Survival of bifidobacteria in yogurt and simulated gastric juice following immobilization in gellan–xanthan beads

A novel acid-stable bead made of gellan gum and xanthan gum was used to immobilize Bifidobacteria. The beads (0.75% gellan and 1% xanthan gum) had an average diameter of 3 mm and did not shrink in 25% lactic acid solution, pH 1.5, or 20% acetic acid solution, pH 1.5, after storage at 4°C for 4 weeks. Bifidobacterium infantis ATCC 15697, the most acid-tolerant strain tested, was immobilized in gellan–xanthan beads and its survival in peptone water, pH 4, pasteurized yogurt, and simulated gastric juice was monitored. In peptone water, pH 4, the reduction in cell count of immobilized cells of B. infantis ATCC 15697 was not significantly different from that obtained with free cells during 6 weeks of storage at 4°C. However, counts of immobilized cells of B. infantis ATCC 15697 remained significantly higher than free cells (P<0.0001) when both were exposed to simulated gastric juices at pH 2.5, 2.0 and 1.5. At pH 2.5, the viable count of free cells dropped from 1.23×109 CFU/ml to an undetectable level (<10 CFU/ml) in 30 min, while the viable count of immobilized cells decreased by only 0.67 log cycle in the same time period. Immobilized cells also survived significantly better than free cells (P<0.05) in pasteurized yogurt after refrigerated storage for 5 weeks.