Growth patterns of Escherichia coli O157:H7 in ground beef treated with nisin, chelators, organic acids and their combinations immobilized in calcium alginate gels

The effects of antimicrobial substances including nisin, acetic acid, lactic acid, potassium sorbate and chelators (disodium ethylenediamine tetraacetic acid [EDTA] and sodium hexametaphosphate [HMP]), alone or in combination and, with or without immobilization in calcium alginate gels, on the growth of Escherichia coli O157:H7 in ground beef were investigated. Results showed that acetic acid and potassium sorbate could inhibit the growth of E. coli O157:H7 effectively at 10degreesC and at 30degreesC. Both EDTA and HMP did not halt the growth of E. coli O157:H7. In an antimicrobial system immobilized with calcium alginate, most of the antimicrobials could not inhibit the growth of E coli O157:H7 in ground beef at 10degreesC and at 30degreesC, with the exception of acetic acid and lactic acid. Immobilization did not enhance the effectiveness of acetic acid against E. coli O157:H7 in ground beef at 10degreesC and at 30degreesC (P > 0.05) but it did enhance the effectiveness of lactic acid at 10degreesC. In a system combining different antimicrobials, treatment with nisin /EDTA or nisin/potassium sorbate at 10degreesC revealed a significantly lower population change of E. coli O157:H7 compared to samples treated with nisin, EDTA or potassium sorbate alone. The use of calcium alginate immobilization further enhanced the effectiveness of the combination system of nisin/EDTA, nisin/acetic acid and nisin/potassium sorbate on the growth of E. coli O157:H7 in ground beef at 10degreesC but it was not effective at 30degreesC. (C) 2002 Elsevier Science Ltd. All rights reserved.