Effects Of Phosphate And Tea Polyphenols On The Structure And Gel Biophysical Properties Of Beef Myofibrillar Protein

With the improvement of living standards,people’s demand for healthy foods is increasing.Compared with traditional meat products,consumers prefer healthy functional meat products.However,the lack of fundamental research has posed a certain obstacle to produce a wide variety of functional meat products in China.Tea polyphenols,as a natural functional polyphenol,have attracted the attention of many food researchers.But it may weaken some properties of meat gel,such as elasticity,cohesiveness,resilience and so on.In addition,exploring the influence mechanism of tea polyphenols and other food additives on myofibrillar protein is very important and basic to develope functional meat products based on tea polyphenols.Phosphates have been widely added in many types of meat products to improve the texture and water holding characteristics of meat products.The joint addition of phosphate and tea polyphenols may reduce or even offset the adverse effects on meat products brought by tea polyphenols.However,there are still some problems when utilizing them in meat products: the specific effect of phosphate on myofibrillar protein molecules has not been clearly studied;The effects of tea polyphenols on myofibrillar protein has not been investigated;The combined effects of phosphate and tea polyphenols on myofibrillar protein is still unknown.To solve these problems,the combined effects between tea polyphenols and phosphates on myofibrillar proteins was investigated by various methods,which provides a theoretical basis for the development of functional meat products based on tea polyphenols.This study is divided into three parts and the conclusions are as follows.(1)Effect of different phosphate species on the microstructure of myofibrillar proteinsMyofibrillar protein isolated from beef muscles was treated with 3 phosphates(sodium hexametaphosphate,sodium tripolyphosphate,sodium pyrophosphate)with different concentrations of 0.3%,0.6%,0.9%,1.2% respectively.Protein solubility,surface hydrophobicity,and reactive sulfhydryl group were determined.Atomic force microscopy was used to observe the microscopic protein surface.SDS-PAGE was carried out to determine the proteolysis of myofibrillar protein.The solubility and surface hydrophobic bond of myofibrillar protein was highly increased and the diameter decreased by SHMP,TSPP,STPP.Reactive sulfhydryl groups increased after SHMP addition,but slightly decreased in STPP and TSPP treated MP.TSPP and STPP had the same effect on myofibrillar microstructure and were different from SHMP.Three phosphates all caused MP to unfold.The MP gel complexity was increased,and roughness was decreased after phosphates addition,indicating phosphates helped to construct a more ordered and smoother gel microcosmic surface.(2)Effects of tea polyphenols on the structural and functional properties of myofibrillar proteinsThe main purpose of this part is to find out how tea polyphenols affect the conformational,functional,and morphological characteristics of beef myofibrillar proteins(MPs).Polyphenols addition did not change amine group contents of MPs but caused a slight increase in carbonyl groups of MPs at high-level addition,and it can also decrease the sulfhydryl groups and induced the formation of disulfide bonds(S-S).The solubility,surface hydrophobicity,and emulsion activity index of MPs were decreased by polyphenols,but the emulsion stability index did not change.Surface morphological analysis of MPs gels showed that polyphenols addition was harmful to the formation process of MPs gels but increased surface complexity of MPs gels.The degree of MPs aggregation was related to how many polyphenols were added to MPs suspension.Low ratio polyphenols caused a small fraction of MPs to aggregate and high ratio polyphenols resulted in excessive aggregation of MPs.(3)Effects of sodium hexametaphosphate,sodium tripolyphosphate coupled with tea polyphenols on the structural and gelling properties of beef myofibrillar proteinsProtein aggregation was observed when tea polyphenols were added,and it was alleviated when combined with phosphates.The gel hardness and fractuability were decreased by sodium hexametaphosphate through slightly clustering myofibrillar proteins nanoparticles,increasing absolute zeta potential value,creating more space between myofibrillar protein particles.Moreover,sodium hexametaphosphate coupled with tea polyphenols did not change these harmful impacts on the gel.However,gel hardness,resilience,cohesiveness,and surface homogeneity were promoted by sodium tripolyphosphate through homogeneously dispersing myofibrillar proteins and promoting cross-linking between myofibrillar proteins.Furthermore,the union of sodium tripolyphosphate and tea polyphenols preserved these benefits while weakening the aggregation caused by tea polyphenols.Therefore,sodium tripolyphosphate is more suitable in developing functional processed meat products based on tea polyphenols.The combination of phosphates and tea polyphenols also improved the emulsifying activity index of myofibrillar proteins.Overall,sodium tripolyphosphate was recommended in developing tea polyphenols based functional processed meat products.