Effect of inulin on the growth and survival of Bifidobacterium longum BB536 in fermented goat's and cow's milk

Fermented dairy products were made from standardized goat and cow milk (2.9 % milk fat) with addition of 3 % skimmed milk powder (control samples), or with addition of 2 % inulin and 1 % skimmed milk powder (experimental samples). Fermentation of samples was carried out at 40 degrees C by thermophilic yoghurt culture YC-380 and probiotic culture Bifidobacterium longum BB536. Desired acidity (pH around 4.5) was achieved in all samples in about 5.5 h. Viable count of probiotic strain (logN/m) increased for all samples for on average 1.4 logarithmic units except for the sample of cow's milk supplemented with inulin, which exhibited the highest growth of bifidobacteria for approximately 1.7 logarithmic units. During fermentation somewhat faster decrease of pH-value was observed in goat milk samples compared to cow milk samples. At the end of fermentation there was no statistically significant difference (P>0.05) in pH-values regardless of milk origin or inulin addition. During thirty days of fermented drink storage at lower temperature (about 6 degrees C), slightly lower pH-values were observed in cow milk samples compared to goat milk, especially in cow milk enriched with inulin. During storage, until the 1511 day, an increase in the number of viable count of probiotic bacteria was observed in all samples, while from 20(th) to 30(th) day a decrease of 0.5 logarithmic units of the same parameter was recorded. In goat milk their survival was somewhat smaller compared to cow milk. The number of bifidobacteria in samples supplemented with inulin on the last day of storage, compared to control samples, was higher for 0.3 logarithmic units, regardless of the milk origin. After thirty days of refrigerated storage, recommended concentration of bifidobacteria was insured in all samples, thus directly implying that these fermented drinks can be included in probiotics.