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Abstract
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 degrees 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 degrees 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 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 significantly
better than free cells (P <0.05) in pasteurized yogurt after refrigerated storage
for 5 weeks.