Extracts find antimicrobial applications.

Some extracts, such as black tea and grape seeds, have antimicrobial applications in addition to health benefits. These extracts can kill bacteria, extend shelf life, add color and enhance the freshness of products. All that processors need to do is formulate the extracts into edible films applied to food surfaces.

Scientists at the University of Arkansas have been incorporating these extracts, which have excellent antimicrobial activities, into edible films. They are going to apply these to food products, such as poultry, sausage, meat and minimally processed fresh-cut fruits and vegetables in a dipping or spraying process.

Investigators found that black tea hot water extract was potent in inhibiting the growth of L. monocytogenes. Grape seed extract inhibited S. typhimurium and E. coli O157:H7. The two types of extracts were the most successful against pathogens among several extracts screened from plants, herbals, vegetables, beans, grains and bran. The extracts can be incorporated into any of several edible films, including soy protein, whey protein, gluten protein, carboxymethyl cellulose, carageenan and pectin films. These films could be sprayed on, or products can be dipped into them. Or you might wrap the film around the product.

The use of extracts in the film on products can extend their shelf life for about two weeks. Also, these extracts serve as antioxidants against rancidity. The extracts kill or minimize pathogen growth. The edible coating can also delay the ripening of tomatoes by two to three weeks. The film can keep the freshness of baby carrots, which usually dry up. The coating retains the product's color and crunchiness for a longer period of time.

The edible films in these experiments incorporated malic acid, an organic acid that is present in apples. When you incorporate the malic acid into the film-forming solution, it not only functions as an antimicrobial, but it also acts as a plasticizer that makes the film more flexible.

That flexibility is helpful when the film is used to coat egg shells. The flexibility keeps the eggs from breaking during transit, which currently happens about 10% of the time. This could be reduced to a 2% breakage rate. Egg shells are also less susceptible to Salmonella when they are coated with the extract-based film. Usually Salmonella can penetrate the shells. So when the researchers coat the whole egg with the film solution, they prevent the microbes from entering through the shell.

Further information. Navam Hettiarachchy, Department of Food Science, University of Arkansas, N-218 Food Science, 2650 N. Young Ave., Fayetteville, AR 72704; phone: [phone]; fax: [phone]; email: [e-mail].