Study on the effect of soymilk on survival of lactobacillus acidophilus, physicochemical and organoleptical properties of probiotic yoghurt

Prebiotics are defined as non-digestible food ingredients that benefit their hosts by selective stimulation of growth or activity of one or limited number of bacteria in gut. Probiotic products, when administered in adequate amounts, by improving internal microflora of body, confer an effective influence on the host from nutritional and health view. Consuming synbiotic products (simultaneous presence of probiotics and prebiotics) has more beneficial effects on consumer's health. In this project effects of replacing soymilk with milk (as a product containing prebiotics) in 3 levels, 0, 10 and 20% (v/v) and every 7 days (days: 1, 7, 14 and 21) on the survival of lactobacillus acidophilus, physiochemical and organoleptical properties of probiotic yoghurt were studied. Lactobacillus acidophilus LA5 was the probiotic starter culture used. Statistical analysis showed that replacing soy milk, resulted in significant decrease (P<0.05) in pH, synersis and hardness, increase in total count of live probiotic bacteria and acidity, in comparison to control samples. The best taste was obtained for samples without soymilk. Generally in all samples, during storage period, total count of live probiotic bacteria, pH and synersis decreased (expect for samples containing 20% soy milk), while acidity (expect for samples containing 20% soy milk) and hardness increased. Among all samples only yoghurt samples that contained 10% and 20% soy milk, obtained the least required number of live probiotics according to FIL/IDF standard (6 log CFU/g).