Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2004
Publication Date: 10/12/2004
Citation: Ukuku, D.O., Fett, W.F. 2004. Effect of nisin in combination with edta, sodium lactate and potassium sorbate for reducing salmonella on whole and fresh-cut cantaloupe. Journal of Food Protection. 67(1):2143-2150. Interpretive Summary: Prepared fresh-cut cantaloupe in the supermarket is becoming very popular with the U.S. consumer due to the benefits of a diet rich in fruits and vegetables. To date, fresh-cut melon is prepared in the supermarket or by regional distributors. National distribution is difficult due to quality and safety concerns. In order to improve the microbial safety of fresh-cut cantaloupe, we studied the use of a combination of nisin (a natural bacterial product) with a compound (EDTA) which facilitates entry of nisin into bacteria and with sodium lactate and potassium sorbate for reducing populations of the human bacterial 'pathogen Salmonella inoculated on whole cantaloupe and fresh-cut pieces. All combination treatments substantially reduced the population of Salmonella on whole cantaloupe, reduced transfer to fresh-cut pieces during cutting and reduced populations of inoculated fresh-cut pieces. Odor, appearance, and overall acceptability ratings for cantaloupe fresh-cut pieces treated with nisin plus sodium lactate or sodium lactate alone were similarly improved compared to the controls for the fresh-cut pieces. The results suggest that treatments with the antimicrobials tested both before and after fresh-cut processing will enhance the microbial safety of fresh-cut cantaloupe for the U.S. consumer
Technical Abstract: Nisin (50 µg/ml), EDTA (0.02 M, disodium salt), sodium lactate (NaL) (2%), and potassium sorbate (KS) (0.02%) were tested individually and in various combinations as sanitizer treatments for reducing Salmonella on whole cantaloupe and fresh-cut pieces. Whole cantaloupe and fresh-cut pieces were inoculated with a five strain cocktail of Salmonella to give 4.7 log CFU/cm2 and 2.67 log CFU/g, respectively. Inoculated whole melons and fresh-cut pieces were stored at 5°C for 7 days. Washing treatments were applied to inoculated whole melons at days 0, 3 and 7 of storage and surviving bacterial populations were determined. The effect of the washing treatments on transfer of Salmonella to fresh-cut pieces prepared immediately after treatment was also determined. Directly inoculated fresh-cut pieces were treated at day 0 and surviving bacteria enumerated at days 0, 3 and 7 of storage. The combination treatments of nisin-EDTA, nisin-NaL, nisin-KS, NaL-KS and nisin-NaL-KS all resulted in reductions of approximately 3 log CFU/cm2 at day 0 for whole melons. When tested alone all compounds along with water washes were ineffective. After 3 and 7 days of storage, the five combination washing treatments were less effective resulting in reductions of approximately 2 log CFU/cm2. None of the combination treatments completely eliminated transfer of pathogen survivors to fresh-cut pieces. The combination treatments nisin-NaL, nisin-KS, NaL-KS and nisin-NaL-KS, but not nisin-EDTA gave significant (p < 0.05) reductions of Salmonella directly inoculated to fresh-cut pieces. Washing with nisin-NaL-KS was significantly (p < 0.05) more effective than the other three combination treatments resulting in a reduction of 1.4 CFU/g. Inhibition due to the four effective treatments carried over from day 0 thru day 7 of storage with no increase in the population of Salmonella on the stored fresh-cut pieces. Sensory evaluations indicated that treatment of fresh-cut pieces with nisin-NaL and NaL-KS, but not nisin-KS and nisin-NaL-KS, were acceptable in terms of appearance, odor and overall acceptability. After any required regulatory approvals treatment of whole cantaloupe with nisin in combination with EDTA, NaL, KS or NaL - KS and fresh-cut pieces with nisin-NaL or NaL-KS may help to ensure the microbiological safety of fresh-cut cantaloupe.