| A large number of byproducts such as crab shells and crab feet will be produced in the processing of the Portunus trituberculatus swimming crab,which includes the rich resource of protein and chitin.In this study,the effect of subcritial water temperature on the properties of swimming crab waste extracts(SCWE)was investigated,then using the swimming crab shell after treated by subcritical water to prepare chitosan.The research results will provide some theoretical guidance for the application of subcritical water in the resource utilization of swimming crab waste.Using the swimming crab waste as the raw material,the swimming crab waste extracts were prepared by subcritical water at the temperature of 140,170,200,230℃,respectively,the physical and chemical properties of SCWE were determined and compared.When the subcritical water temperature increased from 140℃ to 230℃,the contents of total sugar and ash in the SCWE decreased from 1.86%and 9.23%to 0.27%and 6.35%respectively,and the ratio of weight molecular distribution with 180-1000 u increased from 11.09%to 74.88%,while the protein content increased and then declined.Based on the result of amino acid analysis,there was no significant difference in the amino acid composition between the SCWE extracted by subcritical water at 140℃&170℃ when compared with swimming crab meat.However,the contents of aspartic acid,serine,threonine and arginine in the SCWE decreased when the subcritical water temperature further increased.With the increase of subcritical water temperature,the contents of both essential and non-essential amino acids decreased after increased,and the maximum value was founded at the subcritical water temperature of 200℃.The lysine content in the SCWE extracted at subcritical water irrespective of temperature was higher than that in the WHO/FAO model.An isoelectric point was observed in the protein of SCWE extracted at 140℃.Irrespective of pH,the protein solubility of SCWE extracted at 170℃ was higher than that of the other SCWE.The effects of deproteinization and deacetylation temperature on the physical and chemical properties of the chitosan of the swimming crab shell were studied.As a result,compared with chitosan prepared by the traditional method of deproteinization with sodium hydroxide,chitosan prepared by subcritical water treatment had high degree of deacetylation and low viscosity average molecular weight,but there was no significant difference in yield and ash content.Irrespective of the crab shell was treated with sodium hydroxide or subcritical water,the contents of yield,ash content and viscosity average molecular weight of chitosan had a tendency to decrease with the increase of deacetylation temperature,as well as the degree of deacetylation gradually increased.The chitosans prepared by sodium hydroxide and subcritical water treatment had similar fourier transform infrared spectroscopy patterns,and the glycosidic bonds of chitosan were β-configuration.According to the results of X-ray diffraction,scanning electron microscopy and differential scanning calorimetry,it was found that the crystallinity,surface morphology and the thermal stability between chitosan molecules were not affected by the deproteinization treatment.When the deacetylation temperature increased,the crystallinity between chitosan molecules greatly reduced,and the agglomerated floc on the surface of the chitosan disappeared and was replaced by a uniform,finely distributed mass,the thermal stability of chitosan increased.Furthermore,the results of thin layer chromatography showed that chitosan prepared by deproteinization on the swimming crab shell with the subcritical water was more easily decomposed by chitosanase than chitosan prepared by deproteinization of sodium hydroxide,and the higher the deacetylation temperature,the easier it is to be hydrolyzed.In conclusions,the SC WE amino acids extracted from subcritical water at 170℃ were not significantly damaged,and the protein solubility was the best.On the other hand,after extracting chitosan from crab shells treated with subcritical water at 170℃,not only the yield,ash content,crystallinity,thermal stability and surface morphology were not significantly different from those of the traditional sodium hydroxide deproteinization method,and it was easy to be hydrolyzed into chitooligosaccharide by chitosanase.Therefore,after pre-treatment of the swimming crab waste with subcritical water,not only recovered the protein for the production of crab flavoring,but also facilitated the preparation of chitosan and chitooligosaccharide,and promoted the resource utilization and green transformation of the swimming crab waste. |
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