Nour-Eddine Karam

Statistical optimization of lactic acid production by Lactococcus lactis strain, using the central composite experimental design

The individual and interactive effects of a total inoculums size (% v/v), fermentation temperature and skim milk dry matter added (% w/v) on the lactic acid production by Lactococcus lactis LCL strain were studied by quadratic response surface methodology. The central composite design (CCD) was employed to determine maximum lactic acid production at optimum values for process variables and a satisfactory fit model was realized. The mathematical relationship of the lactic acid production on the three significant independent variables can be approximated by a nonlinear polynomial model. Predicted values were found to be in a good agreement with experimental values ( R 2 of 96.7% and R 2 ( adj ) of 92.1% for response Y ). The result of optimization predicted by the model has shown that the maximal result for lactic acid production revolved around 92°D at the optimal condition with 2% of inoculums size, temperature at 30°C and skim milk dry matter added at a central point of 2% (w/v). Keywords: Central composite design, Lactococcus lactis, lactic acid production, inoculum size, temperature, skim milk dry matter. African Journal of Biotechnology , Vol 13(45) 4259-4267

Casein hydrolysates by Lactobacillus brevis and Lactococcus lactis proteases. Peptide profile discriminates strain-dependent enzyme specificity

Casein from ovine and bovine milk were hydrolyzed with two extracellular protease preparations from Lactobacillus brevis and Lactococcus lactis. The hydrolysates were analyzed by HPLC-MS/MS for peptide identification. A strain-dependent peptide profile could be observed, regardless of the casein origin, and the specificity of these two proteases could be computationally ascribed. The cleavage pattern yielding phenylalanine, leucine, or tyrosine at C-terminal appeared both at L. lactis and Lb. brevis hydrolysates. However, the cleavage C-terminal to lysine was favored with Lb. brevis protease. The hydrolysates showed ACE-inhibitory activity with IC50 in the 16-70 μg/mL range. Ovine casein hydrolysates yielded greater ACE-inhibitory activity. Previously described antihypertensive and opioid peptides were found in these ovine and bovine casein hydrolysates and prediction of the antihypertensive activity of the sequences based on quantitative structure and activity relationship (QSAR) was performed. This approach might represent a useful classification tool regarding health-related properties prior to further purification.

Phenotypic Identification and Technological Characterization of Lactic Acid Bacteria Isolated from L’ben, An Algerian Traditional Fermented Cow Milk

The lactic acid bacteria (LAB) involved in production of L’ben, an Algerian traditional fermented cow milk product, were isolated and identified. 10 samples of this product, collected from different regions of western Algeria, were analyzed. A total of 30 LAB strains were isolated and identified by phenotypic and biochemical analyses and API 20 Strep identification system. The results obtained showed that the isolates belong to the species: Enterococcus faecium (36,6%) , Enterococcus faecalis (30%), Enterococcus avium (13,3%), Leuconostoc mesenteroides (13,3%), Lactococcus lactis ssp cremoris (3,3%) and Lactococcus lactis ssp lactis (3,3%). Thereafter, growth kinetic and technological properties of these bacteria including: the acidification ability and the proteolytic activity were studied in a purpose of a possible industrial use. The obtained results were very heterogeneous; this led us to use the Principal Components Analysis “PCA” for strains grouping and comparison of their properties facilitated by graphics presenting all properties of each strain simultaneously to elect among all strains those with the most interesting technological profiles. Only four strains form a distinct group in the positive sense of the vectors of the variables formed and could become leavens for fermenting different kinds of milks, especially that of cow, which represents the ecosystem from which they originate.