73D-6 |
Inhibition of Listeria monocytogenes using nisin-containing packaging film |
N. B. FRANKLIN1, D. K. Cooksey1, and K. J. K. Getty2. (1) Department of Packaging Science, Clemson University, B212 Poole Agricultural Center, Box 340370, Clemson, SC 29634-0370, (2) Department of Food Science and Human Nutrition, Clemson University, 211 Poole Agricultural Center, Clemson, SC 29634 The use of nisin-containing packaging film may reduce Listeria monocytogenes (LM) outgrowth in ready-to-eat food products. The objectives were to 1. Determine type of acid, level of nisin, and pH for optimal inhibition of LM in a solution. 2. Develop a nisin-containing coating using optimal parameters for low density polyethylene (LDPE) film and determine its effectiveness in controlling LM. A drop assay was used to determine the effect of pH range (2-7), acid (ascorbic, acetic, hydrochloric), and nisin level (equal increments from 10,000 IU/mL to 156 IU/mL). Zones of inhibition were measured after incubation (37°C, 48h)on Tryptic soy agar (TSA)plates. Results were analyzed using ANOVA with a 95% confidence level. LDPE film was coated with a cellulose-based solution containing 10,000 IU/mL of nisin dispersed in acetic acid. Modified Oxford (MOX)agar and TSA plates were spiral plated with LM populations ranging from 7 to 10 log CFU/cm2. Film samples (1x1cm) were placed onto the inoculated plates coated side down. Zones of inhibition were observed on plates after 2 ½ weeks and 48 hours at 4°C and 35°C, respectively. Drop assay results indicated that pH 2 was most effective for inhibition and the minimum LM inhibitory concentration of nisin in solution was 156.3 IU/mL. Average zones of inhibition for nisin-containing films on TSA plates (35°C, 48h) at populations 10.48, 9.48, 8.48, and 7.48 log CFU/cm2 were 10.77, 11.74, 12.36, and 13.37mm in diameter, respectively. Average zones of inhibition for films on MOX (35°C, 48h) at populations 10.37, 9.37 and 8.37 log CFU/cm2 were 20.82, 23.84, and 23.64mm in diameter, respectively. MOX plates (4°C, 2 ½ wks) for the same populations completely eliminated LM on the nisin-containing film portion of plates. LDPE film with a coating containing 10,000 IU/mL nisin is effective for inhibition of LM on TSA and MOX plates at 35°C and refrigerated temperature.
Session 73D, Food Packaging
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