Haruto Kumura

Postmortem changes in skeletal muscle, particularly rigor mortis and the subsequent tenderization process, play a central role in determining meat quality and palatability. Proper progression of rigor mortis is essential, as its disruption leads to severe deterioration in meat texture and eating quality. Although the biochemical mechanisms underlying rigor mortis have been extensively studied, most investigations rely on simplified experimental systems and largely neglect the contribution of endogenous low-molecular-weight compounds present in muscle tissue. Imidazole dipeptides, such as carnosine, are abundant in skeletal muscle and are known to contribute to intracellular homeostasis through antioxidant and metal-chelating properties. Recently, these compounds have also been implicated in the regulation of calcium sensitivity in muscle contraction models. In the present study, we investigated the potential involvement of carnosine in rigor mortis by examining its effects on actomyosin ATPase activity under postmortem-like conditions. Under acidic and low-calcium conditions, which are unfavorable for actomyosin ATP hydrolysis, carnosine significantly enhanced ATPase activity. This enhancement was accompanied by increased tryptophan autofluorescence in the myosin head region upon ATP addition, suggesting an increased affinity between myosin and ATP. These findings indicate that carnosine facilitates the actomyosin ATPase cycle under postmortem conditions by enhancing calcium sensitivity and stabilizing ATP–myosin interactions. Our results suggest that endogenous carnosine contributes to the orderly progression of rigor mortis by promoting ATP depletion and contractile activity in postmortem skeletal muscle, providing new insight into the biochemical factors influencing meat quality and postmortem muscle behavior.

Koji made using Aspergillus oryzae shows potential for application as a cheese adjunct; however, flavor defects resulting from volatile free fatty acid (FFA) accumulation should be avoided. Hence, a modified glucose-containing whey solid medium was used to culture A. oryzae AHU 7139, and the triacylglycerol (TG) lipase activity and lipase gene (tglA and mdlB) expression were compared with those of a culture using a conventional whey solid medium. The results showed that TG lipase activity and the expression of both lipase genes were reduced in the modified medium. Moreover, the expression level of farA, a positive transcription factor of the lipase genes, was also reduced. The cheese adjunct prepared by culturing the AHU 7139 strain in the modified medium lowered the FFA content in the cheese products, resulting in comparable FFA levels with those in the adjunct-free cheese. Thus, adding glucose is recommended to prepare the koji adjunct for cheesemaking.

BACKGROUND: Monascus sp. has been used in fermented foods for centuries. It can synthesize yellow, red, and orange pigments as secondary metabolites. Here, we focused on yellow pigment monascin, responsible for anti‐inflammation and antidiabetic effects, and investigated whether whey could be a suitable substrate with or without rice powder for monascin production using M. purpureus AHU 9085, M. pilosus NBRC 4520 and M. ruber NBRC 32318.RESULTS: The growth and monascin production of the three Monascus strains were dependent on three liquid media consisting of whey and/or rice. All strains showed the best growth in a rice and whey mixed medium, in which M. ruber NBRC 32318 exhibited the highest total monascin production. Subsequent investigation of the effects of whey components indicated that a mineral cocktail in whey was particularly effective in stimulating the monascin production efficiency of M. ruber NBRC 32318. However, this recipe exhibited less stimulation, or even inhibition, for M. pilosus NBRC 4520 and M. purpureus AHU 9085, respectively. In terms of total monascin production, rice with whey provided the highest amount due to growth promotion along with relatively high production efficiency.CONCLUSION: The effect of whey on growth and monascin production was strongly dependent on the Monascus strains. Even a mineral cocktail in whey could regulate monascin productivity in a strain‐specific manner. Further studies are needed to elucidate the mechanism behind the diverse responses by the minerals in the production of monascin from Monascus. © 2023 Society of Chemical Industry.

BACKGROUND: Aspergillus sp. has been used in traditional Japanese fermented foods. Protease‐containing culture products of A. oryzae have been applied as the adjunct enzyme source to enrich the flavor in ripened cheese. Although proteolysis was stimulated, the increase of free fatty acids (FFA) was recognized in some products. Since an excess amount of FFA accumulation can cause rancidity in cheese products, the assessment of lipase activity was considered to be essential for the cheese adjunct preparation.RESULTS: Although an equal lipase activity from the adjunct materials of A. kawachii NBRC 4308, A. luchuensis RIB 2604 and A. oryzae AHU 7139 was applied to semi‐hard cheese, the FFA level was significantly higher in A. oryzae cheese than in the others. Furthermore, the profiles of volatile components were different in experimental cheeses. An in vitro study with experimental curds demonstrated that the high FFA might not depend on the lipase retainability on curds. On the contrary, the pronounced activation of the lipases occurred in A. oryzae after incubation with the curds. Moreover, incubation of the insoluble lipase that had been attached to the cells with skim milk curd extracts allowed the release of lipases from the cells into the medium with remarkable activation.CONCLUSION: A. oryzae AHU 7139 possessed a complex lipolytic system comprising extracellular and cell‐binding lipases that were attributed to the increase in FFA in A. oryzae cheese. © 2022 Society of Chemical Industry.

This study assessed the color improvement via zinc protoporphyrin IX (ZnPP) formation in nitrite-free, dry-cured sausages processed using five varieties of ZnPP-forming lactic acid bacteria (LAB). The ZnPP contents and color intensity of the sausages and other technological properties were analyzed during the processing of sausages. LAB count and acidity significantly increased in the LAB-inoculated sausages compared to the control group. The bright red color was observed both inside and outside the sausages inoculated with Lactococcus lactis subsp. cremoris and Leuconostoc lactis. However, a brown color was observed on the surface of the sausage inoculated with Lactobacillus spp. The redness of Lactococcus lactis subsp. cremoris-inoculated sausages was close to that of the nitrite-added group. Moreover, the external bright red color was improved by Lactococcus lactis subsp. cremoris due to the aerobic formation of ZnPP. Therefore, Lactococcus lactis subsp. cremoris can be used to improve the color of fermented meat products.

BACKGROUND: Species belonging to the genus Aspergillus have been used in traditional Japanese fermented foods. Aspergillus sojae is a species responsible for strong proteolytic activity. Freeze‐drying treatments followed by physical disruption enables the pulverization of the mycelia of A. sojae RIB 1045 grown in whey protein‐base solid media. Intracellular proteases were extracted using this protocol to compare extracellular protease activity in terms of the reaction’s pH dependence in the presence or absence of inhibitors.RESULT: With different sensitivities to inhibitors, intracellular and extracellular proteases showed the strongest activity under acidic conditions, which were considered suitable for cheese application. The raw culture product (CP) and its freeze‐dried product (FDP) were mixed with cheese curds, prepared according to Gouda‐type cheese‐making methods, and were allowed to ripen for 3 months. Chemical analysis of the products showed 13.3% water‐soluble nitrogen (WSN) in the control, which had received noncultured media, whereas 20.0% and 21.1% WSN was found in the CP and FDP experimental cheeses, respectively. Although these adjuncts significantly increased WSN, an insignificant difference was found between CP and FDP. Free fatty acids in all experimental cheeses were similar, showing that CP and FDP caused no rancid defects.CONCLUSION: The introduction of freeze‐drying treatments accompanied by cell disruption resulted in a negligible effect in terms of WSN. However, the application of A. sojae can be beneficial when it comes to increasing the level of WSN compared with A. oryzae, as shown in our previous study. © 2020 Society of Chemical Industry

The lipolytic and proteolytic activity of Penicillium camemberti PC TT033 and Penicillium roqueforti PR G3, cultured on the whey solids or simulated cheese media, were compared under several pH reaction conditions. Lipolytic activity was higher when both strains had been cultured on the whey medium than on the simulated cheese medium, whereas proteolytic activity was less influenced by the culture medium. The relationship between the reaction pH and these enzyme activities was dependent on the culture medium, which suggested that the expression level and balance of isozyme rely on the culture substrate.