Effect of Lactiplantibacillus plantarum fermentation on the quality and volatile flavor components of Nanguo pear juice

The Nanguo pear juice was fermented by Lactiplantibacillus plantarum and the variation patterns of physicochemical properties (pH value, total acid, total sugar, reducing sugar, total phenol, total flavonoids) and antioxidant capacity during the fermentation process of Nanguo pear juice were studied. The volatile flavor substances in the Nanguo pear juice before and after fermentation were analyzed by gas chromatography-mass spectrometry (GC-MS) technology. The results showed that L. plantarum grew well in Nanguo pear juice, reaching a viable count of 8.89 lg (CFU/ml) after fermentation for 36 h. During the fermentation process of Nanguo pear juice, the reducing sugar content decreased by 30.57%, the pH value decreased by 1.59, and the contents of total acid, total phenol and total flavonoids increased by 60%, 78.65% and 79.21% respectively. The radical scavenging rates of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) significantly increased, reaching 57.41% and 65.06%, respectively. The GC-MS analysis results showed that 64, 72, and 55 volatile flavor substances were detected in before and after the fermentation of Nanguo pear juice by L. plantarum, and Nanguo pear juice fermented without inoculation, respectively. The fermentation by L. plantarum increased the types and contents of volatile flavor components in Nanguo pear juice. Among them, the relative contents of alcohols, esters and ketones increased by 62.22%, 6.34% and 72.11%, respectively. The flavor of Nanguo pear juice was the optimal when it was fermented for 24 h, with a sensory score of 91.5 points. This indicated that the fermentation by L. plantarum could improve the aroma and taste of Nanguo pear juice.