Comprehensive evaluation of physicochemical properties and antioxidant activity of B. subtilis‐fermented polished adlay subjected to different drying methods

The physicochemical properties and antioxidant activity of B. subtilis‐fermented polished adlay (BPA) subjected to different drying methods (hot‐air drying, HAD; infrared‐radiation drying, IRD; vacuum drying, VD; microwave‐vacuum drying, MVD; and freeze‐vacuum drying, FVD) were evaluated in this study. Results showed FVD was ideal for maintaining the natural appearance and higher contents of proximate compositions, free fatty acids, tetramethylpyrazine (6.91 mg/g DW), coixol (0.62 mg/g DW), coixenolide (4.21% DW), coixan (35.10% DW), and triterpenoids (17.41 mg/g DW). The higher contents of total phenolics and flavonoids, stronger antioxidant activity, and higher color differences were observed in HAD and IRD samples. MVD displayed the shorter drying time, higher γ‐aminobutyric acid content, and higher retention ratios of tetramethylpyrazine (75.54%), coixol (87.10%), coixenolide (98.57%), and coixan (99.11%). Pearson's correlation coefficient exhibited that the positive correlation between the contents of phenolics and flavonoids and the antioxidant activities of all dried BPA samples was observed (R (2) > 0.881, p < .05). Principal component analysis showed that the top three categories of comprehensive quality were FVD‐, MVD‐, and VD‐treated BPA samples. In conclusion, MVD should be a potential preservation method to obtain high‐quality dried BPA for short drying time and high comprehensive quality.