Active MAP of ready-to-eat lettuce: Efficient against browning and microbial spoilage, but not against Salmonella on the leaf surface
V. Rodov, B. Horev, S. Sela, Y. Vinokur, R. Pinto, G. Richard
Abstracts of 7th International Postharvest Symposium 2012 (IPS2012). 25-29 June, 2012. Putra World Trade Centre (PWTC), Kuala Lumpur, Malaysia. 238 pages.
2012
บทคัดย่อ
Oxidative enzymatic browning of cut edges and microbial spoilage caused by bacterial genera Erwinia and Pseudomonas are major deterioration causes in ready-to-eat lettuce. Furthermore, we have recently demonstrated that these two processes are interrelated and the presence of spoilage bacteria on cut surface significantly hastens the accumulation of phenolics in lettuce and concomitantly enhances browning severity. Modified atmosphere packaging (MAP) is commonly used to preserve the quality of minimally processed lettuce by inhibiting the oxidative browning and the growth of microbial populations. In passive MAP, generation of modified atmosphere by produce respiration typically takes one to several days. Initial displacement of air with a gas mixture of desired composition (active MAP) allows the avoidance of this transitional period, thereby improving the quality of the product. Sensory test has clearly demonstrated the superior quality of the produce in active MAP over the passive one in terms of appearance, taste and odor. The present work examined the effects of MAP on indigenous microbial populations and the survival of Salmonella enterica on the surface of the lettuce. Chlorine-washed leaves of romaine lettuce were inoculated with S. enterica serotype Typhimurium or not inoculated and packaged in one of the three systems: (a) passive MAP in polyethylene bags; (b) active MAP in the same bags with a gas mixture of 10% O2, 10% CO2, and 80% N2; and (c) control without MAP. Active MAP had an antimicrobial effect on indigenous lettuce microflora, but not on Salmonella and even favored the survival of the pathogen, possibly due to the elimination of its natural antagonists. The effects of the passive MAP were less pronounced. Our findings demonstrate that, despite its effects against indigenous microflora, active MAP does not protect against Salmonella enterica on lettuce. The use of appropriate sanitation practices to prevent contamination remains the most important measure for ensuring the microbiological safety of ready-to-eat products.