| Heat treatment will cause degradation,oxidation,and denaturation of natural collagen to varying degrees,resulting in an increased degree of polymerization of protein,loss of functional properties such as emulsification performance,changes in amino acid composition,and increased sensitivity to protein hydrolysis.The increase in temperature will also lead to the collapse of the collagen three-strand helix structure,the decrease of α-helix content,the increase of random curling content,the gradual stretching of molecular structure,and the increase of disorder.Irreversible changes in collagen structure eventually lead to changes in the functional properties,digestive properties,and physiological activities of collagen.To explore the effects of different heat treatments on collagen,this study studied the effects of boiling,steaming,and roasting on the physicochemical properties and digestive properties of eel collagen.On this basis,with the help of a photoaging cell model,the anti-photoaging effects of collagen obtained by different heating treatments on the skin were studied.It provides a theoretical basis for the development and utilization of collagen.The main research contents and results of this topic are as follows:(1)Three different heating methods(boiling,steaming,and roasting)were used to process eel and fish.When the central temperature of the fish reached the specified end temperature(30/40/50/60/70/80℃)in the process of cooking(the central temperature reached 80℃),eel collagen was extracted at the temperature,and its emulsification,surface hydrophobicity,and aggregation characteristics were measured.To explore the effects of different heating methods on the physicochemical properties of eel collagen.The main experimental results are as follows: Compared with the control group(in this experiment,collagen extracted without heating treatment(20℃)was used as the control group),when the central temperature of fish was heated to 80℃,the ratio of a collagen extraction efficiency of eel decreased to 59.75%(boiling),55.99%(steaming)and45.42%(roasting),respectively.The surface hydrophobicity and turbidity of eel collagen obtained by three different heating methods increased significantly with the increase in fish temperature.The contents of sulfhydryl groups increased first and then decreased.Emulsifying ability(EAI)increased significantly,emulsifying stability(ESI)decreased significantly,and EAI was negatively correlated with ESI in the temperature range(30-80℃).(2)Based on the above studies,the in vitro gastrointestinal digestion model was established to determine the digestibility of collagen,free amino,and soluble nitrogen contents during the digestion of the stomach and intestine.Meanwhile,the structural changes of eel collagen were analyzed by Fourier infrared spectroscopy(FTIR).The effects of different heating methods on the digestive characteristics of collagen in eels and the relationship between digestive characteristics and structural changes were preliminaries studied.The main experimental results are as follows: With the increase of fish center temperature,the digestibility of collagen and soluble nitrogen content of eel obtained by three different heating methods showed obvious temperature dependence,that is,the increase of fish center temperature was significant.The digestibility of eel collagen without heating(20℃)was 20.43% and the digestibility of the intestine was28.88%.When the center temperature of fish meat reached 80℃,the digestibility of the stomach was 63.78% and the digestibility of the intestine was 72.19%.The gastric digestibility and intestinal digestibility were 58.76% and 71.45% respectively.The gastric digestibility and intestinal digestibility were 47.88% and 61.96% respectively.With the increase in fish temperature,the content of the free amino group in eel collagen obtained by three different heating methods increased first and then decreased.The secondary structure of collagen showed α-helix and β-folding decreased while β-turning and random curling increased.(3)Collagen extracted by different heating methods was used as raw material to prepare collagen peptide through a gastrointestinal digestion model in vitro,and photoaging of cells was induced by UVB to construct a human keratinocyte(Ha Cat)model.By measuring cell viability,reactive oxygen species(ROS),malondialdehyde(MDA),type Ⅰ collagen,matrix metalloproteinase-1(MMP-1),and matrix metalloproteinase-9(MMP-9)contents,the improvement effects of different collagen peptides on photoaged Ha Cat cells were investigated.The results showed that UVB irradiation caused intracellular peroxidation,and the excessive production of ROS and MDA stimulated intracellular overexpression of MMP-1 and MMP-9,leading to the reduction of type I collagen content,collagen degradation and loss,and accelerated skin aging.The addition of collagen peptide can alleviate peroxidation,promote collagen generation,improve the effect of photoaging on cells,and significantly improve cell vitality.Based on the analysis of various photoaging indexes,the best effect of collagen mixed peptides was obtained when the central temperature of fish meat reached 50℃ under boiling conditions.Therefore,three kinds of collagen peptides with different molecular weights(MW)were separated and graded: MW < 3000,5000 > MW > 3000,and MW > 5000.The antiphotoaging effects of the three collagen peptides were evaluated by the same measurement index.The results showed that the collagen peptide with a molecular weight of less than 3000 had the best anti-photoaging effect,the cells had a high utilization rate for it,and the anti-photoaging activity was the strongest. |
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