| Silver carp(Hypophthalmichthys molitrix)is the main freshwater fish variety for frozen surimi processing in China because of its low price and large output.Surimi products are aquatic products obtained from frozen surimi as the main raw material through processing processes such as adding auxiliary materials,chopping and heating.They have delicate taste and rich nutrition,and are deeply loved by consumers.In the process of storage,transportation,sales or consumption,the fluctuation of frozen storage temperature will lead to multiple thawing and refreezing of products.The freezing and thawing of raw materials and subsequent thermal processing may cause fat oxidation and protein degradation in surimi products,and then lead to the formation of advanced glycation end products(AGEs).However,there are few reports at home and abroad on the correlation between fat oxidation and protein oxidative degradation of surimi products and the formation of ages and the influence mechanism of ages formation.In this study,silver carp surimi was used as raw material.The effects of freeze-thaw cycle times and processing procedures on the content of ages in silver carp surimi products and the formation of oxidative degradation products of fat and protein were analyzed by HPLC-MS/MS,GC-MS and HPLC.The correlation between oxidative degradation of fat and protein and the formation of ages was clarified,and the influence mechanism of ages formation was explored,it provides a theoretical basis for optimizing the frozen storage conditions and processing methods of surimi to reduce the formation of ages.The main research conclusions are as follows:(1)The effects of different freeze-thaw cycle temperatures on fat oxidation,protein oxidative degradation and ages formation in the samples are not significantly different.(2)With the increase of freeze-thaw cycles,the content of TBARs,hexanal,nonanal and 1-octene-3-ol in surimi products increased;With the increase of processing procedures,the TBARs value in surimi products first increased and then decreased,and the contents of volatile fat oxidation products hexanal,nonanal and 1-octene-3-alcohol showed different rules.In surimi products with different freeze-thaw cycles and processing procedures,the four dicarbonyl compounds also show different rules.(3)With the increase of freeze-thaw cycles,the content of TCA soluble peptide,total free amino acid,lysine,endogenous fluorescence intensity and Schiff base in surimi products increased,and there was no significant difference between different bands in SDS-PAGE;With the increase of processing procedure,the content of TCA soluble peptide in surimi products increased,the content of total free amino acids and lysine increased first and then decreased,the content of endogenous fluorescence decreased significantly,and the content of Schiff base decreased first and then increased slightly;The myosin heavy chain gradually faded,and proteins with molecular weights of 150 kDa,120 kDa and 30 kDa were added,and the bands of 70～85 kDa were significantly deepened.(4)The freeze-thaw cycle had no significant effect on the content of CML in unheated surimi products,but the freeze-thaw cycle significantly increased the content of CML in heated samples.After 6 times of freeze-thaw,the content of CML in heated samples increased by 0.35～0.53 mg/kg(-20℃)and 0.50～0.69 mg/kg(-60℃).It was found that there was no similar trend in the formation of AGEs in all three freeze-thaw pathways.After freezing and thawing for 6 times,the content of CEL in the sample increased by 1.56～4.65 mg/kg(-20℃)and 2.11～5.00 mg/kg(-60℃);The content of fluorescent AGEs in the sample increased by 39.97～121.83 AU(-20℃)and 26.33～88.60 Au(-60℃).The processing procedure promoted the formation of CML,CEL and fluorescent AGEs in surimi products.One-stage heating increased CML,CEL and fluorescent ages by 0.22～1.24,0.01～0.20 and 0.05～0.17 times respectively,and two-stage heating increased CML,CEL and fluorescent AGEs by 1.94～3.29,0.34～1.02 and 0.47～0.62 times respectively.Heating temperature and time have a decisive impact on the formation of AGEs.(5)CML was significantly correlated with hexanal,1-octene-3-alcohol,MGO,2,3-BD,TCA soluble peptide and endogenous fluorescent substances(p<0.01),and significantly correlated with go and lysine(p<0.05);CEL was significantly correlated with TBARs,hexanal,nonanal,1-octene-3-alcohol,3-DG and TCA soluble peptide(p<0.01),and positively correlated with lysine(p<0.05);Fluorescent ages were significantly correlated with hexanal,1-octene-3-ol,MGO,2,3-BD,TCA soluble peptide and endogenous fluorescent substances(p<0.01),and significantly correlated with nonanal,GO and lysine(p<0.05).In summary,fat oxidation and protein oxidative degradation in surimi products occur simultaneously with the increase of freeze-thaw cycle times and processing procedures.Free radicals,hydroperoxides,aldehydes and other substances produced by fat oxidative degradation can promote protein oxidation.At the same time,the oxidative degradation of proteins(such as myoglobin)will produce iron ions and promote fat oxidation.High temperature and long-time processing will increase the rate of Maillard reaction,lipid oxidation and protein oxidative degradation;Moreover,the number of freeze-thaw cycles of surimi raw materials increases,resulting in more oxidative degradation products of fat and protein,which provides more raw materials and precursors for the formation of AGEs in the processing of surimi products,resulting in more AGEs in the subsequent processing procedures. |
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