Isolation and characterization of lactic acid bacteria from Libyan traditional fermented milk "Laban"

Abstract

Fermented milk product "Laban" in Libya is one of the most traditional fermented milk product consumed as a refreshing drink, particularly in the warm season. The average values of the physicochemical tests on naturally fermented milk samples; titratable acidity, pH, total solids, and fat were 0.73%, 4.16, 8.12%, and 1.54% respectively. Coliform, yeast and mold counts were 21×10⁴, 39×10^⁴, and 41 ×10^³ cfu/ ml., respectively. Most strains of coliform bacteria were Serratia odorifera, Escherichia coli 1, E. coli 2. and Klebsiella oxytoca. The average Lactococcus, Streptococcus, Mesophilic Lactobacillus / Leuconostoc and Thermophilic Lactobacillus counts were 99 ×10⁷, 96 ×10⁷, 93 ×10⁷ and 15 ×10⁷ cfu / ml. respectively. A total of 142 lactic acid bacteria (LAB) isolates were identified to the genus level as Lactobacillus (48.59%), Lactococcus (43.66%), Streptococcus (4.93%) and Leuconostoc (2.82%). Sugar fermentation tests revealed the most frequent Lactobacillus species found to be Lactobacillus delbrueckii ssp. lactis (62.32%), followed by Lactobacillus plantarum (31.88%). Furthermore, other selected LAB isolates were identified by API 50 CH test as Lactococcus lactis ssp. lactics, Lactobacillus pentosus, Lactobacillus brevis, and Leuconostoc mesenteroides ssp. cremoris. Thus, this research has documented the lactic acid bacteria isolated from naturally Libyan fermented milk and will provide fundamental basic and useful information for further studies of strain selection starter culture, with regard to the industrial production of fermented dairy products.

Key words: Lactic acid bacteria, Traditional fermented milk, Isolation, Identification, Characterization.