu (JX) was used for analysis. As we expected, significant higher content of total volatile lactones was observed in SA treated JX peach fruit than controls (Supplementary Fig. S3).
3.4. SA affected transcript levels of genes related to ester formation In order to further investigate how SA affects peach fruit volatiles, changes in expression of genes derived from LOX pathway were analyzed. In agreement with decline in volatile esters during peach fruit postharvest storage (Fig. 4), transcript levels of PpLOX1 tended to decline over experimental period (Fig. 4). For peach fruit treated with SA, transcript levels of PpLOX1 were significant higher than controls during shelf-life after cold storage, being approximately 2.5–4.3 fold (Fig. 4). Transcript levels of PpHPL1 in SA-treated peach fruit were significant higher than controls at C7dS3, C14dS3 and C21dS3 (Fig. 4). Similar decreased expression pattern was also observed for PpADH1, however, no significant difference was observed for peach fruit between SA treatment and controls. A decreased expression pattern was detected for PpAAT1 throughout experimental period. Generally, PpAAT1 transcript levels were higher in peach fruit treated with SA than controls (Fig. 4). Gene expression analysis mentioned above showed that SA treated peach had significant higher transcript levels of PpLOX1 throughout the experimental period, therefore, changes in LOX enzyme activity were investigated. In agreement with decreased pattern of volatile esters and PpLOX1, LOX enzyme activity tended to decline in the present study (Supplementary Fig. S4). Moreover, significant higher LOX enzyme activity was observed for peach fruit treated with SA at C28dS3, consistent with high content of volatile esters and transcript levels of PpLOX1 (Figs.3A and 4).
5
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 3. Effect of postharvest SA treatment on contents of volatile esters, lactones. A, changes in contents of volatile esters. B, changes in contents of volatile lactones. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
Fig. 4. Effect of postharvest SA treatment on transcript levels of genes related to ester formation. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
6
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 5. Effect of postharvest SA treatment on contents of sugars and transcript levels of genes related to sugar metabolism of peach fruit after cold storage. A, changes in contents of sugars. B, changes in transcript levels of genes related to sugar metabolism. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (*P < 0.05 and **P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
3.5. Effect of SA treatment on content of sugars and expression of genes related to sucrose metabolism
3.6. Effect of SA treatment on organic acid content of peach fruit after cold storage
Different location of peach fruit treated with SA was observed based on the e-tongue plot, therefore, contents of flavor-related soluble sugars were investigated. Sucrose content declined gradually during the whole experiment period, and no significant difference was observed between SA treated and control samples (Fig. 5A). In contrast to the sucrose results, content of glucose and fructose, increased with the prolonged storage time. For glucose, SA treated peach fruit produced low contents than controls, and significant lower production was observed at C28dS3 (Fig. 5A). Significant lower content of fructose were also observed for peach fruit treated with SA at C28dS3 than controls. For content of total sugars, there was no significant difference between SA treated and controls. These results indicated that great difference in sugar contents at C28dS3 may contribute to taste difference based on DFA plot using the e-tongue. To determine the effect of SA on sugar contents, we examined expression level of genes related to sugar metabolism. PpSUS4 showed a decreased expression pattern during shelf life after extended cold storage time, similar pattern was observed for PpSPS3 and PpTMT2 (Fig. 5B). For PpSPS3, transcript levels of control fruit at C28dS3 were approximately 40 % of C7dS3. In contrast, an increased expression was observed for peach fruit treated with SA. Postharvest SA-treated peach fruit had significantly higher transcript levels of PpSUS4, PpNINV8 and PpTMT2 than controls at C21dS3 and 28dS3, while no significant difference was observed for PpSPS3 (Fig. 5B). These results indicated that SA treatment affected expression genes related to sugar metabolism during peach fruit shelf-life after cold storage.
Sensory difference observed by the e-tongue prompted us to further test changes in organic acids caused by SA treatment. Citric acid, malic acid and quinic acid were major organic acids of peach fruit. Content of citric acid tended to decrease with extended storage time, while malic acid and quinic acid maintained constant (Fig. 6). No significant difference in content of organic acids were observed between SA treated peach fruit and controls throughout the experiment period. Therefore, expression of genes associated with organic acid metabolism was not performed. 4. Discussion Dissatisfaction with fruit flavor has existed for decades, and postharvest cold storage can negatively impact flavor quality (Zhang et al., 2011; Xi et al., 2012; Zhang et al., 2016; Meethaworn et al., 2019). Although SA treatment could reduce oxidative stress and alleviate chilling injury of peach fruit during cold storage, the effect of SA on flavor quality after storage need to be investigated. In the present study, we showed that postharvest SA treatment could reduce internal browning, maintain fruit softening ability and alleviate chilling injury. These results were consistent with previous studies on other horticultural crops, including sweet basil (Damalas, 2019), strawberry (Asghari and Hasanlooe, 2015), banana (Khademi et al., 2019), winter pineapple (Lu et al., 2011) and peach fruit (Cao et al., 2010; Yang et al., 2012). SA has been shown to stimulate activities of pectinase and cellulase that are related to cell wall degradation in pathogen systems (Wu et al., 2008). Our present study indicated that SA treated peach fruit had higher transcript levels of PpPG1, which may contribute to 7
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
Fig. 6. Effect of postharvest SA treatment on peach fruit organic acids after cold storage. Solid black column represents controls, empty column represents SA treatment. Error bars indicate SE calculated from three biological replicates. Significant differences are indicated with asterisks above the bars (* P < 0.05 and ** P < 0.01). C7dS3: peach fruit transferred to shelf-life (S) for 3 d after 7 d cold storage (C).
suggested that the first enzymatic step of the ester biosynthetic pathway, PpLOX1, is an important transcriptional point for volatile ester production in SA-treated peach fruit after cold storage. Similar to difference observed from e-nose data, e-tongue results also showed different flavor quality of SA-treated peach fruit at C28dS3 when compare to controls having severe chilling injury. Sugars and acids belong to non-volatile chemicals that affect fruit flavor quality, therefore, we measured the sugar contents to clarify the results of etongue. In the preset study, there was no significant difference either for total sugars or for total acids between SA treated peach fruit and controls after cold storage. However, significant difference was observed for contents of individual sugar, not for individual acids. These results suggested that changes in sugar profile contribute to flavor quality difference of peach fruit caused by SA treatment after cold storage. SA treated peach fruit had marked higher sucrose contents than controls after cold storage, accompanying with significant lower contents of glucose and fructose. In agreement with previous study in ripening peach fruit (Borsani et al., 2009), degradation of sucrose and increase of glucose and fructose were also observed in peach fruit during shelf-life after cold storage. Changes in metabolites of peach fruit after cold storage were analyzed, where higher contents of sucrose were observed for chilling injury resistant peach cultivar Elegant Lady after 21 d cold storage followed by shelf-life at 20 °C (Bustamante et al., 2016). Compared to other two cultivars, peach fruit Red Haven had a marked lower incidence of chilling injury, representing with higher levels of sucrose during shelf-life after cold storage (Brizzolara et al., 2016). These results suggested that changes in contents of sucrose, glucose and fructose contributed to taste quality difference of peach fruit after cold storage. Besides to be involved in taste quality, soluble sugars also played important roles in response to chilling during cold storage (Wang et al., 2019; Yu et al., 2016). Negative correlation was observed between content of sucrose and development of chilling injury of peach fruit during cold storage, indicating that sucrose metabolism was associated with cold tolerance (Wang et al., 2013; He et al., 2018). In the present study, we also observed a reversed pattern between sucrose content and IB index, where peach fruit sucrose tended to decline with extended cold storage time, accompanying with the development of chilling injury. Genes related to sucrose accumulation have been identified in peach fruit, where PpSUS4, PpNINV8, PpSPS3 and PpTMT2 were mainly expressed in mature fruit (Vimolmangkang et al., 2016). Transcript levels
maintain softening ability after cold storage. Previous study in tomato fruit showed that methyl salicylate (MeSA) treatment alleviated chilling induced loss of key aroma volatiles such as geranial and geranylacetone (Wang et al., 2015). In the present study, the DFA plot based on e-nose analysis showed sensory difference of peach fruit treated with SA. Difference in volatile profiles was then revealed by GC-MS analysis. Our dataset in peach fruit showed that SA treatment maintained significant higher contents of fruity note volatile esters than controls during shelf-life after cold storage. These fruity esters are mainly consisted of (E)-2-hexenyl acetate, (Z)-3-hexenyl acetate and hexyl acetate, which are positively correlated with consumer liking and are biosynthesized from the LOX-mediated fatty acid oxidation pathway (Kakiuchi and Ohmiya, 1991; Zhang et al., 2010). Besides the volatile esters, the lactones are characteristic components of peach aroma. Their trend in this experiment is interesting, especially after 21 and 28 d storage, where SA treated fruit show a good retention in comparison to control ones. To study the effects of SA on maintaining volatile ester levels, expression of genes derived from the LOX pathway were analyzed during shelf-life after cold storage. Similar to our previous studies (Zhang et al., 2011), decreased expression patterns were observed for PpLOX1, PpHPL1, PpADH1 and PpAAT1 with extended cold storage time. Although there was no chilling injury at C7dS3 (three days at shelf-life after seven days of cold storage), peach fruit treated with SA produced significant higher content of volatile esters, accompanying greater amount of PpLOX1, PpHPL1 and PpAAT1 transcripts. When chilling injury was developed at C28dS3, significant higher volatile ester levels were observed, accompanying with significant higher expression level of PpLOX1. There was no significant difference in transcript levels of PpAAT1 between SA-treated fruit and controls at C28dS3. These results showed that higher emission of volatile esters by SA-treated samples was concomitant with higher levels of PpLOX1 transcript. For apple fruit after cold storage under ultra-low oxygen storage, LOX was suggested to be a key control point for successful recovery of fruit ability for volatile ester production (Altisent et al., 2009), the importance of LOX and HPL in volatile ester production could also been found in banana fruit (Zhu et al., 2018). In the present study, significant higher LOX activity were observed in SA-treated peach fruit than controls at C28dS3. Similar results were also reported for pear fruit, where decreased LOX activity possibly leading to shortage of lipid precursors for volatile ester production (Lara et al., 2003). Results mentioned above 8
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
of two sucrose-cleaving enzyme genes, PpSUS4 and PpNINV8, were significant higher in SA treated peach fruit at C28dS3 than controls. As a vacuolar monosaccharide importer, TMT could transport sucrose and is responsible for sucrose accumulation (Jung et al., 2015). Similar to high content of sucrose in SA treated peach fruit after cold storage, significant higher transcript levels of PpTMT2 was also observed in fruit treated with SA. For transcript levels of PpSPS3 associated with sucrose resynthesis, no significant difference was observed between SA treated fruit and controls. It has been reported that regulation of sucrose metabolism is complex for postharvest peach fruit (Yu et al., 2016; He et al., 2018). In the present study, our results suggested that sucrose metabolism and accumulation were possibly related to the coordinate interaction between PpSUS4/PpNINV8 and PpTMT2, although further studies are required in future. Transcript levels of gene family members encoding for enzymes involved in sucrose metabolism could be analyzed using RNA-sequencing to screen candidate genes for further function analysis. Therefore, mechanism for sugar metabolism need to be further investigated in peach fruit during shelf-life after cold storage.
Borsani, J., Budde, C.O., Porrini, L., Lauxmann, M.A., Lombardo, V.A., Murray, R., Andreo, C.S., Drincovich, M.F., Lara, M.V., 2009. Carbon metabolism of peach fruit after harvest: changes in enzymes involved in organic acid and sugar level modifications. J. Exp. Bot. 60, 1823–1837. https://doi.org/10.1093/jxb/erp055. Brizzolara, S., Hertog, M., Tosetti, R., Nicolai, B., Tonutti, P., 2018. Metabolic responses to low temperature of three peach fruit cultivars differently sensitive to cold storage. Front. Plant Sci. 9, 706. https://doi.org/10.3389/fpls.2018.00706. Bustamante, C.A., Monti, L.L., Gabilondo, J., Scossa, F., Valentini, G., Budde, C.O., Lara, M.V., Fernie, A.R., Drincovich, M.F., 2016. Differential metabolic rearrangements after cold storage are correlated with chilling injury resistance of peach fruits. Front. Plant Sci. 7, 1478. https://doi.org/10.3389/fpls.2016.01478. Cai, H., An, X., Han, S., Jiang, L., Yu, M., Ma, R., Yu, Z., 2018. Effect of 1-MCP on the production of volatiles and biosynthesis-related gene expression in peach fruit during cold storage. Postharvest Biol. Technol. 141, 50–57. https://doi.org/10.1016/j. postharvbio.2018.03.003. Cao, S., Hu, Z., Zheng, Y., Lu, B., 2010. Synergistic effect of heat treatment and salicylic acid on alleviating internal browning in cold-stored peach fruit. Postharvest Biol. Technol. 58, 93–97. https://doi.org/10.1016/j.postharvbio.2010.05.010. Cao, S., Song, C., Shao, J., Bian, K., Chen, W., Yang, Z., 2016. Exogenous melatonin treatment increases chilling tolerance and induces defense response in harvested peach fruit during cold storage. J. Agric. Food Chem. 64, 5215–5222. https://doi. org/10.1021/acs.jafc.6b01118. Cao, X., Xie, K., Duan, W., Zhu, Y., Liu, M., Chen, K., Klee, H.J., Zhang, B., 2019. Peach carboxylesterase PpCXE1 is associated with catabolism of volatile esters. J. Agric. Food Chem. 67, 5189–5196. https://doi.org/10.1021/acs.jafc.9b01166. Cirilli, M., Bassi, D., Ciacciulli, A., 2016. Sugars in peach fruit: a breeding perspective. Hortic. Res. 3, 15067. https://doi.org/10.1038/hortres.2015.67. Damalas, C.A., 2019. Improving drought tolerance in sweet basil (Ocimum basilicum) with salicylic acid. Sci. Hortic. 246, 360–365. https://doi.org/10.1016/j.scienta.2018.11. 005. D’Auria, J.C., 2006. Acyltransferases in plants: a good time to be BAHD. Curr. Opin. Plant Biol. 9, 331–340. https://doi.org/10.1016/j.pbi.2006.03.016. He, X., Wei, Y., Kou, J., Xu, F., Chen, Z., Shao, X., 2018. PpVIN2, an acid invertase gene family member, is sensitive to chilling temperature and affects sucrose metabolism in postharvest peach fruit. Plant Growth Regul. 86, 169–180. https://doi.org/10.1007/ s10725-018-0419-z. Jung, B., Ludewig, F., Schulz, A., Meissner, G., Wostefeld, N., Flugge, U.I., Pommerrenig, B., Wirsching, P., Sauer, N., Koch, W., Sommer, F., Muhlhaus, T., Schroda, M., Cuin, T.A., Graus, D., Marten, I., Hedrich, R., Neuhaus, H.E., 2015. Identification of the transporter responsible for sucrose accumulation in sugar beet taproots. Nat. Plants 1, 14001. https://doi.org/10.1038/nplants.2014.1. Kakiuchi, N., Ohmiya, A., 1991. Changes in the composition and content of volatile constituents in peach fruits in relation to maturity at harvest and artificial ripening. Journal of the Japanese Society for Horticultural Science 60, 209–216. https://doi. org/10.2503/jjshs.60.209. Khademi, O., Ashtari, M., Razavi, F., 2019. Effects of salicylic acid and ultrasound treatments on chilling injury control and quality preservation in banana fruit during cold storage. Sci. Hortic. 249, 334–339. https://doi.org/10.1016/j.scienta.2019.02. 018. Kim, Y.S., An, C., Park, S., Gilmour, S.J., Wang, L., Renna, L., Brandizzi, F., Grumet, R., Thomashow, M.F., 2017. CAMTA-mediated regulation of salicylic acid immunity pathway genes in Arabidopsis exposed to low temperature and pathogen infection. Plant Cell 29, 2465–2477. https://doi.org/10.1105/tpc.16.00865. Lara, I., Miró, R.M., Fuentes, T., Sayez, G., Graell, J., López, M.L., 2003. Biosynthesis of volatile aroma compounds in pear fruit stored under long-term controlled-atmosphere conditions. Postharvest Biol. Technol. 29, 29–39. https://doi.org/10.1016/j. plantsci.2014.04.014. Lin, Y., Lin, H., Lin, Y., Zhang, S., Chen, Y., Jiang, X., 2016. The roles of metabolism of membrane lipids and phenolics in hydrogen peroxide-induced pericarp browning of harvested longan fruit. Postharvest Biol. Technol. 111, 53–61. https://doi.org/10. 1016/j.postharvbio.2015.07.030. Lisec, J., Schauer, N., Kopka, J., Willmitzer, L., Fernie, A.R., 2006. Gas chromatography mass spectrometry-based metabolite profiling in plants. Nat. Protoc. 1, 387–396. https://doi.org/10.1038/nprot.2006.59. Lombardo, V.A., Osorio, S., Borsani, J., Lauxmann, M.A., Bustamante, C.A., Budde, C.O., Andreo, C.S., Lara, M.V., Fernie, A.R., Drincovich, M.F., 2011. Metabolic profiling during peach fruit development and ripening reveals the metabolic networks that underpin each developmental stage. Plant Physiol. 157, 1696–1710. https://doi.org/ 10.1104/pp.111.186064. Lu, X., Sun, D., Li, Y., Shi, W., Sun, G., 2011. Pre- and post-harvest salicylic acid treatments alleviate internal browning and maintain quality of winter pineapple fruit. Sci. Hortic. 130, 97–101. https://doi.org/10.1016/j.scienta.2011.06.017. Lurie, S., Crisosto, C.H., 2005. Chilling injury in peach and nectarine. Postharvest Biol. Technol. 37, 195–208. https://doi.org/10.1016/j.postharvbio.2005.04.012. Meethaworn, K., Luckanatinwong, V., Zhang, B., Chen, K., Siriphanich, J., 2019. Offflavor caused by cold storage is related to induced activity of LOX and HPL in young coconut fruit. LWT - Food Sci. Technol. 114, 108329. https://doi.org/10.1016/j.lwt. 2019.108329. Raithore, S., Bai, J., Plotto, A., Manthey, J., Irey, M., Baldwin, E., 2015. Electronic tongue response to chemicals in orange juice that change concentration in relation to harvest maturity and citrus greening or huanglongbing (HLB) disease. Sensors Basel (Basel) 15, 30062–30075. https://doi.org/10.3390/s151229787. Razavi, F., Hajilou, J., Dehgan, G., Nagshi, R., Turchi, M., 2014. Enhancement of postharvest quality of peach fruit by salicylic acid treatment. Int. J. Biosci. 4, 177–184. https://doi.org/10.12692/ijb/4.1.177-184. Sanhueza, D., Vizoso, P., Balic, I., Campos-Vargas, R., Meneses, C., 2015. Transcriptomic
5. Conclusion In conclusion, our results showed that SA treatment alleviated the development of chilling injury and maintained flavor quality of peach fruit during shelf-life after cold storage. Peach fruit treated with SA had lower flesh browning than controls, and maintained fruit softening capacity with lower firmness. Difference in flavor quality between SAtreated samples and controls could be recognized by the e-tongue and enose. Significant difference were observed for content of a number of fruity note volatile esters, lactones and soluble sugars in peach fruit treated with SA when compared to controls, but not for content of organic acids. The first enzymatic step of the ester biosynthetic pathway, PpLOX1, is an important transcriptional point for volatile ester production in SA-treated peach fruit after cold storage. Declaration of Competing Interest The authors declare no conflict of interest. Acknowledgements This research was supported by National Key R&D Program of China (2016YFD0400101), the National Natural Science Foundation of China (31672100), Fundamental Research Funds for the Central Universities (2019FZA6010) and Zhejiang Provincial Science and Technology Project (2016C04001). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.postharvbio.2019. 111089. References Altisent, R., Echeverria, G., Graell, J., Lopez, L., Lara, I., 2009. Lipoxygenase activity is involved in the regeneration of volatile ester-synthesizing capacity after ultra-low oxygen storage of’ Fuji’ apple. J. Agric. Food Chem. 57, 4305–4312. https://doi.org/ 10.1021/jf803930j. Asghari, M., Hasanlooe, A.R., 2015. Interaction effects of salicylic acid and methyl jasmonate on total antioxidant content, catalase and peroxidase enzymes activity in “Sabrosa” strawberry fruit during storage. Sci. Hortic. 197, 490–495. https://doi.org/ 10.1016/j.scienta.2015.10.009. Aubert, C., Bony, P., Chalot, G., Landry, P., Lurol, S., 2014. Effects of storage temperature, storage duration, and subsequent ripening on the physicochemical characteristics, volatile compounds, and phytochemicals of Western Red nectarine (Prunus persica L. Batsch). J. Agric. Food Chem. 62, 4707–4724. https://doi.org/10.1021/jf4057555. Baldwin, E.A., Bai, J., Plotto, A., Dea, S., 2011. Electronic noses and tongues: applications for the food and pharmaceutical industries. Sensors Basel (Basel) 11, 4744–4766. https://doi.org/10.3390/s110504744.
9
Postharvest Biology and Technology 161 (2020) 111089
C. Yang, et al.
postharvbio.2012.07.003. Xin, R., Liu, X., Wei, C., Yang, C., Liu, H., Cao, X., Wu, D., Zhang, B., Chen, K., 2018. ENose and GC-MS reveal a difference in the volatile profiles of white-and red-fleshed peach fruit. Sensors 18, 765. https://doi.org/10.3390/s18030765. Yang, J., Gao, Y., Li, Y., Qi, X., Zhang, M., 2008. Salicylic acid-induced enhancement of cold tolerance through activation of antioxidative capacity in watermelon. Sci. Hortic. 118, 200–205. https://doi.org/10.1016/j.scienta.2008.06.015. Yang, Z., Cao, S., Zheng, Y., Jiang, Y., 2012. Combined salicylic acid and ultrasound treatments for reducing the chilling injury on peach fruit. J. Agric. Food Chem. 60, 1209–1212. https://doi.org/10.1021/jf2041164. Yu, L., Liu, H., Shao, X., Yu, F., Wei, Y., Ni, Z., Xu, F., Wang, H., 2016. Effects of hot air and methyl jasmonate treatment on the metabolism of soluble sugars in peach fruit during cold storage. Postharvest Biol. Technol. 113, 8–16. https://doi.org/10.1016/j. postharvbio.2015.10.013. Zhang, B., Shen, J., Wei, W., Xi, W., Xu, C., Ferguson, I., Chen, K., 2010. Expression of genes associated with aroma formation derived from the fatty acid pathway during peach fruit ripening. J. Agric. Food Chem. 58, 6157–6165. https://doi.org/10.1021/ jf100172e. Zhang, B., Tieman, D.M., Jiao, C., Xu, Y., Chen, K., Fei, Z., Giovannoni, J.J., Klee, H.J., 2016. Chilling-induced tomato flavor loss is associated with altered volatile synthesis and transient changes in DNA methylation. Proc. Natl. Acad. Sci. 113, 12580–12585. https://doi.org/10.1073/pnas.1613910113. Zhang, B., Xi, W., Wei, W., Shen, J., Ferguson, I., Chen, K., 2011. Changes in aromarelated volatiles and gene expression during low temperature storage and subsequent shelf-life of peach fruit. Postharvest Biol. Technol. 60, 7–16. https://doi.org/10. 1016/j.postharvbio.2010.09.012. Zhou, D., Chen, S., Xu, R., Tu, S., Tu, K., 2019. Interactions among chilling tolerance, sucrose degradation and organic acid metabolism in UV-C-irradiated peach fruit during postharvest cold storage. Acta Physiol. Plant. 41, 79. https://doi.org/10. 1007/s11738-019-2871-4. Zhu, L., Zhou, J., Zhu, S., 2010. Effect of a combination of nitric oxide treatment and intermittent warming on prevention of chilling injury of ‘Feicheng’ peach fruit during storage. Food Chem. 121, 165–170. https://doi.org/10.1016/j.foodchem.2009.12. 025. Zhu, X., Luo, J., Li, Q., Li, J., Liu, T., Wang, R., Chen, W., Li, X., 2018. Low temperature storage reduces aroma-related volatiles production during shelf-life of banana fruit mainly by regulating key genes involved in volatile biosynthetic pathways. Postharvest Biol. Technol. 146, 68–78. https://doi.org/10.1016/j.postharvbio.2018. 08.015.
analysis of fruit stored under cold conditions using controlled atmosphere in Prunus persica cv. “Red Pearl”. Front. Plant Sci. 6, 788. https://doi.org/10.3389/fpls.2015. 00788. Tareen, M.J., Abbasi, N.A., Hafiz, I.A., 2012. Postharvest application of salicylic acid enhanced antioxidant enzyme activity and maintained quality of peach cv. ‘Flordaking’ fruit during storage. Sci. Hortic. 142, 221–228. https://doi.org/10.1016/ j.scienta.2012.04.027. Tong, Z., Gao, Z., Wang, F., Zhou, J., Zhang, Z., 2009. Selection of reliable reference genes for gene expression studies in peach using real-time PCR. BMC Mol. Biol. 10, 71. https://doi.org/10.1186/1471-2199-10-71. Vimolmangkang, S., Zheng, H., Peng, Q., Jiang, Q., Wang, H., Fang, T., Liao, L., Wang, L., He, H., Han, Y., 2016. Assessment of sugar components and genes involved in the regulation of sucrose accumulation in peach fruit. J. Agric. Food Chem. 64, 6723–6729. https://doi.org/10.1021/acs.jafc.6b02159. Wang, K., Shao, X., Gong, Y., Zhu, Y., Wang, H., Zhang, X., Yu, D., Yu, F., Qiu, Z., Lu, H., 2013. The metabolism of soluble carbohydrates related to chilling injury in peach fruit exposed to cold stress. Postharvest Biol. Technol. 86, 53–61. https://doi.org/10. 1016/j.postharvbio.2013.06.020. Wang, K., Yin, X.R., Zhang, B., Grierson, D., Xu, C.J., Chen, K.S., 2017. Transcriptomic and metabolic analyses provide new insights into chilling injury in peach fruit. Plant Cell Environ. 40, 1531–1551. https://doi.org/10.1111/pce.12951. Wang, L., Baldwin, E.A., Plotto, A., Luo, W., Raithore, S., Yu, Z., Bai, J., 2015. Effect of methyl salicylate and methyl jasmonate pre-treatment on the volatile profile in tomato fruit subjected to chilling temperature. Postharvest Biol. Technol. 108, 28–38. https://doi.org/10.1016/j.postharvbio.2015.05.005. Wang, L., Chen, S., Kong, W., Li, S., Archbold, D.D., 2006. Salicylic acid pretreatment alleviates chilling injury and affects the antioxidant system and heat shock proteins of peaches during cold storage. Postharvest Biol. Technol. 41, 244–251. https://doi.org/ 10.1016/j.postharvbio.2006.04.010. Wang, L., Shan, T., Xie, B., Ling, C., Shao, S., Jin, P., Zheng, Y., 2019. Glycine betaine reduces chilling injury in peach fruit by enhancing phenolic and sugar metabolisms. Food Chem. 272, 530–538. https://doi.org/10.1016/j.foodchem.2018.08.085. Wu, H.S., Raza, W., Fan, J.Q., Sun, Y.G., Bao, W., Liu, D.Y., Huang, Q.W., Mao, Z.S., Shen, Q.R., Miao, W.G., 2008. Antibiotic effect of exogenously applied salicylic acid on in vitro soilborne pathogen, Fusarium oxysporum f.sp.nIveum. Chemosphere 74, 45–50. https://doi.org/10.1016/j.chemosphere.2008.09.027. Xi, W., Zhang, B., Shen, J., Sun, C., Xu, C., Chen, K., 2012. Intermittent warming alleviated the loss of peach fruit aroma-related esters by regulation of AAT during cold storage. Postharvest Biol. Technol. 74, 42–48. https://doi.org/10.1016/j.
10