Effect of multiple freeze-thaw cycles on the quality of instant sea cucumber: Emphatically on water status of by LF-NMR and MRI

Instant sea cucumber has become one popular product due to its convenience to eat, favourable taste and minimal loss of nutrients and bioactive components. However, there was rare information about the water dynamic of instant sea cucumber subjected to multiple freeze-thaw cycles. In this study, low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance image (MRI) were employed to investigate the effect of freeze-thaw cycles on water status of instant sea cucumber. Four water populations corresponding to strongly bound water, weakly bound water, immobile water and free water were observed in instant sea cucumber. With the increase of freeze-thaw cycles, the transverse relaxation time of immobile and free water increased, while the peak area of free water decreased significantly. MRI enabled the visualization of water migration of instant sea cucumber during multiple freeze-thaw cycles. Multiple freeze-thaw cycles also led to significant changes of other quality properties including thawing loss, WHC, color parameters, texture and protein content, and enlarge the interspace between fiber network in microstructure. Good correlations between T-22, A(22), A(23) and thaw loss, WHC, L*, hardness and collagen content (0.873 <= r <= 0.958) revealed LF-NMR may be an effective real-time monitoring method of these physicochemical parameters as a non-destructive technique.