| Summary: | Lactic acid bacteria (LAB) are widely utilized in the production of various fermented foods. <i>Lacticaseibacillus casei</i> (<i>Ls. casei</i>) fermentation has been demonstrated to enhance antioxidant activity, flavor, and nutritional value. This study aimed to evaluate the physicochemical properties, proximate chemical compositions, antioxidant activities, and volatile profiles of pineapple juice fermented by <i>Ls. casei</i> LK-1. Strain growth, physicochemical parameters, phenolics and flavonoids, carbohydrates, organic acids (by HPLC), free amino acids (FAAs), antioxidant activities (DPPH and FRAP methods), and volatile profiles (by GC-MS) of fermented pineapple juice were characterized. After 30 h of fermentation, the cell count reached 9.07 log CFU/mL. The fermentation process led to a significant decrease in pH, total soluble solids (TSS), and the <i>a</i>* value (<i>p</i> < 0.05), with an increase in the <i>L</i>* and <i>b</i>* values (<i>p</i> < 0.05). Lactic acid and total umami amino acids were elevated, whereas sucrose and total sweet amino acid levels remained unchanged. The fermented juice exhibited enhanced DPPH scavenging activity and FRAP values. In terms of volatile profiles, esters and terpenes were the dominant volatiles in the fermented pineapple juice. The fermentation resulted in the production of 2-heptanone, 2-undecanone, and a significant reduction in 2-furaldehyde (<i>p</i> < 0.05). These findings demonstrate the feasibility of using <i>Ls. casei</i> LK-1 for fermentation to develop novel fermented pineapple juice with improved antioxidant properties and a modified volatile profile.
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