Omics-based insights into flavor development and microbial succession within surface-ripened cheese

In this study, a young Cheddar curd was used to produce two types of surface-ripened cheese, using two commercial smear-culture mixes of yeasts and bacteria. Whole-metagenome shotgun sequencing was used to screen the microbial population within the smear-culture mixes, and on the cheese surface, comparing microorganisms both at species and strain level. The use of two smear mixes, resulted in the development of distinct microbiota on the surface of the two test cheeses. In one case, most of the species inoculated on the cheese established themselves successfully on the cheese surface during ripening; while in the other, some of species inoculated were not detected during ripening and the most dominant bacterial species, Glutamicibacter arilaitensis, was not a constituent of the culture mix. Generally, yeast species, such as Debaryomyces hansenii and Geotrichum candidum, were the dominant duringin the first stage of ripening, but were overtaken by bacterial species, such as Brevibacterium linens and G. arilaitensis, in the later stages of ripening. Using a correlation analysis, it was possible to associate individual microorganisms with volatile compounds detected by GC-MS on the cheese surface. Specifically, D. hansenii correlated with the production of alcohols and carboxylic acids, G. arilaitensis with alcohols, carboxylic acids and ketones and B. linens and G. candidum with sulfur compounds. In addition, metagenomic sequencing was used to analyze the metabolic potential of the microbial population on the surface of the test cheeses, which was involved in important metabolic processes during ripening, presentingrevealing a high relative abundance of metagenomic clusters associated with , related to the modification of color, variation of pH and flavor development.