Effect Of Irradiation On The Structure,Properties Of Ovalbumin And Development Of Antioxidant Egg White Powder

As a green-processing technology,food irradiation has various advantages such as high throughput,safety and energy-efficient.Owing to its high nutrition and absorptivity,egg is acted as a valuable food source.Egg white protein,which accounts for more than 60%of egg,has prominent characteristics including antioxidant and foaming,resulting in being used as raw materials in food processing.However,for some consumers with allergic potentials to egg allergy,allergenicity from egg white protein leads to certain potential safety hazards in egg products.Previous research results suggested that functional characteristics of protein were further improved after glycosylation and its application in food industry was expanded,but there is no report on glycosylation products generated from the combination method processing including irradiation and glycosylation.Therefore,in order to fill up the void field of research and investigate the effect of irradiation technology on the feature of egg white protein,ovalbumin（OVA）,the main component of egg white protein,was viewed as the research object.This project explored the influence of different irradiation sources on the conformation of OVA,and the effect of ⁶⁰Co-γirradiation on the allergenicity of OVA,meanwhile,the mechanism of allergic alteration was preliminarily studied.This paper also explored the effect of ⁶⁰Co-γirradiation on OVA glycosylation system and optimized the best process conditions to prepare antioxidant egg white powder to promote its functional properties and ensure its safety.The conclusions were as follows:（1）The OVA which irradiated by electron beam and ⁶⁰Co-γirradiation was acted as the object in this chapter.The structural change of OVA was characterized by surface hydrophobicity,fluorescence spectrum,circular dichroism,SDS-PAGE,and chromaticity.Meanwhile,the effect of two irradiation sources was compared.The conclusion was as follows:Two irradiation sources caused the unfolding of the three-dimensional structure of OVA and the remarkable alteration fromα-helix toβ-folding and random coil structure.Simultaneously,the degradation of OVA in a dose-dependent manner and the transformation of apparent color from bluish-green to reddish-yellow as well as being dark were observed.At the same dose,the effect of⁶⁰Co-γirradiation was more significant than that of electron beam irradiation.（2）This OVA was irradiated by ⁶⁰Co-γirradiation at a certain dose.Allergenicity was characterized through its Ig G/Ig E binding capacity.Degree of oxidation was assessed by the changes of carbonyl and free sulfhydryl content.And high-resolution mass spectrometry was used to identify oxidation sites.The conclusion was as follows:During ⁶⁰Co-γirradiation,the Ig G/Ig E binding ability and carbonyl content as well as free sulfhydryl of OVA significantly increased.Interestingly,the oxidative modification was found under ⁶⁰Co-γirradiation,and the oxidation degree increased in a dose-dependent way.Meanwhile,the phenomenon of the broke degree of disulfide bonds exceed the oxidation degree of sulfhydryl groups was observed.Most of the 17 oxidation sites after irradiation treatment increased its allergenicity via the change of conformational epitopes,and 3 oxidation sites resulted in the exposure of linear allergic peptides.（3）The OVA and glucose were viewed as research objects in this chapter.The changes of OVA glycosylation during irradiation were measured by conventional spectroscopy.The reducing power and ABTS⁺radical clearance were measured to evaluate the change of antioxidant capacity.The content of glycosylation products was measured to determine the appropriate dose.The conclusion was as follows:After ⁶⁰Co-γirradiation treatment,the glycosylated degree of OVA increased with the increase of dose.The molecular weight of samples increased significantly,α-helix structureis reduced butβ-Structure（β-folding andβ-turn）increased.Meanwhile,the antioxidant capacity of OVA glycosylation system was significantly improved during⁶⁰Co-γirradiation,especially,it enhanced nearly doubled at the maximum dose.In addition,the changing trends of contents in glycosylation products after ⁶⁰Co-γirradiation were different.Specifically,the contents of fructosamine and acrylamide were increase first and then decrease（the inflection point of dose was 50 k Gy）.The contents of fluorescent AGEs,pentosidine and melanoidin increase in a dose-dependent manner.In comprehensive consideration,the appropriate dose range of⁶⁰Co-γirradiation was within 25 k Gy.（4）Based on the above research results,the optimum processing factors of antioxidant egg white powder in the combination method including ⁶⁰Co-γirradiation and glycosylation were explored through single element experiments and orthogonal trials.The conclusion was as follows:The order of affecting factors was sugar type>ratio of protein to sugar>p H of reaction system.The optimum processing factors was found to prepare antioxidant egg white powder under ⁶⁰Co-γirradiation as follows:the type of sugar,the ratio of protein to sugar and the reaction system were ribose,6:1,and p H=7,respectively.