Changes in microbial flora during manufacture of a traditional fermented milk from ewe's milk

Abstract

Changes in the microbial flora during the manufacture of a sour milk from raw ewe's milk were studied. Mean log counts of lactic acid bacteria, lactobacilli and streptococci (respective values in milk 4.55, 3.19 and 5.56) increased significantly (P<0.05) to 8.46, 6.98 and 8.46, respectively, at 5 days and at the same time the pH decreased from 6.58 in milk to 4.71 in the final product. Levels of total counts, coliforms and psychrotrophs also increased to 108, 107and 106cfu/ml, respectively. Halotolerants and yeasts were counted at quite low numbers throughout manufacture.Isolates of lactic acid bacteria were classified as lactococci, lactobacilli, leuconostocs and enterococci. Enterococci predominated (58.9% of the isolates) over the other lactic acid bacteria after 1 day meanwhile leuconostocs became predominant (46.9%) after 5 days, followed by lactobacilli (29.7%), lactococci (17.2%) and enterococci (6.2%).Lactobacillus plantarumandLeuconostoc mesenteroidessub-spp.cremoriswere the species most frequently isolated. Enzyme activities (API-ZYM tests) of lactococci and leuconostocs were low, in general, but activities ofLb. plantarumstrains were considerably higher. ThreeLc. lactissub-spp.lactisstrains produced diacetyl, four of them formed acetoin, and one was characterized as good active, concerning acidification ability.Results presented here suggest the necessity of using a starter culture, consisting of selected strains of lactococci, leuconostocs and possibly lactobacilli, and pasteurized milk for the production of a high quality product.