Technological characteristics of Lactobacillus spp. isolated from Iranian raw milk Motal cheese

Lactobacilli produce large amounts of bioactive metabolites, which makes them suitable for numerous technological applications. The objective was to evaluate the technological characteristics of 16 Lactobacillus isolates from Iranian raw milk Motal cheese, including acidifying ability, production of extracellular polysaccharides (EPS), gamma-amino butyric acid, proteolytic, lipolytic, autolytic, and amylolytic activity, resistance to acid conditions as well as biogenic amine production and susceptibility to antibiotics. Most of the examined strains presented high proteolytic and autolytic activity. Low acidifying ability was observed for all isolates, except for L. plantarum (M19) which reduced pH to 4.6 after 12 h. The highest proteolytic activity (30-mm clear halo) was observed for L. brevis (M4). Lipolytic activity was never observed and most of the isolates did not produce biogenic amines. The highest percentage of antibiotic resistance (87%) was recorded for kanamycin. All isolates were sensitive to chloramphenicol except L. brevis (M11). EPS production was detected in all strains, most strains (90%) produced mucoid EPS and 10% secreted EPS with a “ropy” character. Acid resistance showed all isolates were able to grow at pH 3.0 and 4.0. L. brevis (M4) presented the best technological characteristics and is proposed for inclusion as co-culture in the production of Motal Cheese.Peer reviewe

Screening of lactic acid bacteria strains isolated from Iranian traditional dairy products for GABA production and optimization by response surface methodology

Abstract A total of 50 lactic acid bacteria (LAB) isolates from Iranian traditional dairy products (Motal and Lighvan cheeses, and artisanal yogurt) were screened for gamma-aminobutyric acid (GABA) production. Firstly, a rapid colorimetric test was performed to evaluate the glutamate decarboxylase (GAD) activity among the LAB isolates examined. Thin layer chromatography (TLC) was then performed on selected strains to identify isolates with high/moderate GABA producing capacity, and a GABase micro-titer plate assay was employed to quantify GABA. Finally, two Lactococcus (Lac.) lactis strains were selected for GABA production optimization via Response Surface Methodology (RSM) following Central Composite Design (CCD). Forty-one out of the 50 isolates showed GAD activity according to the colorimetric assay. Eight isolates displayed strong GAD activity, while nine showed no activity; low to moderate GAD activity was scored for all other isolates. GABA production was confirmed by TLC in all isolates with high GAD activity and in four selected among isoaltes with moderate activity. Among the Lactococcus strains tested, Lac. lactis 311 and Lac. lactis 491 were the strongest GABA producers with amounts of 3.3 and 1.26 mM, respectively. These two strains were subjected to GABA production optimization applying RSM and CCD on three key variables: Monosodium glutamate concentration (MSG) (between 25 and 150 mM), incubation temperature (between 25 and 37 °C), and pH (between 4.0 and 5.0). Optimal conditions for GABA production by Lac. lactis 311 and Lac. lactis 491 of temperature, pH and MSG concentration were, respectively, 35.4 and 30 °C, pH 4.5 and 4.6, and MSG concentration of 89 and 147.4 mM, respectively. Under the above conditions, the amount of GABA produced by Lac. lactis 311 and Lac. lactis 491 was 0.395 and 0.179 mg/mL, respectively. These strains and the optimal culture conditions determined in this study could be used for the biotechnological production of GABA or applied in food fermentations for the development of naturally GABA-enriched foods