Science into Practice: January 2008

Edible coatings to keep pathogens away

Ready-to-eat meats are becoming increasingly popular with consumers. These meals are vulnerable to re-contamination by pathogenic bacteria after initial processing but researchers at the University of Arkansas have found a solution, using an antimicrobial-incorporated edible film coating to fend off the pathogens.

"We have used film coatings with raw and cooked ready-to-eat meat products," explained Navam Hettiarachchy, a food science professor in the University of Arkansas System's Division of Agriculture. "We have also included red meat in our studies as well. In all these products, we have observed a protective effect of antimicrobial incorporated edible films against the pathogens."

A whey protein film coating was used as a vehicle for the antimicrobials. The actual barrier to pathogens was provided by various combinations of grape-seed extract, nisin (a peptide, protein fragment), malic acid and EDTA, which is a ring-forming compound of metal ion known as a chelator.

Tests showed good effects in controlling growth and re-contamination of ready-to-eat meat products by Listeria monocytogenes, Salmonella typhimurium and E. coli O157:H7. Professor Hettiarachchy's team found variations in efficacy between the different combinations of the antimicrobials. For example, in experiments on turkey frankfurters, a combination of nisin, malic acid and EDTA was more effective against E. coli O157:H7 when grape-seed extract was not part of the mix than when it was included.

"In most of the cases, we focused on the type of meat products," Professor Hettiarachchy said. "The types of proteins, lipids and other components vary in each meat product. The protective effect is based on the type of antimicrobials and the product matrix, and the film acts as a vehicle to deliver antimicrobials." She said that the film containing antimicrobials was effective for reducing pathogens on raw chicken and ready-to-eat chicken as well as red meat. The degree of effectiveness also varied between products.

The key to the workings of edible film on meat is the ability to sustain the release of antimicrobials against the pathogens. The antimicrobials are held in the film matrix by weak forces, not by chemical bonding. The antimicrobials' speed of release depends on their affinity to critical elements in the film. The greater the affinity, the slower their release and the longer is the shelf-life of the product.

Some industrial interest is already being shown in the edible film, and there are prospects for its commercialisation.

Food Safety Consortium

Future of salmonella control

Working with molecular biologists and chemists at Sweden's Umeå University and development company, Innate Pharmaceuticals, the IAH team has studied the effects of a new class of drugs called virulence-blocking agents.

Conventional antibiotics aim to kill the bacterium but those that are not killed continue to multiply and over time, they can develop resistance to the antibiotic so that it becomes ineffective. Dr Edouard Galyov from IAH explained that, for the first time, the researchers have shown that the inhibitors specifically block the secretion of virulence factors by type III secretion systems in salmonella. Thus, the bacterium is disarmed rather than killed.

"These inhibitors hold great promise," he said but warned that it is premature to herald them as the next ‘wonder drugs'.

BBSRC business

Causes of carcass defects identified

Using a general linear model, researchers at the University of Bristol in the UK have identified the factors that cause foot pad dermatitis (FPD) and hock burns (HB) in broilers. They generated the data by examining broilers at the slaughterhouse, scoring the carcasses for both types of contact dermatitis lesion, as well as carcass rejects. They then linked this data to that they had collected on the 149 broiler farms involved during the previous 4 days.

The mean percentage of birds in each flock with moderate or severe FPD lesions was 11% (range 0-71.5%) and with moderate or severe HB was 1.3% (range 0-33.3%). At 0.02%, the incidence of breast blisters was very low.

The results indicate that improving litter quality can help reduce both types of lesion. For FPD, other important factors were genotype, feed supplier and season. Scores were worse for birds grown in winter, possibly because of the lower ventilation rate leading to poor litter conditions. Genotype also affected HB score, which was better where birds where slaughtered younger, and were fed diets as mash rather than pellets and with a higher percentage of wheat.

In the paper, the genotypes were identified only as A or B. One was more prone to FPD, while the other tended to have more HB. HB score also seemed to be linked to certain factors at the hatchery supplying the chicks and transportation to the farms.

Haslam S.M. et al., 2007. Factors affecting the prevalence of foot pad dermatitis, hock burn and breast burn in broiler chickens. British Poultry Science, 48: 264-275

Green method of litter disposal

Scientists at Virginia Tech College of Agricultural and Life Sciences have developed a thermo-chemical process to convert poultry litter into bio-oil. They say this provides a safer and more environmentally friendly solution to waste disposal, as well as being economic.

Foster Agblevor, associate professor of biological systems engineering presented a paper on the group's work at the 234th American Chemical Society National Meeting.

The aim of the work was to test technology that would convert poultry litter to three value-added by-products: pyrodiesel (bio-oil), producer gas, and fertiliser. They achieved success using a pyrolysis unit to heat the litter until it vaporises. The vapour is then condensed to produce the bio-oil, and a slow-release fertiliser is recovered from the reactor. The gas can then be used to operate the pyrolysis unit, making it a self-sufficient system.

"The self-contained transportable pyrolsis unit will allow poultry producers to process the litter on site rather than having to haul the litter to a separate location," Professor Agblevor said. "In addition, the thermo-chemical process destroys the microorganisms reducing the likelihood of the transmission of disease to other locations."

Bio-oil yields ranged from 30 to 50% by weight, depending on the age and the bedding content of the litter.

Virginia Tech, USA