Abstract:

Objective: To investigate the effect of NaCl concentration on water distribution and mobility of pork myofibrillar
protein (PMP) during heat-induced gelation in order to reduce the salt content of gel-type meat products. Methods: The
water-holding capacity (WHC), T2 relaxation time, and gel microstructure were determined by centrifugation method, lowfield
nuclear magnetic resonance (NMR) and scanning electron microscope (SEM), respectively. Principal component
analysis (PCA) was conducted to find out the main sources of data variability and the relationship between or within
samples and variables. Results: Obvious changes in WHC, T2 relaxation parameters and gel microstructure of PMP gel were
observed with increasing NaCl concentration from 0 to 0.6 mol/L. The addition of NaCl resulted in a significant (P ＜ 0.05)
increase in the WHC of PMP heat-induced gel, which was ascribed to the more fine microstructure with increase of NaCl
concentration. The distributed water proton and NMR T2 relaxation of different contents of NaCl after heat treatment were
characterized by two minor peaks with relaxation time of 0.62–3.89 ms and 4.62–35.28 ms, a major band with relaxation
time of 59.06–153.22 ms. In addition, a wide peak was also observed in the range between 1 198.75 and 1 518.17 ms. These
four populations probably represent three water states, i.e., bound, immobile and bulk water according to previous literature.
The position of the major peak obviously shifted to higher relaxation time with increasing NaCl level, and the peak area
fraction increased, which contributed to the increasing WHC. The addition of NaCl resulted in gels with quite homogenous
microstructure and decreased pore size after heat treatment, which was observed by SEM. The PCA results showed that the
first two principal components (PC) could explain 91.23% of the total variance. The samples obtained with different NaCl
concentrations revealed a tendency to group into three clusters. The low levels of NaCl were located in the left side of the
PCA score plots, characterized low WHC, T23, P22, whereas the high contents of NaCl were positioned in the right side and
characterized the opposite attributes, and the mediate NaCl concentration located in the middle. The correlation of these
parameters was displayed in the PCA loading score plot, which displayed a strong correlation of WHC to area fraction of
the major NMR relaxometry population. In conclusion, the gel functional properties are improved with increased NaCl
concentration, which is ascribed to the increase of immoblized water.

Key words: low-field nuclear magnetic resonance, myofibrillar, heat-induced gelation, water distribution, principal component analysis