Isolation, identification, and technological characterization of wild leuconostocs and lactococci for traditional Raib type milk fermentation

Abstract

Raib (Rayeb) is a spontaneously fermented milk primarily acidified and flavored by strains of lactococci and leuconostocs. Raib and its by-products are traditionally consumed in many Mediterranean and sub-Saharan countries. Dedicated ready-to-use starter strains are currently missing. The aim of this study was to isolate and characterize wild strains of lactococci and leuconostocs that could be used to produce these dairy products while preserving their traditional characteristics. Dominant lactic acid cocci were isolated on M17 and MRS-vancomycin plates from Algerian cow's, ewe's, goat's, mare's, and camel's milks, either raw and/or fermented under laboratory conditions. The DNA of the isolates was fingerprinted by Rep-PCR. Strain identification was performed by Rep-PCR combined with specific PCR for genus Enterococcus and subspecies lactis/hordniae and cremoris of Lactococcus lactis. Isolates were characterized for three phenotypes essential for Raib manufacture: (a) high acidifying activity over the normal associated temperature range, (b) presence of protease, and (c) ability to metabolize citrate. Eighty-four isolates were characterized including four different strains of lactococci and four different strains of leuconostocs. Vancomycin-resistant enterococci were often coisolated. One strain of Leuconostoc mesenteroides exhibited an atypical genotype compared to the subspecies-type strains and to other wild Leuconostoc strains. Two protease-positive strains of Lactococcus lactis subsp. lactis biovar diacetylactis isolated from camel's fermented milks and the strain Leuconostoc mesenteroides subsp. mesenteroides isolated from mare's fermented milks had high acidifying potential in milk. These three strains were considered as suitable candidates as acidifying starters to preserve the typical sensory characteristics of traditional Raib while improving its safety and shelf life.