Effect of immersion solutions containing enterocin AS-48 on Listeria monocytogenes in vegetable foods

The effect of immersion solutions containing enterocin AS-48 alone or in combination with chemical preservatives on survival and proliferation of Listeria monocytogenes CECT 4032 inoculated on fresh alfalfa sprouts, soybean sprouts, and green asparagus was tested. Immersion treatments (5 min at room temperature) with AS-48 solutions (25 mu g/ml) reduced listeria counts of artificially contaminated alfalfa and soybean sprouts by approximately 2.0 to 2.4 log CFU/g compared to a control immersion treatment in distilled water. The same bacteriocin immersion treatment applied on green asparagus had a very limited effect. During storage of vegetable samples treated with immersion solutions of 12.5 and 25 mu g of AS-48/ml, viable listeria counts were reduced below detection limits at days I to 7 for alfalfa and soybean sprouts at 6 and 15 degrees C, as well as green asparagus at 15 degrees C. Only a limited inhibition of listeria proliferation was detected during storage of bacteriocin-treated alfalfa sprouts and green asparagus at 22 degrees C. Treatment with solutions containing AS-48 plus lactic acid, sodium lactate, sodium nitrite, sodium nitrate, trisodium phosphate, trisodium trimetaphosphate, sodium thiosulphate, n-propyl p-hydroxybenzoate, p-hydoxybenzoic acid methyl ester, hexadecylpyridinium chloride, peracetic acid, or sodium hypochlorite reduced viable counts of listeria below detection limits (by approximately 2.6 to 2.7 log CFU/g) upon application of the immersion treatment and/or further storage for 24 h, depending of the chemical preservative concentration. Significant increases of antimicrobial activity were also detected for AS-48 plus potassium permanganate and in some combinations with acetic acid, citric acid, sodium propionate, and potassium sorbate.