Nmi20 060h 1

The transverse relaxation time (T₂) of shrimp surimi with different starch additions was measured with a low‐field nuclear magnetic resonance (LF‐NMR) instrument (NMI20‐060H‐I, Niumag Electric Corporation, Shanghai, China). The resonance frequency was set to 22.6 MHz, and the magnetic field strength of the instrument was set to 0.47 T. Then, 10 g of shrimp surimi was placed in a 35 mm‐diameter plastic dish, and the transverse relaxation curve was derived using the Carr–Purcell–Meiboom–Gill pulse sequence mode. The NMR imaging (MRI) of shrimp surimi samples was measured by the same LF‐NMR analyzer, according to the methods of Zhang et al., (2019) with minor modifications. Proton density images of samples were obtained by a spin‐echo imaging sequence. Four‐layer cross‐sections were selected for imaging in the middle area of the sample. The thickness of each layer was 1.75 mm, and the interval between layers was 0.65 mm. Then, the scan protocol was set to obtain images according to the following parameters: The scanning frequency was 21.12 MHz, repetition time was 2,200 ms, echo time was 20.00 ms, and average was 4. The gray level images were processed by Niumag NMR Image Processing software (Version 3.0, Niumag Corporation, Shanghai, China) to obtain pseudocolor images.

Surimi gel was cut into small cylinders (40 × 15 × 15 mm³) and placed in a low‐field nuclear magnetic resonance (LF‐NMR) tube with a diameter of 40 mm. The transverse relaxation time (T₂) was determined using a LF‐NMR analyzer (NMI20‐060H‐I; Niumag Co., Ltd., Suzhou, China). The measurement parameters were set as: SFI = 22 MHz, τ = 400 μs, NS = 8, TR = 6 s, EchoCount = 1500. Then, each peak area in integral spectrum of the T₂ was accumulated for calculation moisture distribution and composition on surimi gels (Jiao et al., 2019 (link)).