MIURA TAKAYUKI

ABSTRACT: Wild boar meat containing radioactive cesium (Cs) of approximately 1,000 Bq/kg (134Cs+137Cs) was processed into bacon, sausage, and ham. To understand the concentration and quantity change of radioactive Cs, the processing factor (Pf) and food processing retention factor (Fr) were calculated. The radioactive Cs quantity in the meat did not reduce during smoking. The dehydration-related meat mass reduction during smoking without decrease of radioactive Cs led to Cs condensation in the bacon compared with the raw rib meat before processing, resulting in a Pf of 1.18. Soaking in liquid, such as pickling in liquid and desalting or boiling in water, effectively removed radioactive Cs by leakage into water. Therefore, the Fr value of the boiled ham produced from a loin meat block through three liquid-soaking processes was 0.27. The Pf value of the boiled ham was 0.30 due to meat block mass reduction after boiling as a result of dehydration, along with protein thermal denaturation-related muscle tissue shrinkage. The steamed ham Fr value was 0.53, because the removal of radioactive Cs was less efficient by steaming than by boiling. The Pf value of the steamed ham was 0.54, almost the same as the Fr value, because the mass decrease rate was the same as the radioactive Cs decrease rate by steaming. The Fr and the Pf values of the boiled sausage, whose processing did not include soaking in the pickling liquid, were 0.64 and 0.62, respectively. Steaming the sausage meat did not remove radioactive Cs during the dehydration-related mass reduction, leading to Fr and Pf values of 1.01 and 1.17, respectively. This study found that processing into boiled ham was the most effective measure for reducing radioactive Cs quantity and concentration in raw meat. Processing into bacon and steamed sausage showed no Cs quantity reduction, with the moisture loss resulting in Cs condensation compared with the raw material.

To determine the impact of traditional koji molds on chemical characteristics of soft-type natural cheese, novel surface mold-ripened cheeses with Aspergillus oryzae and Aspergillus sojae were studied by non-targeted metabolite profiling. Comprehensive water-soluble and volatile metabolite profiles of koji cheese were evaluated among five Aspergillus strains and other mold-ripened cheeses. Time-course changes in the metabolite profiles and degrading enzyme activities were also compared with those of an industrial Penicillium candidum starter culture. Koji cheeses differed from Camembert, Brie, and blue cheeses in higher lactic acid, amino acid, and acetoin levels and lower methyl ketone and volatile fatty acid levels. Time-course analysis revealed the associations of rapid accumulations of glutamic, aspartic, and 3-methylbutanoic acids and 3-methylbutanal with higher proteolytic activity, and methyl ketone and fatty acid derivative suppressions with lower lipolytic activity. Ethyl butanoate, diacetyl, and malic acid also characterized koji cheeses as strain-dependent metabolites. This study highlighted the key compositional difference derived from cheese ripening with Aspergillus strains. The findings could help quality improvements of koji cheese product.

More than 2,000 varieties of cheese currently exist in the world, and cheese manufacture continues to flourish. To develop the cheese ripening process, additional ingredients are used during cheese production. In this study, the effect of sake lees as an additional ingredient on the fermentation of cheese using Aspergillus oryzae (koji mold), known as koji cheese, was investigated. Aspergillus oryzae is used in the fermentation of Japanese traditional foods, such as sake and soy sauce, given its strong enzymatic activities, as well as in cheese production (i.e., koji cheese). Sake lees, a by-product of the fermentation of rice with A. oryzae and yeasts in the sake brewing process, contains various metabolites, such as amino acids. Here, supplementation with sake lees enhanced the activities of lactic acid bacteria and affected the color of the cheese. Metabolome analysis revealed that sake lees altered the balance of carbohydrates and fatty acids in the cheese. Remarkably, supplementation with sake lees enhanced the production of umami-enhancing γ-glutamyl (kokumi-active) peptides. This study suggests that a new type of cheese can be produced using A. oryzae and sake lees, and information on the synergistic effects of A. oryzae and sake lees will aid the development of cheese production.