Effect of Immersion Solutions Containing Enterocin AS-48 on Listeria monocytogenes in Vegetable Foods

Abstract

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 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 g of AS-48/ml, viable listeria counts were reduced below detection limits at days 1 to 7 for alfalfa and soybean sprouts at 6 and 15°C, as well as green asparagus at 15°C. Only a limited inhibition of listeria proliferation was detected during storage of bacteriocintreated alfalfa sprouts and green asparagus at 22°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.

Hygienic-sanitary quality of vegetables and evaluation of treatments for the elimination of indigenous E. coli and E. coli O157:H7 from the surface of leaves of lettuce (Lactuca sativa L.)

“…The cell suspensions were transferred to sterile eppendorf tubes, (LIN et al, 2000). Other sanitizers studied for their effectiveness in removing pathogens from fresh fruit and vegetables include trisodium phosphate (ZHUANG; BEUCHAT, 1996, WEBER;OBRIEN;BENDER, 2004;MOLINOS et al, 2005), organic acids (PIROVANI et al, 1998;RHEE et al, 2003;BJORNSDOTTIR;BREIDT;McFEETERS, 2006), hydrogen peroxide (BRENNAN; PORT; GORMLEY, 2000), and ozone (KOSEKI et al, 2001;ACHEN;YOUSEF, 2001;BELTRAN et al, 2005). Although various sanitizers have been examined for their effectiveness, most treatments have been shown to have minimal effects, resulting in less than a 2 log cfu.g -1 (cm 2 ) reduction in bacterial numbers, and most would not be suitable products for use at the household level (BEUCHAT et al, 1998).…”

Natural Antimicrobials for Biopreservation of Sprouts

“…Nevertheless, for both alfalfa and soybean sprouts, the bacteriocin concentrations of 12.5 as well as 25 µg/ml reduced the concentrations of viable listeria below the detection levels from day 1 to day 7 of storage at temperatures of 6ºC as well as 15ºC. These results indicated that residual bacteriocin adsorbed to the treated sprouts was able to provide a protective effect after treatment for samples stored under a broad interval of refrigeration temperatures (Cobo Molinos et al, 2005). Nevertheless, incubation of the treated samples at a higher temperature of 22ºC seriously compromised the protective effect of the bacteriocin.…”

“…Because of its broad spectrum of inhibition and increased stability due to its cyclic structure, enterocin AS-48 can be a sound candidate for decontamination of vegetable foods containing L. monocytogenes and other foodborne bacteria sensitive to this bacteriocin. In experiments carried out for enterocin AS-48 on sprouts, L. monocytogenes was able to grow without bacteriocin on alfalfa and soybean sprouts and in green asparagus at temperatures of 6 to 22ºC and to reach high cell numbers (up to 6 log CFU/g, depending on temperature) during storage (Cobo Molinos et al, 2005). Sprouts inoculated with L. monocytogenes were treated by immersion for 5 min in distilled water or in bacteriocin solutions of 5, 12.5, and 25 µg/ml.…”

“…Enterocin AS-48 is a broad-spectrum cyclic antimicrobial peptide produced by E. faecalis and E. faecium strains (reviewed by Maqueda et al, 2004). This bacteriocin has been widely investigated in food systems against foodborne pathogenic bacteria such as L. monocytogenes, S. aureus, B. cereus, E. coli or S. enterica (Abriouel et al, 2010;Ananou et al, 2005;Cobo Molinos et al, 2005Grande et al, 2006Grande et al, , 2007aMartínez Viedma et al, 2008Muñoz et al, 2007). Partially-purified preparations of enterocin AS-48 can be produced easy on semi-synthetic media (Abriouel et al, 2003) and on whey-based substrates (Ananou et al, 2010), which makes this bacteriocin an amenable antimicrobial for application in foods.…”

“…In order to improve the bactericidal effects against listeria, the bacteriocin (25 µg/ml) was applied on green asparagus in washing treatments in combinations with a variety of antimicrobials: acetic acid, citric acid, lactic acid, potassium lactate, sodium propionate, potassium sorbate, sodium nitrite and nitrate, trisodium-tri-metaphosphate, potassium thiosulfate, potassium permanganate, n-propyl p-hydroxybenzoate, p-hydoxybenzoic acid methyl esther, hexadecylpyridinium chloride, peracetic acid, and sodium hypochlorite (Cobo Molinos et al, 2005; Table 1). The combinations of AS-48, acetic acid, citric acid, sodium propionate, potassium sorbate or sodium nitrite had limited or no effect on viability of listeria compared to the effect of AS-48 alone.…”