Evaluation of fermentation combined with pretreatment to enhance bioactive compounds content and antioxidant activity of wheat germ meal

Abstract

In this study, defatted wheat germ meal was processed with three pretreatment methods, including alkali extraction-acid precipitation, microwave treatment, and ultrasonic assisted enzymatic hydrolysis, and it was then fermented by Bacillus subtilis and Angel yeast. The analyses of fermentation products and antioxidant activity were utilized to screen an effective combination mode for germ meal. The contents of total sugars and reducing sugars decreased significantly following ultrasonic-assisted enzymatic hydrolysis. The fermentations of B. subtilis were much more effective. The contents of soluble proteins were 139.72% higher than that of blank group, the contents of polypeptides reached 0.37 mg/mL, the total contents of phenolics were 0.63 mg/mL, and the content of γ-aminobutyric acid increased by approximately 10-fold. Ultrasonic assisted enzymatic hydrolysis treatment enhanced antioxidant activity of the fermentation broth. The ultrasonic assisted enzymatic hydrolysis largely destroyed the surface structure of the germ meal, and the surface structure after fermentation with B. subtilis was multi-fault and deep cave-like. The ultrasonic-assisted enzymatic hydrolysis could destroy the structure of starch, facilitate the utilization of microorganisms in the fermentation process. It is apparent that the fermentation of B. subtilis after ultrasonic-assisted pretreatment plays an important role in the effective use of germ meal to produce functional nutritional factors and transform the byproducts into high value-added products.