Investigation of ice crystal structure characteristics of different frozen lamb by using mercury intrusion

In order to prove the feasibility of measuring the structure of ice crystal based on mercury intrusion, in this study, fresh lamb were either stored for 3 and 90 days after air freezing or stored for 3 and 90 days after immersion freezing. Ice crystal formed in the frozen meat wasare characterized as indicators for selectingof optimalthe fitness of the freezing methods and storing time on lamb., Ttherefore, the drop rate of central temperature during freezing, the characteristics of ice crystals, and the morphology of muscle fibers were recorded during different freezing processes and different frozen and stored times, and the microstructures of ice crystals formed were analyzed for cross-section area, equivalent diameter, roundness and elongation, ice size, shape, and location., Tthese factors were evaluated and compared with cumulative intrusion, distribution of pores and tortuosity that were measured by mercury intrusion. The mean (±standard deviation) cross-section area of ice crystals were 2 076.15±1 756.22, 555.41±526.72, 637.63±556.58 µm2 for the lamb samples subjected to stored 90 days after air freezing and stored for 3 and 90 days after immersion freezing, respectively. Aas compared with the muscle fibers (1 978.12±1 092.27µm2) that stored 3 days after air freezing. The roundness of the ice crystals formed in frozen lamb that stored 90 days after air freezing and stored for 3 and 90 days after immersion freezing was 0.65±0.17, 2.47±0.78 and 1.92±0.61, respectively, while the roundness of the frozen lamb that stored for 3 days was 0.73±0.14. The elongation of the ice crystals formed in frozen lamb that frozen and stored 90 days after air freezing and stored for 3 and 90 days after immersion freezing was 2.70±1.39, 2.47±0.78 and 1.92±0.61, respectively, while the roundness of the frozen mutton that stored for 3 days was 1.95±0.70. Air freezing, which finished the ice formation process within 549.5 min, created larger and irregular ice crystals, which resulted in severe and irreversible damage to lamb muscles. Immersion freezing produced smaller ice crystals than air freezing and finished the freezing process at a higher speed within 80.5 min. The quick process and short storage created finer ice crystals than long storage and air freezing, while the integrity of muscle fibers remained intact relatively. Because the pores left in the muscle that correspond to the space of the original ice crystals, therefore, the cumulative intrusion, aperture of pores, log differential intrusion and tortuosity of mutton samples were also recorded during different freezing processes after vacuum and freeze-drying. The mean (±standard deviation) maximum cumulative intrusion of pores were 2.16±0.08, 2.33±0.07, 1.76±0.01, 2.29±0.05 mL/g for the mutton samples subjected to be stored for 3 and 90 days after air freezing and stored for 3 and 90 days after immersion freezing, respectively. The distribution of pores showed that the large pores and middle holes were the main pores among different frozen muttons, and the frozen lamb samples that were stored long time have more large pores, middle holes and small holes than the frozen lamb samples that were stored short time. The average aperture dimension of pores were 10.09, 25.73, 3.21 and 14.45µm for the mutton samples subjected to be stored for 3 and 90 days after air freezing and stored for 3 and 90 days after immersion freezing, respectively. The tortuosity of pores were 2.27±0.05, 3.88±0.05, 3.15±0.08 and 4.41±0.16 for the lamb samples subjected to be stored for 3 and 90 days after air freezing and stored for 3 and 90 days after immersion freezing, respectively. The variation trend of maximum cumulative intrusion, distribution of pores and tortuosity were basically consistent with analysis of ice crystals of freeze-sectioning. Results achieved in this research provide mercury intrusion is a useful technical support for ice crystals.