Fermented Thai sacred lotus stamens as a source of neuroprotective phytochemicals: changes in bioactive composition, antioxidant activity, and Alzheimer’s disease-related enzyme inhibition

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Sacred lotus ( Nelumbo nucifera Gaertn.) stamens are rich in bioactive compounds with potential neuroprotective properties. This study investigated the effects of fermentation by Lactiplantibacillus plantarum TISTR 877 (LP877) and Lacticaseibacillus rhamnosus TISTR 2443 (LR2443) on phytochemical composition, antioxidant activity, inhibition of Alzheimer’s disease-related enzymes, and neuroprotective activity of Thai sacred lotus stamen extracts. Fermentation significantly increased total phenolic, flavonoid, and alkaloid contents, with LP877 fermentation for 48 h producing the highest levels of bioactive compounds. UHPLC–MS/MS analysis revealed increased concentrations of gallic acid, chlorogenic acid, quercetin, kaempferol, and nuciferine. Antioxidant activities were markedly improved, reaching 76.90% DPPH, 84.36% ABTS, and 486.51 μmol Fe 2+ /g extract (FRAP). Enzyme inhibition assays were performed using extracts at 1.0 mg/mL. LP877-fermented extract exhibited the strongest inhibition of acetylcholinesterase (43.72%), butyrylcholinesterase (37.86%), and β-secretase (30.41%). Neuroprotective activity was evaluated only for the two 48-h fermented extracts (LP877-48 h and LR2443-48 h) using SH-SY5Y cells pretreated with 100 μg/mL extract before H 2 O 2 exposure. LP877 significantly improved cell viability (89.76%) and reduced intracellular reactive oxygen species levels. These findings demonstrate that LAB fermentation enhances the in vitro neuroprotective potential of lotus stamen extracts and supports their development as functional food ingredients.