Effects Of Calcium Diglutamate Partially Substituting Nacl On Heat-Induced Gel-Forming, Emulsification And Physcochemical Capacities Of Myofibrillar Proteins From Rabbit

Health problems caused by excessive sodium intake have become a global issue in recent years, more and more people pay their attentions to it. The requirements for low sodium meat products increase year by year. As the most important salt-soluble protein of muscle proteins, heat-induced gel-forming and emulsification capacities of myofibrillar proteins have a critical impact on the final quality of products. Dynamic viscoelasticity and water-holding capacity of myofibrillar protein gel determine the final chewiness and production rate of gel-type meat products. Therefore, it is necessary to reduce the sodium content and also to ensure excellent processing characteristics of the protein, which is very significant for process of low-sodium meat products. Partial substitute of salt is one of the important ways for reducing sodium, as a new kind of food additives and calcium supplement preparations with flavor, the application of calcium diglutamate in low-sodium meat products just begins. In this study, myofibrillar proteins from rabbit were as material, fisrt added the same amount of calcium diglutamate, and then 5 different concentration of salt was added. Rheological properties, water-holding capacity (WHC) of the heat-induced gels, emulsifying ability (EAI), emulsifying stability (ESI) of myofibrillar proteins and the water-and fat-binding properties of myofibrillar proteins-lipids emulsion composite gels were tested and compared with those of the control group with 3% salt mixture. On the basis, the differences of salt soluble protein solubility, proteins content of the supernatant and precipitate, secondary structures of protein molecules before or after heat-induced gel-forming, changes of water molecules existing state and gel microstructures between calcium diglutamate substitute samples (1.25% calcium diglutamate and 1.2% salt, w/w) and the control (conventional salt dosage group,3% salt, w/w) were investigated as to provide theoretical guidance for the production of low-sodium gel-type meat products. The detailed contents and results are shown as follows.1. Study on calcium diglutamate partially substituting NaCl on heat-induced gel-forming and emulsification capacities of myofibrillar proteinsEffects of calcium diglutamate partially substituting NaCl on the functional characteristics of myofibrillar proteins from rabbit were studied. Myofibrillar proteins were extracted from Pasoas major (PM) of rabbit and then suspended in 0.4%、0.8%、1.2%、 1.6%、2.0% salt mixture (salt mixture comprised of 70% NaCl and 30% KC1) with 1.25% calcium diglutamate. Rheological properties, water-holding capacity (WHC) of the heat-induced gels, emulsifying ability (EAI), emulsifying stability (ESI) of myofibrillar proteins and the water-and fat-binding properties of myofibrillar proteins-lipids emulsion composite gels were measured and compared with those of the control group with 3% salt mixture. The results showed that when increase in monovalent salt contents increased the storage modulus of heat-induced gels, and the storage modulus of 1.2% samples was higher than that of control group (P<0.05); however, the WHC decreased followed by an initial increase, and the WHC of 1.2% samples was better than the rest of the treatments. EAI increased when salt contents increased, the ESI of 0.8% and 1.2% samples were better and exhibited no significant difference from that of the control group (P>0.05).The water-and fat-binding properties of myofibrillar proteins-lipids emulsion composite gels of 1.2% and 1.6% samples were significantly higher than that of the control group (P<0.05).In conclusion, low sodium conditions, caused by adding calcium diglutamate, improved viscoelasticity and the water-and fat-binding properties of rabbit myofibrillar proteins. Hence, the NaCl contents of gel-type low-temperature meat products could be reduced to 0.84%.2. Study on calcium diglutamate partially substituting salt on physical and chemical properties of myofibrillar proteinsNaCl could be substituted partially by calcium diglutamate in order to reduce sodium contents of the gel-type meat products, but the mechanism was unclear. In this chapter, we wanted to find the underlying reasons of calcium diglutamate partially substituting NaCl. In this study, the salt mixture comprised of 70% NaCl and 30% KCl. The differences of salt soluble protein solubility, proteins content of the supernatant and precipitate (SDS-PAGE), secondary structures of protein molecules before or after heat-induced gel-forming (Raman spectroscopy), changes of water molecules existing state (NMR) and gel microstructures between calcium diglutamate substitute samples (1.25% calcium diglutamate and 1.2% salt, w/w) and the control (conventional salt dosage group,3% salt, w/w) were investigated, and the myofibrillar proteins from Pasoas major (PM) were used as experimental object. Experiments were repeated three times and extracted new myofibrils each time. The protein solubility of treatment group was 24.24%, which was significantly lower than that of the control(P<0.05). We could found from the comparison of dissolved protein fractions that, content of a-actinin and actin showed no significant difference (P>0.05), however, content of the dissolved myosin heavy chain from treatment group decreased by 51.80%(P<0.05), content of C-protein increased by 143.3%(P<0.05). Before or after heating, content of a-helix and (5-sheet in the system showed no significant difference with the control; T22b relaxation time of thermal gels decreased from 305.39 ms of control to 285.50 ms of treatment, indicating the degree of immobilized water combination increased; the gel microstructures of treatment group were different from the control, for example the network strands were thicker, however, the whole gels also appeared regular, exquisite and uniform structures. In the myofibrillar proteins system when NaCl was substituted partially by calcium diglutamate, the protein-water molecules, protein-protein molecules could also get a good balance during gel crosslinking, as well as the three dimensional uniform gel network structure with high water-holding capacity be formed after heating.