Currently, with the preference for a healthy diet and increased awareness of reducing the carbon footprint, the demand for protein is becoming more and more diversified. In this study, the physicochemical properties of yeast protein (YP) and four common plant proteins (soy protein isolate, pea protein isolate, wheat gluten, and peanut protein) were compared. The most prevalent secondary structure in YP is the β-sheet. Furthermore, YP is in an aggregated state, and it has a high surface hydrophobicity. The tryptophan residues are primarily exposed on the polar surface of YP. The results of in vitro digestibility indicated that YP (84.91 ± 0.52%) was a high-quality protein. Moreover, YP has a higher thermal stability and relatively stable low apparent viscosity, which provides ample possibility for its application in food processing and in foods for people with swallowing difficulties. This study provides theoretical basis in the potential of YP as an alternative protein source.

The traditional fermentation process of soy sauce employs a hyperhaline model and has a long fermentation period. A hyperhaline model can improve fermentation speed, but easily leads to the contamination of miscellaneous bacteria and fermentation failure. In this study, after the conventional koji and moromi fermentation, the fermentation broth was pasteurized and diluted, and then inoculated with three selected microorganisms including Corynebacterium glutamicum, Corynebacterium ammoniagenes, and Lactiplantibacillus plantarum for secondary fermentation. During this ten-day fermentation, the pH, free amino acids, organic acids, nucleotide acids, fatty acids, and volatile compounds were analyzed. The fermentation group inoculated with C. glutamicum accumulated the high content of amino acid nitrogen of 0.92 g/100 mL and glutamic acid of 509.4 mg/100 mL. The C. ammoniagenes group and L. plantarum group were rich in nucleotide and organic acid, respectively. The fermentation group inoculated with three microorganisms exhibited the best sensory attributes, showing the potential to develop a suitable fermentation method. The brewing speed of the proposed process in this study was faster than that of the traditional method, and the umami substances could be significantly accumulated in this low-salt fermented model (7% w/v NaCl). This study provides a reference for the low-salt and rapid fermentation of seasoning.