Apple and oregano coating kills E. coli, say scientists

A team of scientists from the US Department of Agriculture and theUniversity of Lleida in Spaindid the research to improve an edible coating for fresh fruits andvegetables. It is composed of apple puree and oregano oil, which acts as anatural antibacterialagent. They say the coating shows promise in laboratory studies of becominga long-lasting, potent alternative to conventional producewashes.

The study provides a possible solution to fruit and vegetable processorslooking to protect theirproducts from pathogens. Public awarness that foodborne diseases couldarrive from such sources washeightened due to a recent deadly E. coli outbreak in spinach. There isgrowing concern by experts that some produce-cleaning techniques may not beeffective in destroying E.coli, say the scientists.

Their study is scheduled for publication in the 29 November issue of theAmerican Chemical Society's Journal of Agricultural and Food Chemistry.

"All produce-cleaning methods help to some degree, but our newcoatings and films may provide a more concentrated, longer-lasting methodfor killing bacteria,"​said research leader Tara McHugh.

McHugh, a food chemist with the USDA's Agricultural Research Service,says as the films are made of fruit or vegetable puree, they also provideadded health benefits such as vitamins, minerals andantioxidants.

Researchers have known about the antimicrobial activity of plant-derivedessential oils for sometime. McHugh says that her group is the first to incorporate them into afruit- or vegetable-based edible food wrap for the purpose of improving foodsafety

Three years ago, she and her associates developed a similar edible foodwrap, but without the antimicrobial properties.The new antimicrobial coatings have not been tested on fresh produce yet,noted McHugh.

The current study only tested the coatings against E. coli O157:H7, apotentially deadly strain of the common bacterium Escherichiacoli. The team plans further tests on other foodborne pathogens, includingSalmonella.

If the coatings continue to show promise as an alternative form ofprotection, they could hit the consumer market in a year or two, estimatesMcHugh.

McHugh and her associates also tested oregano, cinnamon and lemongrassoils in solutions of apple puree and dried films for their effectivenessagainst E. coli. Each compound was tested in a controlled series ofdilutions,say the scientists.

While all of the oils tested inhibited the growth of E. coli, oregano oilwas the most effective, killing over 50per cent of sample bacteria in three minutes at concentrations as small as0.034 per cent, saidMcHugh. She is now working on improving the kill rate.

The second most effective oil was lemongrass, followed by cinnamon oil.The apple-puree film alone did not kill the E. colibacteria.

"However, an advantage of the apple antibacterial film is that it iscomposed of sticky sugars and lipids, which allow the coating to adhere tofruits and vegetables for longer periods than conventional, water-basedproducewashes," she said. "That same stickiness also gives the suspendedantimicrobial agents a more concentrated exposure to bacterial surfaces,increasing the film's germ-killingpotential."

Produce manufacturers could apply the antibacterial coating as a spray ordip for fresh fruits and vegetables, theysay in the study. The resulting product will taste a bit like oregano, whichcan be a desirable trait insalads, stated McHugh.

Other antimicrobial films can also be made from broccoli, tomato, carrot,mango, peach, pear and a variety of other produce items.

Non-antimicrobial versions of these food wraps are now being madecommercially by California-based Origami Foods ina joint project with the USDA. The project is testing these versions on asmall but growing number of food applications, including sushiwraps, stated the USDA.