BACKGROUND AND AIM: PROBIOTICSARE BACTERIA AND YEASTS THAT ARE USEFUL FOR HEALTH, ESPECIALLY DIGESTIVE SYSTEM. THEY ARE NATURALLY FOUND IN BODY. WECAN ALSO FIND THEM IN SOME FOODS AND SUPPLEMENTS. LACTOBACILLUS ACIDOPHILUS IS ONE OF THEM THAT IS BENEFIT FOR HEALTH, SINCE IT PRODUCES VITAMIN K AND LACTASE THEY. COMMONLY USED IN FOOD, SUCH AS Yogurt, OTHER DAIRY PRODUCTS, AND FERMENTED SOY PRODUCTS.THERE IS GOOD EVIDENCE FOR THE USE OF L. ACIDOPHILUS IN TREATING VAGINAL INFECTIONS BOWEL SYNDROME, BRAIN DISORDERS, ASTHMA, HIGH CHOLESTEROL, LACTOSE DIGESTION, OR DIARRHEA. THESE BACTERIA CAN CHANGE THE INTESTINE MICROFLORA.OF THIS RESEARCH WAS TO DETERMINE OPTIMUM CONDITIONS FOR FERMENTING MILK BY L. ACIDOPHILUS….