Heat treatment effect on polyphosphate chain length in aqueous and calcium solutions.

Polyphosphate blends are used in food such as meat and dairy products to improve their texture and stability by sequestering metal ions. This study aims to analyse the impact of high temperature treatments on the composition of polyphosphates with regards to phosphate chain length in aqueous solutions with or without calcium. Temperature treatments of 120°C for 10 min led to the hydrolytic degradation of long-chain phosphates into orthophosphate and trimetaphosphate whereas heating the salts to 100°C in aqueous solutions had little effect on their composition. The presence of calcium increased the hydrolysis rate of long-chain phosphates and led to more trimetaphosphate and pyrophosphate as end products. The evolution of emulsifying salts' composition under heat treatment may lead to a modification of their chelating properties since short-chain phosphates are less efficient to chelate calcium than long-chain phosphates.

Identification of a new Salmonella enterica serovar Enteritidis locus involved in cell invasion and in the colonisation of chicks.

Poultry products contaminated with Salmonella enterica serovar Enteritidis are a major cause of foodborne disease in industrialized countries. Knowledge of how poultry is colonised is essential for reducing contamination of these products. We have characterized the bacterial yfg-eng locus involved in chicken colonisation. Its sequencing revealed four open reading frames (ORF), yfgM, yfgL, engA and yfgJ, all transcribed in the same orientation. An yfgL mutant of S. Enteritidis colonised the caeca (P < 0.05) and the spleens (P < 0.01) of one-day-old chicks subnormally 2 and 5 days after oral inoculation. This lower virulence was correlated with reduced secretion of the SPI-1 and flagellar proteins in the yfgL mutant compared to the wild-type strain. Consistent with this, the S. Enteritidis yfgL mutant was less motile than the wild type and fewer invaded enterocytes (P < 0.05) and avian HD11 macrophages (P < 0.001). All these defects could be partially overcome by inserting the yfg-eng locus into the mutant on a recombinant plasmid.

A new approach to monitoring proteolysis phenomena using antibodies specifically directed against the enzyme cleavage site on its substrate.

Proteolysis is a generic biochemical process that is central in all biological activities. A new strategy for monitoring this biochemical process is proposed here. This approach is based on the production of rabbit polyclonal anti-peptide antibodies directly against the cleavage site on the substrate of the enzyme responsible for proteolysis. So long as the molecule's cleavage site is intact, the antibody will bind to the protein. However, after cleavage of the peptide bond by the protease, the antibody will no longer be able to recognize the substrate. Thus, the development of an ELISA that uses this specific antibody allows hydrolysis of the substrate protein to be monitored. Hydrolysis of beta-casein by plasmin, the main indigenous protease of milk, during the ripening of Swiss-type cheese, has been chosen as a model for this study.