Viability of yoghurt bacteria and probiotic strains in models of fermented and non-fermented milk

摘要

The objective of the study was the qualification of the viability of chosen yoghurt bacteria and probiotic strains in controlled milk models. The aim of this research was to check the predisposition of each culture to meet the requirements of FAO/WHO concerning the therapeutic minimum, and the requirements of FID/IDF concerning the least number of the bacteria throughout the period of product consumption. The controlled milk models were produced with three freeze-dried starter cultures (YC-180, Bb-12, La-5) and one isolate (Lb. casei). The viability of each culture was studied during cold storage (6 degrees C for 4 weeks) of fermented and non-fermented milk samples. The results showed univocally that the viability of LAB in fermented or non-fermented milk samples in cold storage depended on the genus, species and strain of bacteria used, as well on such factors as the acid and oxygen content of the product. During cold storage the yoghurt culture and probiotic strains, except Lb. acidophilus, fulfilled the requirement of the therapeutic minimum in the fermented and non-fermented milk samples. Only the probiotic strain Lb. acidophilus La-5 showed low viability: in the non-fermented milk its population decreased below the required 10(6) cfu/cm(3) already in the 2(nd) week of cold storage. In the fermented milk,however, the population of Lb. acidophilus decreased below the required 10(6) cfu/cm(3) only between the 2(nd) and 4(th) week of cold storage. This study showed the essential influence of storage conditions (time, acid and oxygen content) and the genus, species and strain of bacteria used on their viability.