Effects of lactic acid fermentation-based biotransformation on phenolic profiles, antioxidant capacity and flavor volatiles of apple juice

Apple juice (AJ) was fermented by six select lactic acid bacteria (LAB), namely Lactobacillus plantarum 90 (Lp90), Lactobacillus helveticus 76 (Lh76), Lactobacillus casei 37 (Lc37), Lactobacillus paracasei 01 (Lpc01), Lactobacillus acidophilus 85 (La85) and Bifidobacterium lactis 80 (Bla80). The effects of LAB fermentation on sugars and organic acids contents, phenolic profiles, antioxidant capacity and flavor volatiles of fermented AJ (FAJ) were investigated. Results showed that AJ was an excellent food matrix for LAB strains. Lh76 and Lp90 showed the highest viable counts of 12.7 log CFU/mL at the end of fermentation. Lp90, La85 and Bla80 exhibited strong malolactic conversion capacity and finally produced lactic acid more than 6.5 mg/mL. In addtion, LAB fermentation significantly (p < 0.05) decreased the total phenols and flavonoids levels. However, antioxidant activities based on DPPH and FRAP methods were enhanced during fermentation, especially for La85 which exhibited dramatical DPPH radical scavenging activity (90.05%) and FRAP (0.96 mmol Trolox/L). The improvement of antioxidant activities was suggested to be related to the increase in caffeic acid and phlorizin contents. The analysis of flavor volatiles showed that LAB fermentation resulted in formation of seven new alcohols and six new esters, and improvement of ketones and aldehydes production.