Novel bacteriocins produced by Lactobacillus fermentum strains with bacteriostatic effects in milk against selected indicator microorganisms.

The aim of this work was to isolate and characterize bacteriocins produced by 2 Lactobacillus fermentum strains isolated from artisanal Mexican Cocido cheese. Fractions (F ≤3 kDa) obtained from cell-free supernatants of Lb. fermentum strains J23 and J32 were further fractionated by reversed-phase HPLC on a C18 column. Antimicrobial activities of F ≤3 kDa and bacteriocin-containing fractions (BCF), obtained from fractionation of F ≤3 kDa against 4 indicator microorganisms, were determined by the disk diffusion method and growth inhibition in milk. Subsequently, isolated BCF were analyzed by reversed-phase HPLC tandem mass spectrometry. Results showed that BCF presented antimicrobial activity against the 4 indicator microorganisms tested. For J23, one of the fractions (F3) presented the highest activity against Escherichia coli and was also inhibitory against Staphylococcus aureus, Listeria innocua, Salmonella Typhimurium, and Salmonella Choleraesuis. Similarly, fractions F3 and F4 produced by J32 presented antimicrobial activity against all indicator microorganisms. Furthermore, generation time and growth rate showed that F3 from J23 presented significantly higher antimicrobial activity against the 4 indicator microorganisms (2 gram-positive and 2 gram-negative) when inoculated in milk compared with F3 from J32. Interestingly, this fraction presented a broader antimicrobial spectrum in milk than nisin (control). Reversed-phase HPLC tandem mass spectrometry analysis revealed the presence of several peptides in BCF; however, F3 from J23 that was the most active fraction of all presented only 1 bacteriocin. The chemical characterization of this bacteriocin suggested that it was a novel peptide with 10 hydrophobic AA residues in its sequence and a molecular weight of 2,056 Da. This bacteriocin and its producing strain, J23, may find application as a biopreservative against these indicator microorganisms in dairy products.

Volatile and sensory evaluation of Mexican Fresco cheese as affected by specific wild Lactococcus lactis strains.

Lactococcus lactis is the lactic acid bacteria most frequently used for the production of cheese starter cultures, mainly because of their efficient production of aroma compounds. However, commercial cultures do not always produce the typical aroma notes of artisanal raw-milk cheeses. Thus, the objective of this study was to characterize the volatile compounds generated by wild L. lactis strains in Mexican Fresco cheese made with pasteurized milk. Four strains of wild L. lactis were evaluated for their aroma production in Mexican Fresco cheese using sensory and instrumental analysis. The aroma profiles were evaluated by descriptive sensory analysis. Volatiles were determined by solid-phase microextraction and gas chromatography-mass spectrometry. Principal component analysis was applied to interpret analytical and sensory data. Mexican Fresco cheese aroma was described as milkfat, yogurt, yeasty, barny, dirty socks, and Fresco cheese. Cheese with L. lactis strains R7 or B7 were most similar to commercial raw milk Fresco cheese in all aroma descriptors. Volatiles identified in all cheeses were esters, acids, alcohols, ketones, and aldehydes, but the main differences were found for total volatile relative abundance. Also, volatile concentrations (µg/g) in commercial raw milk Fresco cheese and cheeses made with L. lactis R7 or B7 were 4 methyl esters [C4 (4.15 vs. 5.47-13.74), C6 (0.12 vs. 1.53-15.34), C8 (1.06 vs. 0.32-6.65), and C10 (0.62 vs. 0.41-3.74)], 7 acids [C4 (1.92 vs. 0.30-9.29), C6-C10 (0.05-4.48 vs. 0.11-30.45), and C12 (0.13 vs. 0.28-0.30)], 2 alcohols [(3-methyl-1-butanol (3.48 vs. 3.4-13.13) and phenylethyl alcohol (0.10 vs. 0.63-2.04)], and 1 ketone (acetoin; 1.22 vs. 0.28-0.99). The first 3 principal components explained 78.2% of the total variation and clearly distinguished 3 main groups. Cheese made with L. lactis R7 was classified in the same group as key compounds associated with Fresco cheese aroma and show potential as a starter in Mexican Fresco cheese manufacture.

Poro de Tabasco cheese: Chemical composition and microbiological quality during its artisanal manufacturing process.

Poro de Tabasco cheese (PTC) is one of the most popular cheeses in southern Mexico. It has been made by traditional, nonstandardized artisanal techniques dating back more than 50 yr. These techniques result in the cheese having a heterogeneous chemical and microbiological composition and, consequently, distinct organoleptic characteristics. Scientific interest in artisanal cheese is growing because it represents a source of bacteria with potential health benefits. However, the quality of raw-milk cheeses often does not comply with official sanitary standards. The objective of the present study was to explore the chemical composition and microbiological quality of PTC and to describe its production process. Based on chemical composition, this cheese can be classified as a hard, full-fat, fresh cheese, with moisture on a fat-free basis and fat in dry matter ranging from 41 to 55% and from 49 to 57%, respectively. The chemical and microbiological composition of PTC varied among the evaluated dairies due to the lack of standardization in the production process. Microbial populations decreased during production, which may be associated with high acidity and high salt and low moisture contents, the presence of lactic acid bacteria or antimicrobial substances, and the drainage of whey. However, despite the absence of Escherichia coli, Salmonella spp., and Listeria monocytogenes in final cheeses for all dairies, Staphylococcus aureus and its toxins were found in some samples from one dairy. Therefore, heat treatment for milk and good manufacturing practices should be implemented throughout the entire production process to ensure a safe product.

Artisanal Sonoran cheese (Cocido cheese): an exploration of its production process, chemical composition and microbiological quality.

BACKGROUND: The objective of this study was to explore and document the production process of artisanal Cocido cheese and to determine its chemical composition and microbiological quality, considering samples from six dairies and four retailers. RESULTS: Cocido cheese is a semi-hard (506-555 g kg-1 of moisture), medium fat (178.3-219.1 g kg-1 ), pasta filata-type cheese made from raw whole cow's milk. The production process is not standardized and therefore the chemical and microbiological components of the sampled cheeses varied. Indicator microorganisms significantly decreased (P < 0.05) during the processing of Cocido cheese. Salmonella spp. were not found during the production process, and both Listeria monocytogenes and staphylococcal enterotoxin were absent in the final cheeses. CONCLUSION: This study provides more information on one of the most popular artisanal cheeses with high cultural value and economic impact in northwestern Mexico. In view of the foregoing, good manufacturing practices need to be implemented for the manufacture of Cocido cheese. Also, it is of utmost importance to make sure that the heat treatment applied for cooking the curd ensures a phosphatase-negative test, otherwise it would be necessary to pasteurize milk. Nevertheless, since Cocido cheese is a non-ripened, high-moisture product, it is a highly perishable product that could present a health risk if not properly handled. © 2017 Society of Chemical Industry.

Tejuino, a Traditional Fermented Beverage: Composition, Safety Quality, and Microbial Identification.

This study aims to analyze the chemical and microbial composition and characterize volatile compounds from the artisanal and commercial Tejuino beverage. For this, eight samples are analyzed (four artisanal and four commercial). The chemical and microbiological quality is determined by standard methods, and volatile compounds are determined by solid-phase microextraction. Overall, the physicochemical composition and microbiological quality are higher for artisanal Tejuino (p < 0.05). The pH values were 3.20 and 3.62, and 0.76 and 0.46 meq of lactic acid for artisanal and commercial Tejuino, respectively. With volatile compounds analyzed, esters, benzenes, and aldehydes were predominant; meanwhile, ethanol was a volatile compound with the highest concentration for all samples. Saccharomyces cerevisiae and Limosilactobacillus fermentum were identified in artisanal Tejuino; yeasts of the Pichia genera and Lactiplantibacillus plantarum, for commercial Tejuino, and Enterococcus genus were identified in both samples. The characterization of both types of Tejuino allows us to update the information available on this important Mexican beverage. In addition, the isolation of lactic acid bacteria, as representative bacteria of both drinks, offers an area of opportunity to know the potential functionality of these bacteria in traditional fermented products.

Cooperation between Lactococcus lactis NRRL B-50571 and NRRL B-50572 for Aroma Formation in Fermented Milk.

The aim of the present study was to characterize the aroma and volatile profiles of milk fermented by wild Lactococcus lactis NRRL B-50571 (FM-571) and NRRL B-50572 (FM-572) and co-fermented with both strains (co-FM). Milks fermented by these strains have been reported to have an antihypertensive effect, yet their sensory characteristics, which are of great importance for consumer acceptance of functional foods, have not been studied. In the study, volatiles were determined using solid-phase microextraction gas chromatography mass spectrometry (SPME-GC-MS) and aroma was determined by quantitative descriptive sensory analysis (QDA). Volatile compounds identified in FM-571, FM-572, and co-FM were mainly acids, alcohols, aldehydes, and ketones. FM-571 showed higher total relative volatile abundance than FM-572 or co-FM. Furthermore, the concentrations of specific amino acids (aa) were lower in FM-571 and co-FM than in FM-572. Thus, these results suggested that FM-571 or co-FM are more efficient in transforming specific aa into the corresponding volatiles than FM-572. Indeed, several alcohols and aldehydes, associated with the catabolism of these aa, were found in FM-571 and co-FM, but not in FM-572. Additionally, QDA showed that FM-571 and co-FM presented higher yeasty and cheesy aroma descriptors than FM-572. Also, total aroma intensity scores for FM-571 were higher than those for co-FM or FM-572. Thus, results suggested that the combination of these two specific wild L. lactis strains may complement amino acid catabolic routes that resulted in the enhancement or attenuation of aroma production of single strains, presenting new possibilities for the preparation of custom-made starter cultures.

Milk Fermented by Specific Lactobacillus Strains Regulates the Serum Levels of IL-6, TNF-α and IL-10 Cytokines in a LPS-Stimulated Murine Model.

Studies report that metabolites, such as peptides, present in fermented milk with specific lactic acid bacteria, may regulate cytokine production and exert an anti-inflammatory effect. Hence, the cytokine regulatory effect of fermented milk by specific Lactobacillus strains was evaluated in a lipopolysaccharide (LPS)-stimulated murine model. From twelve strains, three (J20, J23 and J28) were selected for their high proteolytic and acidifying capacities in milk and used for the in vivo study. Three treatments (fermented milk, FM; pasteurized fermented milk, PFM; and its 0.05) reduced pro-inflammatory cytokine (IL-6 and TNF-α) concentrations and significantly increased anti-inflammatory (IL-10) cytokine concentrations in comparison to the control; also, pro-inflammatory cytokines were reduced for animals treated with PFM10 (p < 0.05). RP-HPLC-MS/MS analysis showed that water-soluble extracts (.