Development of a heat-processing method for koji to enhance its antioxidant activity

Shochu Koji Microstructure and Starch Structure during Preparation

In this study, we investigated the changes in composition, microstructure, and starch molecular structure of shochu koji during preparation. We observed that the gelatinized and outer part of starch was decomposed in priority during the early and middle preparation stages. The gap between the starch granules increased with the delayed time. Finally, the koji microstructure became spongy. Shochu koji mold produced two α-amylases in different expression manners. Acid-labile α-amylase was produced in the early and middle preparation stages. Acid-stable α-amylase and saccharification power were produced in the middle and late stages. Throughout the koji preparation, reducing sugars content reached approximately 13-20 % of the total sugar content, with glucose representing over 70 % of the reducing sugars. α-Glucan fragments with C chains of degree of polymerization (DP) 4-73 were observed in the early and middle stages (<23 h), indicating the degradation of amylopectin at long B chains. In the latter stage, the amount of C chains of DP 6-30 decreased, while the longer C chains (DP 30<) did not change. These results showed that acid-labile α-amylase, acid-stable α-amylase, and saccharification enzymes including glucoamylase and α-glucosidase work preferentially on the amorphous regions of starch granules, and cooperative action of these enzymes during koji preparation contributes to the formation of the observed microstructure. Our study is the first report on the decomposition schemes of starch and the microstructure forming process in shochu koji.

Increasing Protease Activities and Antioxidant Properties of Koji for Soy Sauce Brewing by Adding a Medicinal Herb Rhodiola rosea

Koji preparation is the key step in soy sauce brewing. In this study, 21 medicinal herbs were tested for their abilities in enhancing the protease activities of soy sauce koji. Among these herbs Rhodiola rosea was found to be the most efficient in increasing protease activities. Kinetic analyses revealed that R. rosea addition not only promoted microbe growth and increase the activities of neutral and acid proteases (by 29.8% and 13.4%, respectively) but also elevated α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging activity and total phenolics and flavonoids (by 9.5%, 47.1% and 14.1%, respectively); the formations of proteases and antioxidant properties depend largely on microbe growth; and the promotion effects of R. rosea addition were mainly displayed in later stage of fermentation. Using the R. rosea koji for soy sauce production resulted in 8.9%, 19.1%, 6.6%, 23% and 102% higher of total and amino-type nitrogen contents, protein utilization, total phenolics and flavonoids, respectively.

Non-targeted metabolomic reveals the effect of salt stress on global metabolite of halotolerant yeast Candida versatilis and principal component analysis

As one of the major microbes in the soy sauce fermentation, Candida versatilis enriches the flavor and improves the quality of soy sauce. In this study, a combination of five different GC-MS and LC-MS-based metabolome analytical approaches was used to analyze the intracellular, extracellular and whole metabolites of C. versatilis. Our results found out that a total of 132, 244 and 267 different metabolites were detectable from the intracellular, extracellular and whole part, respectively. When exposed to 0. 9 and 18 % salt, respectively, 114, 123 and 129 different intracellular metabolites, 184, 200 and 178 extracellular metabolites and 177, 188 and 186 whole metabolites were detected, respectively. Our data showed that salt enhances the metabolic capacity of C. versatilis, especially its amino acid and enhances the synthesis and secretion of some metabolites of C. versatilis, especially the aldehydes and phenols, such as vanillin, guaiacol and 5-hydroxymethylfurfural. Our data also showed that special attention has to be paid to the generation of biogenic amines when C. versatilis was treated with salt.

Rice koji reduced body weight gain, fat accumulation, and blood glucose level in high-fat diet-induced obese mice

Rice koji is considered a readily accessible functional food that may have health-promoting effects. We investigated whether white, yellow, and red koji have the anti-obesity effect in C57BL/6J mice fed a high-fat diet (HFD), which is a model for obesity. Mice were fed HFD containing 10% (w/w) of rice koji powder or steamed rice for 4 weeks. Weight gain, epididymal white adipose tissue, and total adipose tissue weight were significantly lower in all rice koji groups than in the HFD-rice group after 4 weeks. Feed efficiency was significantly reduced in the yellow koji group. Blood glucose levels were significantly lower in the white and red koji groups with HOMA-R and leptin levels being reduced in the white koji group. White and red koji increased glucose uptake and GLUT4 protein expression in L6 myotube cells. These results showed that all rice koji have the anti-obesity or anti-diabetes effects although the mechanisms may differ depending on the type of rice koji consumed.