Impact of thermal processing and storage temperature on the phenolic profile and antioxidant activity of different varieties of lychee juice

LWT - Food Science and Technology 116 (2019) 108578

Contents lists available at ScienceDirect

LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt

Impact of thermal processing and storage temperature on the phenolic profile and antioxidant activity of different varieties of lychee juice

T

Dongxiao Sua,∗,1, Zhineng Wangb,c,1, Lihong Dongb, Fei Huangb, Ruifen Zhangb, Xuchao Jiab, Guangxu Wuc, Mingwei Zhangb,c,∗∗ a

School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006, PR China Guangdong Key Laboratory of Agricultural Products Processing, Sericultural & Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510610, PR China c College of Life Science, Yangtze University, Jingzhou 434025, PR China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Lychee Phenolic Antioxidant activity Thermal processing Storage

Lychee pulp is rich in phenolic compounds and has a variety of biological activities. However, their thermal stability are unknown. The results showed that after heat-treated at 121 °C (HT121), the total phenolic content (TPC) and total flavonoid content of the lychee juices were significantly increased compared to those of the unheated (UH) and 70 °C heat-treated (HT70) lychee juices. Nine individual phenolic compounds, gallic acid, (-)-gallocatechin, procyanidin B2, vanillic acid, quercetin-3-rutinose-7-rhamnoside, syringic acid, procyanidin A2, ferulic acid and rutin, were detected in lychee juice by HPLC-DAD. After heat treatment at 121 °C and high temperature storage at 45 °C, the gallic acid content in lychee juice was increased. In particular, (-)-gallocatechin was generated after thermal processing at 121 °C. (-)-Gallocatechin accounted for 89.50% of the total phenolic compounds in HT121 lychee juice. However, with prolonged storage time (72 h) and increased storage temperature (45 °C), the (-)-gallocatechin degraded and disappeared. In summary, the thermal stability of most phenolic compounds in lychee pulp is good, and heat treatment could promote the release of phenolic compounds in lychee juice and improve their antioxidant activity. The variety of Guiwei lychee is more suitable for fruit juice manufacturing.

1. Introduction Lychee (Litchi chinensis Sonn.) is a tropical to subtropical fruit that has a bright red pericarp, translucent fleshy aril and delicious taste. Several prospective studies have reported that lychee pulp contains a large number of phenolic compounds (Zhang et al., 2013). Phenolic compounds are secondary metabolites of plants (Ripari, Bai, & Gänzle, 2019). Quercetin-3-rutinose-7-rhamnoside, epicatechin, procyanidin B2 and rutin are the major phenolic compounds in lychee pulp (Su et al., 2014, 2017). Previous studies have shown that lychee pulp phenolic compounds have antioxidant, anti-inflammatory, hypoglycemic and lipid-lowering effects (Lv et al., 2014; Su et al., 2014, 2017). Lychee fruits are harvested in the hot and rainy seasons of June to August which cannot be preserved for long periods of time, vulnerable to microbial effects and spoilage (Wu, Yi, Zhou, Zeng, & Huang, 2007).

The lychee pulp can be made into lychee juice, which can not only retain the original fragrance of lychee but also reach longer shelf life and has a widespread potential market. Heat treatment has been widely used in the food industry because of its efficacy in inactivation of enzymes and prevention of microbial spoilage (Alves Filho et al., 2018; You et al., 2018). Aaby, Grimsbo, Hovda, and Rode (2018) reported that strawberry juice could be stored in cold storage conditions (6 °C) for 49 d after heat treatment at 85 °C. In addition, thermally processed fruits and vegetables have significantly increased their biological activities due to their various chemical changes during heat treatment (Choi, Lee, Chun, Lee, & Lee, 2006; Lv et al., 2014; Oliveira, Pintado, & Almeida, 2012). The changes in phenolic composition and antioxidant activity of lychee juice treated and stored at different temperatures were rarely reported. The aim of the present study was (1) to investigate the effects of different heat treatments and different storage

∗

Corresponding author. School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006, PR China. Corresponding author. Guangdong Key Laboratory of Agricultural Products Processing, Sericultural & Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510610, PR China. E-mail addresses: [email protected] (D. Su), [email protected] (M. Zhang). 1 The two authors should be considered joint first authors. ∗∗

https://doi.org/10.1016/j.lwt.2019.108578 Received 17 April 2019; Received in revised form 29 August 2019; Accepted 30 August 2019 Available online 30 August 2019 0023-6438/ © 2019 Elsevier Ltd. All rights reserved.

LWT - Food Science and Technology 116 (2019) 108578

D. Su, et al.

temperatures on the composition and content of phenolic substances and the antioxidant activity of different varieties of lychee, (2) to explore the thermal stability of phenolic compounds in lychee juice, and (3) to provide theoretical support for the lychee juice thermal processing.

juice was expressed as mg RE/100 mL. The results were presented as means ± SD for three replications obtained from three samples.

2. Materials and methods

All compounds were identified by HPLC UltiMate 3000 system (Thermo Fisher Scientific, Waltham, MA, USA) equipped with an Orbitrap Fusion Tribrid mass spectrometer (MS, Thermo Fisher Scientific, USA) operating in both negative and positive ion ESI mode for MS analyses as described by Su et al. (2017). Continuous mass spectra were collected by using a max injection time of 100 ms and a target resolution of 120,000 and scanning from 100 to 1000 m/z units. The phenolic compounds in the lychee juice were quantified using a reverse-phase HPLC-diode array detector (DAD) method as described by Zhang et al. (2013). HPLC analysis was performed using an Agilent 1260 HPLC system (Agilent Technologies Deutschland GmbH, Oberhaching, Germany) consisting of an Agilent 1260 series DAD detector, a four element pump delivery system and an automatic sampler. Phenolic compounds were separated at a flow rate of 1.0 mL/min using a YMCPack ODS-A column C18 (250 × 4.6 mm, 5 μm, YMC technique, Japan), and the column temperature was maintained at 30 °C. A binary gradient elution was carried out using solvent A (water/acetic acid, 996:4, v/v) and solvent B (acetonitrile). The gradient was programmed as follows: 0–40 min, 5–25% solvent B; 40–45 min, 25–35%; solvent B; and 45–50 min, 35–50% solvent B. The injection volume was 20 μL. Chromatographic data were collected at 280 nm. The quantified values are expressed as μg/g of lychee pulp FW. The data are reported as the mean ± SD of three replicates obtained from three samples.

2.4. Qualitative and quantitative analysis of lychee juice phenolic compounds by HPLC-MS/MS and HPLC-DAD

2.1. Materials Fresh, ripe lychee (cv Guiwei, Huaizhi and Nuomici) fruits were purchased at commercial maturity with bright red pericarp from a local fruit market in Guangzhou, China. Gallic acid, (-)-gallocatechin (GC), procyanidin B2, vanillic acid, lilac acid, procyanidin A2, ferulic acid, and rutin were purchased from Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai, China). Quercetin3-rutinose-7-rhamnoside was prepared by our lab previously reported method (Su et al., 2014). The ferric reducing antioxidant power (FRAP) kit was purchased from Nanjing Jiancheng Bioengineering Institute (Nanjing, China). Folin-Ciocalteu reagent was purchased from Macklin Reagent Co., Ltd. (Shanghai China). 2′,7′-dichlorofluorescin diacetate, fluorescein disodium salt and 2′,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) were obtained from Xiya Reagent Co., Ltd. (Chengdu China). HPLC-grade methanol, acetic acid and acetonitrile were purchased from Thermo Fisher Scientific (Waltham, MA, USA). 2.2. Preparation of lychee juice The lychee fruits were rinsed with tap water, manually peeled and then crushed with a whole food Total Nutrition Center blender (TNC1036, Zhengbang Electric Co., Ltd. Guangzhou China). The juice was centrifuged at 4000 rpm for 5 min to obtain the lychee juice sample. Unheated (UH) juice was used as the control. Lychee juice (50 mL) was placed in a glass container and treated at 70 °C or 121 °C for 30 min. Afterwards, the lychee juices were stored in two groups: one group was deposited at low temperature (4 °C) for 0, 24, 72, 120 and 168 h in a refrigerator. And the other group, as reported by Rao, Rocca-Smith, Schoenfuss, and Labuza (2012) for accelerated shelf-life, was stored at high temperature (45 °C) for 0, 6, 24, 48, 72 h in an electrothermal air dryer with constant temperature (GZX-9420 MBE, Boxun Industrial Co., Ltd., Shanghai, China). The samples were removed at the indicated time and stored in a freezer at −80 °C for analysis.

2.5. Ferric reducing antioxidant power (FRAP) assay FRAP antioxidant capacity was determined according to the kit instructions. Lychee sample or standard solution (5 μL) was seeded in 96well microplate, then FRAP working fluid (180 μL) was added in. After incubating at 37 °C for 5 min in microplate reader (TECAN Infinite 200, TECAN, Switzerland), the absorption was recorded at 593 nm. Ferrous sulfate was used as the standard. The FRAP results were expressed as mmoL ferrous sulfate equivalents (FeE)/100 mL. The results are presented as the mean ± SD of three replicates obtained from three samples. 2.6. Determination of ORAC

2.3. Determination of total phenolic and flavonoid content The oxygen radical absorbance capacity (ORAC) assay was carried out using an Infinite M200pro microplate reader (TECAN Infinite 200, TECAN, Switzerland) following the method reported by Su et al. (2014). The lychee juice was diluted with 75 mmol/L potassium phosphate buffer (pH 7.4, working buffer), and 20 μL of lychee juice, Trolox standard solution (concentration range 6.25–50 μmol/L) or blank control was added to black 96-well plates. The wells were prepared in triplicate for each of the above solutions. Then, 200 μL of 0.96 μM fluorescein was added to the black plate. After a 20 min incubation at 37 °C, 20 μL of AAPH (119 mM) was added to each well. Excitation and emission spectra were recorded at 485 and 520 nm, respectively, every 4.5 min for a total of 35 measurements. The ORAC value was expressed as μmol Trolox equivalents (TE)/100 mL. The results are reported as the mean ± SD of three replicates obtained from three samples.

Total phenolic content was determined using the method described by Su et al. (2014). Sample or standard solution (125 μL) and deionized water (0.5 mL) were added to 125 μL Folin-Ciocalteu reagent. After 6 min, 1.25 mL of an aqueous sodium carbonate solution (7%, m/v) and 1.00 mL deionized water were added in turn. After mixing thoroughly, this solution was reacted for 90 min avoiding light. Finally, the absorbance was recorded at 760 nm using a Shimadzu UV-1800 spectrophotometer (Shimadzu Co., Ltd, Japan). Gallic acid was used as the standard. The total phenolic content of lychee juice was expressed as mg GAE/100 mL. The results were presented as means ± SD for three replications obtained from three samples. Total flavonoid content was determined by the method reported by Su et al. (2014). 300 μL sample or standard solution was added in 0.5 mL deionized water and then 90 μL of aqueous sodium nitrite (5%, m/v) was added in the above solution. Then the solution was kept at room temperature for 6 min after mixed well. 180 μL of an aqueous aluminum chloride hexahydrate (10%, m/v) was added to the solution and reacted for 5 min avoiding light. After that, 0.6 mL of aqueous sodium hydroxide solution (1 mol L−1) and 330 μL of deionized water were added to the solution. The absorption was measured at 510 nm. Rutin was used as the standard. The total flavonoid content of lychee

2.7. Color parameter measurement Lychee juice color was measured using Ultra Scan VIS (Hunter Lab, USA) with the CIELAB method (Wibowo et al., 2015). The control (UH), the 70 °C heat-treated (HT70) and the 121 °C heat-treated (HT121) samples were diluted 3 times. Wibowo et al. (2015) reported that the L* and ΔE* values represent lightness and total color difference, 2

LWT - Food Science and Technology 116 (2019) 108578

D. Su, et al.

Fig. 1. Effects of different heat treatments and different storage temperatures on the total phenolic content of different varieties of lychee juice. Values with different letters in same variety are significantly different. UH, unheated; HT70, 70 °C heat-treated; and HT121, 121 °C heat-treated.

heat treatment at 121 °C could promote the release of phenolic compounds from lychee juice. A significant impact of storage at 45 °C on the TPC of lychee juice was shown. The TPC of the UH and HT70 lychee juices (Guiwei, Huaizhi and Nuomici) was significantly increased after 72 h of storage compared with that before storage (p < 0.05). Further analysis revealed that the TPC of the Guiwei and Nuomici varieties of lychee juice that underwent heat treatment at 70 °C and were stored for 72 h increased by 50.48%, while that of the UH juices stored for 72 h increased by 11.05%. The results showed that high temperature storage at 45 °C could promote the release of phenolic compounds from HT70 lychee juice but decrease the phenolic content of HT121 lychee juice.

respectively. The a* and b* values indicate greenness (negative) to redness (positive) and blueness (negative) to yellowness (positive), respectively. The L*, a*, b* and ΔE* values were calculated using the formula reported by Sun, Ma, Han, Huang, and Zhan (2017). Specifically, ΔE* is a parameter used to distinguish between two colors (You et al., 2018). 2.8. Statistical analysis The experimental results are expressed as the mean ± SD of three replicates obtained from three samples. Statistical and variance (ANOVA) analysis was performed using IBM SPSS24 statistical software. A Tukey (Figs. 1, 2, 4 and 5) or LSD (Figs. 4 and 5) test was used to compare the statistical significant differences, and the significance level was p value less than 0.05.

3.2. Heat treatment and storage temperature increase the total flavonoid content of lychee juice

3. Results

Three varieties (Guiwei, Huaizhi and Nuomici) of lychee juice were treated with heat and compared with untreated juice. The resulting changes in the TFC of the three varieties of lychee juice are presented in Fig. 2. When the heat-treated and untreated samples were stored at 4 °C, the changes in the TFC of Guiwei, Huaizhi and Nuomici lychee juices were consistent with the changes in the TPC of the juices. There was no significant reduction in TFC after 168 h of storage. However, compared with that of the UH group before storage, the TFC of Guiwei, Huaizhi and Nuomici lychee juices in the HT121 group before storage increased by 40.01%, 86.50% and 121.82%, respectively. The results showed that heat treatment at 121 °C could promote the formation of flavonoids in lychee juice, and no significant decrease was observed with storage at 4 °C for 168 h. The TFC of HT121 lychee juice began to decrease at 6 h of storage and reached the lowest value at 72 h. However, the TFC of Guiwei and Nuomici lychee juice was still significantly higher than that of UH lychee juice before storage. The results showed that most of the

3.1. Heat treatment and storage temperature enhance the total phenolic content of lychee juice The changes in the TPC of the different varieties lychee juice (Guiwei, Huaizhi and Nuomici) induced by different heat treatments and storage at 4 °C and 45 °C are shown in Fig. 1. After storage at 4 °C for 168 h, the TPC of the UH, HT70 and HT121 lychee juices (Guiwei, Huaizhi and Nuomici) was not significantly reduced compared with that of the different lychee juices before storage (p < 0.05). In addition, compared to the TPC of the UH juices before storage, the TPC of HT70 Guiwei and Huaizhi lychee juices increased by 13.04% and 3.94%, respectively; however, the TPC of the Nuomici lychee juice was reduced by 13.06%. Compared with that of the UH group before storage, the TPC of HT121 Guiwei, Huaizhi and Nuomici lychee juices increased by 165.16%, 123.58% and 109.54%, respectively. The results showed that 3

LWT - Food Science and Technology 116 (2019) 108578

D. Su, et al.

Fig. 2. Effects of different heat treatments and different storage temperatures on the total flavonoid content of different varieties of lychee juice. Values with different letters in same variety are significantly different. UH, unheated; HT70, 70 °C heat-treated; and HT121, 121 °C heat-treated.

flavonoids in fresh lychee juice thermally stable and did not significantly decrease after storage at 45 °C for 72 h. The TFC of HT121 lychee juice before storage was significantly higher than that of UH lychee juice before storage; however, after storage at 45 °C for 72 h, there was a significant reduction. Therefore, the increase in flavonoids caused by heat treatment was not thermally stable, and the flavonoids easily degraded under storage at high temperature.

3.4. High storage temperatures decrease the phenolic content of lychee juice The HPLC results describing the Guiwei, Huaizhi and Nuomici lychee juices after storage at 45 °C for 72 h (Fig. 3, Fig S2 and Fig S3,Fig. S2 and Fig. S3) showed that the content of gallic acid in the HT121 juices was significantly higher than in the UH and HT70 juices. In addition, (-)-gallocatechin was only detected in HT121 lychee juice and had a large absorption peak at 280 nm. The gallic acid contents in the UH and HT70 Guiwei, Huaizhi and Nuomici lychee juices were significantly higher after storage at 45 °C for 72 h than before storage. Combined with the results of the TPC and TFC determinations in lychee juice under storage at 4 °C and 45 °C (Figs. 1 and 2), the increase in the gallic acid content of lychee juice and the formation or disappearance of (-)-gallocatechin in lychee juice may be the main influencing factors of changes in the TPC and TFC of lychee juice.

3.3. Heat treatment and storage temperature improve the composition and content of phenolic compounds in different varieties of lychee juice The heat treatment-induced changes in the composition and content of phenolic compounds in lychee juice are shown in Table 1. Nine individual phenolic compounds were detected in lychee pulp by HPLCDAD: gallic acid, (-)-gallocatechin, procyanidin B2, vanillic acid, syringic acid, quercetin-3-rutinose-7-rhamnoside, procyanidin A2, ferulic acid and rutin. The contents of procyanidin B2 and procyanidin A2 increased as the heat treatment and storage temperatures increased and decreased with prolonged storage time. During heat treatment at 121 °C, the content of gallic acid in lychee juice was significantly increased (p < 0 05). However, after storage at 45 °C for 72 h, the content of gallic acid in the HT121 Guiwei, Huaizhi and Nuomici lychee juices decreased by 8.25 μg/g, 17.14 μg/g and 3.31 μg/g, respectively. Notably, the content of gallic acid in the UH and HT70 lychee juices after 72 h of storage was significantly higher than that in the UH and HT70 lychee juices before storage. The contents of quercetin-3-rutinose-7-rhamnoside, ferulic acid and rutin were the highest in Guiwei lychee juice, followed by Huaizhi lychee juice and Nuomici lychee juice. (-)-Gallocatechin was generated after thermal processing at 121 °C; (-)-gallocatechin accounted for 89.50% of the total phenolic compounds in HT121 lychee juice. However, with prolonged storage time and increased storage temperature (-)-gallocatechin decreased; it was degraded and undetected after storage at 45 °C for 72 h.

3.5. Heat treatment and storage temperature change the antioxidant activity of lychee juice The antioxidant activity of Guiwei, Huaizhi and Nuomici lychee juices was determined by the FRAP assay (Fig. 4). The relative FRAP antioxidant capacity of the three varieties was as follows: Guiwei, Nuomici and Huaizhi (from strong to weak). Before storage, the FRAP value of HT70 Guiwei lychee juice was significantly decreased compared with that of UH Guiwei lychee juice, while the antioxidant capacities of Huaizhi and Nuomici lychee juices as determined by the FRAP assay were not significantly reduced. The FRAP antioxidant capacity of HT121 lychee juice before storage was significantly increased compared with those of UH and HT70 lychee juices before storage. At 4 °C, the antioxidant capacities of UH, HT70 and HT121 lychee juices were decreased. However, after storage at 45 °C for 72 h, the antioxidant capacities of UH and HT70 lychee juices were significantly stronger than UH 0 h and HT70 0 h, respectively. Compared to the 4

5

UH HT70 HT121 UH HT70 HT121 UH HT70 HT121 UH HT70 HT121 UH HT70 HT121 UH HT70 HT121 UH HT70 HT121 UH HT70 HT121 UH HT70 HT121

Phenolic Compounds (μg/mL) Gallic acid (-) -Gallocatechin 4.23 ± 0.44a ND 4.03 ± 0.76a ND 99.62 ± 13.67gh 2284.94 ± 40.56b 3.54 ± 0.21a ND 3.68 ± 0.43a ND 100.21 ± 10.98gh 2307.91 ± 66.76b 12.38 ± 3.21b ND 101.55 ± 11.76h ND 91.37 ± 8.94f ND 1.46 ± 0.03a ND 1.48 ± 0.03a ND 101.49 ± 9.65h 3928.86 ± 39.72c 1.40 ± 0.02a ND 1.44 ± 0.03a ND 95.69 ± 5.34g 3849.52 ± 51.98c 81.79 ± 6.77e ND 22.48 ± 2.10c ND 84.35 ± 11.04e ND 0.96 ± 0.02a ND 1.15 ± 0.02a ND 75.39 ± 10.08d 1628.80 ± 44.19a 0.97 ± 0.01a ND 1.01 ± 0.02a ND 124.68 ± 13.16i 1628.80 ± 49.02a 7.43 ± 1.78a ND 12.94 ± 2.08b ND 72.08 ± 8.89d ND Procyanidin B2 0.45 ± 0.02a 0.78 ± 0.02b 1.1 ± 0.04c 0.35 ± 0.02a 0.64 ± 0.04b 1.03 ± 0.07c 0.69 ± 0.01b 1.1 ± 0.03c 1.16 ± 0.03c ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

Vanillic ND ND ND ND ND ND ND 5.23 ± 5.37 ± ND ND 4.92 ± ND ND 4.28 ± ND ND 1.76 ± ND ND ND ND ND ND ND ND ND 0.19a

0.34b

00.23c

0.45c 0.60c

acid

Syringic acid 1.24 ± 0.11a 1.2 ± 0.08a ND 1.5 ± 0.04a 1.14 ± 0.04a ND 1.58 ± 0.05a ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND 3.96 ± 0.95c ND ND 3.23 ± 0.77b

Quercetin-3-rutinose-7-rhamnoside 139.71 ± 3.45g 211.93 ± 4.55i 150.68 ± 2.89g 184.77 ± 3.64h 183.1 ± 4.01h 111.59 ± 6.86f 229.68 ± 7.11j 147.29 ± 3.23g 143.23 ± 4.44g 139.71 ± 5.88g 89.51 ± 5.18e 153.65 ± 4.03g 86.77 ± 2.88e 85.88 ± 3.69e 69.02 ± 4.77cd 182.64 ± 8.96h 181.86 ± 9.91h 182.64 ± 8.02dh 58.94 ± 3.11dbc 75.36 ± 4.32de 31.72 ± 2.22a 69.79 ± 6.12cd 52.04 ± 5.56b 49.26 ± 4.78b 77.74 ± 4.38de 79.32 ± 6.23de 33.12 ± 3.33a

Procyanidin A2 0.67 ± 0.02cdef 0.98 ± 0.01fgh 2.23 ± 0.24j 0.65 ± 0.06cdef 0.81 ± 0.03defg 1.91 ± 0.05f 1.03 ± 0.02fgh 1.54 ± 0.02i 2.69 ± 0.11k 0.34 ± 0.04abc 0.51 ± 0.04abcd 2.01 ± 0.10j 0.29 ± 0.01abc 0.52 ± 0.02abcd 2.14 ± 0.09j 0.58 ± 0.02bcde 0.78 ± 0.08defg 2.22 ± 0.31j 0.33 ± 0.01abc 0.49 ± 0.02abcd 0.83 ± 0.02defg 0.15 ± 0.01a 0.26 ± 0.01 ab 0.91 ± 0.04efgh 0.86 ± 0.04defg 1.23 ± 0.10h 1.09 ± 0.16gh

Ferulic acid 6.26 ± 1.01g 2.04 ± 0.15b 4.24 ± 0.65e 5.26 ± 0.23f 5.23 ± 0.08f 3.17 ± 0.17d 6.13 ± 0.71g 4.12 ± 0.34e 4.01 ± 0.56e 1.91 ± 0.05b 0.94 ± 0.02a 4.31 ± 0.61e 1.91 ± 0.06b 1.87 ± 0.06b 1.53 ± 0.08b 2.71 ± 0.22c 2.63 ± 0.19c 1.71 ± 0.04b 1.52 ± 0.03b 1.84 ± 0.11b 0.93 ± 0.09a 1.81 ± 0.04b 1.6 ± 0.11b 1.58 ± 0.04b 1.78 ± 0.04b 1.8 ± 0.51b 1.07 ± 0.02a

Values that do not share a common letter in the same row are significantly different (p < 0.05). UH: unheated; HT70: 70 °C heat treatment; HT121: 121 °C heat treatment. Mean ± SD, n = 3.

Nuomici 45 °C 72 h

Nuomici 4 °C 168 h

Nuomici 0h

Huaizhi 45 °C 72 h

Huaizhi 4 °C 168 h

Huaizhi 0h

Guiwei 45 °C 72 h

Guiwei 4 °C 168 h

Guiwei 0h

Cultivars

Table 1 Effects of heat treatment and storage temperature (4 °C and 45 °C) on monomeric phenolic content in different varieties of lychee juice as determined by HPLC-DAD. Rutin 14.11 ± 2.10k 8.36 ± 1.98g 10.78 ± 2.66i 11.07 ± 3.11i 10.83 ± 2.65i 7.35 ± 1.56f 13.29 ± 3.24j 9.69 ± 2.11h 9.31 ± 2.33h 4.16 ± 1.17de 3.35 ± 0.77c 11.14 ± 1.13i 4.37 ± 0.44e 4.19 ± 0.81de 3.68 ± 0.03cde 15.81 ± 3.11l 17.05 ± 2.36m 29.03 ± 4.12n 3.7 ± 0.39cde 4.3 ± 0.52e 2.73 ± 0.06b 3.92 ± 0.08cde 3.44 ± 0.74cd 3.62 ± 0.45cde 4.03 ± 0.18cde 3.89 ± 0.05cde 2.21 ± 0.03a

D. Su, et al.

LWT - Food Science and Technology 116 (2019) 108578

LWT - Food Science and Technology 116 (2019) 108578

D. Su, et al.

Fig. 3. Effects of different heat treatments on the phenolic composition of the Guiwei lychee variety by HPLC. UH, unheated; HT70, 70 °C heat-treated; and HT121, 121 °C heat-treated.

3.6. Changes in the CILAB color parameters of lychee juice after different heat treatment temperatures

HT121 0 h lychee juice, the antioxidant capacity of HT121 lychee juice was significantly decreased with storage at 45 °C for 72 h. Specifically, after storage at 45 °C for 72 h, the FRAP values of HT70 Guiwei and Nuomici lychee juices were 21.30% and 43.11% higher, respectively, than those of the corresponding UH juices. Therefore, the antioxidant capacities of UH and HT70 lychee juices were increased after storage at 45 °C for 72 h, the antioxidant capacities of HT121 lychee juice was decreased. The relative ORAC levels of the three lychee juice varieties were as follows: Guiwei, Huaizhi and Nuomici (from strong to weak) (Fig. 5). Before storage, the antioxidant capacities of the HT121 Guiwei, Huaizhi and Nuomici lychee juices were 48.88%, 103.32% and 162.37% higher, respectively, than those of the corresponding UH groups. Moreover, before storage, the antioxidant capacities of the HT70 Guiwei, Huaizhi and Nuomici lychee juices increased by 52.66%, 103.44% and 115.47%, respectively, compared with those of the corresponding UH groups. This result was consistent with the results of the TPC determination and FRAP assay, which indicated that heat treatment can improve the antioxidant capacity of lychee juice. The antioxidant capacity of HT70 Guiwei and Huaizhi lychee juice did not significantly decrease with storage at 4 °C for 168 h, but the antioxidant capacity of Nuomici lychee juice did significantly decrease with prolonged storage. In addition, after 72 h of storage, the ORAC values of HT70 Guiwei and Nuomici lychee juices were increased by 25.77% and 40.40%, respectively, compared with those of UH Guiwei and Nuomici lychee juices. The above results are consistent with the results of the FRAP assay, which further indicates that heat treatment and high temperature storage can promote the release of phenolics and increase their antioxidant activity.

According to the ΔE* values of HT70 and HT121 Guiwei, Huaizhi and Nuomici lychee juices (Table S1), there was a very small difference in the colors of the HT70 and UH lychee juices. However, the color of HT121 lychee juice had a perceptible difference from that of UH lychee juice. It was observed that the color of fresh lychee juice deepened as the heat treatment temperature increased and that there was a perceptible difference between the color of fresh lychee juice and the color of heat-treated lychee juice. 4. Discussion Phenolic compounds are important secondary metabolites of plants and have high content in fruits. Phenolic compounds possess strong antioxidant activities, which are positively correlated with TPC and TFC (Zhang et al., 2013). In fact, the overall antioxidant capacity depends on the composition of phenolic compounds. Studies have reported that phenolic compounds protect biological macromolecules (such as DNA, proteins, and lipids) from oxidative damage (Zeng et al., 2019). After storage at 4 °C for 168 h, the TPC and TFC of the UH, HT70 and HT121 lychee juices were not significantly reduced. A study by dos et al. reported that the TPC and TFC of fresh orange juice were not significantly reduced after heat treatment at 88 °C and storage at 8 °C for 15 d (dos Reis, Facco, Flôres, & Rios, 2018). After storage at 45 °C for 72 h, the TPC of UH and HT70 lychee juices was significantly higher than the TPC of UH lychee juice before 6

LWT - Food Science and Technology 116 (2019) 108578

D. Su, et al.

Fig. 5. Effects of different heat treatments and different storage temperatures on the antioxidant capacity of different varieties of lychee juice as determined by ORAC. Bars with different letters in same variety are significantly different. Bars with an asterisk (*) are significantly different (p < 0.05). UH, unheated; HT70, 70 °C heat-treated; and HT121, 121 °C heat-treated.

Fig. 4. Effects of different heat treatments and different storage temperatures on the antioxidant activity of different varieties of lychee juice as determined by FRAP. Bars with different letters in same variety are significantly different. Bars with an asterisk (*) are significantly different (p < 0.05). UH, unheated; HT70, 70 °C heat-treated; and HT121, 121 °C heat-treated.

depending on the molecular weight) aglycone form or esterified with gallic acid (Li, Peng, Zhu, Cheng, & Li, 2017; Margalef, Pons, Bravo, Muguerza, & Arola-Arnal, 2015). In this study, (-)-gallocatechin was produced during heat treatment at 121 °C and accounted for approximately 89.5% of the total phenolic compounds in HT121 lychee juice. Previous studies investigating flavonoids, including (-)-epicatechin, procyanidin B2 and catechin, have shown that the increase in phenolic substances that occurs with pasteurization can be attributed to the thermal-induced hydrolysis of thermally unstable compounds such as epigallocatechin gallate and procyanidin polymers, leading to the release of dimers and monomers (Alongi et al., 2018). The filled and bottled tea drinks sterilized at 120 °C, after that the low concentrations of (-)-epicatechin present in the beverage can be converted into their corresponding epimers during transportation and sale. The concentrations of these epimers are similar to or even higher than those of (-)-epicatechins (Z. Chen, Zhu, Tsang, & Huang, 2001; Li et al., 2017). After storage at 45 °C for 72 h, (-)-gallocatechin disappeared because thermal decomposition caused the loss of bioactive compounds, which depend on the chemical structure of the phytochemicals. For example, molecules with unsaturated covalent bonds are more prone to degradation than molecules without these types of bonds (Oliveira et al., 2012). Vanillic acid was detected after heat treatment at 121 °C, which indicates that the degradation of thermally instability phenolic compounds in lychee juice and led to the formation of vanillic acids (SeokMoon Jeong et al., 2004). It has been reported that vanillic acid can be formed at 150 °C for 30 min (Seok-Moon Jeong et al., 2004). Syringic acid was detected in Guiwei and Nuomici lychee juice, but not detected in the Huaizhi lychee juice. These would be related to the transformation of phenolic compounds causing the formation of syringic acid in Guiwei and Nuomici lychee juice during storage period. The food matrix

storage; this difference was mainly due to the increase in gallic acid content. It was also reported that when tea powder was stored for 21 h at 15 °C, 20 °C and 25 °C, the gallic acid content in the tea powder increased storage time and storage temperature increased; specifically, increasing storage temperature resulted in increases of 50%, 131.25% and 212.5%, respectively (Ye et al., 2018). These results indicated that high temperature storage would increase the TPC by promoting the release of phenolic compounds. Immediately after heat treatment at 121 °C, the TPC of Guiwei, Huaizhi and Nuomici lychee juices was determined and found to be significantly increased compared with that of UH lychee juices before storage. This result is consistent with the findings reported by Choi et al. (2006). In addition, Alongi, Verardo, Gorassini, and Anese (2018) reported that after apple juice was treated at 90 °C for 14.8 min, the TPC increased to 6 times that of the original TPC. Hydrogen bonding can be affected by temperature. Therefore, under heat treatment, the phenolic compounds would interact with proteins, causing the increase in phenolic compounds (Ozdal, Capanoglu, & Altay, 2013). In addition, the TFC of Guiwei, Huaizhi and Nuomici lychee juices was significantly higher immediately after heat treatment at 121 °C than in UH lychee juice and immediately after heat treatment at 70 °C. It has been reported that the TFC of fruit juice–soymilk beverages increased by 61.54% after heat treatment at 90 °C (Morales-de la Peña, Salvia-Trujillo, Rojas-Graü, & Martín-Belloso, 2011). These results indicated that phenolic acid and flavonoid contents were affected by heat treatment. (-)-Gallocatechin is one of 8 types of catechins classified as flavanol compounds These flavanol compounds exist in monomeric (catechin and epicatechin) or oligomeric (proanthocyanidins or condensed tannins, 7

LWT - Food Science and Technology 116 (2019) 108578

D. Su, et al.

relationships which may be considered as potential competing interests:

would also could act as a barrier to heat effect or to induce the degradation. Therefore, the composition of phenolic compounds in different food matrix is different (Ioannou, Hafsa, Hamdi, Charbonnel, & Ghoul, 2012). The relative ORAC results of the three lychee juices were as follows: Guiwei, Huaizhi and Nuomici (from strong to weak) (Fig. 5). This result was inconsistent with the FRAP results. It was reported that the reaction mechanism of FRAP assay was based on electron transfer (Boutakiout et al., 2018), while, the ORAC assay was based on hydrogen atom transfer (Aguilar-Garcia, Gavino, Baragaño-Mosqueda, Hevia, & Gavino, 2007). Therefore, this discrepancy was due to the differences in the principles of antioxidant capacity determination of the two methods and the different structural properties of antioxidant substances (Alam, Bristi, & Rafiquzzaman, 2013; Shahidi & Zhong, 2015). The antioxidant capacity of HT121 lychee juice was stronger than those of UH and HT70 lychee juices. These results are consistent with those of Chen et al. who reported that the antioxidant capacity of green asparagus juice after high temperature sterilization at 121 °C for 3 min was approximately 1.68 times that of fresh asparagus (X. Chen et al., 2015). During heat treatment, nonenzymatic reaction products with antioxidant capacity were formed, such as melanoidins. Melanoidins are the final products of the Maillard reaction, and they have different biological activities, including antioxidant capacity (Rufián-Henares & Morales, 2007). After heat treatment at 121 °C, the color of HT121 lychee juice was brown and perceptibly different from that of UH lychee juice (Table S1 and Fig. S1). Maillard reaction would take place and produced a large number of melanoidin compounds, which resulted in the browning of the lychee juice.

References Aaby, K., Grimsbo, I. H., Hovda, M. B., & Rode, T. M. (2018). Effect of high pressure and thermal processing on shelf life and quality of strawberry purée and juice. Food Chemistry, 260, 115–123. Aguilar-Garcia, C., Gavino, G., Baragaño-Mosqueda, M., Hevia, P., & Gavino, V. C. (2007). Correlation of tocopherol, tocotrienol, γ-oryzanol and total polyphenol content in rice bran with different antioxidant capacity assays. Food Chemistry, 102(4), 1228–1232. Alam, M. N., Bristi, N. J., & Rafiquzzaman, M. (2013). Review on in vivo and in vitro methods evaluation of antioxidant activity. Saudi Pharmaceutical Journal, 21(2), 143–152. Alongi, M., Verardo, G., Gorassini, A., & Anese, M. (2018). Effect of pasteurization on in vitro α-glucosidase inhibitory activity of apple juice. Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology, 98, 366–371. Alves Filho, E. G., Silva, L. M. A., de Brito, E. S., Wurlitzer, N. J., Fernandes, F. A. N., Rabelo, M. C., et al. (2018). Evaluation of thermal and non-thermal processing effect on non-prebiotic and prebiotic acerola juices using 1H qNMR and GC–MS coupled to chemometrics. Food Chemistry, 265, 23–31. Boutakiout, A., Elothmani, D., Hanine, H., Mahrouz, M., Le Meurlay, D., Hmid, I., et al. (2018). Effects of different harvesting seasons on antioxidant activity and phenolic content of prickly pear cladode juice. Journal of the Saudi Society of Agricultural Sciences, 17(4), 471–480. Chen, X., Qin, W., Ma, L., Xu, F., Jin, P., & Zheng, Y. (2015). Effect of high pressure processing and thermal treatment on physicochemical parameters, antioxidant activity and volatile compounds of green asparagus juice. Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology, 62(1), 927–933 Part 2. Chen, Z., Zhu, Q., Tsang, D., & Huang, Y. (2001). Degradation of green tea catechins in tea drinks. Journal of Agricultural and Food Chemistry, 49(1), 477–482. Choi, Y., Lee, S. M., Chun, J., Lee, H. B., & Lee, J. (2006). Influence of heat treatment on the antioxidant activities and polyphenolic compounds of shiitake (lentinus edodes) mushroom. Food Chemistry, 99(2), 381–387. Ioannou, I., Hafsa, I., Hamdi, S., Charbonnel, C., & Ghoul, M. (2012). Review of the effects of food processing and formulation on flavonol and anthocyanin behaviour. Journal of Food Engineering, 111(2), 208–217. Li, K. K., Peng, J. M., Zhu, W., Cheng, B. H., & Li, C. M. (2017). Gallocatechin gallate (GCG) inhibits 3T3-L1 differentiation and lipopolysaccharide induced inflammation through MAPK and NF-κB signaling. Journal of Functional Foods, 30, 159–167. Lv, Q., Si, M., Yan, Y., Luo, F., Hu, G., Wu, H., et al. (2014). Effects of phenolic-rich litchi (litchi chinensis sonn.) pulp extracts on glucose consumption in human HepG2 cells. Journal of Functional Foods, 7, 621–629. Margalef, M., Pons, Z., Bravo, F. I., Muguerza, B., & Arola-Arnal, A. (2015). Plasma kinetics and microbial biotransformation of grape seed flavanols in rats. Journal of Functional Foods, 12, 478–488. Morales-de la Peña, M., Salvia-Trujillo, L., Rojas-Graü, M. A., & Martín-Belloso, O. (2011). Changes on phenolic and carotenoid composition of high intensity pulsed electric field and thermally treated fruit juice–soymilk beverages during refrigerated storage. Food Chemistry, 129(3), 982–990. Oliveira, A., Pintado, M., & Almeida, D. P. F. (2012). Phytochemical composition and antioxidant activity of peach as affected by pasteurization and storage duration. Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology, 49(2), 202–207. Ozdal, T., Capanoglu, E., & Altay, F. (2013). A review on protein–phenolic interactions and associated changes. Food Research International, 51(2), 954–970. Rao, Q., Rocca-Smith, J. R., Schoenfuss, T. C., & Labuza, T. P. (2012). Accelerated shelflife testing of quality loss for a commercial hydrolysed hen egg white powder. Food Chemistry, 135(2), 464–472. dos Reis, L. C. R., Facco, E. M. P., Flôres, S. H., & Rios, A.d. O. (2018). Stability of functional compounds and antioxidant activity of fresh and pasteurized orange passion fruit (passiflora caerulea) during cold storage. Food Research International, 106, 481–486. Ripari, V., Bai, Y., & Gänzle, M. G. (2019). Metabolism of phenolic acids in whole wheat and rye malt sourdoughs. Food Microbiology, 77, 43–51. Rufián-Henares, J. A., & Morales, F. J. (2007). Functional properties of melanoidins: In vitro antioxidant, antimicrobial and antihypertensive activities. Food Research International, 40(8), 995–1002. Seok-Moon, J., Kim, S.-Y., Kim, D.-R., Jo, S.-C., Nam, K. C., Ahn, D. U., et al. (2004). Effect of heat treatment on the antioxidant activity of extracts from citrus peels. Journal of Agricultural and Food Chemistry, 52(11), 3389–3393. Shahidi, F., & Zhong, Y. (2015). Measurement of antioxidant activity. Journal of Functional Foods, 18, 757–781. Sun, X., Ma, T., Han, L., Huang, W., & Zhan, J. (2017). Effects of copper pollution on the phenolic compound content, color, and antioxidant activity of wine. Molecules, 22(5), 726. Su, D., Ti, H., Zhang, R., Zhang, M., Wei, Z., Deng, Y., et al. (2014). Structural elucidation and cellular antioxidant activity evaluation of major antioxidant phenolics in lychee pulp. Food Chemistry, 158, 385–391. Su, D., Zhang, R., Hou, F., Chi, J., Huang, F., Yan, S., et al. (2017). Lychee pulp phenolics ameliorate hepatic lipid accumulation by reducing miR-33 and miR-122 expression in mice fed a high-fat diet. Food & Function, 8(2), 808–815. Wibowo, S., Vervoort, L., Tomic, J., Santiago, J. S., Lemmens, L., Panozzo, A., et al. (2015). Colour and carotenoid changes of pasteurised orange juice during storage. Food Chemistry, 171, 330–340. Wu, Y., Yi, G., Zhou, B., Zeng, J., & Huang, Y. (2007). The advancement of research on

5. Conclusion Heat treatment and storage temperature had significant effects on the composition and antioxidant activity of phenolic-rich lychee juice. Heat treatment at 121 °C could promote the release of phenolic compounds from lychee juice. However, the heat treatment at 121 °C had a marked influence on the color quality of lychee juice, while heat treatment at 70 °C maintained the original color of lychee juice, with only a small difference from the color of UH lychee juice. There was no significant change in phenolic content after storage at the low temperature of 4 °C. Therefore, 70 °C could be used as an appropriate temperature for the heat treatment of lychee juice, and the content of phenolic compounds in lychee juice could be well preserved under storage at 4 °C. In summary, the Guiwei lychee variety is more suitable for fruit juice manufacturing. Conflicts of interest There is no conflict of interest. Acknowledgments The project was supported by the National Natural Science Foundation of China (31601469) and the Science and Technology Program of Guangzhou (201604020089). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.lwt.2019.108578. Declaration of interests ☑The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal 8

LWT - Food Science and Technology 116 (2019) 108578

D. Su, et al.

during refrigerated storage. Innovative Food Science & Emerging Technologies, 48, 1–10. Zeng, Z., Hu, X., McClements, D. J., Luo, S., Liu, C., Gong, E., et al. (2019). Hydrothermal stability of phenolic extracts of brown rice. Food Chemistry, 271, 114–121. Zhang, R., Zeng, Q., Deng, Y., Zhang, M., Wei, Z., Zhang, Y., et al. (2013). Phenolic profiles and antioxidant activity of litchi pulp of different cultivars cultivated in Southern China. Food Chemistry, 136(3), 1169–1176.

litchi and longan germplasm resources in China. Scientia Horticulturae, 114(3), 143–150. Ye, Y., Yan, J., Cui, J., Mao, S., Li, M., Liao, X., et al. (2018). Dynamic changes in amino acids, catechins, caffeine and gallic acid in green tea during withering. Journal of Food Composition and Analysis, 66, 98–108. You, Y., Li, N., Han, X., Guo, J., Zhao, Y., Liu, G., et al. (2018). Influence of different sterilization treatments on the color and anthocyanin contents of mulberry juice

9