Fermentation Flavor Characteristics and Chemical Characterization of Lactococcus lactis in Commercial Starters

In order to deeply analyze the flavor contribution and characteristic aroma components of Lactococcus lactis in fermented milk, twenty-one strains of Lactococcus lactis were isolated from different commercial starters, and subjected to single-strain fermentation. The aroma type was defined according to the results of sensory evaluation, and then determination of volatile flavor compounds in fermented milk was performed using GC-IMS technology, and finally flavor substances were analyzed by chemometric method. The results showed that these single-strain fermented milk can be divided into three flavor types: Milk flavor, cream flavor, and butter flavor. Twenty-five compounds were identified by GC-IMS, including nine alcohols, eight ketones, three aldehydes, one carboxylic acid, and four esters. By drawing the GC-IMS fingerprint map, the characteristic compound composition of fermented milk from different strains was presented. The fermented milks of four strains of Lactococcus lactis subsp. lactis var. diacetylactis were well distinguished by principal component analysis, and the results were consistent with the sensory evaluation results. The correlation between sensory flavor classification and volatile components was analyzed by PLSR, and it was found that the volatile flavor components that had a greater contribution to the “butter flavor” were 1-hexanal and 1-hexanol, the compound which had a greater contribution to the “creamy flavor” was ethyl acetate, the compounds which contributed to the “milk flavor” were obscure, and further analysis was needed for revealing the key ingredients. This research provides a reference for exerting the flavor enhancement effect of Lactococcus lactis in fermented milk.