《现代食品工程高新技术》课程教学资源（文献资料）食品包装、杀菌新技术 Comparing quality changes of cupped strawberry treated by high hydrostatic pressure and thermal processing during storage.pdf

food and bioproducts processing 1 0 0 ( 2 0 1 6 ) 221–229 Contents lists available at ScienceDirect Food and Bioproducts Processing journal h om epage: www.elsevier.com/locate/fbp Comparing quality changes of cupped strawberry treated by high hydrostatic pressure and thermal processing during storage Ge Gao a,b,c,d, Pengyan Rena,b,c,d, Xiamin Cao a,b,c,d, Bing Yana,b,c,d, Xiaojun Liao a,b,c,d, Zhijian Suna,b,c,d, Yongtao Wang a,b,c,d,∗ a Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing 100083, China b College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China c National Engineering Research Center for Fruit & Vegetable Processing, Beijing 100083, China d Key Laboratory of Fruit & Vegetable Processing, Ministry of Agriculture, Beijing 100083, China a r t i c l e i n f o Article history: Received 3 April 2015 Received in revised form 1 June 2016 Accepted 28 June 2016 Available online 22 July 2016 Keywords: High hydrostatic pressure processing Cupped strawberry Texture Anthocyanins Color a b s t r a c t High hydrostatic pressure (HHP) and thermal processing of strawberry in ethylene vinyl alcohol copolymer cups were evaluated by examining their impacts on microorganism survival and growth, texture, nutritional properties (total phenols, total anthocyanins and antioxidant capacity) and color during 45 days of storage at 4 and 25 ◦C. During storage, total aerobic bacteria and yeasts and molds were not detected in all treated samples except for those HHP-treated and stored at 25 ◦C (3.08 and 2.58 log10 CFU/g at day 45, respectively). There was a reduction in hardness, total phenols, total anthocyanins and antioxidant capacity of flesh, being more striking in samples stored at 25 ◦C and thermal processing treated samples, and an increase in viscosity, total phenols, total anthocyanins and antioxidant capacity of syrup during storage. Moreover, a significant decrease in the total level of nutritional properties in cupped strawberry (combined flesh and syrup) was observed during storage. All samples showed noticeable color changes, and E values significantly increased during storage. Samples treated by HHP and stored at 4 ◦C showed higher hardness, total phenols, total anthocyanins and antioxidant capacity and better color than samples treated by thermal processing and stored at 25 ◦C, indicating that HHP processing and lower storage temperature were very useful tool in preserving the quality of cupped strawberry. © 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction Strawberries are a soft juicy and palatable berry with brightred color, and an important bioresource with good processing potential as functional foods. They are abundant in bioactive compounds with antioxidant properties, mainly including phenolic compounds, especially anthocyanins (Terefe et al., 2009; Cao et al., 2012). The antioxidant capacity of strawberry can participate in the prevention of cancer, cardiovascular and ∗ Corresponding author at: College of Food Science & Nutritional Engineering, China Agricultural University, No. 17, Qinghua East Road, Haidian District, Beijing 100083, China. Fax: +86 10 62737434. E-mail address: wangyongtao102@163.com (Y. Wang). other chronic diseases (Oszmianski ´ and Wojdyło, 2009). However, strawberries have a very short postharvest life since they are rather susceptible to physical damage and fungal attack, and are also very sensitive to deterioration in color, texture and flavor during transport, storage and processing (Terefe et al., 2009). In recent years, strawberry with syrup in EVOH (ethylene vinyl alcohol copolymer) cups, preserved using thermal processing (TP) has become popular in China. However, TP can deteriorate the quality of processed strawberries, http://dx.doi.org/10.1016/j.fbp.2016.06.017 0960-3085/© 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

222 food and bioproducts processing 1 0 0 ( 2 0 1 6 ) 221–229 including the color, texture, taste, and functional compounds, due to the heat sensitivity of the strawberry and its labile constituents. High hydrostatic pressure (HHP) is a non-thermal food preservation technique which subjects foods to up to 1000 MPa at room or mild process temperatures (<60 ◦C) (Cao et al., 2012). Pathogens and vegetative spoilage microorganisms are inactivated by HHP processing thereby enhancing safety and shelf life of perishable foods (Knorr, 1993; Mújica-Paz et al., 2011). HHP processing is a good alternative to heat treatment because it does not lead to deterioration of the color, flavor, texture, and nutritional values of foods due to its limited effect on the covalent bonds of low molecular-mass compounds (Balasubramaniam et al., 2008; Oey et al., 2008; Mújica-Paz et al., 2011; Cao et al., 2012). Up to now, HHP has been applied to process many fruit products such as blackberry puree (Patras et al., 2009), apple puree (Landl et al., 2010), pomegranate juice (Varela-Santos et al., 2012), strawberry puree and juice (Patras et al., 2009; Cao et al., 2011, 2012), mango pulp (Liu et al., 2012) and yellow peach in pouches (Zhang et al., 2012). Previous studies demonstrated that endogenous enzymes related to food quality may show pressure resistance or even be activated by HHP processing (Oey et al., 2008; Cao et al., 2011). The residual activity of endogenous enzymes, such as pectin methyl esterase (PME), polyphenol oxidase (PPO) and peroxidase (POD), induced the changes in texture, nutritional properties and color in HHP-treated fruit and vegetable products during processing and storage (Patras et al., 2009; Nguyen et al., 2010; Landl et al., 2010; Cao et al., 2011; Torres et al., 2011; Varela-Santos et al., 2012). Therefore, the total inactivation of endogenous enzymes may be propitious to preserve the quality of HHP-processed fruit and vegetable products. However, literature data on the effect of HHP processing on the quality of fruit and vegetable products in the absence of endogenous enzymes is very limited. The objective of this work was to evaluate the impact of HHP and TP of cupped strawberry on microorganisms, texture, total phenols, total anthocyanins, antioxidant capacity and color during storage. This study will provide technical support for commercial application of HHP technique in strawberry processing. 2. Materials and methods 2.1. Preparation of cupped strawberry In this study, the strawberry variety “Camarosa”, harvested at commercial maturity in March 2012, was obtained from Tianyi Bio-engineering Company in Changping county (Beijing, China). Fresh strawberries were rinsed in tap water, blanched by steam (core temperature of strawberries 100 ◦C) for 1min in a steam pan (CJ128, Zhenghan Stainless Steel Factory, Guangzhou, Guangdong) heated by an electromagnetic furnace (Midea RT 2103, Guangdong Midea Electrical Co., Ltd., Foshan, Guangdong) to inactivate the endogenous enzymes, cooled to 25 ◦C by running water immediately, and placed in plastic cups (EVOH, 227mL). 80 g strawberries were packed in each cup, and then 154mL syrup (boiled for 10min and cooled to 60 ◦C) with 16 g/L sucrose (Beijing Sugar Tobacco & Wine Co., Beijing, China) and 0.16 g/L citric acid was poured into each cup. The cups were vacuum sealed (0.04 MPa) immediately with plastic film (nylon/polyethylene), and cooled to 25 ◦C by running water within 30min. 2.2. HHP and TP treatments of cupped strawberry HHP treatments were carried out using a hydrostatic pressurization unit (HHP-700, Baotou Kefa Co., Ltd., Inner Mongolia, China) with a capacity of 7 L at ambient temperature (25 ± 1 ◦C). The diameter of the cylinder was 150mm. The pressurization rate was about 120 MPa/min and the depressurization was immediate (<3 s). Distilled water was used as the pressure-transmitting fluid. The treatment time in this study did not include the pressure-increase time and pressurerelease time. TP treatment was carried out by heating samples also stored in EVOH cups in water in a thermostatic water bath (LY-9A, Qingyuan Science & Technology Development Co., Ltd., Beijing, China). A thermocouple was inserted into the center of the strawberry located at the package cold point. When samples achieved a core temperature of 75 ◦C, they were held at this temperature for 20min. Then, samples were immediately cooled to 25 ◦C by running water. According to our previous studies, after HHP (400 MPa/5min) and TP (75 ◦C/20min) treatments, total aerobic bacteria (TAB) and yeasts and molds (Y&M) were not detected, and good hardness and color of samples was preserved. Therefore, cupped strawberries were treated by these treatments, and the qualities of these treated samples were evaluated during storage in this study. The control sample was a vacuum sealed cup of strawberries in syrup that did not receive any further treatment. 2.3. Storage conditions and sampling dates The treated samples were stored at 4 ◦C and 25 ◦C in the dark. Sample analyses were carried out after 0, 15, 30 and 45 days of storage. 2.4. Microbiological analysis TAB and Y&M were estimated using the method described by Wang et al. (2012). Treated and control samples were serially diluted with sterile 0.85% NaCl solution, and 1.0mL of each dilution was plated into duplicate plates of appropriate agar. All measurements were made in triplicate. 2.5. Measurement of pH Strawberry flesh was pulped by juice extractor (JY-610, Joyoung Co., Ltd., Shandong, China) for 5min, and equilibrated at 25 ◦C. pH value was measured at 25 ◦C with a thermo Orion 868 pH meter (Thermo Fisher Scientific, Inc., MA, USA). All measurements were made in duplicate. 2.6. Hardness of flesh The hardness of flesh was determined using the method described by Trejo Araya et al. (2007) with some modifications. Texture profile analysis was used to evaluate the hardness of flesh by using a texture analyzer (TA-XT2i, Stable Micro System, Surrey, UK). Samples were equilibrated to 25 ◦C before textural analysis. One single fruit was taken from syrup, cut into cylinders (10mm long with a diameter of 12mm) by a hole puncher, and placed on the base plate of the texture analyzer. The sample was measured with a 250 N cell at a deformation rate of 1mm/s on the platform as an upright cylinder. The crosshead pre-test, test, and post-test speed was 1mm/s

food and bioproducts processing 1 0 0 ( 2 0 1 6 ) 221–229 223 with a rest period of 5 s between cycles, and the deformation was 30% of the original height. Ten determinations were performed for each treatment. 2.7. Viscosity measurement of syrup The viscosity of syrup was determined using an AR550 rheometer (TA Instruments, Waters Co., Ltd., Surrey, UK) with a conical end concentric cylinder (stator radius 15mm, rotor radius 14mm, immersed height 42mm, gap 5.92mm). An aliquot of syrup (13.5mL) was applied at each measurement at 25 ± 0.1 ◦C controlled by circulating water in a thermostatic system. In the test, the shear rate was increased from 4 to 63 s−1, and three determinations were performed for each treatment. 2.8. Quantification of total phenols Strawberry flesh was pulped by juice extractor (JY-610, Joyoung Co., Ltd., Shandong, China) for 5min. 5 g of strawberry pulp was mixed with 30mL of methanol, and then the mixture was kept in the dark for 30min at 4 ◦C, centrifuged at 12,000 × g for 10min at 4 ◦C (GR21G, Hitachi Koki Co., Ltd., Tokyo, Japan). The supernatant was collected for further analysis. The total phenols were determined using the Folin–Ciocalteu method described by Cao et al. (2011) with some modifications. A 0.4mL volume of flesh extract (or syrup) was mixed with 2mL of Folin–Ciocalteu reagent (previously diluted 10-fold with distilled water) and set for 1h in the dark at room temperature. After that, 1.8mL of sodium carbonate solution (7.5%) was added to the mixture and reacted for 15min, and then the mixture absorbance was immediately measured at 765nm using a spectrophotometer (UV-726, Shimadzu, Shanghai, China). Results were expressed as mg of gallic acid equivalent (GAE) per 100 g of flesh (mg GAE/100 g), or 100mL of syrup (mg GAE/100mL). All measurements were made in duplicate. 2.9. Quantification of total anthocyanins Strawberry flesh was pulped for 5min to be made into strawberry syrup. 5 g strawberry pulp was mixed with 10mL of 0.1% HCl in methanol, and then the mixture was kept in the dark for 2h at 4 ◦C, centrifuged at 12,000 × g for 10min at 4 ◦C. The supernatant was collected for further analysis. The spectrophotometric pH differential method (Xu et al., 2010) was used to quantify anthocyanins in the extracts in this study. Two dilutions of the same sample (flesh extracts or syrup) were prepared using 0.025 M potassium chloride solution and 0.4 M sodium acetate solution adjusted to pH 1.0 and 4.5 with HCl, respectively. The absorbance of each dilution was measured at 520nm against a distilled water blank using a spectrophotometer (UV-726, Shimadzu, Shanghai, China). Anthocyanin content was calculated by the following equation. Anthocyanin content of flesh (mg/100 g) = A × MW × DF × V × 100 ε × L × m (1) Anthocyanin content of syrup (mg/100mL) = A × MW × DF × 100 ε × L (2) where A = ApH1.0–ApH4.5, MW is the molecular weight of pelargonidin-3-glucoside (433 g/mol); DF, the dilution factor; V, the volume of flesh extract (mL); ε, the molar absorptivity of pelargonidin-3-glucoside (22,400 L cm−1 mol−1); L, the path length (1 cm); m, the weight of flesh (g). Total anthocyanin content was reported as milligrams anthocyanins per 100 g of flesh (mg/100 g), or 100mL of syrup (mg/100mL). All measurements were made in duplicate. 2.10. Antioxidant capacity measurements The DPPH and FRAP assays were performed as described by Wang et al. (2012) with some modifications. A 100L aliquot Table 1 – Changes of color parameters in cupped strawberry during storage at 4 ◦C and 25 ◦C. Storage time (day) Flesh Syrup HHP 4 ◦C TP 4 ◦C HHP 25 ◦C TP 25 ◦C HHP 4 ◦C TP 4 ◦C HHP 25 ◦C TP 25 ◦C L* 0 38 ± 2 41 ± 5 38 ± 2 41 ± 5 32 ± 0 32 ± 0 32 ± 0 32 ± 0 15 39 ± 2 44 ± 3 41 ± 1 44 ± 2 17 ± 0 16 ±0 17 ± 0 18 ± 0 30 40 ± 0 43 ± 2 41 ± 0 43 ± 2 14 ± 0 17 ± 0 21 ± 0 16 ± 0 45 42 ± 2 46 ± 1 38 ± 4 40 ± 5 17 ± 0 20 ± 0 24 ± 0 28 ± 0 a* 0 25 ± 5 27 ± 2 25 ± 5 27 ± 2 10 ± 0 10 ± 0 10 ± 0 10 ± 0 15 24 ± 6 24 ± 1 22 ± 3 23 ± 2 21 ± 0 19 ± 0 18 ± 0 20 ± 0 30 24 ± 2 23 ± 1 21 ± 2 21 ± 2 17 ± 0 20 ± 0 20 ± 0 16 ± 0 45 24 ± 0 23 ± 2 18 ± 1 22 ± 2 17 ± 0 19 ± 0 18 ± 0 22 ± 0 b* 0 12 ± 3 12 ± 0 11 ± 3 12 ± 2 5 ± 0 6 ± 0 5 ± 0 6 ± 0 15 11 ± 3 12 ± 1 11 ± 2 11 ± 1 23 ± 0 16 ± 0 17 ± 0 16 ± 0 30 11 ± 1 11 ± 0 10 ± 1 10 ± 1 17 ± 0 19 ± 0 17 ± 0 19 ± 0 45 11 ± 2 12 ± 1 7 ± 1 9 ± 0 12 ± 0 16 ± 0 14 ± 0 18 ± 0 E 0 0 0 0 0 0 0 0 0 15 2 4 4 5 25 21 21 20 30 3 4 6 7 23 22 19 21 45 4 6 6 8 18 18 14 18 TP, thermal processing; HHP, high hydrostatic pressure processing. All data were the means ± SD, n = 3.

224 food and bioproducts processing 1 0 0 ( 2 0 1 6 ) 221–229 Fig. 1 – The change of flesh hardness of cupped strawberry during storage. HHP-treated samples stored at 4 ◦C; HHP-treated samples stored at 25 ◦C; TP-treated samples stored at 4 ◦C; TP-treated samples stored at 25 ◦C. Values with different letters within the same storage time are significantly different (P < 0.05). All data were the means ± SD, n = 10. of flesh extract (or syrup) was mixed with 4mL methanolic DPPH (Sigma–Aldrich, St. Louis, USA) solution (0.14mM). The samples were kept in the dark for 45min at room temperature before measurement of the decrease in the absorption at 517nm. Freshly prepared FRAP solution contained 25mL 0.3 M acetate buffer (pH 3.6), 2.5mL 10mM tripyridyltriazine (Sigma–Aldrich, St. Louis, USA, dissolved in 40mM HCl) and 2.5mL 20mM ferric chloride. 4mL FRAP solution was mixed with 100L trolox solution or sample (flesh extracts or syrup) at 37 ◦C. Ten minutes later, the ferric reducing ability of samples was measured by monitoring the increase of absorbance at 593nm using the spectrophotometer. Trolox (Sigma–Aldrich, St. Louis, USA) solutions within the range of 50–1000M were used for calibration. A new trolox calibration curve was made for each assay. The results were expressed as mg of trolox per 100 g flesh (mgTrolox/100 g), or 100mL syrup (mgTrolox/100mL). All measurements were made in duplicate. 2.11. Color assessment Color assessment was conducted at 25 ± 2 ◦C using a color measurement spectrophotometer (HunterLab ColorQuest XE, Hunter Associates Laboratory, Inc., Virginia, USA) in the reflectance mode for flesh and the transmission mode for syrup. Color was expressed in L*, a* and b* values. All measurements were made in triplicate and results were averaged. In addition, total color difference (E) were calculated using the following equation, where L∗ 0, a∗ 0 and b∗ 0 are the values for samples without any storage. E = [(L∗ − L∗ 0) 2 + (a∗ − a∗ 0) 2 + (b∗ − b∗ 0) 2 ] 1/2 (3) Fig. 2 – Changes of viscosity of syrup in cupped strawberry during storage at 4 and 25 ◦C. (A) HHP-treated samples stored at 4 ◦C; (B) HHP-treated samples stored at 25 ◦C; (C) TP-treated samples stored at 4 ◦C; (D) TP-treated samples stored at 25 ◦C; 0 day; 15 day; 30 day; 45 day.

food and bioproducts processing 1 0 0 ( 2 0 1 6 ) 221–229 225 Fig. 3 – Changes of total phenols and anthocyanins in cupped strawberry during storage at 4 ◦C and 25 ◦C. (A) Total phenols in flesh; (B) total phenols in syrup; (C) total anthocyanins in flesh; (D) total anthocyanins in syrup. HHP-treated samples stored at 4 ◦C; HHP-treated samples stored at 25 ◦C; TP-treated samples stored at 4 ◦C; TP-treated samples stored at 25 ◦C. Values with different letters within the same storage time are significantly different (P < 0.05). All data were the means ± SD, n = 2. 2.12. Statistical analysis The data were analyzed using the Statistical Program for Social Sciences (SPSS 12.0, Chicago, IL, USA) software for analysis of variance and Duncan’s test. The significance was established at P ≤ 0.05. 3. Results and discussion For all samples, the pH value (3.2) of strawberry flesh showed no significant change during storage at 4 and 25 ◦C (data not shown). 3.1. Microbiological analysis of cupped strawberries As shown in Table 1, the initial counts of TAB and Y&M in untreated sample were 4.62 and 3.71 log10 CFU/g, respectively. Both HHP and TP treatments resulted in reduction of TAB and Y&M to a level below the detection limit, and the counts of TAB and Y&M in HHP-treated samples stored at 4 ◦C and TP-treated ones stored at 4 and 25 ◦C remained lower than the detection limit during 45 days of storage. Therefore, HHP-treated samples stored at 4 ◦C and TP-treated ones at 4 and 25 ◦C exhibited a better microbiological stability during storage. Interestingly, the counts of the TAB and Y&M in HHPtreated samples stored at 25 ◦C were lower than the detection limit before day 30, but increased to 3.08 and 2.58 log10 CFU/g respectively at day 45, respectively. This was interpreted as existence of a sublethal injury of cells after HHP and TP treatment, which prevented their growth until they later recovered during storage. Penas ˜ et al. (2010) ascribed the increase of TAB in sauerkraut during the third month of refrigerated storage after HHP to the recovery of microorganisms that were sublethally injured by HHP. Ritz et al. (2001, 2006) also found that no cell growth occurred after HHP treatment on plate count agar, and recovery was observed for L. monocytogenes after 4 days of storage at 20 ◦C in phosphate (pH 7.0) and citrate (pH 5.6) buffer, but no recovery was observed in pressurized samples stored at 4 ◦C. These earlier studies indicated that elevated incubation temperatures may be critical for repair of HPP-induced physiological damage, and recovery was completed at elevated incubation temperatures, which then allowed rapid growth. It was similar to our result in this study. The recovery of TAB and Y&M in HHP-treated samples was observed after 45 days at 25 ◦C, however, at 4 ◦C injured cells could not be recovered. 3.2. Hardness of flesh of cupped strawberries As shown in Fig. 1, at day 0, the hardness of HHP-treated samples was 6.1 ± 0.3 N, whereas the hardness was 2.4 ± 0.1 N in TP-treated ones, indicating that HHP treatment retained the hardness of the flesh. Similarly, Nguyen et al. (2010) and Zhang et al. (2011) proposed that HHP processing improved texture retention while thermal processing led to texture softening of carrot, jicama and yellow peach. All treated samples showed a significant reduction in the hardness of flesh during storage at 4 and 25 ◦C (P ≤ 0.05)