Effect of Mixed Cooling on Postmortem Energy Metabolism and Meat Quality of Yellow-Feathered Broilers

In order to investigate the effect of low-temperature air cooling on the postmortem energy metabolism and meat quality of yellow-feathered broilers during mixed cooling (first water cooling and then air cooling), 85-day-old broilers were slaughtered and divided into three groups: treatment (water cooling at 0—4 ℃ followed by air cooling at -8, -18, -25 or -31 ℃), control (traditional water cooling at 0—4 ℃) and traditional mixed cooling (water cooling at 0—4 ℃ followed by air cooling at 0—4 ℃) groups. Finally, all carcasses were cooled to an internal temperature of 4 ℃, and the optimal air cooling temperature was determined by measuring cooling rate, pH, energy metabolism and quality indexes. The results showed that the cooling time of air cooling at -25 and -31 ℃ was 2537 and 2272 s, respectively, which was shortened by 27.78% and 35.33% compared with the traditional water cooling and by 51.87% and 56.90% compared with the traditional mixed cooling, respectively. Air cooling at -25 and -31 ℃ delayed the decrease in pH, reduced the drip loss and cooking loss of broiler breast muscle, significantly increased the shear force and the content of immobilized water compared with the control group (P < 0.05). Compared with the other groups, the activities of muscle hexokinases, phosphate-3-phosphate dehydrogenase and lactate dehydrogenase in the air cooling treatments at -25 and -31 ℃ were lower, and the consumptions of adenosine triphosphate (ATP) and glycogen, the production of lactic acid and adenosine monophosphate (AMP) and AMP/ATP ratio were the smallest (P < 0.05). The above findings showed that air cooling at -25 and -31 ℃ significantly inhibited the rate of anaerobic glycolysis during the early postmortem period in chicken meat, delayed the rate of pH decline, and effectively improved muscle water retention. From the perspective of industrial energy saving, -25 ℃ is determined as the best temperature for air cooling treatment.