Antilisterial activities of salad dressings, without or with prior microwave oven heating, on frankfurters during simulated home storage

Abstract

This study evaluated the antilisterial effects of salad dressings, as well as oils mixed with lemon juice or vinegar, on frankfurters during simulated home storage, without or with prior microwave oven heating. Frankfurters were inoculated (2.4 ± 0.1 log CFU/cm 2) with Listeria monocytogenes (10-strain mixture) and stored aerobically in bags at 7 °C. At 0, 7 and 14 days, frankfurters were immersed (5 or 20 min, 25 ± 2 °C) in sunflower oil plus lemon juice or vinegar, extra virgin olive oil plus lemon juice or vinegar, or salad dressings (i.e., Vinaigrette, Ranch, Thousand island, and Caesar), or distilled water (DW), without or with prior microwave oven heating (1100 Watts, 2450 MHz, high power) for 30 s. Samples were analyzed for microbial growth during storage, and survivors following application of treatments, on tryptic soy agar plus 0.6% yeast extract and PALCAM agar. Immersion in salad dressings and in the combinations of oils with lemon juice or vinegar caused significant ( P < 0.05) reductions of L. monocytogenes, compared to dipping in DW. Reductions increased with previous product storage, from 0.5–0.9 (day-0) to 1.2–2.1 (day-14) log CFU/cm 2, as levels of contamination also increased. Reductions of pathogen counts by each treatment increased ( P < 0.05) when applied following exposure to microwave oven heating; ranging from 1.2–1.9 (day-0) to 2.2–3.3 (day-14) log CFU/cm 2. Reductions were not ( P ≥ 0.05) different between 5 and 20 min of immersion in most treatments. In general, the reduction effects of salad dressings decreased in the order of sunflower or extra virgin olive oil plus vinegar ≥ sunflower or extra virgin olive oil plus lemon juice > Caesar ≥ Thousand island ≥ Ranch ≥ Vinaigrette. The results of the present study indicated that salad dressings and oils with lemon juice or vinegar may contribute to control of L. monocytogenes on ready-to-eat meat products in the home environment, especially when these products are treated and used in salads.