The uses of microorganisms for the production of bioactive foods, due to high consumer acceptance are increasing. Probiotics are defined as live microorganisms that confer health effects to the host when administrated in an adequate amount (10 7 CFU.mL -1 ). Any undesirable changes in the cellular environment, which lead to biological response, are categorized as stress. Based on recent studies facing stress leads to increasing the viability of cells in further stress. Lactobacillus plantarum are widespread species. It has the biggest genome among other lactobacilli, therefore has better potential to tolerate stress. Native species have more adaptability in regional environmental and digestive system. Ice cream as a non-fermented dairy product is a suitable carrier for Probiotics In this study native probiotic Lactobacillus plantarum A 7 were obtained from culture collection of food microbiology laboratory of Isfahan University of Technology. The natural viability of cells was evaluated in five different pH and Oxgall concentration during 24 hours by enumeration of live cell in MRS agar. To increase the viability of cells in acid, cells was treated by five pH from higher pH to lower pH, gradually. The same procedure has been carried out to increase bacteria viability in Oxgall. Resistant cells were used for production of Ice cream; numbers of viable cells were enumerated during 12 weeks. Finally survived cell in the ice cream were reused for production of Ice cream. The results show a notable increase in viability of acid and bile treated cells. In pH=2.5 cells kept their population after 24 hours, also in 0.6% Oxgall concentration after 24 hours a considerable increase were observed in cell population. Additionally, the survival rate of acid and bile treated bacteria in Ice cream was more than bacteria with natural tolerance after 12 weeks storage in -20°C. The highest cell viability was observed in ice cream, which is contained separated bacteria from previous ice cream. Affter 12 weeks storage the number of survived cell was (10 7 CFU.mL -1 ). Key words : Probiotics, Lactobacillus plantarum , Ice cream, Cross protection, Viability, Sub-lethal tresses
