Bactericidal Effects of Lactobacillus reuteri and Allyl Isothiocyanate on Escherichia coli O157:H7 in Refrigerated Ground Beef

Abstract

Two naturally occurring antimicrobial agents were tested in packages of refrigerated ground beef for their ability to reduce the viability of Escherichia coli O157:H7 during storage. Allyl isothiocyanate (AITC) and Lactobacillus reuteri were tested separately and together for their action against a cocktail of five strains of E. coli O157:H7 in ground beef held at 4 degrees C for 25 days. Ground beef prepared from whole, raw inside round beef roasts was inoculated with low (3 log CFU/g) or high (6 log CFU/g) levels of the E. coli O157:H7 mixture. The beef was treated with AITC (about 1,300 ppm), L. reuteri, or both, along with 250 mM of glycerol per kg of meat at two levels (3 and 6 log CFU/g) and according to a design that yielded 8 controls plus 10 different treatments. Samples were analyzed for E. coli O157:H7 survivors, numbers of total bacteria, and lactic acid bacteria on days 0 to 25 at 5-day intervals. L. reuteri at both input levels with glycerol killed E. coli O157:H7 at both inoculated levels before day 20. AITC completely eliminated E. coli O157:H7 at the low-inoculum level (3 log CFU/g) and reduced viability >4.5 log CFU/g at the high-inoculum level (6 log CFU/g) by the end of the storage period. The combination of L. reuteri and AITC did not yield an additive effect against E. coli O157:H7 viability. L. reuteri in the presence of glycerol was highly effective against E. coli O157:H7 in ground beef during refrigerated storage (4 degrees C) in modified atmosphere packages. Sensory testing is planned to evaluate effects of treatments.

Survival of E. coli O157:H7 during manufacture of dry‐cured Westphalian ham surface‐treated with allyl isothiocyanate or hot mustard powder

“…These results are in agreement with other work that found microencapsulated AIT only slightly inhibited LAB starter cultures in dry-fermented sausage 20 and that volatized AIT did not inhibit the growth of indigenous LAB in nitrogenpackaged ground beef. 27 In contrast, it is evident from the results that mustard powder prevented LAB recovery on MRSS agar.…”

Elimination ofEscherichia coliO157:H7 from Fermented Dry Sausages at an Organoleptically Acceptable Level of Microencapsulated Allyl Isothiocyanate

“…These organisms were comparable in their resistance toward AIT to pathogenic human clinical and hamburger isolates of E. coli O157:H7 (6,24,26). These strains were maintained in TSB (BBL) and subcultured twice at 37°C for 18 h before use in experiments.…”

“…AIT is one of several naturally occurring compounds formed when glucosinolates present in cruciferous vegetables are hydrolyzed by the enzyme myrosinase (8). AIT is a potent inhibitor of a large number of pathogenic microorganisms (9,19), and it has been successfully used for elimination of E. coli O157:H7 from ground beef, roast beef, and hamburger patties (24,26,32). In general the application of AIT in the food industry has been limited due to its volatility; however, this obstacle was overcome by microencapsulation (6).…”

Food applications of natural antimicrobial compounds

“…It has been found to be more effective against Gram-negative bacteria with less or no effect on lactic acid bacteria. Although its antimicrobial activity varies widely (Delaquis and Mazza, 1995), the volatile compound particularly inhibits E. coli (Nadarajah et al, 2002; Muthukumarasamy et al, 2003). …”