Antibacterially active honey is preservative.

Honey is naturally antibacterially active. The pH of undiluted honey is about 4. The water activity falls between 0.5 and 0.6. The acidity and lack of available water make honey an inhospitable environment for microorganisms. Spores, however, can survive in honey.

Scientists at Cornell University wanted to determine the efficacy of honey's antibacterial activity in minimally processed foods. Their goal was to improve their safety or extend the products' shelflife. It appears that honey containing medium to high levels of hydrogen peroxide antibacterial activity could be useful in preserving foods.

Raw honey contains the enzyme glucose oxidase. This enzyme converts glucose into gluconic acid. Hydrogen peroxide is a by-product of this process. The enzyme is essentially inactive until honey becomes diluted. Glucose oxidase is sensitive to heat and light, and could be destroyed in the processing of commercial honey.

Hydrogen peroxide levels in honey are extremely low since the glucose oxidase works better at a less acidic pH and a lower sugar concentration than undiluted honey. Hydrogen peroxide levels increase with increased levels of glucose oxidase (from bees) and decrease with increased catalase levels (from plants). This makes sense because catalase will break down hydrogen peroxide into oxygen and water. The levels are low and are affected by both the bees and the pollen source.

Four raw honeys with known levels of hydrogen peroxide antibacterial activity were applied to raw ground turkey, hot dogs, fresh apple cider and apple slices. Investigators conducted shelflife and challenge studies using synthetic honey and sterile water as the controls. For the shelflife studies, uninoculated food samples were cut and stored in sterile stomacher bags or centrifuge tubes at 7 C. The researchers added 5% honey and mixed the materials.

Triplicate samples were evaluated for total aerobic plate count, and amounts of yeast and molds on days 0, 3, 7, 10 and 14 of testing. For challenge studies, the foods were prepared as previously described, but they were inoculated with bacterial culture before the honey was added. The scientists both separately added E. coli O157:H7 and S. typhimurium to apple slices, cider and turkey. L. monocytogenes was added to slices of hot dogs. Samples taken twice weekly were enumerated for pathogen levels using differential media.

Levels of Salmonella in apple cider and Listeria in hot dogs were significantly reduced in the presence of select antibacterially active honeys. The efficacy was higher in cider than in apple slices due to better mixing. Listeria counts for the samples that contained honey and high or medium levels of hydrogen peroxide activity were lower than the hot dogs that contained other types of honey or water.

Research is continuing. Since adding honey in its entirety imparted a noticeable flavor on the food, the investigators are trying to isolate the antimicrobial activity so that it can be added at higher levels without changing the product's taste.

Further information. Melissa Mundo, Department of Food Science and Technology, Cornell University, New York State Agricultural Experiment Station, 630 W. North St., Geneva, NY 14456; phone: [phone]; email: [e-mail] <mailto:[e-mail]>.