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.

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.

Antimicrobial activity and partial characterization of bacteriocin-like inhibitory substances produced by Lactobacillus spp. isolated from artisanal Mexican cheese.

Lactobacillus spp. from Mexican Cocido cheese were shown to produce bacteriocin-like substances (BLS) active against Staphylococcus aureus,Listeria innocua,Escherichia coli, andSalmonella typhimurium by using the disk diffusion method. Crude extracts of Lactobacillus fermentum showed strong inhibitory activity against Staph. aureus, L. innocua, E. coli, and Salmonella cholerae. Complete inactivation of antimicrobial activity was observed after treatment of crude extracts with proteinase K, pronase, papain, trypsin, and lysozyme, confirming their proteinaceous nature. However, antimicrobial activity was partly lost for some of the crude extracts when treated with α-amylase, indicating that carbohydrate moieties were involved. The antimicrobial activity of the crude extracts was stable at 65°C for 30min over a wide pH range (2-8), and addition of potassium chloride, sodium citrate, ethanol, and butanol did not affect antibacterial activity. However, antimicrobial activity was lost after heating at 121°C for 15min, addition of methanol or Tween 80. Fourteen out of 18 Lactobacillus spp. showed antimicrobial activity against different test microorganisms, and 12 presented bacteriocin-like substances. Generation time and growth rate parameters indicated that the antimicrobial activity of crude extracts from 3 different strains was effective against the 4 indicator microorganisms. One of the crude extracts showed inhibition not only against gram-positive but also against gram-negative bacteria. Bacteriocin-like substances produced by this specific Lactobacillus strain showed potential for application as a food biopreservative.