The traditional immersion vacuum cooling of meats can result in product defects. To optimize these processes, different salt ion concentrations in the immersion solution (0%, 3%, 5%, and 7%) were assessed, in relation to the cooling rate, cooling loss rate, color, texture, moisture status, and microstructure of chicken drumsticks. The cooling rate at 5% salt ion concentration was the fastest and most similar to the conventional vacuum cooling method, which can reduce the central temperature of drumsticks from 75 to 25 °C in 15 min. Immersion vacuum cooling did not cause weight loss and the 5% salt ion concentration was the best for weight maintenance, which can increase the weight of drumsticks by 2.3%. The L* and b* values first decreased and then increased with increasing salt ion concentrations, but not significantly. Hardness gradually decreased, whereas the low-field nuclear magnetic data showed that the transverse relaxation time of free water (T22) in the drumsticks increased from 200.01 ms to 237.79 ms with increasing salt ion concentrations. Scanning electron microscopy images revealed irregular and smaller pores between the muscle fibers with increasing salt ion concentrations. The 5% salt ion concentration in the immersion solution during vacuum cooling was optimal as it increased the cooling rate and improved the edible quality without cooling loss. Thus, adjusting the salt ion concentration of the immersion solution is a feasible way to improve economic benefits and quality characteristics of meat products.
Keywords: cooling rate; drumsticks; immersion vacuum cooling; low-temperature processing; nuclear magnetic resonance; salt ion concentration.