Comparison between Physico-Chemical, Microbiological and Rheological Properties of Yoghurt Containing Lb.rhamnosus and Lb.paracasei with Conventional Yoghurt Samples during the Shelf Life

One of the novel methods of food preservation for extending the shelf life of food product is biological preservation. In this method, without addition of chemical preservatives and mainly using lactic acid bacteria, the minimum thermal processing is applied for food preservation. In this study, yoghurt samples containing Lb. rhamnosus and Lb.paracasei were prepared. The samples were evaluated for physico-chemical, lactic acid bacteria and viscosity tests, during the first, 10th, and 21th days of shelf life. In addition, the enumeration and viability of Lb. bulgaricus, Lb.paracasei, Lb.rhamnosus and Str. thermophilus in the samples were studied. Not significant pH, total solid and fat changes was showed between samples containing Lb.rhamnosus and Lb.paracasei with blank ones but the viscosity of former samples were significantly increased and the amount of syneresis reduced. The number of Streptococci bacteria decreased and Lactobacilli population increased during 21 days shelf life of yoghurt samples.