Evaluation Of The Nutritional Quality Of Kelp And Effects Of Cooking Technologies On The Properties Of Soluble Dietary Fiber

China is a great country in the production of kelp.2017 China Fisheries Statistics Yearbook displayed that the area of kelp farming was 44,400 hectares,and the production was 146.11 million tons in 2016.As one of the most important economic algae in China,Kelp has been widely applied in many industries,such as food,medicine,health care,agriculture,chemical industry and so on.In this thesis,the nutritional composition of 13samples of fresh kelp samples originated from Dalian,Rongcheng and Xiapu area were firstly measured,and then the principal component analysis was used to evaluate the nutritional quality of the samples.Then,the nutritional quality differences of Rongcheng fresh kelp,dried and salted products were compared and analyzed.Finally,the effects of atmospheric cooking,autoclaving and microwaving on the structural characteristics,physicochemical properties and antioxidative activity of soluble dietary fiber?SDF?from kelp were studied.These results can provide theoretical bases for the establishment of fresh kelp nutritional quality evaluation system,the optimization of kelp processing technology,the development and utilization of soluble dietary fiber?SDF?from kelp,and promote the development of the kelp industry in China.The specific research contents and conclusions are as follows:1.The coefficient of variation?CV?of 19 kinds of main nutrients in fresh kelp?dietary fiber,alginate,mannitol,iodine,glutamate,aspartic acid,glycine,alanine,serine,proline,methionine,magnesium,potassium,calcium,iron,zinc,manganese,phosphorus and sodium?are more than 15%.The coefficient of variation?CV?of iron,zinc,manganese and iodine were 97%,66%,66%and 58%respectively,and correlation analysis found that there was simple correlation between some nutrients,which was suitable for principal component analysis.In principal component analysis,5 principal components were extracted,with a total cumulative contribution rate of 87.428%,which could reflect most of the information of 19 indicators.The contribution rate of mannitol,kelp polysaccharide,sweet amino acid,umami amino acid and mineral elements to the evaluation of kelp nutrient quality was higher,could be used as an important nutrients to assess the evaluation on kelp nutritive quality.Based on the characteristic value,the comprehensiveevaluationfunctionwasestablished:F=0.2822F₁+0.2405F₂+0.2010F₃+0.1537F₄+0.1226F₅.As a result,the top three scoring points were Sample No.6?Xiapu?,Sample No.13?Rongcheng?,and Sample No.11?Rongcheng?.2.The results?dry basis?of the comparative analysis of the main nutrients of Rongcheng fresh kelp and its dried and salted products showed that the content of dietary fiber,total sugar and alginate in dried kelp was 9.21%,18.40%and 14.60%,significantly lower than that of fresh kelp.The content of mannitol and iodine in salted kelp decreased significantly?6.60%,0.18%?.There were sixteen kinds of amino acids detected in in fresh kelp,dry kelp and salted kelp,seven of which were essential amino acids,and protein composition was conformed to the ideal protein pattern recommended by FAO/WHO.Compared with fresh kelp,the contents of mineral elements such as potassium,calcium,sodium,magnesium and iron in dried kelp decreased significantly.Besides,the sodium content in the salted kelp was significantly increased,and the other mineral elements were obviously decreased.The above results showed that two kinds of primary processing methods of drying and salting could cause the loss of nutrients in the kelp.3.The effects of cooking technologies on the yield and structural characteristics of SDF from kelp were analyzed.The results showed that the yield of SDF from kelp after autoclaving was 22.53%,which was significantly higher than that of the control group?21.56%?.The X-ray diffraction pattern showed that the diffraction peak of SDF from kelp was not significantly different from that of the control group,indicating that the cooking process had no effect on its crystallization characteristics.The determination results of molecular weight and particle size distribution showed that the molecular weight and average particle size of SDF from kelp after atmospheric cooking and autoclaving were decreased.The molecular weight and average particle size of the SDF from kelp were increased after microwaving,and the dispersion coefficient and the difference of D_V10 and D_V90 showed that the molecular weight and particle size distribution of microwaving group were the most homogeneous.The scanning electron microscope?SEM?showed that three kinds of cooking technologies caused the fracture of SDF from kelp to varying degrees,and the structure was more loose,with the most obvious change after autoclaving.Infrared spectra showed that the main absorption peaks of SDF in the 400⁴000cm^-1 range had no significant changes after three kinds of cooking technologies,and all of them had characteristic absorption peaks of polysaccharides,indicating that there was not significant effect on the chemical functional groups of SDF from kelp in the cooking processes.4.The effects of cooking technologies on the physicochemical properties of SDF from kelp were measured.The results showed that the solubility and swelling power of the control group were 90.16%and 6.56 mL/g,respectively.The solubility of the atmospheric cooking?93.48%?was significantly improved,and the swelling power?6.74mL/g?had no obvious change.The solubility and swelling power?88.12%,5.67 mL/g?were significantly reduced after microwaving.But the solubility and swelling power of autoclaving?91.20%,6.67 mL/g?had no obvious change.The water holding capacity of SDF from kelp after atmospheric cooking,autoclaving and microwaving were 6.06 mL/g,5.97 mL/g and 5.72 mL/g,which were significantly lower than that of the control group?6.12 mL/g?.The three kinds of cooking technologies had no significant effect on the water binding capacity,fat absorption capacity and glucose adsorption capacity of SDF from kelp.Under the condition of simulated gastric fluid and simulated intestinal liquid,the ability of SDF from kelp to adsorb cholesterol after microwaving was 9.63mg/g and 12.33 mg/g respectively,which was significantly higher than that of the control group?8.43 mg/g,11.25 mg/g?.But there was no significant effect on the atmospheric cooking and autoclaving groups.Under the condition of simulated gastric fluid,the nitrite adsorption capacity of SDF from kelp after autoclaving and microwaving?35.46?mol/g,33.04?mol/g?was significantly lower than that of the control group?36.81?mol/g?,and there was no obvious change in the atmospheric cooking?36.49?mol/g?.Under the condition of simulated intestinal liquid,three kinds of cooking technologies had no significant influence on nitrite adsorption capacity of SDF from kelp.The cation exchange capacity of SDF from kelp was 0.76 mmol/g and 0.87 mmol/g respectively after autoclaving and microwaving,which was significantly higher than that in the control group,while the change of the atmospheric cooking group?0.70 mmol/g?was not obvious.5.The effects of cooking technologies on the antioxidant activity of SDF from kelp were measured.There was found that the three kinds of cooking technologies had different effects on the antioxidant activity of SDF from kelp.The scavenging ability of SDF from kelp to ABTS⁺,DPPH free radicals,superoxide radicals?24.78%,53.52%,36.30%?and the reducing capacity?0.3675?increased significantly after autoclaving,and the scavenging ability against hydroxyl radicals and the ability of the chelating ferrous ions?48.25%,23.14%?decreased significantly.The scavenging ability of ABTS⁺,DPPH free radicals,hydroxyl radicals and the chelating ferrous ions of SDF from kelp decreased significantly after atmospheric cooking and microwaving.