THE USE OF OXYGEN SCAVENGERS TO PREVENT THE TRANSIENT DISCOLORATION OF GROUND-BEEF PACKAGED UNDER CONTROLLED, OXYGEN-DEPLETED ATMOSPHERES

Rates of O-2 absorption from air were determined for a type of commercial O-2 scavenger that is formulated for rapid O-2 absorption at chiller temperatures. Rates of O-2 absorption from N-2 atmospheres containing 600 ppm O-2 were determined for trays that each contained 350 g of ground beef. Packs with controlled atmospheres of N-2 that contained ground beef and O-2 scavengers were prepared, to determine the conditions under which the scavengers could prevent the transient discolouration of the meat which arises from its reaction with the residual O-2 initially present in pack atmospheres. The rates of O-2 absorption by individual scavengers varied from the average by +/- 50%. The rate of O-2 absorption declined with decreasing oxygen concentration, from an average value per scavenger of about 12 ml h(-1) when O-2 concentrations were between 20 and 10%. At O-2 concentrations <1% (10,000 ppm) the rate of O-2 absorption was directly proportioned to the O-2 concentration so that the O-2 concentration in an atmosphere in a gas-impermeable pouch declined exponentially with time. The absorption of O-2 by ground beef was similarly dependent on the O-2 concentration. At 2 degrees C, the transient discolouration of beef in atmospheres initially containing about 50 ppm O-2 was prevented by the presence of 17.5 scavengers per l of atmosphere. At -1.5 degrees C, discolouration was prevented by 5 scavengers per l. The findings indicate that the O-2 concentration in pack atmospheres has to be reduced below 10 ppm within 30 min at 2 degrees C, or 2 h at -1.5 degrees C if ground beef is not to transiently discolour. It is unlikely that the required rates of O-2 absorption could be obtained economically with currently available, commercial O-2 scavengers.