GROWTH AND SURVIVAL OF BIFIDOBACTERIA IN MILK

The incorporation of intestinal species such as bifidobacteria and Lac tobacillus acidophilus into fermented milk products is attracting incr easing interest in various countries, because of supposed health-promo ting effects associated with these species. To manufacture fermented m ilk products containing large numbers of viable bifidobacteria, growth and survival were studied of species belonging to this genus. Several Bifidobacterium strains belonging to different species were tested fo r their growth potential in pure milk or in milk supplemented with cas ein hydrolysate. Out of 17 strains, 15 did not grow in pure milk. Howe ver growth required the presence of peptides or amino acids derived fr om casein degradation. Since these strains lack proteolytic activity, they could be grown by adding casein hydrolysates or sometimes by co-c ulturing with proteolytic species such as lactobacilli, e.g. L. acidop hilus. In co-culture, milk with a sufficiently low initial oxygen cont ent should be used to obtain the low redox potential required in the e arly phase of incubation for good growth of bifidobacteria. If the str ains were incubated together with species like Streptococcus thermophi lus that rapidly acidified the milk before the redox potential was suf ficiently low, they did not grow. The manufacture of fermented milk pr oducts with bifidobacteria therefore requires the use of an inoculum c ontaining the final number of cells of Bifidobacterium required for th e product. Survival of the strains in the fermented milk product was a lso studied during storage at low temperature. Of the 17 strains, 14 c ompletely lost their viability in the first week of storage. The loss of viability was reduced if the product was less acidic. Good survival in fermented milk products is therefore an exceptional property among bifidobacteria and should be a criterion for selecting strains for ma nufacturing products aimed at probiotic effects.