Influence of sonication-assisted fermentation on the physicochemical features and antioxidant activities of yogurts fortified by polyphenol-rich pineapple peel powder with varied chemical profiling

This study investigated the effects of pineapple peel powder with varied chemical profiles and sonication-assisted polyphenol biotransformation during fermentation on the quality characteristics of yogurt products. It aimed at exploring the feasibility of sonication-assisted fermentation to enhance the physicochemical properties, control post-acidification, and improve antioxidant activities in yogurts fortified with polyphenol-rich pineapple peel powder. Targeted analysis showed that polyphenol-rich pineapple dietary fiber obtained by ultrasonication-assisted extraction (NPFU) exhibited the slowest rates of acidification, highest antioxidant capacity, and lowest degree of whey separation at 21.67 %. Sonication pretreatments significantly increased transformation of free phenolic acids derived from pineapple peel fiber during fermentation, particularly increasing the accumulation of ferulic acid, caffeic acid and 5-hydroxyflavone, revealing the positive effects of sonication-mediated fermentation in promoting the hydrolysis of conjugated phenolics into free fractions. Yogurts fortified with pineapple peel fiber displayed significantly higher antioxidant activities (p < 0.05) compared to those with pineapple peel whole powder, corresponding with the increased free phenolics. Non-targeted metabolomics analysis was employed to explore the mechanisms underlying the alleviated post-acidification by sonication-assisted fermentation during storage. Metabolomic profiling revealed that the bioactive components from pineapple peel extract significantly influenced the metabolism pathways of lactic acid bacteria particularly involving galactose metabolism, glycerophospholipid metabolism, closely associated with the acid production of the strains and the regulation of the post-acidification rates of yogurt during storage. These results confirmed the potential of ultrasound-assisted fermentation combined with the addition of pineapple dietary fiber to enhance yogurt quality, providing an innovative tool to develop future yogurt products with high marketability.