Determination of starter bacteria viability and probiotic in vitro gastrointestinal digestion tolerance in fermented milk added with prebiotics

The effect of inulin, polydextrose and Hi-maize resistant starch on culture bacteria viability and Lactobacillus acidophilus La-5 and Bifidobacterium animalis subsp. lactis Bb-12 survival under simulated gastrointestinal conditions in ABT (L.acidophilus La-5, B.animalis Bb-12 and Streptococcus thermophilus) fermented milk was investigated during 28 days of storage. The impact of prebiotics on sensory characteristics was also assessed. Probiotic viabilities ranged from 6 to 8 log cfu/g throughout the storage period, and none of the prebiotics affect the viable counts of La-5 and Bb-12. Bb-12 presented higher survival rates under gastrointestinal stress than L.acidophilus La-5 did however, both probiotic viability decreased during the in vitro assay in all the treatments. Exposure to conditions of low pH (2.2-2.6) resulted in a significant higher reduction in La-5 viability than that of Bb-12. Although inulin addition enhanced viable counts of La-5 more than those of other prebiotics during gastric and enteric- I phases, all samples showed similar La-5 survival after enteric-II phase. The supplementation with Hi-maize indicated a protective effect on Bb-12 tolerance to simulated gastrointestinal conditions on 14th and 28th days. Inulin or Hi-maize did not affect the sensory properties of fermented milk whereas the product supplemented with polydextrose had the lowest scores specifically at the end of the storage.