Bacteries lactiques du lait cru de vache et microorganismes pectinolytiques des olives noires et vertes

Abstract

Sixty six strains are isolated starting from 18 samples from cow's raw milk in six breeding stations at Constantine. Their identification enabled us to obtain the following species: Sc. thermophilus, Ln. lactis, Ln. mesenteroides subsp. dextranicum, Lc. lactis subsp. lactis, Lc. lactis subsp. cremoris, Ec. faecium, Ec. feacalis, Ec. durans, Pc. pentosaceus, Pc. parvulus, Pc. urinae equi, Pc. acidilactici, Lb. cellobiosus, Lb. plantarum, Lb. acidophilus, Lb. delbrueckii / delbrueckii, Lb brevis and Lb acidophilus. Twenty four strains are isolated from the black and green olive samples. The culture medium MP5 (to 0,5 % of pectin) used made it possible to obtain a species very varied and able to degrade the substrate pectin. The strains obtained belong to the kinds: Bacillus, Leuconostoc, Pediococcus, Lactobacillus, Rhodotorula, Cryptococcus, Candida, Endomyces, Rhizopus and Aspergillus Niger. The various tests of the pectinolytic activity realized on the forty two strains made it possible to distinguished eight strains belonging to the kinds Bacillus (ONB13), Lactobacillus (LLb6), Leuconostoc (LLn1 and OVLn9), Streptococcus (LSc2), Pediococcus (LP5), Rhodotorula (ONRh9) and Aspergillus (ONAs14). They showed the highest potentials of degradation of pectin and polygalacturonase is most active for them. The kinetics of productions of PG and biomass carried in the MP5 medium by the eight strains made it possible to obtain two strains, ONRh9 (Rhodotorula) and LLn1 (Leuconostoc) with polygalacturonases activities the high ones. Two parameters which characterize the production of polygalacturonase are studied in the MAPG5 medium. They show that the two strains have an activity PG for equivalent pH and fewer acids. On the other hand the concentrations in APG used are very different. The optimization of the production of the enzyme in the fermentor with the established parameters, indicates that the control of the pH makes it possible the two strains to produce a quantity of more important enzyme PG. The cells of the two strains observed under the microscope with fluorescence present at the ONRh9 strain, same morphology and are numerous in the two culture media used Saboureaud and MAPG5. While at the LLn1 strain, the cells cultivated in medium MAPG5 smaller, are isolated for the majority and less fluorescent and in the medium of Mayeux, they are more numerous and more fluorescent.