|
Shrimp head, a by-product produced during the processing of shrimp products, such as headless shell-on shrimp (HLSO) and peeled prawns (PUD), containing abundant chitin, is ideal for the production of chitin or chitosan. However, it’s often discarded right now, not yet fully utilized. There are still many problems in the traditional method of preparing chitin or chitosan because of the big acid-base use, like high cost, serious apparatus corrosion, environmental pollution, large wastage of protein, inferior product quality, complex operation and long producing cycle.In this thesis, the optimum conditions of improved preparation technology for chitin and chitosan from Litopenaeus vannamei head by autolysis method, chelation of EDTA·Na2 for calcium and deacetylation in ethanol-sodium hydroxide system under ultrasonic wave pretreatment were studied. This improved technology, with the much less use of acid-alkali and mild reaction conditions, could solve forementioned problems which were common in traditional technology. Then the structure characterization and characteristic analysis of chitins and chitosans were conducted with the combination of physicochemical method and instrumental method. Finally, scale-up of the improved preparation technology for chitin was studied, expecting to provide theory foundation for the industrial production.On the basis of results of single factor experiments, the effects of the factors, i.e. the concentration of EDTA·Na2, the reaction time and the pH value, on the decalcification rate were investigated according to decalcification rate by Box-Behnken central composite design and response surface methodology. Then this improved process was compared with traditional one with the nitrogen and ash content of product, product yield as criteria. The results showed that the optimum parameters of decalcification process with EDTA·Na2 as chelant were as follows: concentration of EDTA·Na2 9 % (w/v), reaction time 2.5 h, pH 8.00. On the above conditions, the decalcification rate was up to 99.56±0.06 %. The product yields of chitin prepared by improved process and the one prepared by traditional process were 17.56±0.13 % and 11.26±0.15 %, respectively. Both accorded with the SC/T 3403-2004 level of food-grade chitin.The effects of factors, namely the concentration of ethanol, the concentration of sodium hydroxide, the reaction time and the ultrasonic wave pretreatment time, on the deacetylation degree (D.D.) were explored by single factor experiments according to D.D. And then the conditions of deacetylation process were optimized by the orthogonal experiments based on the preceding results. After that, this improved process was compared with traditional one with D.D. and product yield as criteria.The results indicated that the optimal parameters of deacetylation process were ultrasonic wave pretreatment time of 3 h, concentration of ethanol of 55 % (w/wtotal), concentration of sodium hydroxide of 28 %(w/wtotal), reaction time of 8 h. On the above conditions, solubility of chitin was 1 %, and D.D. of chitosan was 88.00±0.06 %. Chitosan prepared by improved process, D.D. of which was slightly lower, and chitosan prepared by traditional process both accorded with the SC/T 3403-2004 level of industrial grade chitosan; the product yields were 27.88±0.08 % and 7.94±0.11 %, respectively.The structure of chitins and chitosans prepared by different technologies was characterized by Fourier transform infrared (FT-IR) spectrometry, powder X-ray diffraction (XRD) spectrometry, thermogravimetry (TG) and thermal field emission scanning electron microscope (TFESEM) observation. And the characteristics of products, i.e. viscosity and relative molecular weight, were also determined. The results revealed that four kinds of products wereαanomer, and there was no change in their structure. But chitin prepared by improved technology has partly deacetylated, which was beneficial to its preparation for chitosan. Chitins, with more intermolecular/ intramolecular hydrogen bonds and more regular molecular arrangement than chitosans, showed better crystalinity and thermostability. Both two kinds of chitins presented the typical organizational structure, i.e. the out surface was net vein characteristics, while the inner surface assumed the shape of honeycomb. The result of deproteinization in improved technology, in which calcium could be partly removed, was second to that in traditional technology. Chitin prepared by improved technology, keeping natural structure considerably under the mild conditions, showed better crystalinity and thermostability, the relative molecular weight of which was (74.24±0.16)×10~4, larger than that {(9.4958±0.18)×10~4} of chitin prepared by traditional technology. Comparing with chitins, the amido bonds in chitosans decreased remarkably, so the D.D. of theirs rised correspondingly. The higher D.D. of chitosan is, the better its crystalinity and thermostability are. Therefore, chitosan with slightly higher D.D. prepared by traditional technology showed better crystalinity and thermostability. But its viscosity and relative molecular weight were 68.40±0.04 mPa·s, (7.5312±0.17)×10~4 respectively, being lower as result of kickbackrevulsion, which would contribute to hydrolysis of more glucosidic bonds. Thus application of it would be limitated. Accordingly, the viscosity and relative molecular weight of chitosan prepared by improved technology were 152.50±0.07 mPa·s, (58.88±0.09)×10~4, respectively.At last, scale-up of the improved preparation technology for chitin, the magnification of which was 100, was investigated. And then, material balance and cost estimating were carried out. Following that, FT-IR spectra and primary components of product were analyzed. The results indicated that this scale-up technology was feasible, with the extraction percent up to 99 % and cost price equivalent to 33023 yuan per ton; the product with typical structure ofα-chitin accorded with the SC/T 3403-2004 level of food-grade chitin.
|