Dynamic changes on sensory property, nutritional quality and metabolic profiles of green kernel black beans during Eurotium cristatum-based solid-state fermentation.

Eurotium cristatum, a unique probiotic in Fu brick tea, is widely used in food processing to enhance added values. Here, green kernel black beans (GKBBs) were solid-fermented with E. cristatum and dynamic changes in flavour, chemical composition and metabolites during fermentation were investigated. As results, E. cristatum fermentation altered aroma profiles and sensory attributes of GKBBs, especially reduced sourness. After fermentation, total polyphenolic and flavonoid contents in GKBBs were elevated, while polysaccharides, soluble proteins and short-chain fatty acids contents were decreased. E. cristatum fermentation also induced biotransformation of glycosidic isoflavones into sapogenic isoflavones. During fermentation, dynamic changes in levels of 17 amino acids were observed, in which 3 branched-chain amino acids were increased. Non-targeted metabolomics identified 51 differential compounds and 10 related metabolic pathways involved in E. cristatum fermentation of GKBBs. This study lays foundation for the development of green kernel black bean-based functional food products with E. cristatum fermentation.

Characterization of a novel cold-adapted GH1 ß-glucosidase from Psychrobacillus glaciei and its application in the hydrolysis of soybean isoflavone glycosides.

The novel ß-glucosidase gene (pgbgl1) of glycoside hydrolase (GH) family 1 from the psychrotrophic bacterium Psychrobacillus glaciei sp. PB01 was successfully expressed in Escherichia coli BL21 (DE3). The deduced PgBgl1 contained 447 amino acid residues with a calculated molecular mass of 51.4 kDa. PgBgl1 showed its maximum activity at pH 7.0 and 40 °C, and still retained over 10% activity at 0 °C, suggesting that the recombinant PgBgl1 is a cold-adapted enzyme. The substrate specificity, Km, Vmax, and Kcat/Km for the p-Nitrophenyl-ß-D-glucopyranoside (pNPG) as the substrate were 1063.89 U/mg, 0.36 mM, 1208.31 U/mg and 3871.92/s, respectively. Furthermore, PgBgl1 demonstrated remarkable stimulation of monosaccharides such as glucose, xylose, and galactose, as well as NaCl. PgBgl1 also demonstrated a high capacity to convert the primary soybean isoflavone glycosides (daidzin, genistin, and glycitin) into their respective aglycones. Overall, PgBgl1 exhibited high catalytic activity towards aryl glycosides, suggesting promising application prospects in the food, animal feed, and pharmaceutical industries.

Characterization of a Novel Hyperthermophilic GH1 ß-Glucosidase from Acidilobus sp. and Its Application in the Hydrolysis of Soybean Isoflavone Glycosides.

A putative ß-glucosidase gene, BglAc, was amplified from Acidilobus sp. through metagenome database sampling from a hot spring in Yellowstone National Park. BglAc is composed of 485 amino acid residues and bioinformatics analysis showed that it belongs to the GH1 family of ß-glucosidases. The gene was successfully expressed in Escherichia coli with a molecular weight of approximately 55.3 kDa. The purified recombinant enzyme showed the maximum activity using p-nitrophenyl-ß-D-glucopyranoside (pNPG) as the substrate at optimal pH 5.0 and 100 °C. BglAc exhibited extraordinary thermostability, and its half-life at 90 °C was 6 h. The specific activity, Km, Vmax, and Kcat/Km of BglAc toward pNPG were 357.62 U mg-1, 3.41 mM, 474.0 µmol min-1·mg-1, and 122.7 s-1mM-1. BglAc exhibited the characteristic of glucose tolerance, and the inhibition constant Ki was 180.0 mM. Furthermore, a significant ethanol tolerance was observed, retaining 96% relative activity at 10% ethanol, and even 78% at 20% ethanol, suggesting BglAc as a promising enzyme for cellulose saccharification. BglAc also had a strong ability to convert the major soybean isoflavone glycosides (daidzin, genistin, and glycitin) into their corresponding aglycones. Overall, BglAc was actually a new ß-glucosidase with excellent thermostability, ethanol tolerance, and glycoside hydrolysis ability, indicating its wide prospects for applications in the food industry, animal feed, and lignocellulosic biomass degradation.