Abstract: In this paper, the solid state fermentation of whole oat grains was carried out by simultaneous inoculation with Lactobacillus plantarum 70810 (L. plantarum 70810) and Rhizopus oryzae (R. oryzae). Our aim was to evaluate fermentation characteristics and the effect of mixed fermentation on the protein nutritional quality of oat. Bacterial growth and ergosterol content were investigated by plate count method and high-performance liquid chromatography (HPLC), respectively. Proteolysis during the fermentation process was measured using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the Bradford assay and the o-phthaldialdehyde (OPA) method. Results showed that the number of viable bacterial cells and ergosterol content gradually increased during mixed culture fermentation, reaching (8.46 ± 0.04) (lg(CFU/g)), 7.14% higher than that of pure culture fermentation with L. plantarum 70810, and (137.04 ± 6.13) μg/g at 72 h, respectively. pH value decreased from 5.34 ± 0.12 to 3.74 ± 0.04, and total acidity increased from (0.23 ± 0.02)% to (1.08 ± 0.08)%. As significant proteolysis occurred at 72 h , the soluble protein content (calculated as bovine serum albumin equivalent) was raised to (11.58 ± 0.16) mg/g, and the content of peptides (calculated as casein tryptone equivalent) with molecular mass lower than 10 kDa reached its highest value of (366.51 ± 1.30) mg/g. Fermented oat had higher protein nutritional value and improved amino acid composition with a significant increase in lysine content. In addition, the essential amino acid index (EAAI) increased to 75.63 ± 0.10, and the protein biological value (BV) to 70.74 ± 0.13 after mixed culture fermentation as compared to pure culture fermentation.

Key words: double strains, solid state fermentation, whole oat grains, oat protein, nutritional value