Effects of the pressure, flow rate and delivered volume of brine on the distributions of brine and bacteria in brine-injected meat

Eye of round primal cuts were bisected longitudinally, and the halved cuts were each injected with a brine-containing 5% NaCl, 5% polyphosphate, 200 ppm FDC Blue #1 dye, and Listeria innocua at about 106 cfu/ml. Brine was injected into each halved primal from a hypodermic needle with its tip at the geometric centre of the cut. Brine was injected at rates of 5 or 15 ml/min, with injection of 3, 5 or 7 ml of brine at each rate, using a syringe pump. The pressure in the line to the needle was recorded at 2 s intervals while brine was being injected. Each rate and volume condition was used for injection of 7, 8 or 9 halved primals. Each halved primal was cut across at the injection site, and the two portions were each cut into four or five 2 cm thick steaks, starting from the newly exposed surface. The volume of dyed tissue in each steak was estimated from the dyed areas of steak surfaces. The volume of brine and the number of bacteria in each steak were determined from the amount of dye and numbers of bacteria recovered from dyed tissues in steaks. The results showed that approximately ovoid volumes of tissue contained brine after injection. The long axis of the ovoid volume paralleled the muscle fibres and extended further behind than in front of the bevelled opening of the needle. Increasing volumes of brine and the higher rate of brine injection increased the radial dimensions of the ovoid volume but did not extend the long axis. The steaks closest to the needle contained more bacteria than would be expected from the amounts of brine in the steaks. Pressures maintained in the brine line during injection ranged from <10 to >50 kPa. The pressure had no effect on the distributions of brine or bacteria in the meat. The findings suggest that much of the brine injected into meat flows by capillary action into the same channels through which water from meat flows to be lost as drip.