Factors affecting the growth and survival of probiotic in milk

Abstract

Probiotic bacteria have been added to dairy products and as adjunct cultures to impart health benefits to consumers. However, to gain maximum therapeutic benefit, the bacteria must remain viable over the entire shelf-life period of the product. Studies have shown that the viability of these bacteria decreases significantly over this period and in some products their presence is negligible towards the end of the shelf life. Various studies have used different strains of probiotics to get better viability but even the probiotic with special characteristics such as oxygen tolerant and acid resistance, still face significant survival problems in dairy products. Several studies have indicated that carbohydrates, peptides and amino acids added to dairy products at various concentrations showed positive effect on the growth and survival of many strains of probiotic bacteria in dairy products. Bifidobacterium lactis Bb12 has been found to have a wide use in dairy products because of their oxygen tolerance and acid resistance, which made it one of the chosen strain in this study. The growth rate was indirectly measured by the rate of change of the pH in fermented skim milk while the survival was measured as the total count, cfu/ml, over the storage period of 28 days at 4°C±1.The results showed that the addition of prebiotics such as fructooligosaccharides (FOS) at 5% or Inulin at 3% to skimmed milk enhanced the growth and survival of B lactis Bb12 in comparison to the control. The growth rate was better in both cases and the survival in the sample with 5% FOS was significantly better (P<0.05). The effect of the hydrolyzed skim milk on the growth and survival of B lactis Bb12 showed that skim milk with Degree of Hydrolysis DH<5% with trypsin at 1:20000, enhanced the growth and survival significantly (P<0.05) compared to the control. The synergistic effect of the combination of prebiotics, fructooligosaccharides (FOS) at 5% and Inulin at 3%, and DH<5% hydrolysed milk (called Mix Design Skim Milk or MDSM) on the growth and survival of B lactis Bb12 showed to be the best combination with significant (P<0.05) growth rate and survival for Bifidobacteria and Lactobacillus with a decrease in fermentation time by 12 hours and a significant (P<0.05) survival compared to the control. The sensory qualities of the product made with MDSM and B lactis Bb12 showed to be of good quality and comparability to the commercially available products.