Evaluation of the viability of starter bacteria and physicochemical properties in functional yogurt enriched with wheat germ powder and a mixture of processed plant essential oils

According to the increasing demand of advanced societies for the consumption of functional foods, especially in dairy products, the use of natural-based materials such as plant essences in the field of enriching food products with their antimicrobial and antioxidant compounds, as well as the use of wheat germ powder as a rich source of dietary fibers and vitamins and minerals and their effects on the viability of starter bacteria (due to their prominent role in improving human health) are seem to be necessary. Investigating the effects of using processed essential oils and wheat germ powder simultaneously in yogurt is considered in this research. Sensory, physicochemical characteristics and bacterial conting of set yogurt including Streptococcus thermophilus and Lactobacillus bulgaricus, were tested during the storage period to study the simultaneous effect of plant essential oils and sprouted wheat powder. The essential oils used included tarragon and thyme with different proportions and at three levels (400, 1200, 2000 microliters per liter of yogurt). Yogurt physicochemical tests such as acidity and water holding capacity, hedonic sensory test, rheology test (apparent viscosity) and microbial count tests were conducted to check the viability of starter bacteria in yogurt during the 14-day storage period. Based on the results obtained from the analysis of variance of the tested samples, the concentration of essential oil significantly (p<0.05) reduced the acidity and viability of starter bacteria of the product, but it had not a significant effect on the viscosity the sensory characteristics. In this regard, thyme and wheat germ powder showed a negative and unfavorable effect, especially in high concentrations.