Assessing the ability of nisin A and derivatives thereof to inhibit gram-negative bacteria from the genus Thermus

peer-reviewNisin is a bacteriocin that is globally employed as a biopreservative in food systems to control gram-positive, and some gram-negative, bacteria. Here we tested the bioactivity of nisin A-producing Lactococcus lactis NZ9700 and producers of bioengineered variants thereof against representatives of the gram-negative genus Thermus, which has been associated with the pink discoloration defect in cheese. Starting with a total of 73 nisin variant-producing Lactococcus lactis, bioactivity against Thermus was assessed via agar diffusion assays, and 22 variants were found to have bioactivity greater than or equal to that of the nisin A-producing control. To determine to what extent this enhanced bioactivity was attributable to an increase in specific activity, minimum inhibitory concentrations were determined using the corresponding purified form of these 22 nisin A derivatives. From these experiments, nisin M17Q and M21F were identified as peptides with enhanced antimicrobial activity against the majority of Thermus target strains tested. In addition, several other peptide variants were found to exhibit enhanced specific activity against a subset of strains

Assessing the ability of nisin A and derivatives thereof to inhibit gram-negative bacteria from the genus Thermus

peer-reviewNisin is a bacteriocin that is globally employed as a biopreservative in food systems to control gram-positive, and some gram-negative, bacteria. Here we tested the bioactivity of nisin A-producing Lactococcus lactis NZ9700 and producers of bioengineered variants thereof against representatives of the gram-negative genus Thermus, which has been associated with the pink discoloration defect in cheese. Starting with a total of 73 nisin variant-producing Lactococcus lactis, bioactivity against Thermus was assessed via agar diffusion assays, and 22 variants were found to have bioactivity greater than or equal to that of the nisin A-producing control. To determine to what extent this enhanced bioactivity was attributable to an increase in specific activity, minimum inhibitory concentrations were determined using the corresponding purified form of these 22 nisin A derivatives. From these experiments, nisin M17Q and M21F were identified as peptides with enhanced antimicrobial activity against the majority of Thermus target strains tested. In addition, several other peptide variants were found to exhibit enhanced specific activity against a subset of strains

Dairy chemistry and biochemstry/ Fox

xiv, 478 hal. : ill. ; tab ; 21 cm

Dairy chemistry and biochemstry/ Fox

xiv, 478 hal. : ill. ; tab ; 21 cm

Peptidolytic, esterolytic and amino acid catabolic of selected bacterial strains from the surface of smear cheese

Enzymes produced by bacteria present on the surface of smear cheeses play essential roles in flavour development during cheese ripening. In this study, strains including brevibacteria, corynebacteria, staphylococci and brachybacteria, from the surface of two smearcheese (Tilsit and Gubeen) were screened for a range of enzyme activities including aminopeptidase (substrates: Leu-pNA and His-pNA), dipeptidase (Met–Ala, Ala–Met, Pro–Ala, His–Leu and Pro–Leu), tripeptidase (Phe–Gly–Gly, Gly–Gly–Gly and Leu–Ala–Pro), esterase (β-naphthyl butyrate, β-naphthyl caprate and β-naphthyl palmitate), l-methionine aminotransferase and cystathionine lyase activities. There were marked differences in the activities observed between different bacteria studied. Brachybacteria showed low activity on all substrates assayed. There was no consistency in activities within groups of related bacteria. For example, Staphylococcus equorum 14 showed higher activity than S. equorum 6 on all the substrates tested. Among the corynebacteria, Corynebacterium ammoniagenes CA8 had greatest aminopeptidase, esterase and cystathionine lyase activity while C. casei B showed more di- and tri-peptidase activity. It was noted that individual bacteria displayed similar activities on all three esterase substrates, i.e., the chain length of the fatty acid did not appear to affect activity. l-Methionine aminotransferase activity was observed in only one strain (S. equorum 14) whereas all strains had cystathionine lyase activity

Partial identification of peptides from the water-insoluble fraction of Cheddar cheese

International audienc

Influence of starters on chemical, biochemical, and sensory changes in Turkish White-brined cheese during ripening

PubMedID: 16162519Turkish White-brined cheese was manufactured using Lactococcus strains (Lactococcus lactis ssp. lactis NCDO763 plus L. lactis ssp. cremoris SK11 and L. lactis ssp. lactis UC317 plus L. lactis ssp. cremoris HP) or without a starter culture, and ripened for 90 d. It was found that the use of starters significantly influenced the physical, chemical, biochemical, and sensory properties of the cheeses. Chemical composition, pH, and sensory properties of cheeses made with starter were not affected by the different starter bacteria. The levels of soluble nitrogen fractions and urea-PAGE of the pH 4.6-insoluble fractions were found to be significantly different at various stages of ripening. Urea-PAGE patterns of the pH 4.6-insoluble fractions of the cheeses showed that considerable degradation of ?s1-casein occurred and that ß-casein was more resistant to hydrolysis. The use of a starter culture significantly influenced the levels of 12% trichloroacetic acid-soluble nitrogen, 5% phosphotungstic acid-soluble nitrogen, free amino acids, total free fatty acids, and the peptide profiles (reverse phase-HPLC) of 70% (vol/vol) ethanol-soluble and insoluble fractions of the pH 4.6-soluble fraction of the cheeses. The levels of peptides in the cheeses increased during the ripening period. Principal component and hierarchical cluster analyses of electrophoretic and chromatographic results indicated that the cheeses were significantly different in terms of their peptide profiles and they were grouped based on the use and type of starter and stage of ripening. Levels of free amino acid in the cheeses differed; Leu, Glu, Phe, Lys, and Val were the most abundant amino acids. Nitrogen fractions, total free amino acids, total free fatty acids, and the levels of peptides resolved by reverse phase-HPLC increased during ripening. No significant differences were found between the sensory properties of cheeses made using a starter, but the cheese made without starter received lower scores than the cheeses made using a starter. It was found that the cheese made with strains NCDO763 plus SK11 had the best quality during ripening. It was concluded that the use of different starter bacteria caused significant differences in the quality of the cheese, and that each starter culture contributed to proteolysis to a different degree. © American Dairy Science Association, 2005.This research was funded in part by Scientific Research Project Units of Cukurova University (Adana, Turkey)