____________________________________________________________________________________________ *Corresponding author: Email: nezami_man@yahoo.com; Annual Research & Review in Biology 4(24): 4091-4103, 2014 SCIENCEDOMAIN international www.sciencedomain.org Optimization of Lactobacillus acidophilus La-5, Feta Cheese Starters and Salt Content in Iranian Ultrafiltered Soft Cheese Formula Mohammad A. Nezami 1* , Mohammad R. Ehsani 1 , Ali. Mohammadi-Sani 2 , and Kianoush Khosravi-Darani 3 1 Department of Food Science and Technology, Science and Research Campus, Islamic Azad University, Tehran, Iran. 2 Department of Food Science and Technology, Quchan Branch, Islamic Azad University, Quchan, Iran. 3 Research Department of Food Technology, National Nutrition and Food Technology Research Institute, Shahid Beheshti University of Medical Sciences, Tehran, P. O. Box: 19395-4741,Iran. Authors’ contributions This work was carried out in collaboration among all authors. Author MAN performed all the experiments and wrote the first draft of the manuscript. Author MRE supervised the searches and provided the facilities for the use of pilot-plant UF system at membrane laboratory of Tehran University. Author AMS managed the literature searches and edited the manuscript analytically. Author KKD performed the statistical analysis, wrote the Taguchi design protocol and edited the manuscript statistically. All authors read and approved the final manuscript. Received 27 th April 2014 Accepted 11 th June 2014 Published 27 th July 2014 ABSTRACT Aims: To optimize the process variables including: Lactobacillus acidophilus La-5, total starter (a mixture of mesophilic cheese starters (MCS) and thermophilic yoghurt starters (TYS), mesophilic cheese starter: thermophilic yoghurt starter (MCS: TYS) ratio and salt content in probiotic Iranian ultrafiltered soft cheese (IUSC). Methodology: In order to choose the best probiotic cheese formula with the highest Lactobacillus acidophilus La-5 count, a total of eight samples with 20 % total solids were produced using a small scale ultrafiltration system. Probiotic bacteria of Lactobacillus Original Research Article