Investigating Inoculation Size of Mixed Starter Cultures for Making Probiotic Milk Co-Fermented with Mesophilic and Thermophilic Lactic Acid Bacteria

Importance of development of novel probiotic fermented milk and challenge made for its acceptability is well known. In this research, the impact of different inoculum size of yogurt and DL-type starter culture (mesophilic and thermophilic LAB) on some physicochemical, sensorial and microbial properties of fermented milk was investigated.
Sensorial and microbial characteristics of produced milk were studied by applying probiotic starter culture (2% v/v inoculum with equal ratio of Lactobacillus acidophilus and Bifidobacterium bifidum). Fermented milks were analyzed for determination of titratable acidity, viscosity, viability of mesophilic starter cultures and sensory properties in 5 days intervals. Then the most suitable treatments were selected for the production of probiotic milk. Lactococcus lactis and L. cremoris were counted on M17 agar (at 25°C for 72 h), while Leuconostoc and Lactobacillus were counted on tomato juice agar and MRS bile agar (both aerobiocally at 37°C for 72 h). Bifidobacterium was cultured anaerobically on MRS bile agar.
According to results, the best organoleptic properties were achieved in the product prepared with 2% the mesophilic and thermophilic starter cultures and 2% probiotic. This product had a high viscosity and ropy consistency. So, Iranian probiotic Langfil with desired properties was produced using the best treatment prepared; it was very stable and had a low tendency to wheying off.