No abstract

Cheese ripening is effected by various microorganisms and results in the characteristic flavors of cheese. Owing to the complexity of the microbiota involved, the relationship between microorganisms and components during ripening remains unclear. In this study, metagenomics and metabolomics were integrated to reveal these relationships in three kinds of surface mold-ripened cheeses and two kinds of bacterial smear-ripened cheeses. The microbiota is broadly divided into two groups to correspond with different cheese types. Furthermore, surface mold-ripened cheese showed similar microbiota regardless of the cheese variety, whereas bacterial smear-ripened cheese showed specific microbiota characterized by marine bacteria (MB) and halophilic and alkaliphilic lactic acid bacteria for each cheese variety. In the metabolite analysis, volatile compounds suggested differences in cheese types, although organic acids and free amino acids could not determine the cheese characteristics. On the other hand, Spearman correlation analysis revealed that the abundance of specific bacteria was related to the formation of specific organic acids, free amino acids, and volatile compounds. In particular, MB was positively correlated with esters and pyrazines, indicating their contribution to cheese quality. These methodologies and results further our understanding of microorganisms and allow us to select useful strains for cheese ripening.

No abstract

Our previous study revealed that the existence of various bacteria, such as lactic acid bacteria, Actinobacteria , and Proteobacteria , clearly correlated with the abundance of flavor components, such as volatile compounds, in soft-type ripened cheeses via a multiomics approach that used 16S rRNA gene amplicon sequencing and headspace gas chromatography-mass spectrometry. However, this approach only showed correlations derived from statistical analyses rather than causal relationships.

Halophilic and alkaliphilic lactic acid bacteria (HALAB), such as Marinilactibacillus and Alkalibacterium , have been frequently isolated from marine environment affected by the physicochemical features of sea water. On the other hand, although these HALAB also existed in fermented food containing salt, such as ripened cheeses, their derivation have not been revealed. Therefore, to elucidate HALAB diversity of isolation sources, we isolated HALAB from various sea-salts that may be used for fermented food production. Among the 23 kinds of solar sea-salts, the strains belonging to the genus Alkalibacterium were isolated from two kinds of French solar sea-salts by the enrichment culture. These isolates had halophilic and alkaliphilic properties, and were identified as Alkalibacterium putridalgicola originally isolated from marine environment. On the other hand, the isolates did not grow under 20% NaCl and required sugar compound for their growth, indicating that they may not stimulate growth but survive on the surface of solar salt. Based on these findings, it can be considered that HALAB existed in the marine environment will adhere and survive on the solar sea-salt and propagate to various salted food manufacturing environments.