Physiochemical and microbiological properties of probiotic set yoghurt affected by Milk somatic cell levels

The objective of this study was to evaluate probable effects of somatic cell (SC) level of yoghurt milk on viability of Lactobacillus acidophilus LA_5 and Bifidobacterium BB-12 in probiotic yoghurt. Yoghurt samples were produced using milk with different levels of SC (Low: <200000, Medium: 200000-800000 and High: >800000 cells ml-1). Chemical composition of yoghurt milk with different SC levels, included lactose, fat, total solids (TS), crude protein (CP), pH and titratable acidity (TA) were analysed. Physicochemical characteristics, growth rate during incubation and viability of probiotic bacteria were also determined 1,7,14 and 21 days after production. Increased level of SC reduced growth rate of L.acidophillus La-5 to the higher extent. Yoghurt samples prepared from low SC milk attained viable probiotic count above 6 log cfu/ml during storage time. At the end of the storage time, the counts of L. acidophilus LA-5 were 1.6 and 1.76 log cfu/ml lower for yoghurt samples with medium and high SCC. However, as the SC level increased in yoghurt a marked reduction of 2.39 log cfu/ml was in the viability of Bifidobacterium BB-12 during shelf life. It was assumed that reduction of milk composition, as well as higher TA and proteolysis due to the activity of proteases such as plasmin, in medium and especially high SC yoghurt samples result in lower viability of probiotic bacteria which declines the opportunity of functional dairy product production as well.

کلیدواژه ها:

Somatic cell level ، Milk Chemical composition ، Probiotic bacteria ، viability