Enhancing the safety of Ready-To-Eat meats by Ultraviolet light intervention against L. monocytogenes and its influence on product quality
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The efficacy of UV light was determined against Listeria monocytogenes at different growth phases (log and stationary) and growth temperatures (37 and 4°C). Different UV parameters such as intensity and exposure times were evaluated to optimize this post lethality treatment as an intervention strategy in the post processing environments. Listeria monocytogenes serotype 4b was cultured in Brain Heart Infusion (BHI) broth at 37°C. Cells were harvested during their log and stationary phase and subjected to low (3 – 4 mW/ sq. cm) and high (7-8 mW/ sq. cm) intensity of UV light. Listeria monocytogenes in growth media (BHI) was subjected to UV for 0,10,30,50,70,90 and 110s while for bologna, L. monocytogenes was spray inoculated followed by 30 min of attachment time and exposed under UV every 30s for up to 300s. Cells were recovered on Modified Oxford agar (MOX) after 36h of incubation at 37°C. Additionally, shelf life along with the quality attributes such as color and lipid oxidation due to UV radiation was assessed over a period of 8 weeks on the bologna stored at 0 and 4°C under vacuum. UV treatment was effective (p<0.05) in reducing the growth of L. monocytogenes both in the growth medium and on bologna. Populations of L. monocytogenes were significantly reduced (p<0.05) after 10 and 30s of exposure times in growth media irrespective of the growth temperature and UV light intensities. On bologna, 180s of UV exposure significantly reduced (p<0.05) L. monocytogenes populations irrespective of UV intensities. Irrespective of the UV light intensity and exposure times, significantly higher (p<0.05) reductions were observed in the log phase cells as compared to the stationary phase cells. Furthermore, application of UV affected (p<0.05) the lightness (L) and redness (a) of the meat but did not cause any lipid oxidation on the Ready-to-Eat meat irrespective of the storage temperatures. The data suggests the potential use of UV light as a possible post process intervention in the food processing plants.