| "Clean label" is a major development trend in the food industry at present.The most important element of the clean label is using natural food or ingredients that consumers can understand and using simple green processes to produce products,so that there are few or no food additives in the food label.With the acceleration of the pace of modern life,consumers pay more attention to whether food is natural,nutritious and safe.Compared with ordinary label food,they have higher acceptance of clean label food.Meat is one of the most popular foods in People’s Daily life.In the process of meat production,some emulsifiers and thickeners are often added to improve the water and oil retention ability of meat products,and improve the texture and flavor of meat products.However,the use of additives does not conform to the concept of clean label and can not meet the needs of consumers for clean label food.Therefore,it is of great significance to develop alternative thickeners and emulsifiers in meat processing to provide support for the production of clean label meat products.Pig skin is a byproduct of pork processing,and its main component is collagen.It is theoretically feasible to use pig skin as raw material to prepare functional protein powder with certain emulsification and gelling properties,which can replace thickeners and emulsifiers in meat processing.In this study,pig skin was used as raw material.Green process was constructed to prepare functional protein powder(FPP).The emulsifying properties of FPP and its synergistic gel properties with Myofibrillar proteins(MP)were studied systematically.The conclusions were as follows:(1)Using pig skin as raw material,the functional protein powder(Protein powder A: FPP40、FPP55 and FPP70,Protein powder B: FPP160、FPP190)was prepared by two green processes(method A: dry grinding,method B: wet grinding).The chemical composition,physicochemical properties and functional properties of the protein powder were studied.The results showed that the chemical composition of the two kinds of protein powder was similar,and the main component was collagen.Protein powder A showed irregular fragmentation and smooth surface,which had better dispersion in cold water(0 ～ 10°C),while Protein powder B had smaller particle size,spherical shape and concave surface,which was easy to embed into each other and not easy to disperse in cold water.Protein powder B has better water-oil holding performance due to more internal hydrophilic and oleophilic group exposure.Protein powder A retained more α,β chains and hydrogen bonds of collagen during processing,and had A more complete triple helix structure,so it had better gel properties than Protein powder B.DSC results showed that Protein powder A and B had good thermal stability,among which FPP55,FPP70 and FPP160 had better thermal stability.FPP55 was selected for subsequent experiments based on the analysis of the research results.(2)The emulsion was prepared by adding different concentrations of FPP(0.5%,1%,1.5%,2%,3%)with soybean oil as oil phase.The emulsifying properties of FPP were evaluated by studying the physicochemical properties,microstructure and the influence of thermal induction on emulsion properties.The results show that the emulsion can be formed by adding FPP when the volume of oil phase is 30% ～ 80%,and the emulsion with the volume of oil phase is 50% ～ 70% is more stable.Under the condition of 60% oil volume,the emulsion can be formed when the concentration of FPP is 0.5% ～ 3%.With the increase of FPP concentration,the emulsion droplet size gradually decreased,and the emulsion stability and water holding capacity gradually increased.The rheological results show that the emulsion does not have a stable linear viscoelastic zone when the concentration of FPP is 0.5%.At the concentration of 1% ～3%,the emulsion is the dominant system of elastic structure,and with the increase of concentration,the viscosity of the emulsion increased.The network structure is more stable when the concentration is 1.5% ～ 3%.In the concentration range of 0.5%-3%,all the emulsions were stable when stored at 4°C for 30 days,but the emulsions with the concentration of 2% ～ 3% had better centrifugal,freeze-thaw and thermal stability.When the emulsion is heated,its viscosity increases and a heat-induced gel can be formed.With the increase of FPP concentration,the hardness,cohesion and water holding capacity of heat-induced emulsion gel were significantly enhanced.When the concentration of FPP is 3%,the texture and holdability of heat-induced emulsion gel are significantly better than other samples.The emulsion gel can withstand long time heating at 80?C for 60 min and repeated heating for three times.In general,the addition of FPP can obviously improve the properties of emulsion and emulsion gel.FPP has good emulsifying performance.(3)Different amounts of FPP(0.2%,0.4%,1%,2%,4%)were added to MP to prepare gels.Myofibrin gels with 0.4% carrageenan addition were used as control.The effect mechanism of FPP addition on the properties of MP gel was studied.The results showed that the addition of FPP had little effect on the whiteness of the gel,and both FPP and carrageenan could significantly improve the water holding capacity and texture properties of the gel.As the concentration of FPP increases,FPP fills the MP gel,which makes the original loose structure become more compact and uniform,promotes the exposure of hydrophobic groups,and reduces hydrophobic interactions.In addition,in the process of gel formation,FPP molecules slow down the aggregation and degeneration of myosin,which is conducive to the cross-linking and aggregation of protein molecules,and promotes the formation of disulfide bonds between MP molecules.When the addition level of FPP increased from 0% to 0.4%,the hydrogen bond increased significantly,and the main force maintaining the gel sample changed from hydrophobic interaction to hydrogen bond and hydrophobic interaction.When the addition amount of FPP continues to increase(1% ～ 4%),the negatively charged MP and positively charged FPP generate electrostatic interaction to form ionic bond,and hydrogen bonding and hydrophobic interactions are further reduced.At this time,ionic bond and disulfide bond become the main force to maintain the gel structure.FPP and MP cooperate to form a more uniform,compact and ordered gel network structure. |
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