Tetramethylpyrazine from adlay (Coix lacryma-jobi) biotransformation by Bacillus subtilis and its quality characteristics

Adlay, as a traditional Chinese medicine, has been used in nourishing foods, which are rich in a variety of nutrients (special biological compounds). The study was designed to optimize the fermentation parameters of dehulled, polished and broken adlay fermented by Bacillus subtilis BJ3-2 with regard to tetramethylpyrazine (TMP) yield and fibrinolytic enzyme activity. Then the proximate and bioactive components of B. subtilis-fermented adlay were evaluated. Box-Behnken design results showed that the TMP yield was 6.93 mg/g DW (dried weight) of B. subtilis-fermented polished adlay, which was about 136 times higher than that of B. subtilis-fermented soybean (BSB). The fibrinolytic enzyme activity was 2236.17 U/g in B. subtilis-fermented dehulled adlay, and slightly less than in BSB. B. subtilis-fermented adlay contained higher fat, free amino acids and fatty acids contents but lower protein and starch contents than raw adlay. Except for coixol and coixan, the levels of γ-aminobutyric acid, triterpenes, phenolics, flavonoids and coixenolide in B. subtilis-fermented adlay increased by 14.05, 2.02, 2.31 and 1.36 times, respectively. The contents of phenolic acids including caffeic, gallic, catechinic and chlonogenic acids in the free phenolic extracts significantly increased (p < 0.05). The results demonstrated that the biotransformation of high-yield TMP, fibrinolytic enzyme and other bioactive components of B. subtilis-fermented adlay products was realized. B. subtilis-fermented adlay could be a promising value-added food, and that is more suitable for human consumption.