Anti-Listeria monocytogenes Activity of Heat-Treated Lyophilized Pomegranate Juice in Media and in Ground Top Round Beef

摘要

Heat treatment can affect antimicrobial activity of plant by-products by altering phenolic content and composition and forming melanoidins. The antilisterial efficacy of heat-treated and unheated lyophilized pomegranate juice (LPJ) was determined. The LPJ was heated at 100℃ for 0, 30, 60, or 120 min and added at 2% (wt/wt) to ground top round beef, which was then cooked and inoculated with individual L. monocytogenes strains. Samples of meat stored at 5 C were taken at days 1,8, 14, and 21 and plated onto Oxford medium for enumeration of bacteria. The MIC of LPJ was determined, and agar well diffusion assays were conducted. Against five L. monocytogenes strains, LPJ had a MIC of 1.50 to 1.75% (wt/vol) and 16.8- to 20.0-mm zones of inhibition. In general, no significant differences in L. monocytogenes levels between the various treatments, including the commercial sodium lactate-sodium diacetate combination, were detected at days 1 and 8. The LPJ (0, 30, 60, and 120 min of heating) significantly inhibited growth of all five L. monocytogenes strains in refrigerated ground cooked beef by 1.80 to 4.61 log CFU/g at day 21. Heating did not negatively impact LPJ antilisterial activity. Addition of LPJ lowered pH values by 0.3 units. The L~*, a~*, and b~* values of cooked ground beef with LPJ changed during the study by 3.4 to 4.43, 0.44 to 0.8, and 0.57 to 1.36 units, respectively, compared with the control. This is the first investigation to confirm pomegranate's antilisterial activity in vitro and in ground beef.