Selective enumeration of Lactobacillus casei from yogurts and fermented milk drinks

A selective medium (LC agar) was developed for enumeration of Lactobacillus casei populations from commercial yogurts and fermented milk drinks that may contain strains of yogurt bacteria (Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus), probiotic bacteria (Lactobacillus acidophilus and bifidobacteria) and L. casei. Appropriate dilutions were pour-plated in specially formulated LC agar acidified to pH 5.1 and the plates incubated at 27°C for 72 to 96 h under anaerobic conditions. Growth of S. thermophilus was prevented by adjusting pH to 5.1. L. delbrueckii ssp. bulgaricus did not ferment ribose as the carbon source, as a result the organisms did not form colonies. L. acidophilus formed colonies on MRS-ribose agar; however, this organism did not grow in the specially formulated LC agar containing ribose. Similarly, Bifidobacterium spp. did not form colonies in LC agar. L. casei formed colonies on LC agar.link_to_subscribed_fulltex

Microencapsulation of probiotic bacteria and their survival in frozen fermented dairy desserts

A procedure was developed to entrap probiotic bacteria (Lactobacillus acidophilus MJLA1 and Bifidobacterium spp. BDBB2) into calcium alginate beads. The effects of sodium lauryl sulfate and Tween 80 on bead sizes and the release of the organisms from the encapsulated beads in the presence of acid and bile were investigated. The external and internal appearances of the bead were observed using scanning electron microscopy. The encapsulated beads were freezedried and incorporated into the mix for making frozen fermented dairy desserts prior to freezing. Two batches of fermented frozen dairy desserts were made with or without encapsulated probiotic bacteria and viable counts of probiotic bacteria were enumerated in fermented frozen dairy desserts at fortnightly intervals for 12 weeks. The mean diameter of the beads without any sodium lauryl sulfate and Tween 80 was 1.17 mm, but the size of the beads decreased as the concentrations of sodium lauryl sulfate and Tween 80 increased. The average diameter of the beads with 1% sodium lauryl sulfate and 0.3% Tween 80 was 0.064 mm. The beads appeared to be ellipsoidal in shape and the microorganisms were located in the matrices formed in the beads. The entrapped bacterial cells were released by shaking in O.1M phosphate buffer for 5 min and in the presence of bile, but not in the presence of acid. In general, the survival of probiotic bacteria in fermented frozen dairy desserts was improved with encapsulation.link_to_subscribed_fulltex

Viability of probiotic bacteria in fermented frozen dairy desserts

Yogurt bacteria (Streptococcus thermophilus and Lactobacillus delbruekii ssp. bulgaricus) and probiotic bacteria (Lactobacillus acidophilus and Bifidobacterium spp.), 41 strains in all, were screened for ability to survive under frozen conditions, in presence of sugar (8 and 16%) and under acidic conditions. Three batches of yogurt prepared using three different strains each of 5. thermophilus, L. delbrueckii ssp. bulgaricus, L. acidophilus and Bifidobacterium spp. were mixed with a base mix and frozen. In a separate experiment, three batches of yogurt were made with yogurt bacteria only and probiotic bacteria were added just before freezing. The viability of yogurt and probiotic organisms in the frozen desserts was monitored for 12 weeks. Further, two 1000 L batches of fermented dairy desserts were made using selected strains of yogurt and probiotic bacteria and the viability of both organisms was monitored for 12 weeks. Most of the organisms survived freezing, acidic conditions and the presence of high levels of sugar.link_to_subscribed_fulltex

Effect of acid casein hydrolysate and cysteine on the viability of yogurt and probiotic bacteria in fermented frozen dairy desserts

The effect of acid casein hydrolysate and cysteine on the viability of yogurt bacteria (Streptococcus salivarius ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus) and probiotic bacteria (Lactobacillus acidophilus and bifidobacteria) during a storage period of 12 weeks was assessed in fermented frozen dairy desserts. Three batches of fermented frozen dairy desserts were made with milk supplemented with acid casein hydrolysate or cysteine. The control batch was made with milk supplemented with 2% skim milk powder. Viable counts of yogurt bacteria and probiotic bacteria were enumerated and pH, titratable acidity and β-D-galactosidase activity measured at fortnightly intervals for 12 weeks. S. salivarius ssp. thermophilus was most stable in all the samples of fermented frozen dairy desserts with counts ≥107 cfu/g throughout the storage period. The counts of L. delbrueckii ssp. bulgaricus was reduced by 2 log cycles in the control sample, whereas in those supplemented with acid casein hydrolysate and cysteine, the counts decreased by 1 and 2 log cycles respectively. The counts of L. acidophilus and bifidobacteria decreased to 105 cfu/g in the samples supplemented with acid casein hydrolysate or cysteine. The β-D-galactosidase activity decreased rapidly in the control sample during 12-weeks storage at -18°C, as compared with those prepared with acid casein hydrolysate and cysteine.link_to_subscribed_fulltex

Influence of water activity on fermentation, organic acids production and viability of yogurt and probiotic bacteria

Five one-litre batches of probiotc yogurts were made using reconstituted skim milk supplemented with 0, 4, 8, 12 or 16% sucrose. The incubation time to decrease the pH to 4.5 and changes in organic acids production and counts of yogurt bacteria (Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus) and probiotic bacteria (Lactobacillus acidophilus and Bifidobacterium spp.) in yogurt were assessed for up to 30 days. As the sugar level increased, the water activity decreased and the incubation time to reach pH of 4.5 increased. The organisms produced pyruvic acid, acetic acid, lactic acid and propionic acid at varying levels. There were no major differences in the initial counts of yogurt and probiotic bacteria in all the five batches. However, the counts of all the four groups of organisms declined during storage, in particular in the batches containing 12% and 16% sugar. Thus, sugar addition may be deleterious to the growth of yogurt and probiotic bacteria, especially in products such as fermented frozen dairy desserts, which contain approximately 16% sugar.link_to_subscribed_fulltex