Use of deodorized yellow mustard powder to control Escherichia coli O157:H7 in dry cured Westphalian ham

Dry cured (uncooked) hams with low water activity and pH ≥5.6 seem a likely food vehicle for Escherichia coli O157:H7. In previous work, isothiocyanates produced from mustard glucosinolates by bacterial myrosinase-like activity converted deodorized mustard into a potent antimicrobial in dry sausage. In this study its value in controlling E. coli O157:H7 survival in Westphalian ham was investigated. Hams were inoculated with a 7.5 log cfu g(-1) cocktail of E. coli O157:H7, 4% or 6% (w/w) deodorized yellow mustard powder was surface applied and monitored 80 d for pathogen survival. In one trial to accelerate formation of isothiocyanate, a Staphylococcus (S.) carnosus meat starter culture was added to hams at 45 d (after salt equilibration). At 21 d, E. coli O157:H7 was reduced by 3 log cfu g(-1) on hams treated with mustard powder compared to only a 1 log cfu g(-1) reduction in the control. By 45 d, mustard powder caused a reduction of >5 log cfu g(-1)E. coli O157:H7, whereas it took 80 d for numbers in control hams to be similarly reduced. Although the commercial process used caused a 5 log cfu g(-1) reduction of E. coli O157:H7 in 80 d, 4% or 6% deodorized mustard accelerated this reduction and the S. carnosus starter culture may have contributed to the maintenance of this effect.