Study of Natural Starter Culture of Lactic Acid Bacteria in fermented Tunisian milk "Rayeb"

Fifty samples of traditional fermented milk "Rayeb" were randomly collected from villages near Sfax governorate, Tunisia and subjected to determination of pH, sensory evaluation and isolation and identification of lactic acid bacteria. The obtained results revealed that pH ranged from 3.7 to 4.4 with a mean of 3.93±0.04, most of the examined samples (46%) were judged as very good. The isolated lactic acid bacteria were lactobacillus, lactococcus, leuconostoc and streptococcus as 14.70, 40.20, 33.34 and 11.76%, respectively, the majority of identified isolates were Lact. Lactis subsp. Lactis (36%), Leuco. mesen cremoris (28%) followed by St. salivaris var thermophilus (12%), both L. delbrukii var bulgaricus and L. acidophilus represented as (9%) while the lowest percent (6%) was L. delbrukii var delbrukii. There are several factors which influence the quality of fermented milks, these include type of milk, processing conditions, storage conditions and however, quality of starter culture is the most important factor that influences the development of fermented milks. The choice of starter culture being based on their production of lactic acid, aromatic compounds as well as their therapeutic values to some types used.