Young-Wook Chin

Enzymatic hydrolysis has attracted attention as a safer and more sustainable alternative to conventional acid hydrolysis for producing hydrolyzed soy protein (HSP). However, the effects of protease combination, reaction conditions, and post-hydrolysis thermal treatment on amino acid and volatile compound formation remain limited. This study investigated the effects of five commercial proteases and their combinations on the amino acid and volatile profiles of HSP and optimized hydrolysis conditions using response surface methodology (RSM). Among the enzyme combinations tested, Alcalase + Protana Prime produced the most favorable amino acid profile, characterized by elevated sweet- and umami-related amino acids and relatively low levels of bitter amino acids. Subsequent heat treatment markedly increased pyrazines, furans, aldehydes, and sulfur-containing compounds, resulting in volatile profiles comparable to those of acid-hydrolyzed products. RSM identified optimal conditions of 15.91 h reaction time and 5.85% enzyme concentration, which increased total, sweet, and umami amino acid contents while reducing enzyme usage. Under the optimized conditions, taste activity values of umami and sweet amino acids were approximately twofold higher than those under the high-enzyme-concentration treatment. These findings demonstrate the potential of combining optimized enzymatic hydrolysis and controlled thermal processing as a clean-label strategy for producing flavor-enhanced HSP.

Saccharomyces cerevisiae is a generally recognized as safe (GRAS) workhorse strain widely used in the food industry for the cost-effective production of food ingredients. However, the heme production yield in yeast is significantly lower than in bacteria for two main reasons: (1) the heme biosynthetic pathway is bifurcated into the cytosol and mitochondria, and (2) yeast’s heme biosynthetic protoporphyrin-dependent (PPD) pathway is thermodynamically unfavorable compared with bacteria’s coproporphyrin-dependent (CPD) pathway. To overcome these limitations, the PPD and CPD pathways were compartmentalized into the mitochondria by attaching mitochondria-targeting sequences (MTSs) to the N-terminus of the enzymes. All the enzyme activities required for the CPD pathway are present in S. cerevisiae, except for copro-heme decarboxylase (HemQ); therefore, bacterial HemQ with the N-terminal MTS was introduced to complete the CPD pathway. The resulting S. cerevisiae H4+_MTS9HemQ^Cg strain with mitochondrial PPD and CPD pathways showed 65% higher heme concentration than the engineered strain with only the mitochondrial PPD pathway. Furthermore, the functional expression level of HemQ from Corynebacterium glutamicum was significantly enhanced in vitro and in vivo by the co-expression of Group-I HSP60 chaperonins (GroEL and GroES) derived from Escherichia coli. The engineered S. cerevisiae H4+_MTS9HemQ^Cg+GroELS strain containing the mitochondrial PPD and CPD pathways and the Group-I HSP60 chaperonins produced the highest heme concentration (4.6 mg/L), which was 17% higher than that produced by the H4+_MTS9HemQ^Cg strain.

Yeast formulations such as dry yeast are essential for supplying microbial starters to the alcoholic beverage industry. In Korea, the expensive freeze-drying method is used to manufacture brewer’s dry yeast, and therefore an economical process such as fluidized bed drying is needed. In the dry yeast manufacturing process, the medium and drying conditions are key factors that determine its quality and manufacturing cost. In this study, we aimed to optimize the medium composition and fluidized bed drying conditions for the efficient production of dry yeast. Muscovado and corn steep liquor were used as the carbon and nitrogen sources, respectively, and their optimal concentrations were identified using response surface methodology for efficient cultivation of Saccharomyces cerevisiae ReY4-7 isolated from nuruk. Central composite design analysis revealed that the optimal medium composition was 146.12 g/L muscovado and 58.68 g/L corn steep liquor. A dry cell weight of 36 g/L was achieved during 24 h of batch fermentation in a 30-L bioreactor containing this medium. Analysis of protective agents against fluidized bed drying revealed Span 80 as the strongest protective agent for S. cerevisiae ReY4-7. Response surface methodology revealed 50 °C and 41.45 min as the optimal fluidized bed drying conditions, under which the viable cell count reached 10.28 log CFU/g, comparable to that of the commercial dry yeast products. Overall, optimization of the medium and drying conditions significantly improved the final cell concentration in the cultivation process and the viable cell count in the drying process of dry yeast.

The microbial community of a soy sauce is one of the most important factors in determining the sensory characteristics of that soy sauce. In this study, the microbial communities and sensory characteristics of twenty samples of Korean soy sauce (ganjang) were investigated using shotgun metagenome sequencing and descriptive sensory analysis, and their correlations were explored by partial least square (PLS) regression analysis. The metagenome analysis identified 1332 species of bacteria, yeasts, molds, and viruses across 278 genera, of which Tetragenococcus, Bacillus, and Enterococcus accounted for more than 80% of the total community. In the fungal community, Zygosaccharomyces rouxii, Candida versatilis, Rhodotorula taiwanensis, Debaryomyces hansenii, and Aspergillus oryzae were dominant, while the viral community consisted entirely of bacteriophages, with Bacillus phages SIOphi accounting for 93%. According to the results of the PLS analysis, desirable sensory characteristics, such as umami, sweet, and roasted soybean, as well as preference, were associated with Tetragenococcus, Lysinibacillus, Enterococcus, Staphylococcus, Lactobacillus, Pediococcus, and Weissella. The musty flavor, which is a typical property of traditional fermented foods, was related to Halomonas and Psychrobacte, while the bitter, acrid taste and sour smell were closely associated with Chromohalobacter. The results of this study provide comprehensive information on the microbial community of ganjang and may be used to select starter cultures for soy sauces.

Bisphenol A (BPA), one of the most widely used plasticizers, is an endocrine-disrupting chemical that is released from plastic products. The aim of this study was to screen and characterize bacteria with excellent BPA-degrading abilities for application in foods. BPA degradation ability was confirmed in 127 of 129 bacterial strains that were isolated from fermented soybean foods. Among the strains, B. subtilis P74, which showed the highest BPA degradation performance, degraded 97.2% of 10 mg/L of BPA within 9 h. This strain not only showed a fairly stable degradation performance (min > 88.2%) over a wide range of temperatures (30–45 °C) and pH (5.0–9.0) but also exhibited a degradation of 63% against high concentrations of BPA (80 mg/L). The metabolites generated during the degradation were analyzed using high-performance liquid chromatography–mass spectrometry, and predicted degradation pathways are tentatively proposed. Finally, the application of this strain to soybean fermentation was conducted to confirm its applicability in food.

This study aimed to investigate the physicochemical characteristics, sensory attributes, and consumer acceptance of the Certification of Quality of Traditional Food (CQT) ganjang samples produced in different provinces of Korea. Wide variations in physicochemical properties were found among the samples, especially in lipids, total nitrogen, acidity, and reducing sugar. Traditional fermented foods are known to be closely tied to regional features, but the composition and characteristics of CQT ganjangs might be influenced much more by individual ganjang producers than by region. Preference mapping was performed to understand consumer behavior towards ganjang, and most consumers tended to have similar preferences, implying shared a common sensory ideal. The results of the partial least squares regression revealed drivers of liking for ganjang among sensory attributes, free amino acids, and organic acids. Overall, sensory attributes such as sweetness and umami were positively associated with acceptability, while the terms related to fermentation were negatively associated. In addition, amino acids, such as threonine, serine, proline, glutamate, aspartate, and lysine, and organic acids, such as lactate and malate, were positively associated with consumer acceptance. The important implications of the findings of this study for the food industry can be utilized to develop and optimize traditional foods.

Herein, the skin whitening effect of the fermentation residue of Saccharomyces cerevisiae was investigated. The fermentation residue showed radical scavenging activity and attenuated tyrosinase activity. Furthermore, the fermentation residue of S. cerevisiae significantly suppressed melanin generation in B16F10 cells. Interestingly, the sample-containing formulation exhibited increased skin whitening activity compared with that by the control formulation in a clinical study. Notably, the endogenous tyrosinase expression was not altered by the fermentation residue of S. cerevisiae; however, the enzymatic activity of tyrosinase was inhibited. Furthermore, the sample did not change TRP1 and TRP2 expression in B16F10 cells. Thus, the fermentation residue of S. cerevisiae was assumed to directly suppress the tyrosinase enzyme. It was confirmed that the fermentation residue of S. cerevisiae was a competitive inhibitor of tyrosinase. Taken together, the fermentation residue of S. cerevisiae could be a novel skin whitening agent originating from the traditional Korean liquor production process.