Effects And Mechanism Of Microbial Transglutaminase And Sarcoplasmic Proteins On Gel Properties Of Porcine Myofibrillar Protein

China has great meat consumption annually. Heat-induced gel properities of muscle protein play an important role in the processing of meat products and directly related to the rheological characteristics, texture, water retention and taste of the meat products. Sarcoplasmic proteins have been reported to have positive impact on the gelation process of MP. To our knowledge, no similar studies comparing the effects of MTG and porcine sarcoplasmic proteins(SP) on MP gels have been reported. While traditional pork dried meat slice products are not suitable for the elderly and children by reason of instable moisture content, lacking of flexibility, dry and hard mouth feeling.In this research, it was studied that the effects of microbial transglutaminase(TGase) and different amounts of pork sarcoplasmic proteins(SP) on the properties of myofibrillar protein gels. Furthermore, the mechanisms of the impacts of TGase and sarcoplasmic proteins on myofibrillar protein gels characteristics were explored by IR spectrum, DSC(differential scanning calorimetry), SEM(scanning electron microscopy), intermolecular chemical interactions and surface hydrophobicity. And, it was studied that the effects of 0.5% TGase and different amounts of SP on properties of pork dried meat slice. The study could provide new ideas for improving the performance of protein gels and exploting more satisfactory dried meat slice products. The results were as follows:1. Effects of TGase and different amounts of SP on gels properties of porcine myofibrillar protein:(1) The results of SDS-PAGE showed that comparing with MP sol without TGase, the sol formed in the presence of TGase had a reduced intensity of expressed proteins, especially MHC, troponin T and tropomyosin. Clearly, the intensity of these protein bands reduced gradually as the amount of added SP increasing until SP concentration reached 1.5 g/100 g, after which they were reversed.(2) Comparing with the control group, addition of 0.5%TGase significantly increased cooking loss, a* value, b* values, breaking force, gel strength, hardness, elasticity, cohesiveness, and chewiness of porcine myofibrillar protein gels(P<0.05), remarkably decreased L* value and whiteness(P<0.05), small changes happened in breaking distance.(3) After addition of 0.5%TGase, with increasing SP concentrations, cooking loss, L* value, a* value, whiteness of porcine myofibrillar protein gels decreased; breaking force, breaking distance, gel strength, hardness and chewiness increased, cohesiveness and elasticity basically unchanged.2. The mechanisms of the impacts of TGase and SP on gel characteristics of porcine myofibrillar protein:(1) Scanning electron microscopy showed that the control MP gels appeared to consist of protein strand with a large amount of void spaces or pores; after adding TGase, microstructures of TGase-treated gels with or without SP showed a visibly compact and finely structure. It was clear that the structures became smoother and smoother with the increasing dosage of SP. Moreover, addition of 2.0g/100 g SP into TGase-treated gels resulted in the smoothest structure.(2) The rheological results showed that, after the addition of TGase, G’ values and elasticity increased, and as the increasing dosage of SP, temperature points which made G’ values dramatically increase gradually moved to lower temperatures; viscoelastic ratio(tanδ value) was reduced because of the addition of TGase and SP. DSC results showed that, 0.5%TGase reduced the denaturation temperatures of myosin heavy chain and actin from 57.8oC and 77.8 oC to 55.9 oC and 76.9 oC, respectively. After 2.0% SP were added, they were reduced from to 55.0 oC and 75.9 oC. TGase and SP reduced the denaturation temperatures of MP.(3) Surface hydrophobicity of myofibrillar protein decreased after adding TGase, but increased with the addition amount of SP increasing; when at the maximum amount of SP(2.0%), the hydrophobicity lowed again, but was still higher than the sample just adding TGase.(4) Hydrophobic interaction was the main chemical interactions in ionic bonds, hydrogen bonding and hydrophobic interaction. The addition of TGase and SP significantly reduced ionic bonding, hydrogen bonding and hydrophobic interactions. But SP minimized the effects of the TGase on various forces. After TGase was added, the ε-(γ-glutamyl) lysine isopeptide bonds significantly increased, and with the increasing of SP concents, ε-(γ-glutamyl) lysine isopeptide bonds increased.3. The impacts of 0.5%TGase and different concents of SP on pork dried meat slice:(1) After adding 0.5% TGase, comparing with the control group, L* value, the yields of pork dried meat slice were decreased significantly, while each texture indexs(hardness, elasticity, chewiness and cohesiveness), shear forces, color values significantly increased; water activity, moisture content, a* value, b* value, organizational status, impurities, taste, chewiness and overall degree of preference were different, but not obvious.(2) After adding 0.5%TGase, as the increasing of SP concentrations, a* value, b* value, yields, hardness, shear forces and sensory evaluation indicators of pork dried meat slice increased; water activity, L* value decreased; moisture content, cohesiveness, elasticity and chewiness changed unobviously; each sensory index scores fell after increasing. When SP concentration exceeded 1.5%, impurity and chewiness scores were higher than 5, but other indicator scores were less than 5, indicating that when the amount of SP exceeded 1.5%, pork dried meat slice was basically not accepted by consumers.