Survival and [beta]-D-galactosidase activity of encapsulated and free Lactobacillus acidophilus and Bifidobacterium lactis in ice-cream

Three types of ice-cream containing probiotic cultures (Lactobacillus acidophilus DD910 and Bifidobacterium lactis DD920) were prepared: 1. With free probiotic cultures. 2. With alginate-encapsulated probiotic cultures. 3. As in 2 but fermented by adding encapsulated probiotic cultures, together with Streptococcus thermophilus DS224. The survival of L. acidophilus and B. lactis, and p-D-galactosidase activity, were monitored during the product's storage for 24 weeks at -20°C. The L. acidophilus count showed an average of 2.52 log decrease for free cells after 24 weeks, while the encapsulated state of the same strain showed decreases of 2.06 log and 2.27 log in the non-fermented and fermented ice-creams, respectively. B. lactis showed 1.80 log and 2.42 log decreases in the free and encapsulated state of cultures, respectively, in the non-fermented ice-cream. In fermented ice-cream, the decrease was 2.02 log for the same strain. The non-fermented ice-cream with encapsulated and free probiotic cultures had a mean β-D-galactosidase activity of 9.4 ±0.5 U/g and 20.9 ±1.0 U/g, respectively, and the fermented ice-cream had the highest activity of 95.7 ±3.3 U/g. The latter was due to the presence of the additional cultures, S. thermophilus, which were used to prepare the fermented product. Overall, the results indicate that encapsulation of probiotic bacteria does not significantly increase their survival in ice-cream over an extended shelf-life. It was also not possible to conclude whether there was any preservation of p-D-galactosidase enzyme activity due to the encapsulation of bacteria. This study, however, shows that frozen milk products, such as ice-cream, can serve as good carriers for delivering probiotic bacteria to consumers.