Lactobacillus delbrueckii subsp. lactis as a starter culture significantly affects the dynamics of volatile compound profiles of hard cooked cheeses

Abstract

Lactobacillus delbrueckii (LD) is a species usually found in raw milk hard cooked cheeses. Present in raw milk, it grows in cheeses during ripening, but it can also be added in large concentrations with acidifying starter cultures. Its role in cheese proteolysis has been largely demonstrated, but its role in the formation of volatile compounds in cheeses remains to be documented. For this purpose, 16 experimental hard cooked cheeses were made from raw milk using adjunct cultures made up of Streptococcus thermophilus and Lactobacillus helveticus with the addition or not of LD, and ripened for 184 days. Bacterial populations and volatile compounds were monitored throughout ripening. The LD addition affected the early growth of the starters but not the dynamics of the native microbiota. LD had a major effect on proteolysis and on the composition of volatile compounds. Of the 85 volatile compounds identified in the cheeses, 6 of the 7 acids, 10 of the 16 aldehydes, 11 of the 17 alcohols, 10 of the 17 ketones, 10 of the 23 esters, and 4 of the 5 sulphur compounds were affected by the LD addition at one or more stages of ripening. At the end of ripening, levels of the 31 compounds affected by LD were higher in the cheeses with LD added, except one secondary alcohol and 2 methyl-ketones. The question of the effective involvement of LD in these observations, whether due to the metabolic activity of LD or interactions with other microbial populations, is raised.