Formation Of Typical Volatile Lipid Oxidation Products And Advanced Glycation End Products In Precooked Ground Pork During Cold Storage-reheating

Pre-cooked meat dishes are convenient foods that are cooked in advance,refrigerated or frozen,and then reheated.With the acceleration of people’s pace of life,the convenient and fast pre-cooked meat dishes market has always maintained a rapid development trend.In addition,the quality and safety of pre-cooked meat and nutritional health have also become the focus of attention.Meat is boiled by heating to cause muscle tissue damage,releasing more metal ions and active substances（such as free radicals,peroxides,etc.）,making the storage and reheating processes prone to lipid and protein oxidation,reducing food quality and even endangering health.Therefore,it is of great significance to study the quality changes of pre-cooked meat products during storage and reheating.However,the current research on pre-cooked meat products was limited to the cold storage time,processing conditions and odor changes caused by reheating.There are few reports on the composition and quality changes of volatile substances during the whole process of cold storage and reheating,and there is a lack of research on protein hazards（such as advanced glycation end products）.The purpose of this study was to investigate the changes in volatile components and advanced glycation end products in pre-cooked ground pork during cold storage-reheating,and to analyze the relationship between lipid oxidation,protein oxidation and Maillard reaction in pre-cooked ground pork under the influence of cold storage-reheating.To clarify the influencing factors and mechanisms of quality change in pre-cooked ground pork during cold storage-reheating,and provide theoretical support for quality control.The details are as follows:（1）The volatile compounds produced during the reheating process of pre-cooked（100°C,10 min）minced pork after storage（0°C,0-14 days）were identified and analyzed.By combining the reheating process with the headspace solid-phase microextraction process,the extraction was performed at 75°C for 30 min to achieve reheating safety while obtaining volatile substances to reflect the real changes of volatile substances during reheating.With the increase of storage time,the concentrations of hexanal（6.05±0.86–12.05±0.44 mg/kg）,（E）-2-octenal（1.54±0.16–3.07±0.08 mg/kg）,（E,E）-2,4-heptadienal（1.52±0.44–2.58±0.31 mg/kg）and other eight selected volatiles in reheated pork increased.The selected 11substances were in accordance with the kinetic zero-order reaction model（R²=0.876-0.997）.The increase of hexanal was 2.9-199 times faster than that of other volatiles,which was most affected by storage.The k values of nonanal and octanal were 5.56 and 2.08μg·kg^-1·d^-1,respectively,which were least affected by storage time.This is consistent with the formation pathway and correlation analysis results.Octanal and nonanal are mainly produced by the oxidation of oleic acid（C18:n-9,monounsaturated fatty acids）（r=0.969）,and the remaining nine are mainly derived from the oxidative cleavage of polyunsaturated fatty acids.The results showed that the simultaneous reheating and headspace extraction process could better monitor the volatile substances in the reheating process of pre-cooked pork,which provided new ideas and methods for the analysis of volatile substances in the reheating process.（2）Different fat contents（LF:1.3%;HF:26.5%,w/w）pre-cooked（100°C,10 min）ground pork was reheated（100°C,5 min）after storage（0°C,0-11 days）,and the TBARs value,tryptophan fluorescence intensity,GO,MGO,CML and CEL content of the samples before and after reheating were measured.The role of hydroxyl radicals in the formation of dicarbonyl compounds was calculated by DFT,and the production and influencing factors of advanced glycation end products of pre-cooked minced pork during storage-reheating were explored.The results showed that TBAR value（LF:0.46±0.20–6.76±0.55mg MDA/kg;HF:0.82±0.10–5.60±0.97 mg MDA/kg）,CML（17.53±5.19–37.81±9.64mg/kg protein）and CEL（LF:23.38±5.54–29.74±4.68 mg/kg protein;HF:25.3±4.24–35.68±5.5 mg/kg）showed an upward trend during storage（P<0.05）,and TBAR and CEL were affected by fat content（P<0.05）.GO and MGO reached the maximums（5.86±2.35mg/kg and 2.41±0.88 mg/kg）on the fifth day,while tryptophan fluorescence showed a downward trend.After reheating,TBAR value,tryptophan fluorescence,GO and MGO content decreased,while CML and CEL content increased during reheating.Through DFT calculation,free radical substances produced by lipid oxidation promoted the formation of GO and MGO,providing more substrates for CML and CEL.In addition,TBAR,tryptophan fluorescence,GO,MGO,CML and CEL contents were not affected by storage time during the reheating process（P>0.05）,which shows that the thermal effect is the main factor in the reheating process.