The effects of different lactic acid bacteria fermentation and in vitro digestion on the physicochemical properties, bioactive substances, antioxidant capacity, and volatile organic compounds of walnut milk

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To investigate the effects of different LAB strains on the quality of walnut milk, we measured changes in its physicochemical properties, organic acids, phenolic compounds, soluble sugars, amino acids, volatile organic compounds, and digestion characteristics were measured. Relative to the CON (control) samples, exhibited decreased pH, total sugar, and soluble protein content across all fermentation groups. The antioxidant capacity of the fermentation group was significantly enhanced, with the LR ( Lactobacillus rhamnosus ) sample showing the highest ABTS and CUPRAC scavenging activities. Lactic acid bacteria fermentation significantly increased the content of lactic acid and acetic acid, while reducing the content of malic acid. Compared with the CON samples, the content of gallic acid in the fermentation group significantly increased. The amino acid composition was also altered by fermentation. Notably, umami amino acids increased significantly in the LPC ( Lactobacillus paracasei subsp. paracasei ), while aromatic amino acids were markedly elevated in the LB ( Lactobacillus bulgaricus ). Additionally, the sweet amino acid content in both groups was substantially higher than in the others. After fermentation, the types and contents of esters and alcohols increased, providing a broader range of flavor compounds and improving the overall flavor profile. Fermentation also enhanced the bioaccessibility of bioactive substances during simulated digestion processes. These results indicate that LAB fermentation significantly improves the quality characteristics of walnut milk.