Yocidophilus Case Study

Follow the fate of probiotic and lactic acid starter in yogurt during storage time Viability and activity of probiotic bacteria are important considerations, because the probiotic bacteria must survive in the food during shelf life, as one of the important criteria in selecting probiotic bacteria .The changes in viable counts of L. acidophilus during storage period in selective medium, lactic acid starter of yogurt along with L. acidophilus in reference medium (MRS) , and the counts of lactic acid starter of yogurt without L. acidophilus (yogurt bacteria) are presented in (Table 2) . The average viable cell counts of L. acidophilus significantly decreased from 8.31 ± 0.02 log CFU /g on time 0 to
explains changes in average values of L. acidophilus in selective media, and in reference medium (MRS) for the probiotic yogurt were subjected to the re-pasteurization before inoculating with L. acidophilus. The ended product was re-pasteurized by heating at 75°C for 15 min to destroy all starter cultures. The average viable cell counts of L. acidophilus declined from 8.70 ± 0.19 log CFU /g on time 0 to 7.86 ± 0.36 log CFU /g on the day14 in selective media while the average viable cell counts of L. acidophilus declined from 8.54 ± 0.31 on time 0 to 8.09 ± 0.17 on the day14 in reference media . There were significant differences (P< 0.05) among the viable counts of L. acidophilus in selective media only during cold storage of bio- yogurt. L. acidophilus as probiotic in reference media is more stable than it in selective media is during cold storage (Table
bulgaricus that responsible of ՙover- acidification̛ by re-pasteurization, probiotics are more stable throughout the refrigerated storage (Table 3). Over- acidification is found to cause loss of viability of probiotic bacteria. Lactobacillus delbrueckii subsp. bulgaricus produces sufficient hydrogen peroxide to display inhibition of probiotic. Accumulation of hydrogen peroxide in growth media can happen because lactobacilli do not have catalase enzyme responsible for degradation of hydrogen peroxide to water and oxygen. Hydrogen peroxide and other toxic oxygenic metabolites such as superoxide anion and hydroxyl radical can react with other components eventually lead to microbial cell death [Shah, 2000]. According to Ng et al.[2011], yogurt prepared with L. delbrueckii ssp. bulgaricus alone generated seven- to nine-fold higher quantities of H2O2 than those prepared with S. thermophilus alone or with both species .Marty-Teysset et al. [2000] reported that L. delbrueckii ssp. bulgaricus creates H2O2 mainly due to the action of NADH: H2O2 oxidase , while the presence of S. thermophilus helps decompose H2O2 via NADH peroxidase , an enzyme converting H2O2 into water to regenerate NAD+ [Smart & Thomas,1987]. Rybka & Kailasapathy [1995] also observed less viability of L. acidophilus in yoghurts with L. delbrueckii subsp.