Survival of bifidobacteria in yogurt and simulated gastric juice followingimmobilization in gellan-xanthan beads

A novel acid-stable bead made of gellan gum and xanthan gum was used to imm obilize 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 degrees C for 4 weeks. Bifidobacterium infantis ATCC 15697, the most acid-tolerant strai n tested, was immobilized in gellan-xanthan beads and its survival in pepto ne water, pH 4, pasteurized yogurt, and simulated gastric juice was monitor ed. In peptone water, pH 4, the reduction in cell count of immobilized cell s of B. infantis ATCC 15697 was not significantly different from that obtai ned with free cells during 6 weeks of storage at 4 degrees C. However, coun ts of immobilized cells of B. infantis ATCC 15697 remained significantly hi gher than free cells (P < 0.0001) when both were exposed to simulated gastr ic juices at pH 2.5, 2.0 and 1.5. At pH 2.5, the viable count of free cells dropped from 1.23 X 10(9) 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 signifi cantly better than free cells (P < 0.05) in pasteurized yogurt after refrig erated storage for 5 weeks. (C) 2000 Elsevier Science B.V. All rights reser ved.