## 2 Results  
### Effect of Low-Sodium Salts on the Physicochemical Properties of Dry-Cured Meat  
#### 2.1.1 Metal Ion Content, Weight Loss, Moisture, Water Activity, and Water State of Dry-Cured Meat  
Table 1 provides the measured content, theoretical content value, and permeability of each metal ion in dry-cured meat products. The contents of Na\({}^{+}\), K\({}^{+}\), and Mg\({}^{2+}\) in each group of samples were proportional to the formula content, which was consistent with expectations. The amount of Na\({}^{+}\) added was relatively low in the groups SPMA, SPM, and SP compared to S, but they exhibited higher Na\({}^{+}\) permeability values. It was speculated that the introduction of K\({}^{+}\) would sharply promote the penetration of Na\({}^{+}\). However, the Na\({}^{+}\) permeability decreased in SM, which showed that adding Mg\({}^{2+}\) to the low-sodium salt formulations with relative higher sodium contents may hinder the permeation of Na\({}^{+}\). Mg\({}^{2+}\) can strongly combine with the polar groups of proteins and strengthen the interaction between proteins [16], thereby hindering the penetration of Na\({}^{+}\). [PERSON] et al. [17] also found divalent cations decreased salt penetration into dry-cured ham. In SPMA, SPM, and SP, the K\({}^{+}\) permeability reaches about 100 times the theoretical value. The reason may be that the charge density of K\({}^{+}\) is lower than that of Na\({}^{+}\) and Mg\({}^{2+}\), making it easy to diffuse in the meat to produce a concentration effect and concentrate at the sampling point. The Mg\({}^{2+}\) permeability was only about 20% due to the large charge density of divalent ions [18]. No significant difference was observed in the Mg\({}^{2+}\) permeability of SPMA, SPM, and SM, indicating that Na\({}^{+}\) and K\({}^{+}\) had no effect on the penetration of Mg\({}^{2+}\). As shown in Table 1, the weight loss rate of each group basically remained between 45.46% and 55.68%, though the weight loss rate of S (55.68%) was higher than that of other groups; in particular, it was significantly higher than that of SPM (47.42%) and SM (45.46%), indicating that low-sodium salt is beneficial to maintaining the moisture of dry-cured meat products. The lower weight loss of SM may be related to the permeation of ions. As shown in Table 1, SM showed the lowest permeability of Na\({}^{+}\) and Mg\({}^{2+}\). The moisture content of dry-cured meat products gradually decreases as the fermentation time progresses, eventually reaching a stable range, and \(A_{\text{w}}\) will also decrease as the moisture content decreases. \(A_{\text{w}}\) affects the nutrition value, color, flavor, and texture of food. In addition, \(A_{\text{w}}\) has an important role in food preservation. As shown in Table 1, the moisture content of each group decreased by about 65% and finally stabilized between 24% and 28%. Although there were no significant differences between the groups, it was noteworthy that the SP had lower moisture content, which was also found in the samples salted with a mixture of NaCl and KCl [17]. As shown in Table 1, the \(A_{\mathrm{w}}\) of all groups was below 0.75, among which the \(A_{\mathrm{w}}\) values of SPMA (0.723) and SPM (0.729) were significantly higher than SP (0.704). In Table 1, it also can be seen that the moisture contents of SPMA, SPM, and SM were higher than that of SP. The higher moisture content was in parallel with a higher \(A_{\mathrm{w}}\) value [17]. Ultimately, the moisture content and \(A_{\mathrm{w}}\) of the Mg\({}^{2+}\)-containing groups (SPMA, SPM, and SM) were higher; [PERSON], [PERSON], Toldra and Barat [17] also found the same results. Low-field NMR can be used to analyze the distribution and migration of moisture in meat products. The relaxation time \(T_{2}\) represents the strength of water mobility; that is, a shorter relaxation time represents lower mobility. As shown in Figure 1a, it can be seen that all groups contain three to four relaxation peaks, which has also been reported in the surimi-starch system [19].