Polyphenol Remodeling in FOS-Fortified Longan Juice Fermented with Probiotics: Gastrointestinal Bioaccessibility and Cytoprotective Properties

This study evaluated strain- and time-dependent polyphenol remodeling in fructooligosaccharide (FOS)-fortified longan (Dimocarpus longan Lour.) juice fermented with Lactobacillus acidophilus LA-5 or Lacticaseibacillus casei 01 for 24 or 48 h. Both strains maintained viable populations above 8 log CFU/mL. Fermented beverages exhibited marked strain- and time-dependent differences in individual polyphenol profiles, with L. acidophilus LA-5 fermentation for 48 h (LA48) yielding the highest total quantified polyphenols (299.00 mg/L) and apparent phenolic bioaccessibility after simulated gastrointestinal digestion (73.81%). LA48 also exhibited the greatest post-digestion antioxidant capacity and probiotic growth-promoting scores (1.21–1.55). In a separate cellular assay using undigested cell-free beverage supernatants rather than gastrointestinally bioaccessible fractions, at a single concentration of 100 μg dry solids/mL, LA48 maintained 92.76% cell viability and reduced intracellular reactive oxygen species to 132.58% of the untreated control following H2O2-induced oxidative injury in SH-SY5Y cells. These findings demonstrate that probiotic strain and fermentation duration substantially influence polyphenol remodeling and the measured functional properties of FOS-fortified longan beverages, with L. acidophilus LA-5 fermentation for 48 h producing the most favorable overall profile under the conditions evaluated, without establishing comparative cytoprotective potency.