Yoghurt has become a popular fermented dairy product. The main pattern of acid production is controlled by the yoghurt starter . Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus are the dominant species in yoghurt production. High quality yoghurt products are characterised by smooth texture, suitable viscosity, good flavour and low post fermentation acidification. Among these, weak post acidification property has recently been considered as an
important factor for yoghurt starter selection