Formation of volatile compounds by wild Lactococcus lactis strains isolated from raw ewes’ milk cheese

Abstract

The formation of volatile compounds in fresh cheese by 32 wild strains of Lactococcus lactis was investigated, and compared to volatile compounds formed by six collection strains of lactococci. Hierarchical cluster analysis of the relative abundances of volatile compounds determined by GC-MS was used for the classification of strains. Seven compounds (1-propanol, 2-propanol, 2-methyl propanol, 3-methyl butanol, 3-methyl butanal, 2,3-heptanedione and isoamyl acetate) separated the strains into two main branches, one of which contained all collection strains. The standard addition method was used to quantify these seven compounds in cheeses. All but 1-propanol and 2-propanol were at levels exceeding their respective odour thresholds. Sensory evaluation by a trained panel was carried out on cheeses. Abnormal odours were detected in cheeses made with 27 out of the 32 wild L. lactis strains. Odour quality of cheeses was positively correlated to 2-propanol, α-pinene and descriptors butter, yoghurt and fresh cheese, whereas odour intensity was positively correlated to 13 volatile compounds (six alcohols, two aldehydes, four ketones and one ester) and descriptors branched-chain volatiles, fruity and roasted hazel nuts.