Effects of mint extract on the viability of probiotic bacteria in a native Iranian dairy drink (Doogh)

In this work, production of a native Iranian dairy drink containing active probiotic bacteria, so-called (bio-) doogh, was studied. Two commercial strains of probiotic bacteria, Lactobacillus acidophilus and Bifidobacterium lactis, inoculated into three types of doohg, including plain doogh as control, and samples containing 1% or 2% mint extract. Survival of probiotic bacteria, pH, acidity and flavor of bio- doogh was examined weekly during nine-week storage in 4°C. The results obtained showed mint extract depending on its concentration can reduce or increase survival of the bacteria. After storing at 4°C, viable B. lactis reduced by 2 logCFU/ml, while L. acidophilus reduced to zero after eight weeks at 4°C. There was no significance difference (P<0.05) between pH and acidity of bio-doogh during storage period. Statistical result revealed that there was no significant difference betwee n flavors of various samples of bio-doogh. Bio-doogh with mint extract had a higher flavor score than bio-doogh without mint extract.