Influence of multiple freeze-thaw cycles on quality characteristics of beef semimembranous muscle: With emphasis on water status and distribution by LF-NMR and MRI.

Influences of multiple freeze-thaw (F-T) cycles on water status and distribution, microstructure and physicochemical properties of beef were investigated. Low-field nuclear magnetic resonance (LF-NMR) relaxation showed three water components were assigned to bound, immobilized and free water in beef matrix. With the increase of F-T cycles, the relaxation time and peak area of immobilized water decreased significantly (P < 0.05), which suggested the freedom and population of immobilized water decreased. T1 and T2 magnetic resonance images displayed a continuous decrease of water intensity in beef during multiple F-T cycles. The cryo-scanning electron microscopy results revealed repeated F-T cycles resulted in more and more large holes in the beef muscle fiber. The repeated F-T cycles also led to decrease of pH value, WHC, L* and a* values, hardness, springiness, cohesiveness and resilience, and the increase of thawing loss, cooking loss, b* and TBARS value. Partial least-squares regression models stated the potential of LF-NMR to predict the quality of beef as a non-destructive method.