The influence of milk supplementation on the microbiological stability and textural characteristics of fermented milk

In the present work, the effect of milk supplementation on the viability of probiotics and textural characteristics of fermented milk was studied. Three powders, namely skim milk powder (SMP) as a control, fructooligosaccharides (FOS), and whey protein concentrate (WPC) were tested as supplements. Milk was fermented by a commercial starter culture (ABT-7) containing Lactobacillus acidophilus La 5, Bifidobacterium animalis subs. lactis Bb 12, and Streptococcus thermophilus. S. thermophilus was found to be the most numerous starter culture in all samples, and in general the addition of FOS and WPC did not affect its viability significantly (p>0.05). The viability of L. acidophilus increased by supplementation with FOS when compared to WPC supplementation until the 21st day. However, the viable counts of bifidobacteria were maintained above 7 log cfu g-1 in only WPC-supplemented fermented milks during storage. In the presence of WPC, apparent viscosity and gel firmness decreased in comparison with that of SMP (p<0.05).