Effect of rosmarinic acid on microbial activity, antioxidant capacity, and metabolite profiles of fermented milk containing Lactiplantibacillus plantarum

This study aimed to elucidate how rosmarinic acid (0, 0.01, 0.03 g/100 mL) affects the microbial activity, antioxidant capacity, and metabolite profiles of fermented milk co-cultured with <i>Lactiplantibacillus plantarum</i> and commercial starter. Rosmarinic acid supplementation significantly (<i>P</i> < 0.05) boosted bacterial survival. Furthermore, incorporation of rosmarinic acid accelerated acid-producing capacity of starter cultures, and improved antioxidant capacity of fermented milk, particularly at a concentration of 0.03 g/100 mL. Metabolomics analysis revealed that rosmarinic acid induced distinct metabolic alterations, leading to the identification of 80 differential metabolites in samples treated with 0.03 g/100 mL rosmarinic acid compared to the untreated samples. Notably, rosmarinic acid-fortified samples exhibited higher levels of peptides and polyphenol metabolites but lower levels of oligosaccharide and lipid metabolites compared to the non-fortified samples (<i>P</i> < 0.05). Overall, rosmarinic acid can be incorporated as an active ingredient in milk fermentation to develop a novel functional food with substantial health benefits.