Inhibition of growth of nonproteolytic Clostridium botulinum type B in sous vide cooked meat products is achieved by using thermal processing but notnisin

The safety of refrigerated processed foods of extended durability (REPFEDs) with respect to nonproteolytic Clostridium botulinum is under continuous e valuation. In the present study, mild (P-85.0(7.0) values 0 to 2 min [P, pa steurization value; z-value 7.0 degreesC; reference temperature 85.0 degree s Cl) and increased (P-85.0(7.0) values 67 to 515 min) heat treatments were evaluated in relation to survival of nonproteolytic C. botulinum type B sp ores in sous vide processed ground beef and pork cubes. The use of two conc entrations of nisin in inhibition of growth and toxin production by nonprot eolytic C, botulinum in the same products was also evaluated. A total of 96 samples were heat processed and analyzed for C, botulinum by BoNT/B gene-s pecific polmerase chain reaction and for botulinum toxin by a mouse bioassa y after storage of 14 to 28 days at 4 and 8 degreesC. Predictably, after mi ld processing all samples of both products showed botulinal growth, and one ground beef sample became toxic at 8 degreesC. The increased heat processi ng, equivalent to 67 min at 85 degreesC, resulted in growth but not toxin p roduction of C, botulinum,2 in one ground beef sample in 21 days at 8 degre esC; in the pork cube samples no growth was detected. The increased heating of both products resulted in higher sensory quality than the milder heat t reatment. Nisin did not inhibit the growth of nonproteolytic C. botulinum i n either product; growth was detected in both products at 4 and 8 degreesC, and ground beef became toxic with all nisin levels within 21 to 28 days at 8 degreesC. Aerobic and lactic acid bacterial counts were reduced by the a ddition of nisin at 4 degreesC. The study demonstrates that the mild proces sing temperatures commonly employed in sous vide technology do not eliminat e nonproteolytic C. botulinum type B spores. The intensity of each heat tre atment needs to be carefully evaluated individually for each product to ens ure product safety in relation to nonproteolytic C. botulinum.