Increase of γ-aminobutyric acid content and improvement of physicochemical characteristics of mulberry leaf powder by fermentation with a selected lactic acid bacteria strain

Strain JS35, isolated from silkworm intestines, exhibited the highest γ-aminobutyric acid (GABA)-producing ability among the screened strains. 16S rRNA gene sequencing revealed that JS35 belonged to Pediococcus pentosaceus. The tolerance of JS35 to acids, bile salts, and heat was also confirmed. Based on the GABA-producing ability, the fermentation conditions of JS35 were optimized, and mulberry leaf powder (MLP) was fermented with JS35 at 30 °C for 48 h. Morphological observations showed that fermented MLP had a looser surface structure with a larger number of holes and gaps than the unfermented sample. The results of GC/MS showed that fermentation improved flavor by increasing the contents of benzyl alcohol, phenylethyl alcohol, isospathulenol, and acacia alcohol. GABA, total phenolics and total flavonoids in fermented MLP were increased by 951.3%, 16.5% and 22.2%, respectively. The anti-nutritional factor phytic acid was decreased by 20.0%. Additionally, the DPPH radical scavenging capacity and the reducing ability of the fermented MLP extract were significantly improved. Fermented by JS35 increased the contents of active compounds and improved the flavor of MLP, suggesting that JS35 could be a potential microorganism for the further processing of MLP products.