Preparation Of Antarctic Krill (Euphausia Superba) Chitin By Microwave Optimization And Properties Of Chitosan

Antarctic krill is a small and shrimp-like invertebrate,which is also a high nutrient resource with huge biological reserves in the Antarctic ecosystem but it is mostly used as aquatic feed and has not been fully developed and utilized.Antarctic krill shells are rich of chitin,which is the second largest renewable organic matter after cellulose in nature so far.Chitin can be deacetylated to obtain chitosan with wide applications.Chitosan and its derivatives are nontoxic,adsorbable,biocompatible,and can be used in food,medicine,environment,materials and other fields.At present,the research scope of chitin and its derivatives in Antarctic krill is still at the level of chemical extraction and preliminary characterization,and there is no deep study on its performance,structure and application in the world.In this paper,firstly,the chitin in Antarctic krill was extracted by microwave optimization,and further deacetylation was carried out to obtain chitosan.Then,the physicochemical properties of chitosan were studied systematically,and the characterization of chitosan was carried out.Finally,the rheology and antibacterial application of chitosan in Antarctic krill were studied.This paper can be divided into the following three parts:(1)Preparation of Antarctic krill chitin by microwave optimization:the common extraction of chitin is mainly based on the waste shell of shrimp and crab by traditional acid-base method.In order to reduce material pollution and extraction time of traditional acid-base method,this chapter takes Antarctic krill as raw material and improves the technology on the basis of traditional acid-base method using microwave digestion method to extract chitin and optimizes the extraction process by single factor and orthogonal test,then compares the yield and preparation time of traditional method and microwave digestion method to extract chitin,and finally certifies safety of fluoride of microwave digestion method.The results of microwave optimization orthogonal test show that the optimal conditions of deproteinization process:microwave power 240 W,material liquid ratio 1:8,reaction time 8 min,Na OH concentration 5%;the optimal conditions of deashing process are microwave power 240 W,material-liquid ratio 1:20,reaction time 2 min,HCl concentration 6%.Under the optimum conditions,the protein removal rate and ash removal rate of chitin were 83.7%and 97.50%,respectively.The extraction rate of chitin by microwave optimization was 14.42±0.94%,and the extraction time was 5.33±0.15 h,which was better than that by traditional acid-base method:extraction time(11.68±1.21%),and the extraction time was 18.25±0.35 h.The chitin prepared by microwave optimization method has no fluorine residue.(2)Preparation and characterization of chitosan:chitosan is the simplest derivative of chitin,which is obtained by deacetylation of chitin.The source of chitosan is the same as chitin in industry,which is obtained from the discarded shell of shrimp and crab but the research of chitosan of Antarctic krill is few at present.In this paper,chitosan was prepared by deacetylation of Antarctic krill chitin with 50%Na OH(material-liquid ratio1:15)in 120?on electric plate for 8 h by concentrated alkali method which is most commonly used in industry.In order to verify the source specificity of Antarctic krill chitosan,the properties and characterization of Antarctic krill were compared with those of white shrimp(Penaeus vanname)and giant river prawn(Macrobrachium rosenbergii).The results showed that the yield of chitosan from Antarctic krill was the highest among all experimental shrimps;The results of degree of deacetylation of chitosan from white shrimp,giant river prawn and Antarctic krill were 78.7%,71.1%and 72.5%,respectively.The average molecular weight of viscosity of krill was the lowest(1109.3kda),but it has the highest ash content(0.45%).Scanning electron microscopy(SEM)showed that the surface of Antarctic krill chitosan was more uneven than other samples;FTIR and XRD showed that krill chitosan had similar chemical groups and crystallinity index with other samples of chitosan;DSC curve showed that krill chitosan had the similar endothermic peak and exothermic peak temperature of thermal decomposition with food-grade chitosan.(3)Study on rheology and antibacterial properties of chitosan:chitosan has better biological activity than chitin,and it is widely used in food.It can be used as food stabilizer,bacteriostatic agent,thickener and so on.In this chapter,we continue to study the properties and characterization of Antarctic krill,and further study the rheological and antibacterial applications of Antarctic krill chitosan.The self-made chitosan extracted from white shrimp and giant river prawn and food-grade chitosan were also compared with Antarctic krill chitosan.The chitosan was dissolved in 1%(w/_V)acetic acid aqueous solution to 0.5%solutions.The change of apparent viscosity of chitosan solution with shear rate as variable was studied,and change of modulus of chitosan solution with different frequency,strain,time and temperature was observed.The effect of chitosan solution on Escherichia coli and Staphylococcus aureus was verified by turbidity method with minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)to determine antibacterial activity.The results showed that white shrimp chitosan had lower viscosity and krill chitosan had lower modulus.Time and temperature have little effect on the modulus.In addition,MBC of all self-made chitosan is similar,but the antibacterial ability of krill chitosan is worse than that of other chitosans.At the same time,the antibacterial effect of gaint river prawn chitosan against Escherichia coli is the best and the antibacterial effect of all chitosan to Gram-negative bacteria is better than Gram-positive bacteria,and the antibacterial ability of all self-made chitosan is better than that of commercial chitosan.The research is beneficial to the development of high value-added products of Antarctic krill,aiming to improve the comprehensive utilization rate of Antarctic krill,expand the source range of chitin and chitosan,and provide new ideas for its application in food at the same time.