Extraction Of Crab Oil From Precocious Chinese Mitten Crab And Preparation And Characterization Of Emulsion Containing Crab Oil

Chinese mitten crab?Eriocheir sinensis?is an important economic aquatic species in China.However,in recent years,the proportion of one-year precocious crab has gradually increased.As a result of the small size and low value of precocious crab species,it is always a chronic problem to block the crab industry.In this paper,the hepatopancreas of precocious crab were used as raw materials for extracting the crab oil.Through spectroscopy and physicochemistry analysis,the difference between precocious and mature crab oil were studied.Using ultrasonication method,the crab oil nanoemulsion was prepared and characterized.Firstly,the effects of four different extraction methods?Folch,Soxhlet,two-step and enzyme-assisted extraction?on the yields,lipid class,fatty acid compositions,minor components??-carotene,cholesterol and?-tocopherol?and thiobarbituric acid reactive substances?TBARS?values of crab oil were measured.The yield of crab lipids extracted by Soxhlet with petroleum ether was the highest?43%?and the triacylglycerides were the main constituent?89%-97%?of the extracted crab lipids.The lipid extracted using enzyme-assisted extraction had higher?-carotene?50.76mg/100 g?and lower cholesterol content?1.03 mg/g?.Moreover,the TBARS values using Soxhlet and the enzyme-assisted method were significantly lower than the other two methods.The single factor experiment and orthogonal methodology were used to determine the optimum conditions for extraction of crab oil.The maximum yield was obtained when the temperature,pH,liquid-material ratio and enzyme concentration were 50?,7.0,3:1?mL/mg?,and 3400 U/g,respectively.The differences between precocious and mature crab oil were analyzed by spectroscopy?Fourier one-dimensional,two-dimensional mid-infrared and nuclear magnetic resonance?combined with gas chromatography.Fourier infrared and nuclear magnetic resonance imaging showed that the compositions and structures of precocious and mature crab oil were not differ much.Gas chromatography results showed that the main fatty acids in crab oil were palmitic acid,oleic acid and linoleic acid.Oleic acid was the most abundant fatty acid in precocious crab oil?3313.19 mg/kg?,significantly higher than?P<0.05?mature crab oil.The contents of eicosapentaenoic acid?EPA?and docosahexaenoic acid?DHA?in precocious crab oil were 253.59 mg/kg and 274.88mg/kg respectively,which were similar to those in mature crab oil.At the same time,the quantitative analysis of fatty acid by nuclear magnetic resonance spectroscopy showed similar results with gas chromatography method.To further understand the application value of precocious crab oil,physicochemical properties,fatty acid compositions,?-tocopherol and volatile compounds of precocious crab oil and four kinds of edible plant oils?peanut oil,soybean oil,corn oil,and sunflower seed oil?were compared.The results showed that the compositions of fatty acids in crab oil and peanut oil were similar,with oleic acid and linoleic acid as the main fatty acids.For physicochemical properties,the crab oil and other four edible oils had little difference.The iodine value and saponification value of crab oil were similar with sunflower seed oil,and the content of?-tocopherol in crab oil reached 765.17mg/kg.Through solid phase micro-extraction/gas chromatography/mass spectrometry?SPME/GC/MS?,33 kinds of compounds were detected in crab oil,mainly aldehydes and alcohols,etc.Crab oil had unique flavor components compared to other four kinds of edible oils,thus having the potential for development and application.In order to improve the stability of crab oil,the nanoemulsion of crab oil was prepared by ultrasonic emulsification.The effects of emulsifier,crab oil and water addition on the particle size of coarse emulsion were investigated by single factor experiments,and their contents in coarse emulsion were optimized by Box-Behnken experimental design.Furthermore,the nanoemulsion with an average particle diameter of 68 nm was obtained by ultrasonic emulsification.Compared with the coarse emulsion,the nanoemulsion showed better physical stability at different temperatures?20-100??,pH?3-9?and calcium ion concentration?100-500 mM CaCl₂?.After the digestion experiment in vitro,the releasing of fatty acids and the bioavailability of?-carotene of nanoemulsion were better than those of coarse emulsion.The ultrasonic dispersion method could improve the stability of crab oil as an additive in food system,and may have wide application prospects.