Ginger essential oil-based microencapsulation as an efficient delivery system for the improvement of Jujube (Ziziphus jujuba Mill.) fruit quality

Journal Pre-proofs Ginger essential oil-based microencapsulation as an efficient delivery system for the improvement of Jujube (Ziziphus jujuba Mill.) fruit quality Zhaojun Ban, Jinglin Zhang, Li Li, Zisheng Luo, Yongjiang Wang, Qiuping Yuan, Bin Zhou, Haidong Liu PII: DOI: Reference:

S0308-8146(19)31753-4 https://doi.org/10.1016/j.foodchem.2019.125628 FOCH 125628

To appear in:

Food Chemistry

Received Date: Revised Date: Accepted Date:

9 June 2019 27 September 2019 30 September 2019

Please cite this article as: Ban, Z., Zhang, J., Li, L., Luo, Z., Wang, Y., Yuan, Q., Zhou, B., Liu, H., Ginger essential oil-based microencapsulation as an efficient delivery system for the improvement of Jujube (Ziziphus jujuba Mill.) fruit quality, Food Chemistry (2019), doi: https://doi.org/10.1016/j.foodchem.2019.125628

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Ginger essential oil-based microencapsulation as an efficient delivery system for the improvement of Jujube (Ziziphus jujuba Mill.) fruit quality Zhaojun Bana,b,1,*1, Jinglin Zhanga,1, Li Lic, Zisheng Luoc, Yongjiang Wanga, Qiuping Yuana, Bin Zhoud, Haidong Liub a School

of Biological and Chemical Engineering, Zhejiang University of Science and Technology,

Zhejiang Provincial Key Laboratory of Chemical and Biological Processing Technology of Farm Products, Zhejiang Provincial Collaborative Innovation Center of Agricultural Biological Resources Biochemical Manufacturing, Hangzhou 310023, China; b Tianjin

c Key

Gasin-DH Preservation Technology Co., Ltd, Tianjin 300300, China;

Laboratory for Agro-Products Postharvest Handling of Ministry of Agriculture and Rural Affairs,

College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; d

Zhejiang Silver-Elephant Bio-engineering Co., Ltd, Taizhou 317200, China

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These authors contributed equally to this work.

E-mail address: [email protected] (Z. Ban), [email protected] (J. Zhang), [email protected] (L. Li), [email protected] (Z. Luo), [email protected] (Y. Wang), [email protected] (Q. Yuan), [email protected] (B. Zhou), [email protected] (H. Liu).

* Corresponding author: Dr. Zhaojun Ban (Email: [email protected]; Tel: +86-571-85070390; Fax: +86-571-85070390; Liuhe Road 318, West Lake District, Hangzhou 310023, China). 1

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Abstract: Microencapsulation of Zingiber officinale essential oil (EO) in polysaccharide, chitosan (CH) and sodium carboxymethyl cellulose (CMC) based on the electrostatic interaction between charged polysaccharides at pH 3.0 in dual delivery system. Ratio variations of CH and CMC in microencapsulation were studied at 1:2, 2:1 and 1:1. This study aimed to evaluate the influence of the encapsulating materials combination on freeze-dried EO powders and to present the mechanisms for loading and releasing EO involved in the preparation of CH/CMC microcapsules. The spectroscopy analysis, physical properties, microstructural, encapsulation efficiency and EO release behavior in obtained EO microparticles were evaluated by using the analysis of fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and gas chromatography mass spectrometry (GC-MS), respectively. Afterwards, the above prepared microcapsules were applied on winter jujube fruit (Ziziphus jujuba Mill.) preservation. Results demonstrated that both the microstructure and stability of microencapsulation were improved in delivery system loading with CH and CMC (1:1) with the encapsulation efficiency of 88.50 %, compared to other ratios of CH and CMC (1:2 and 2:1). Furthermore, the microencapsulation had a capacity to control and reduce the EO release, therefore the morphological and sensory quality of jujube fruits in EO delivery system during storage was enhanced significantly (P < 0.05), in comparison to control. Results revealed that the microparticles produced with CH and CMC (1:1) was considered to present better characteristics of microstructure, encapsulation efficiency, as well as to maintain higher nutritional quality for jujube fruit. Thus, EO microencapsulation loaded in CH/CMC-based dual delivery system has potential application and developmental value prospects in food industries.

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Keywords: Microencapsulation; essential oil; microstructure; FTIR; encapsulation efficiency; jujube

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1.

Introduction

Ginger essential oil (EO) extracted from ginger (Zingiber officinale L.) have been applied in food industries, not only for the pungent taste and characteristic odor which is its specific fragrance, but also for the antimicrobial, antioxidant, antibiotic, chemopreventive potential (Debbarma, Kishore, Nayak, Kannuchamy, & Gudipati, 2013; Kota, Panpatil, Kaleb, Varanasi, & Polasa, 2012). Many recent studies have reported that essential oil has been widely applied to extend shelf-life and maintain quality of fresh produce (Hassoun, & Emir Çoban, 2017；Atarés, & Chiralt, 2016). Cinnamon essential oil packaging enhanced the antioxidant capacity and inhibited the incidence of Alternaria alternate in tomatoes than control (Black-Solis, Ventura-Aguilar, Correa-Pacheco, Corona-Rangel, & Bautista-Baños, 2019). Pepper tree essential oil coating effectively reduced weight loss rate, firmness and controlled postharvest diseases of avocado fruits (Chávez-Magdaleno, González-Estrada, Ramos-Guerrero, Plascencia-Jatomea, & Gutiérrez-Martínez, 2018). Tarragon, Thymus capitatus and cinnamon essential oils were also showed excellent antioxidant and antimicrobial capacities, and they effectively applied on fruit preservation of kumquat, strawberry and peach, respectively (Hosseini, Amraie, Salehi, Mohseni, & Aloui, 2019; Martínez, Ortiz, Albis, Gilma Gutiérrez Castañeda, Valencia, & Grande Tovar, 2018; Lee, Jang, Aguilar, Park, & Kim, 2019). However, stabilization, solubilization and release of active components of most essential oils (particularly for the EO) were extremely sensitive to external factors, such as temperature, oxidation, ultraviolet light, and humidity (Hermanto et al., 2016). However, when we directly applied EO on fruit, meat or vegetable, sensory characteristics and fungal infectivity of fresh product could be tremendously influenced by exposure of EO, which was resulted from the extremely low flavor threshold and the highly water insolubility of EO (Kalemba & Kunicka, 2003).

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Several embedding techniques on food packaging delivery systems, mainly the capsulation of bioactive films and coatings, have been used to study the effect on quality maintenance of fresh food. Similarly, microencapsulation technology as a new embedding approach where microcapsules acted as small encapsulating system of active materials, it also has the ability to effectively increase the EO stabilization, control release of volatile or active ingredients and obtain products with high value. Moreover, the wall system of microencapsulation enabled the minimization of volume/weight ratio and contained chemical groups with hydrophilic and hydrophobic properties, as well as protected the enclosed essential oil against environmental stress stimuli. The wall materials always have features of encapsulating agent, availability, low cost, such as polysaccharide (chitosan, sodium carboxymethyl cellulose, etc) and protein (maltodextrin, modified starch, whey protein, etc) have been widely used in the microencapsulation (Carneiro, Tonon, Grosso, & Hubinger, 2013; Touré, Lu, Zhang, & Xueming, 2011). It was previously reported that the microencapsulation of Nigella sativa oleoresin, Pimenta dioica essential oil, cinnamon oil and EO showed good physical and chemical properties (Dima, Cotârlet, Alexe, & Dima, 2014; Edris, Kalemba, Adamiec, & Piątkowski, 2016; Hermanto et al., 2016; Rialita, Nurhadi, & Puteri, 2018). Dima et al. (2014) presented the antimicrobial property of Pimenta dioica essential oil could be used in meat product. Edris et al. (2016) formulated Nigella sativa oleoresin powder which was used in the fortification of processed food and nutraceuticals. Wu et al. (2015) demonstrated that allyl isothiocyanate microcapsule enlarged the application possibility of bioactive compounds on tomato preservation. Nevertheless, there was no available useful work has been reported about the microencapsulation of EO which could be used in postharvest jujube fruit. Chitosan (CH) is a natural polysaccharide obtainable from the shells of crustacean (Mende,

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Schwarz, Steinbach, Boldt, & Schwarz, 2016). Technological interest in CH and CH derivatives is based on its properties including biodegradable, biocompatible, non-toxic and for being a natural polymer. Due to CH protonated in acidic pH solution could easily complex with negatively charged materials, such as sodium carboxymethyl cellulose (CMC), the combination of CH and CMC could be used in the preparation of stable microcapsules (Gök, Demir, Cevher, Özgümüş, & Pabuccuoğlu, 2019). In this context, the objective of this study was (1) to encapsulate the ginger essential oil in CMC and CH through complex coacervation method; (2) to evaluate the microencapsulation by X-ray, Fourier transform infrared spectroscopy, scanning electron microscopy and gas chromatography mass spectrometry analysis; and (3) to investigate the characteristic quality traits of jujube (Ziziphus jujuba Mill.) fruit by regulation of EO microencapsulation. 2. Materials and Methods 2.1. Materials Ginger (Zingiber officinale L.) essential oil (EO) (99% (w/w) pure; main volatile compounds: gingerol, curcumene and zingiberene; density: 0.872-0.895) was purchased from Guangzhou Endless Biotech Co., Ltd (Guangzhou city, Guangdong, China). Chitosan (CH, 99% (w/w) pure, molecular weight Mw = 161.16 kDa, deacetylation degree 95%) was obtained from Golden-shell Pharmaceutical (Taizhou city, Zhejiang, China) and sodium carboxymethyl cellulose (CMC, 98% (w/w) pure, Mw = 242.16 kDa) from Sinopharm Chemical Reagent (Shanghai, China). Jujube (Ziziphus jujuba Mill.) fruits were manually picked at fully mature stage from a private garden (38° 42′ N, 118° 8′ E, Binzhou city, Shandong, China) in early October 2018. Fruits were then selected based on the uniformity in size, shape and as well as the lack of injuries, pest and disease symptoms.

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2.2. Emulsion Preparation The wall materials of CH solution and CMC solution (15 g/L, w/v) were prepared 1 d before emulsification and kept at room temperature for 16 h to ensure the biopolymers completion of molecule saturation. EO was gradually added into the wall material solution by stirring at 13000 rpm for 5 min using a homogenizer (AD500S-H, Shanghai Ding Ke Scientific Instrument Co., Ltd., Shanghai, China). EO emulsions were immediately subjected to the ultrasonication at 160 W for 5 min (FS-150N, Shanghai Shenghe Ultrasonic Instrument Co., Ltd., Shanghai, China). Ultrasonication used a standard tapered horn with a 3 mm diameter tip was immersed 4 cm into EO emulsion. EO: Wall material weight ratio of 1:4 (w/w), means that concentration of EO was 3.75 g/L (w/v); CMC: CH weight ratios of 1:1, 1:2 and 2:1 (w/w) were used, with a total biopolymer content of 2.0% and pH 3.0. Then we used C11, C12 and C21 to label the samples with the CMC: CH weight ratios of 1:1, 1:2 and 2:1. 2.3. Microencapsulation preparation via freeze-drying EO emulsions were pre-frozen at −81︒C for 24 h in a freezer (Thermo Scientific Forma 88700V, Thermo Fisher Technology Co., Ltd., Shanghai, China) and then freeze-dried in a vacuum freeze drier (Bulk Tray Dryer Labconco Freezone, Beijing Instrument and Equipment Co., Ltd., Beijing, China) operating at 0±0.3 Pa for 48 h. The resulting powder was packaged in airtight low-density polyethylene bags and stored in a desiccator containing silica gel at indoor temperature for further analyses. 2.4. Properties of EO microcapsules 2.4.1. Fourier transform infrared (FTIR) spectroscopy FTIR spectroscopy study was applied as described by Fernandes et al. (2016a). The measurements were taken at 15︒C, in the range of 400-4000 cm−1 with an increment of 1 cm-1 each 0.05 second, using a Fourier transform infrared spectrometer (Bluker Optics Vertex 70v, Bluker Technology Co.,

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Ltd., Beijing, China). Each sample was measured three times. 2.4.2. X-ray diffraction (XRD) XRD was determined as described by Botrel et al. (2016) with some modifications. Measurements were performed using radiation wavelength of 1.54 Å at 40 kV and 40 mA. Samples were analyzed at angles from 5° to 70° with an increment of 0.02° (2° min−1). Each sample was measured three times. 2.4.3. Scanning electron microscopy (SEM) The microcapsules were examined by SEM accelerating voltage 5 kV as described by Edris et al. (2016). Prepared powders were firstly gold sputtered by mounting on aluminum stubs with double sided adhesive tape, and then coated with gold using an Ion Sputter Coater (Shenzhen Supro Instruments Co., Ltd, Shenzhen, China), final observed by SEM (Hitachi SU 1510, Hitachi Consumer Marketing (China) Ltd. Xiamen, China) at 20000 × magnifications. 2.4.4. Gas chromatography mass spectrometry (GC-MS) analysis The encapsulation efficiency and the retention rate through the process of release in EO microcapsules were evaluated using GC-MS analysis as described by Touré et al. (2011) with some modifications. The temperature of the column was programmed initially at 50 °C for 1 min and then increased at a rate of 5 °C min−1 to 120 °C for 10 min and then increased at a rate of 3 °C min−1 to a final temperature of 250 °C. Injector and detector temperatures were maintained at 280 °C. For all injections, 1 µL of the concentrated volatile extracts was used in a split (5:1) injection mode. These measurements were taken at room temperature, using a gas chromatography mass spectrometry with Triple-Axis Detector (Agilent 7890-5975C, Agilent Technologies Inc., Beijing, China). Each sample was measured three times. 2.4.5. In-vitro release of EO

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The encapsulation efficiency of the EO microcapsules was defined as ratio of the extracted (encapsulated) volatile oil. Encapsulation Efficiency (%) = M / MO *100 where M is the amount (mg) of volatile oil in microparticles and Mo is the initial volatile oil amount (mg) added to the emulsion. Volatile oil content was measured by GC-MS and determined as described by Touré et al. (2011) with some modifications. Two hundred mg of sample was dissolved in 40 mL distilled water at 40 °C for 10 min. And then assisted by ultrasound at 95% for 2.5 min, followed by 10 mL hexane addition and mixing for 1 min. EO was extracted with hexane at room temperature for 30 min. The hexane was separated from the aqueous phase by centrifugation at 4000 rpm for 5 min. The amount of EO in hexane was determined by GC-MS. Each sample was measured three times. Main volatile compounds (include decanal, gingerol, 2-butanone, curcumene and zingiberene) contents in microcapsules were also determined with hexane and determined by GC-MS. Each sample was measured three times. 2.4.6. Quality determination of jujube in EO microencapsulation system About 750 g of jujube fruits were randomly packed and sealed in microporous plastic bags, in which every 3 g of EO microcapsule was putted in non-woven fabric filter bag, and then stored at room temperature for 14 days. To evaluate the postharvest quality (soluble solids content, titratable acidity, red index, decay index, sensory evaluation) of jujube with EO microcapsule treatment on days 0, 7, and 14. EO microcapsules were place on the top of bags and it were not in contact with jujube fruit. Jujube fruits package without EO microcapsule was set as control, with every 5 bags were in each group. Three technical replications and three biological replications were performed for every treatment.

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The ginger essential oil release test of ginger essential oil microencapsulation (C11) during storage of jujube fruits was determined by GC-MS followed the method of 2.4.4 and 2.4.5 described. Three samples were taken at 0, 1, 2, 3, 4, 5, 10 and 15days, during jujube preservation treatment period. The jujube soluble solids content (SSC) and titratable acidity (TA) were measured by a PAL-BX/ACID F5 (ATAGO7100, Shanghai Tech Front Electronics Co., Ltd, Shanghai, China). Each sample was measured at least three times. The red index (RI) and decay index (DI) were measured followed the method of Zhang and Li (2013) with some modifications. Sixty fruits classified under 5 categories (0, 1, 2, 3, 4) of red surface coverage. Red index = [(∑rank × quantity) / (highest category × 60)] × 100. Similarly, sixty fruits classified under 5 categories of rotting: 0, not rate; 1, rotten surface less than 1/8; 2, rotten surface between 1/8 and 1/4; 3, rotten surface between 1/4 and 3/8; 4, rotten surface more than 3/8. The panel of sensory evaluation consisted of 10 panelists. The panel evaluated the following attributes followed Galindo et al. (2015): appearance, sweetness, crunchiness, firmness, juiciness, fruity flavor. For quantifying the intensity of the sample attributes, the panel used a numerical scale between 0 and 10, where 0 represents ‘none’ and 10 ‘extremely strong’. 2.5. Statistical analysis Statistical analysis of the single factor experimental data used Origin 8.6 and Microsoft Excel 2016. All experiments were performed in triplicate and analysis of all samples were run in triplicate and averaged. Three technical replications and three biological replications were performed for every experiment. Statistical analyses of preservation experiments were performed with SPSS Version 20.0 (SPSS Inc., Chicago, IL, USA). All data were presented as mean values ± standard deviations (SD). Duncan Multiple Range Test was used for the comparison of means, with significance assigned at

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P<0.05. 3. Results and discussion 3.1. Characterization of EO microcapsules 3.1.1. Fourier transform infrared (FTIR) spectroscopy analysis FTIR spectroscopy analysis was applied to investigate the characteristics of the encapsulated EO into different wall material ratios. Fig. 1A showed the spectra of all raw materials applied in microencapsulation and it presented the changes of spectral absorption in EO microencapsulation with different wall material ratios. EO bands are associated to C=C stretching, C=C-C=C stretching and C-H bending at 1745, 1640 and 1377 cm−1 respectively. Another important vibrational mode associated to C=C-H, CH2, C-C-H groups is presented in EO spectrum at 3008, 2966 and 2855 cm−1. Bands that characterized CMC are present at 3300, 2925 cm−1 (unsaturation C-C, CH2 stretching), 1382 cm−1 (CH2 bending), 1425 cm−1 (C-H bending), 1080 cm-1 (C-O stretching) and 1608 cm−1 (C=O stretching). Bands that characterize CH are present at 3300 cm−1 (unsaturation C-C stretching and O-H stretching), 1425 cm−1 (C-H bending), 1382 cm−1 (CH2 bending) and 1080 cm-1 (C-O stretching). CMC and CH present almost similar spectrum profile, featuring at 3300 and 1080 cm-1 respectively. Fig. 1A also shows similar FTIR spectra profiles in EO microcapsules and the raw materials. It demonstrates that CMC and CH matrix are chemically stable due to the absence of wave number shifting. However, the group of C21 showed stronger transmittance of bending at 2966 and 1745 cm-1 than C11and C12, which might relate to the influence of C=C stretching on surface EO or the crosslinking reaction between CH and CMC. It was revealed that the group of C21 and C12 had more surface oil and less encapsulation efficiency in EO microcapsules. The same results also confirmed by GC-MS (Fig.3A) in which C11 showed higher encapsulation efficiency compared to C12 and C21.

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These may be resulted from the differentiation in wall material ratios. Fernandes et al. (2016b) reported that the same profile spectra which used different constituted cashew gum and inulin as wall materials of EO microencapsulation. However, Zhang et al. (2018) found the different results that EO/β-cyclodextrin/CH microsphere had a red shift of characteristic vibration absorption peaks which were associated with the crosslinking reaction between β-cyclodextrin and CH. These differences showed the structure variations on microcapsules. And it may be due to the effect of content variations on wall material. 3.1.2. X-ray diffraction (XRD) analysis X-ray diffraction profiles obtained at different wall materials of EO microcapsules are presented in Fig. 1B. In general, a crystalline material presents sharp peaks while amorphous products provide a broader peak (Caparino et al. 2012). A reduction in 20° of microcapsules were observed, compared to pure wall materials due to the crosslinking reaction between CMC and CH. Nevertheless, there appeared three characteristic diffraction peaks at 33°, 47° and 57° both on group C12 and C21. These differentiations may be resulted from the different wall material ratios, different wall material ratios influenced the balance of negative charge and positive charge in emulsion and then it influenced the crosslinking of CH and CMC. The microcapsules of group C11 had an amorphous structure with a minimum of crystallinity, as indicated by diffuse and broad peaks in the diffractograms. Microencapsulation products which contained some crystalline components tend to dissolve slowly in solution, because the dissolution of crystals occurs only on the surface, exposed to the solvent (Fernandes et al., 2016a). The flowability and rehydration properties (such as solubility and dispersibility) of microencapsulation were influenced by the product crystallinity (Botrel et al., 2016). Microencapsulation powder, compared to the crystalline state, was dissolved quickly because the low

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energy level of bonds between molecules (Marabi et al., 2007). Botrel et al. (2016) also confirmed that amorphous materials tend to be more hygroscopic than the crystalline ones. Therefore, it was illustrated that EO encapsulated with CMC and CH (1:1, w/w) imparted better physical properties with less amorphous materials and better hygroscopic nature, compare to 1:2 and 2:1. The crystallinity of microcapsules was similar as that of the EO powders using blends of gum arabic, maltodextrin and inulin (Fernandes et al., 2016a, b). The variations of crystalline properties occurred during the process of spray drying while the inulin or β-cyclodextrin/chitosan used as wall materials (Botrel et al., 2016; Zhang et al., 2018). However, Zhou et al. (2017) demonstrated the presence of new crystalline phases for walnut oil microcapsules which used soybean protein isolate and maltodextrin as wall materials. 3.1.3. Scanning Electron Microscopy (SEM) analysis As the presence of positive charge of CH and the negative charge of protein or other polysaccharide materials, the hydrogel matrix of CH/CMC was generated by emulsion crosslinking from the neutralization of opposite charges (Xiao, Liu, Zhu, Zhou, & Niu, 2014). Fig. 2 illustrated different micro-crosslinking-structure on surface of EO microcapsules with different wall material ratios. Significant difference of the surface roughness and density were observed among them (roughness: C21＞C12＞C11). Results demonstrated that the rougher the surface the lower encapsulation efficiency of EO microcapsule (Fig. 2 and Fig. 3A). SEM analysis revealed that the microstructure of EO microencapsulation was observed to be smooth surface and it much more similar to powder (lower agglomeration) in the case of both CMC and CH used as wall materials (1:1), while the structures of EO microencapsulation in groups C12 and C21 were dense and roughness. Meanwhile the SEM results of EO microcapsules further provided evidence for the XRD results which confirmed the presence of amorphous structure, because the lower dense, roughness, agglomeration and higher ductility in C11.

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Similarly, EO/β-cclodextrin/CH particles prepared using the vacuum freeze-drying technology, showed the folded surface and loose internal structure (Caparino et al. 2012). Meanwhile, the morphological of EO microcapsules demonstrated that some small lumps on the surface, possibly because the effect of a non-uniform cross-linked reaction between CH and CMC (Jayanudin, Fahrurrozi, Wirawan, & Rochmadi, 2019). Touré et al. (2011) produced spray-dried EO/maltodextrin /whey protein isolate particles which had the spherical shape and a smooth surface. Edirs et al. (2016) observed small bubbles or craters exited on the skin surface of Nigella sativa oleoresin powder by spray drying technology. 3.1.4. In vitro release of volatile EO Using GC-MS analysis, it was determined that the major volatile components of the extracted EO were: gingerol (35.27 %), decanal (5.71 %), curcumene (14.62 %), 2-butanone (6.59 %) and zingiberene (24.53 %). Gingerol and zingiberene were the most two main volatile constituents emitted from EO. However, gingerol had higher retention rate than zingiberene during the process of vacuum freeze-drying (Fig. 3B). Additionally, Noori, Zeynali and Almasi (2016) detected the major organic compound of EO which extracted from mature rhizomes of ginger was zingiberene. Agarwal, Walia, Dhingra and Khambay (2001) reported that curcumene is the major constituent of fresh rhizomes of ginger. These differences may be due to the changes of ginger maturity, weather conditions, distillation conditions and the soil composition of ginger plant materials (Rehman, Hanif, Mushtaq, & Al-Sadi, 2015). Fig.3A depicts the encapsulation efficiency of EO microencapsulation with different wall material ratios. Microencapsulation in delivery system loading with CH and CMC (1:1) had the highest encapsulation efficiency of 88.50 %. Analyzing the different volatile profiles of EO components

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exhibited with different wall material ratios, in the case of EO microcapsules, it was observed that the particles of C11 with higher percentage content of gingerol, decanal, curcumene and zingiberene, compared to C12 and C21 (Fig. 3B). Results revealed that C11 endowed the highest oil retention and encapsulation efficiency. What’s more, Fig. 3B showed higher retention rate of gingerol, 2-butanone than decanal, curcumene and zingiberene, these effects may be related to the thermal decomposition of EO components by the process on ultrasound, which meant decanal, curcumene and zingiberene were more susceptible to influence by ultrasound. Changes in chitosan concentration produced irregular diffusion coefficients. A release system of EO in microcapsules and the effect of different CH concentration on EO release model had been found by Jayanudin, Fahrurrozi, Wirawan and Rochmadi (2018) and Jayanudin et al. (2019). It confirmed that CH-based microencapsulation was efficient to control EO release, and results indicated that the mathematical models are useful for operational design and evaluation of EO delivery system. 3.2. Quality traits of jujube fruit in EO delivery system 3.2.1. Verification of controlled release in EO delivery system The release rate of EO microencapsulation with CH and CMC (1:1) as wall material was monitored during 15 days room temperature storage (Fig. 3C). It was showed that cumulative release rate of EO was gradually increased during 15 days storage in room temperature. Moreover, CH/CMC-based microencapsulation was very benificial for controlling the release delivery system of EO. Therefore, EO microencapsulation is regarded as a very suitable delivery system applied on food preservation, because of the presence of antimicrobial, antioxidant and antibiotic properties of EO. Meanwhile, EO microencapsulation significantly improved the efficacy, increased safety and reduced environmental pollution. The similar statement was also reported by Jayanudin et al. (2019) that chitosan as wall

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material had a positive effect on the red ginger oleoresin release from microcapsules by cross-linking emulsion method. 3.2.2. Morphological characteristics of jujube fruit Fruits and vegetables suffer from postharvest losses during storage caused by physiological disorders, such as chilling damage, browning and diseases (Ahmad & Ali, 2018). Appearance is regarded as the most critical quality trait for selection of fresh products. It could be observed in Fig. 4 that EO microencapsulation delayed senescence and prolonged the shelf-life of jujube fruits. Severe black spots could be detected on the surface of untreated control after 7 d storage and several large areas rotting appeared after 14 d of storage. However, no rotten jujube fruits in response to EO microencapsulation were found after 7 d of storage. These results indicated that EO microencapsulation had positive effect on maintenance jujube appearance during storage at room temperature. In agreement with our results, Pires, Souza and Fernando (2018) reported that EO added to fresh poultry meat which spurred its desirable appearance up to 15 days. The similar result also endorsed by Noori et al. (2017) who confirmed the potential utility of EO nanoemulsion in chicken breast fillets preservation. 3.2.3. Jujube SSC and TA SSC and TA content in fruits showed a generally increasing trend at the early stage of storage, and thereafter dropped dramatically (Rialita et al. 2018). Both jujube SSC and TA contents at room temperature condition were significant increased at higher levels than the control (P<0.05, Fig. 5A, 5B). Results demonstrated that EO microencapsulation contributed to the inhibition of jujube SSC and TA change and had positive effect on quality maintenance of jujube fruit during postharvest storage at room temperature. Meanwhile, Vilaplana, Pérez-Revelo and Valencia-Chamorro (2018) reported that the thyme oil treatment had a positive effect on SSC and TA of pineapples.

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3.2.4. Red index (RI) and decay index (DI) RI and DI were closely related to the postharvest quality maintenance of fresh products during ripening and senescence. Furthermore, it could be used to evaluate the freshness and sensory evaluation of jujube fruit. Red index indicated the degree of maturity, which arises from anthocyanin oxidation during fruit development and ripening (Zhang et al., 2013). Results in present study demonstrated that EO microencapsulation could significantly inhibit the rise of RI, in comparison to control (Fig. 5C). It provided EO microencapsulation could effectively limit anthocyanin oxidation, mature development and enhance disease resistance activity, antifungal activity in jujube fruit. Similar study demonstrated that the red turning and browning are associated with the decrease of anthocyanin content (Kou et al., 2019). Decay index showed the disease resistance and antifungal activity (Guo, Yang, Ren, & Zhu, 2015). As shown in Fig. 5D, the antioxidant activity of jujube fruits was increased by EO microencapsulation treatment. Meanwhile, exogenous EO microencapsulation significantly lower the disease incidence of jujube fruit during storage period in comparison to control (Fig. 5D). EO are regarded as low risk natural products which can increase the fruit fungal resistance and maintain a similar or longer useful lifespan than currently used chemical fungicides (Vilaplana et al., 2018). In previous studies, thyme EO was reported to reduce postharvest decay development in pineapples, strawberries and oranges (Vilaplana et al., 2018). And Daniel, Lennox and Vries (2015) proved that clove EO effectively prevented postharvest decay on apples. 3.2.5. Sensory quality In response to EO microencapsulation, the sensory analysis of jujube fruits after 14 d of storage was

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shown in Fig.6. Results showed that EO microcapsules significantly maintained better sensory quality than control, especially in the appearance, crunchiness, firmness, juiciness. Specially, it provided evidence that EO microcapsules effectively maintained highest scores of total acceptances, texture and the freshness of jujube fruits. EO microencapsulation loaded in CH/CMC-based dual delivery system has potential application and developmental value prospects in food industries. Similar results were reported that the chicken meat coated with EO nanoemulsion exhibited pleasant acceptance score (Agarwal et al., 2001). Furthermore, it was evident that the browning of button mushroom was inhibited and the postharvest quality was maintained by Satureja khuzistanica essential oil (Nasiri, Barzegar, Sahari, & Niakousari, 2018). 4.

Conclusions

Rather than assigning ginger essential oil (EO) directly on postharvest jujube fruit, it is a combination of chitosan (CH) and sodium carboxymethyl cellulose (CMC) as wall materials that likely function synergistically to form EO capsules. Results given by GC-MS analysis indicated that the EO microencapsulation with CH and CMC (1:1) had highest encapsulation efficiency and retention rate of volatile EO release. SEM analysis displayed that EO microencapsulation at the same ratio of CH and CMC with a stronger ability to bind EO, forming a crosslinking structure with low dense, roughness, agglomeration and high ductility. Therefore, the balance of CH and CMC better retained EO emission, encapsulation efficiency and structural stability. EO microencapsulation effectively maintained postharvest quality and prolonged the shelf-life of jujube, mainly with the relatively lower decay rate and red rate, as well as the higher firmness, juiciness, SSC and TA content. Results further provided evidence for the potential utility of EO microcapsules on quality maintenance of fresh products. Continued work on building an understanding of the relationship between chitosan–EO interactions and

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host-mediated responses are next steps in the development of a long-term delivery platform for cell protection. Acknowledgments The authors are grateful to the Zhejiang Province Public Welfare Technology Application Research Project Foundation (No. LGN18C200022), Natural Science Foundation of Zhejiang Province (No. LY17C200008), the Youth Science Fund of Zhejiang University of Science and Technology (2019QN21) and National Key Research and Development Plan in 13th Five-Year of China (No. 2017YFD0401305) for financial support.

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Figure Captions Fig. 1 The physical and structure properties (A) Fourier transform infrared (FTIR) spectroscopy of ginger essential oil (EO) microcapsules; (B) X-ray diffraction (XRD) for ginger essential oil (EO) microcapsules. C11 means CMC:CH = 1:1; C12 means CMC:CH = 1:2; C21 means CMC:CH = 2:1; GO means ginger essential oil; CH means chitosan; CMC means sodium carboxymethyl cellulose. Fig. 2. Scanning electron microscopy (SEM) images at 20,000 x magnification of ginger essential oil (EO) microcapsules. C11 means CMC:CH = 1:1; C12 means CMC:CH = 1:2; C21 means CMC:CH = 2:1. Fig. 3. The GC-MS analysis of the ginger essential oil (EO) microcapsules. (A) The encapsulation

efficiency of ginger essential oil (EO) microcapsules; (B) The retention rate of major phytochemical components on ginger essential oil microencapsulation (using the percentage of peak area to describe); (C) The cumulative percent of release generated from ginger essential oil microencapsulation (C11) during storage of jujube fruits in room temperature for 15 days. All data were expressed as mean values ± standard deviations (SD). Duncan Multiple Range Test was used for the comparison of means, with significance assigned at P<0.05. C11means CMC:CH = 1:1; C12 means CMC:CH = 1:2; C21 means CMC:CH = 2:1. Fig. 4. The morphological changes of jujube fruits during storage. Fig. 5. Soluble solids content (SSC), titratable acidity (TA), red index (RI) and decay index (DI) of jujube fruits during storage. All data were expressed as mean values ± standard deviations (SD). Duncan Multiple Range Test was used for the comparison of means, with significance assigned at P<0.05. CT means control; EO means ginger essential oil microencapsulation.

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Fig. 6. Sensory Evaluation (appearance, sweetness, crunchiness, firmness, juiciness, fruity flavor) of jujube fruits after storage. CT means control; EO means ginger essential oil microencapsulation.

Highlights ·

Polysaccharide was used as microencapsulating agents for ginger essential oil.

·

Microencapsulation in delivery system loading with CH and CMC (1:1) showed best encapsulation efficiency and stability.

·

Ginger essential oil microcapsules controlled the release of ginger during room temperature storage.

·

EO microcapsules contributed to the quality maintenance of postharvest jujube.

Fig.1. A

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C11 C12

Transmittance/(%)

C21 GO

CH CMC

500 1000 1500 2000 2500 3000 3500 4000

Wavenumber/(cm-1)

B C11

Intensity/(counts)

C12 C21

CH CMC

0

10

20

30

40

50

Diffraction angle/(o)

28

60

70

Fig. 2. C11

C12

C21

29

Fig. 3. A

c

C21

b

C12

a

C11

0

20

40

60

80

100

Encapsulation efficiency/(%)

B 20

Percentage of peak area/(%)

18

a

C11 C12 C21

b c

16 14 12 10 8

b

6 4 2 0

a a a Decanal

a

a bb

a

b

b b

Curcumene Zingiberene 2-Butanone

Different component in ginger EO

30

Gingerol

C 90

a

80

b

Release rate/(%)

70 60 50

d

40 30

e

20 10 0

cd

c

e

f 0

2

4

6

8

10

Days of storage/(d)

31

12

14

16

Fig.4.

32

Fig.5.

B

CT EO a

b c

c

a a b

b 20

bc

c

15

10

0 7 14 Days of storage/(d)

a 80 C b b 70 c 60 50 40 30 20 d d 10 0 0 7 14 Days of storage/(d)

33

25

a

a

TA/(%)

A

16

0 7 14 Days of storage/(d)

a

D

12

DI/(%)

RI/(%)

SSC/(%)

24 23 22 21 20 19 18 17 16 15

b

8

b

4 0

c c

c

0 7 14 Days of storage/(d)

Fig.6.

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 relationships which may be considered as potential competing interests:

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