鲜食核桃仁抑制褐变与脱色方法及货架期保鲜效应

Browning Inhibition and Decolorization of Fresh Walnut Kernels and Their Effect on Browning-Related Enzyme Activity,Antioxidant Properties and Quality Attributes during Cold Storage

鲜核桃仁因易于褐变而难以作为成品生产与销售。本实验以‘香玲’核桃湿鲜坚果为试材,分别对新鲜核桃仁、已褐变核桃仁进行不同工艺参数下4种方法抑制褐变以及2种方法脱色处理,根据20℃货架期下色值变化和感官观测结果,选取两组实验的最佳处理条件分别为1.0%(质量分数,后同)抗坏血酸(ascorbic acid,AsA)+0.05%柠檬酸(citric acid,CA)浸泡5 min(抑制褐变)以及1.0%AsA 20℃下浸泡1 h(脱色)。分别用两种方法单独处理或与1 kJ/m^(2)短波紫外线(ultraviolet radiation C,UVC)复合处理,以同等条件下去离子水处理为对照组,统一用30μm厚的聚乙烯袋包装,5℃货架保鲜。结果表明,两组实验中,单独处理和UVC复合处理均可持续抑制多酚氧化酶(polyphenol oxidase,PPO)、过氧化物酶(peroxidase,POD)活力升高,苯丙氨酸解氨酶(phenylalanine ammonia lyase,PAL)活力在货架14~21 d时较对照组显著提高(P<0.05),第56天时抑制褐变的单一和复合处理组及脱色的复合处理组酸价均显著低于对照组(P<0.05)。两组实验中复合处理可同时延缓细菌和霉菌的滋生,部分提高总抗氧化活性(ferric reducing/antioxidant power,FRAP);核桃仁过氧化值(peroxide value,POV)有所增加,含油率未受明显影响,1,1-二苯基-2-三硝基苯肼(1,1-diphenyl-2-picrylhydrazyl,DPPH)自由基清除能力与对照组差异不明显。核桃仁种衣和去皮核桃仁的PPO活力均受AsA的竞争性抑制。5℃货架56 d时,脱色组复合处理核桃仁的亮度(L*值)达到与抑制褐变处理同等效果,且核桃仁无可见霉变。本研究结果可为鲜核桃仁的商品化生产提供理论与技术依据。

Fresh walnut kernels are prone to browning,making it difficult to produce and market it as a finished product.In this study,fresh walnut kernels(cv.‘Xiangling’)were subjected to four browning inhibition methods and browned kernels were decolorized by two methods.According to the changes of color parameters and sensory quality during storage at 20℃,dipping in 1.0%ascorbic acid(AsA)+0.05%citric acid(CA)for 5 min and dipping in 1.0%AsA at 20℃for 1 h were found to be the best browning inhibition and decolorization conditions,respectively.To evaluate their effect on the quality maintenance of walnut kernels,the two treatments were performed individually or in combination with 1 kJ/m2 ultraviolet radiation C(UVC),and the treated samples were subsequently packed in polythene(PE)bags(30μm thick)and stored at 5℃.Those treated with deionized water under the same conditions served as a control group.Results showed that both individual and combined treatments inhibited the increase in the activities of polyphenol oxidase(PPO)and peroxidase(POD)during storage.The activity of phenylalanine ammonia-lyase(PAL)was significantly enhanced during 14-21 d in comparison to controls(P<0.05).On 56 d,acid value(AV)of both individual and combined treatments in browning inhibition group as well as the combined treatment in decolorization group were significantly lower than their controls(P<0.05).Combined treatments in two experiments simultaneously delayed the breeding of bacteria and mould,partially promoted the ferric reducing antioxidant power(FRAP),and the peroxide value(POV)was increased,while the oil content was little changed.The 1,1-diphenyl-2-picrylhydrazyl(DPPH)scavenging capacity was not significantly different from that of the control group.AsA competitively inhibited PPO activity in walnut kernel skins and skinless walnut kernels.After 56 days of storage at 5℃,the brightness(L*)value of decolorized walnut kernels was similar to that of the browning inhibition group,and no mildew was observed.The results from this study could provide a theoretical and technical basis for the commercial production of fresh walnut kernel.