*2.3. LF-NMR Transverse Relaxation Measurements*

The relaxation measurements were performed on a Meson NMI20-040H-I LF-NMR analyzer (NMI20-040H-I, NIUMAG Electronic Technology Co., Ltd., Shanghai, China) with a magnetic field strength of 0.5 T and corresponding resonance frequency for protons of 20 MHz. The shrimp samples were placed in a cylindrical glass tube, and a 30-mm diameter radio frequency coil was used to collect Carr–Purcell–Meiboom–Gill sequence (CPMG) decay signals, with a π-value (the time between pulses 90 and 180) of 200 μs; the lengths of these two pulses were 9.52 μs and 18.48 μs, respectively. The repetition time between two scans was 1500 ms. Distributed multiexponential fitting analysis was performed on the T2 relaxation data using MultiExp Inv Analysis software (NIUMAG Electronic Technology Co., Ltd., Shanghai, China). The T2 relaxation spectra were obtained from this analysis; the lateral and vertical axes represent the relaxation time and signal intensity, respectively (corresponding to the proportion of water molecules exhibited at that relaxation time).
