IMPROVING VIABILITY OF BIFIDOBACTERIA BY MICROENTRAPMENT AND THEIR EFFECT ON SOME PATHOGENIC BACTERIA IN STIRRED YOGHURT

Abstract

Fifteen batches of stirred youghurt were made to study the effect of microentrapment on the viability of bifidobacteria and their ability to inhibit the growth ofE. coliandStaph. aureus. Entrapped cells ofBifidobacterium bifidumandBifidobacterium infantiswere able to produce antimicrobial agents which inhibitedE. coliandStaph. aureusused as test organisms. Viable counts of unentrapped bifidobacteria decreased sharply, while entrapped cells of bifidobacteria were quite stable during refrigerated storage of stirred yoghurt.Bif. infantiswas more tolerant to storage conditions thanBif. bifidum. Microentrapment of bifidobacteria improved their survival during storage of stirred yoghurt, especiallyBif. bifidum, whose viability was not significantly (P≯0.05) different from entrappedBif. infantis. Viable counts ofE. colidecreased during storage of stirred yoghurt. Addition to bifidobacteria caused a sharp decrease in the viability ofE. coli.E.coligrowth was not detected at the 5th day, when entrapped cells of bifidobacteria were added to stirred yoghurt, whileE. coligrowth was not detected at the 7th day of storage in yoghurt containing unentrapped bifidobacteria. Addition ofBif. bifiduminhibited the growth ofE. colimore effectively thanBif. infantis. Staph. aureusshowed similar patterns toE. coli, except theStaph. aureuswas more tolerant to storage conditions. The counts of total bacteria, lactobacilli andStreptococcus salivariussubsp.thermophilusincreased up to the third day then declined till the end of storage. Titratable acidity increased gradually during the first 3 days of storage then increased slightly up to the end of storage, while pH values dropped during storage. Adding bifidobacteria,E. coliandStaph. aureusdid not affect significantly (P≯0.05) the counts of lactobacilli andStr. salivariussubsp.thermophilus, acidity and pH value.\u