Abstract

Gelareh Shafiee , Amir Mohammad Mortazavian2*, Mohammad Amin Mohammadifar Mohammad Reza Koushki , Abdorreza Mohammadi and Reza Mohammadi

Combined effects of milk non-fat dry matter content (4, 8 or 12%), incubation temperature (37, 40 or 44°C) and final pH of fermentation (4.2 or 4.5) on biochemical and microbiological characteristics of probiotic fermented milk (Lactobacillus acidophilus LA-5, Bifidobacterium lactis BB-12, and yogurt bacteria) during and immediately after fermentation were investigated. Treatments containing higher dry matter contents had slower pH and redox potential decline rates, faster acidity increase rate, longer incubation time and greater final titrable acidity. Treatments fermented at higher temperatures with lower final pH displayed longer fermentation time and greater final titrable acidity. Treatments with higher dry matter non-fat contents, lower incubation temperatures and higher final pH of fermentation possessed greater viability of probiotic bacteria. The concentration of lactic acid in treatments increased in parallel with the titrable acidity and the concentration of acetic acid were proportional to the viability of bifidobacteria.