梨汁在加工过程中极易褐变，乳酸菌发酵能有效保护梨汁的色泽。本研究测定梨汁发酵及储藏过程中色泽、多酚氧化酶活性、酚类物质、抗坏血酸含量等指标的变化，并与未发酵梨汁和添加柠檬酸的调酸梨汁对比，探索乳酸菌发酵对果蔬汁的护色机理。30天储藏期内，未发酵梨汁褐变指数从0.073变化至0.310，显著高于发酵梨汁（0.134）；乳酸菌发酵作用有效抑制了多酚氧化酶的活性，使得发酵梨汁中的酚类物质的保存率（43%）显著高于未发酵梨汁（16%）；发酵梨汁中抗坏血酸稳定性更高，保存率（85%）较未发酵梨汁高（50%），减少了非酶褐变。乳酸菌通过在梨汁中发酵产酸，抑制多酚氧化酶的活性，保存酚类、抗坏血酸等物质，从而保护梨汁色泽。

Pear juice easily turns brown during processing, and lactic acid bacteria fermentation could effectively protect the color of pear juice. This study determined the changes in indices like color, polyphenol oxidase activity, contents of phenolics and ascorbic acid in pear juices during fermentation and storage, and compared with unfermented pear juice and citric acid-fortified pear juice to explore the mechanism underlying the color protection via Lactic acid bacteria fermentation for fruit and vegetable juices. During the 30-day storage, the browning index of unfermented pear juice changed from 0.073 to 0.310, which was significantly higher than that of fermented pear juice (0.134). The fermentation using Lactic acid bacteria effectively inhibited the activity of polyphenol oxidase, leading to a significantly higher retention rate (43%) for the phenolics in the fermented pear juice than that of the unfermented pear juice (16%). The stability of ascorbic acid in the fermented pear juice was higher with, the retention rate (85%) being higher than that of unfermented pear juice (50%), by which non-enzymatic browning was reduced. Lactic acid bacteria could inhibit the activity of polyphenol oxidase through producing organic acid via fermentation in pear juice, and preserve substances such as phenolics and ascorbic acid to protect effectively the color of pear juice.

国家重点研发计划项目（2017YFD0400400）；中央高校基本科研业务费专项资金资助项目（x2skD2170940）