Effect Of Heating Degree On The Molecular Structure And Digestive Characteristics Of Three Muscle Proteins

Heating is one of the most common processing methods,which is an important part of meat from raw to mature.It has an great impact on meat quality and protein structure.It is recognized that protein oxidation and aggregation during heating.Gelatination of collagen can be occurred during longer time heating.The change of protein will further affect digestibility.However,there is a lack of systematic research on the structural changes and digestion of meat protein.The objective of this study was to investigate the effects of heating temperature on the structure of those proteins by using multiple spectral techniques and other detection methods.A nano liquid chromatography system coupled with LTQ Orbitrap(Nano LC-LTQ-Orbitrap XL MS/MS)was applied to characterize protein digestion products.And changes in the sensitivity of protein to pepsin were analyzed by enzymatic reaction kinetics and peptide analysis.1.The effects of heating degree on protein structuresThe effects of heating on protein multilevel structure were studied with three pure proteins(myosin,myoglobin and collagen).The results showed that the secondary structure of myosin was transformed from ?-helix to other irregular structure.The sulfhydryl group of myosin was exposed gradually and converted to disulfide bond,which resulted in the degeneration and aggregation of the protein.After heating,the content of Metmyoglobin in myoglobin increased.However,the secondary structure of myoglobin changed little.This indicates that myoglobin was resistant to temperature to some degree.After hcating,the triple helix of collagen is released and transformed into other irregular structure.The fluorescence intensity of phenylalanine weakens,which indicating that collagen aggregates.2.The effects of heating degree on protein digestionThree kinds of proteins were hydrolyzed with pepsin.Then the enzymatic process curve and Michaelis constant Km value were determined.LC-MS/MS was used to identify the digestion products.The results showed that the degree of heating had different effects on different protein.After heating,the myosin structure is expanded to expose the enzyme site,which is beneficial to pepsin digestion.After heated at 70?,myosin was most easily to digested.After heating at 100 ?,the oxidation and aggregation degree was higher,therefore it was not sensitive to pepsin.The structure of myoglobin is difficult to be hydrolyzed by pepsin enzyme,and it is resistant to temperature to some degree.Therefore,heating can only improve the digestion of myoglobin in a certain extent.The amino acid composition of collagen has certain resistance to enzymatic hydrolysis of digestive enzymes.Although heating releases the triple helix of collagen,while protein aggregation reduces the sensitivity of collagen to pepsin.In addition,the peptide of sequence digestion products of collagen product contains glycine.