Nano-imaging by atomic force microscopy, thermogravimetric characteristics, and bioactive compounds of thermally treated and fermented mash beans

Abstract

The novel processing of black mash bean flour through the synergistic combination of gelatinization and fermentation via Saccharomyces cerevisiae MK-157 and Lactobacillus sp. E14 was explored. The results of the atomic force microscopy (AFM) indicated significant structural transformative changes in the nanomorphological features. Specifically, the average particle size has been decreased to 122.65 nm for raw mash bean flour (RMBF) and 66 nm for gelatinized and fermented flour (GMBF) via S. cerevisiae MK-157. The enhanced beta-glucan distribution of fermented samples was highlighted by fluorescence microscopy, exhibiting health-promoting qualities. The RMBF fermented by S. cerevisiae MK-157 showed the strongest FRAP-IC50 (18.58 mg/mL) and DPPH inhibition-IC50 (54.62 mg/mL). Additionally, fermentation elevated the total phenol content (TPC) which resulted in 2.68% increase for GMBF fermented by Lactobacillus E14. Similarly, the largest increase (5.02 %) in total flavonoid content (TFC) was observed for GMBF fermented by S. cerevisiae MK-157. Certain metabolites, such as lactic acid, which contribute to the antioxidant capacity were identified by 1H NMR. Thermogravimetric analysis showed remarkable thermal stability regarding residual masses of 27.54% for GMBF fermented by S. cerevisiae MK-157 and 32.18% for RMBF fermented by Lactobacillus E14 at 500 °C. Thus, the current study may contribute to the development of the legume processing.