Effect Of HL-salt Substitute And Its Components Histidine And Lysine On The Physico-chemical And Heat-induced Gel Properties Of Pork Myosin

Myosin is the most imortant composition of muscle proteins. Its good gel-forming ability is one of the important functionalities of meat processing, contributing to the texture and sensory quality of the meat. In the meat processing, a certain amount of salt is added to extract myosin,which is considered to be dissolve in a certain ionic strength solution during meat prcessing. In our daily life, about 77% of salt intake is from food processing,especially meat processing. However, excessive sodium intake can cause hypertension,cardiovascular disease et al, which has attracted widespread attention of consumers and food industry, thereby development of low sodium meat products has become a major concern for resear chers and industry. How to reduce the sodium content and maintain the good functionality of myosin is a big issue in low sodium meat products research at home and abroad. Based on our developed HL-salt substitute, taking myosin from porcine longissimus dorsi as material, the objective of research were to study the effect of HL-salt substitute and its components (L-his and L-lys) on the physico-chemical and heat-induced gel properties of myosin, eludicate its mechanism, and develop a procssing technology of low sodium gel product. The results showed as follows:1. Effect of HL-salt substitute and its components histidine and lysine on the physico-chemical properties of myosinHL-salt substitute and its components L-histidine and L-lysine affected the solubility,turbidity, surface hydrophobicity, sulphydryl content and conformational characteristics of myosin at various salt concentrations (0.001mol/L?0.15mol/L?0.6mol/L) were investigated.The results showed that the solubility of myosin was increased in the presence of L-his,L-lys and HL-salt substitute at various salt concentrations(p<0.05). Notably, L-lys contributed more to the solubility of myosin than the L-his (p< 0.05). At high (0.6mol/L)salt concentration, the solubility of myosin was respectively increased by 3.97%, 6.07%and 7.53% in the presence of L-his, L-lys and HL-salt substitute. At physiological(0.6mol/L) salt concentration, the solubility of myosin was respectively increased by 3.68%, 9.12% and 13.89% in the presence of L-his, L-lys and HL-salt substitute. At low(0.6mol/L) salt concentration, the solubility of myosin was respectively increased by 6.21%, 8.37% and 9.95% in the presence of L-his, L-lys and HL-salt substitute. The presence of L-lys and HL-salt substitute reduced the turbidity of myosin at high and physiological (p<0.05) but low salt concentration (p>0.05). L-his, L-lys and HL-salt substitute caused increases in the surface hydrophobicity at high, physiological and low salt concentrations, and L-lys contrihuted more than L-his (p< 0.05). In addition, L-his, L-lys and HL-salt substitute caused increases in the reactive sulphydryl content at high and low salt concentrations (p< 0.05). At physiological salt concentrations, the content of reactive sulphydryl group was increased in the presence of L-his and HL-salt substitute (p<0.05) but L-lys (p>0.05).Circular dichroism revealed the unfolding of myosin and a significant decrease of a-helical content with an increase of random coils, ?-turns and ?-sheets in the presence of L-his, L-lys and HL-salt substitute at various salt concentrations.In conclusion, the result elucidate the mechanism of improving the solubility of myosin by HL-salt substitute: L-his and L-lys, the components of HL-salt substitute, caused the unfolding of myosin and transformed the conformation of myosin molecule, which exposed buried hydrophobic and sulphydryl groups to the myosin surface, making myosin dissociated from myosin filaments, ultimately increasing the solubility of myosin.2. Effect of HL-salt substitute and its components histidine and lysine on the heat-induced gel properties of myosinHL-salt substitute and its components L-histidine and L-lysine affected the rheological properties, hardness, cooking loss, water holding capacity (WHC) and T2 relaxation time of myosin gels. The results showed that L-his, L-lys and HL-salt substitute decreased the gel forming time, increased the storage modulus (G') and increasing rate of storage modulus(?G')). At high salt concentration, compared with NaCl, L-his, L-lys and HL-salt substitute caused G' to increased by 8Pa?7.1Pa and 5.4Pa,?G' to increase by 332.62?1143.22 and 1733.98 (p<0.05), respectively. At physiological and low salt concentration, same tendency was observed. Hardness of myosin gels was increased in the presence of L-his, L-lys and HL-salt substitute at low and high salt concentrations (p<0.05) but physiological salt concentration (p>0.05). At low salt concentration, L-his, L-lys and HL-salt substitute decreased the cooking loss and increased the WHC of myosin gels (p<0.05). At physiological salt concentration, a significant increase of WHC was observed in the presence of L-his, L-lys and HL-salt substitute (p<0.05), but no changes in cooking loss was observed (p>0.05). At high salt concentration, WHC and cooking loss had no significant changes in the presence of L-his, L-lys and HL-salt substitute. The results of distributed water proton and NMR T2 relaxation showed that L-his, L-lys and HL-salt substitute decreased the mobility of water and increased immobile water content with the decrease of bulk water content, which contributed to the increasing WHC.In a word, L-his, L-lys and HL-salt substitute advanced the gel forming temperature,improved G' and ?G' values, increased immobile water content, and reduced water mobility and bulk water content in the gel network structure, resulting in better gel properties.3. Effect of HL-salt substitute on the heat-induced gel properties of porcine salt-soluble proteinsEffects of HL-salt substitute (the same quality conentration and ionic strength with NaCl) on the solubilty, turbidity, yield, WHC, gel springness, gel strength and rheological properties of salt-soluble protein from porcine longissimus dorsi. The results showed that,compared with 3% NaCl, HL-salt substitute with the same ionic strength improved the solubility of salt-soluble protein from 76.22% to 83.03% (p<0.05), decreased the turbidity but yield of protein (p>0.05). However, no significant effects were observed on solubility,turbidity and yield of salt-soluble protein when treated with the same quality concentration of HL-salt substitute (p>0.05). Compared with 3% NaCl, HL-salt substitute with the same ionic strength advanced thermal transition temperature by 10?, and improved G' and ?G'value by 59.63% and 89.90%, respectively (p<0.05) . In addition, HL-salt substitute with the same quality concentration and same ionic strength both increased the WHC and gel strength of salt-soluble protein (p<0.05),but didn't changed the gel springness.4. Application of HL-salt substitute in pork gel productEffect of different proportion of HL-salt substitute on the color, WHC, texture, sensory and storage properties of pork gel product was investigated to develop a good low sodium pork gel product with pure salty, good texture and sensory properties. The result showed that 50% proportion of HL-salt substitute increased the WHC of product by 2.27% (p<0.05),whlie 75% and 100% proportion of HL-salt substitute decreased the WHC (p<0.05). 25%and 50% of proportion of HL-salt substitute increased color L* value and decreased color a* value,but didn't affect color b* value. 75% proportion of HL-salt substitute increased color L* value and decreased color a* and b* value, while 100% proportion of HL-salt substitute decreased color b* value but not color L* and b* value. A significant increase of gel hardness was observed in the presence of 50%, 75% and 100% proportion of HL-salt substitute substitute (p<0.05) and the 50% proportion of HL-salt substitute substitute was the best, while no changes of springiness was observed (p>0.05). Sensory evaluation showed that pork gel product made by 25%, 50% and 75% proportion of HL-salt substitute had the same favorite degree with salt control, with had pure salty, moderate salinity, good taste, brittleness and elasticity. Compared with the control group, HL-salt substitute didn't affect the colony forming units, and 25%?75 % proportion of HL-salt substitute decrease the purge loss of samples whlie storing for 15days at 0-4?. In conclusion, the produte made by 50% proportion of HL-salt substitute was the best, which had good texture, color,sensory quality and storage properties.