Efficacy of Essential Oils and Cold Plasma to Improve Food Safety of Produce, Raw Beef and Ready-to-eat Meat by

Abstract

Foodborne diseases remain problematic in the U.S., resulting in illness, financial losses, and in some circumstances, death. Food processors have used traditional methods of chemical additives and thermal processes to reduce microbial loads, but current consumer trends are driving the food industry to develop natural, minimally processed antimicrobial technologies to enhance food safety. Essential oils derived from plants have shown to be effective against microorganisms. In addition, the development of novel non-thermal technologies have some potential applications in food safety. In this study, we determined the minimal inhibitory concentration (MIC) of carvacrol and lauric arginate (LAE) against E. coli and compared it to the previously determined MIC of white mustard essential oil (WMEO). Using this data, we determined concentrations to use as a produce wash on lettuce challenged with Escherichia coli. Washes were made in various combinations, some with acetic acid, and compared to washes prepared with chlorine at 150 ppm as the industry standard. We also determined the effects of cold plasma at 5-, 10- and 15-minutes exposure against E. coli on raw whole-muscle beef and Listeria innocua on deli meat. To show if there were combined effects for treatments, rinses of tap water, chlorine, WMEO, carvacrol, WMEO + acetic acid, carvacrol + acetic acid and WMEO + acetic acid + carvacrol (WAC) were combined with cold plasma treatments of 5 and 10 minutes on lettuce challenged with E. coli. The MICs for carvacrol and LAE against E. coli were determined to be 0.05% (w/v) [0.5 mg/mL] and 0.005% (w/v) [0.05 mg/mL], respectively. The previously determined MIC of WMEO was 0.84% (w/v) [8.4 mg/ mL]. The pH of the solutions were as follows: tap water 6.9 to 7.49; Chlorine 8.1 to 8.49; WMEO 3.4 to 3.99; WMEO + acetic acid 2.49 to 2.9; carvacrol 4.25 to 4.7; carvacrol + acetic 2 acid 3.75 to 4.51; WMEO + acetic acid + carvacrol (WAC) 3.1 to 3.76; LAE 4.6 to 5; LAE + acetic acid 2.7 to 3; and WMEO + acetic acid + LAE (WAL) 2.4 to 3.1. In the experiment of combination of WMEO and LAE on lettuce against E.coli BAA- 1296, the wash effect of tap water resulted in a 1.08 log reduction as compared to the control. The WMEO solution and the LAE solution caused 1.62 and 1.53 log reductions, respectively. Combining the antimicrobial compounds WMEO + acetic acid caused a 1.78 log reduction. Additional combinations, LAE + WMEO and WMEO + acetic acid + LAE (WAL), resulted in 1.82 log reductions for both washes, which is equivalent to the effect of chlorine solution (1.90 logs reduction, p>0.05). In the experiment of combination of WMEO and carvacrol on lettuce against E. coli BAA-1296, the tap water caused a 0.77 log reduction. The WMEO solution and carvacrol alone caused 1.32 and 1.35 logs reduction respectively (p>0.05). The combination of the WMEO + acetic acid and carvacrol + WMEO caused 1.96 and 1.88 log reductions, respectively (p>0.05), which are greater than the WMEO and carvacrol alone. The WMEO+ acetic acid + carvacrol (WAC) caused a reduction of 2.32 logs, which did not have significant differences when compared to chlorine solution (2.28 logs reduction, p>0.05). In the experiment of cold plasma on raw beef against E. coli k-12, the reductions of E. coli are averaged 1.75 logs with no significant differences (P>0.05) between treatment times. We chose the E.coli k-12 since it is an non-pathogenic strain that could be used in Physics Building. In the experiment of cold plasma on ham against Listeria innoca, 5 minutes of cold plasma treatment resulted in a 1.02 log reduction of Listeria, while 10-minute caused less than 1.5 log reduction (1.35 log reduction) and 15-minute resulted in more than 1.5 logs (1.75 logs) reduction (p<0.05). 3

In the experiment of combination of cold plasma and WMEO-based produce wash on lettuce against E. coli k-12, wash effect (Tap water) caused a 0.48 log reduction. The produce wash (WAL) solution caused 2.71 logs reduction. The cold plasma treatment (5 and 10 minutes) alone caused 2.14 and 2.29 logs reduction respectively (p>0.05). Tap water combined with cold plasma (5 and 10 minutes) caused 2.31 and 2.39 logs reduction respectively (p>0.05). The WMEO and chlorine solutions without cold plasma treatment caused 2.71 and 2.55 logs reduction (p>0.05), respectively. Five minutes of cold plasma with chlorine could cause 2.81 log reductions, 10 minutes of cold plasma with chlorine could cause 3.13 logs reduction. A treatment of 5 minutes of cold plasma with produce wash solution could cause 3.41 logs reduction, 10 minutes of cold plasma with produce wash solution could cause 3.94 logs reduction, which is more effective than 150 ppm industry standard chlorine solution 2.56 logs reduction (p<0.05). Our research showed that both WMEO-based produce wash and cold plasma have antimicrobial effect and the combination of them have a better effect.