Of crab shell

Two hundred grams of eleaned and dried crab shells (Note 1) ground to a fine powder is placed in a 2-1. beaker, and an excess of dilute (approximately 6 N) commercial hydrochloric acid is added slowly to the powdered material until no further action is evident. Much frothing occurs during the addition of the acid, and care must be exercised to avoid loss of material due to foaming over the sides of the beaker. After the reaction has subsided, the reaction mixture is allowed to stand from 4 to 6 hours to ensure complete removal of calcium carbonate. The residue is then filtered, washed with water until neutral to litmus, and dried in an oven at 50-60°. The weight of dried chitin is usually about 70 g., but with some lots of crab shells it may be as low as 40 g. 

The hard outer skeleton of insects and shellfish contains chitin, a polymer very like cellulose but made of acetyl glucosamine instead of glucose itself. It coils up in a similar way and provides the toughness of crab shells and beetle cases. 

After cellulose, it is the second most abundant natural polymer found in the nature. Figure 8.9 shows the exoskeleton structure of crab shells, where chitin was derived. Chitin can also be synthesized artificially through chitinase-catalyzed polymerization of a chitobiose oxazoline derivative. Chitosan, a very important derivative of chitin, is obtained... 

In bacterial fermentation for chitin and chitosan production, the most often applied strains are Lactobacillus sp., Bacillus sp., Pseudomonas sp and S. marcescens. The microbial DP process is little efficient, ranging between 50% and 85% DP rate depending on materials, used microorganism, fermentation type, and time. Rao et al. (2000) cultured shrimp biowaste with L. plantarum and achieved 75% DP. Bautista et al. (2001) achieved 81.5% DP from crayfish using Lactobacillus pentosus 4023. Fermentation of crab shell wastes with 10% S. marcescens FS-3 inoculum resulted in DP of 84% and DM of 47% at 7 days culture (Jo et al. 2008). Squid pen for the preparation of P-chitin were deproteinized by 73% for 3 days with Bacillus sp. TKU004 (Wang et al. 2006). Also, the shrimp shells were deproteinized by 75% and 87% at 30°C for 6 days with Candida parapsilosis and Pseudomonas maltophilia, respectively (Chen 2001). 

Jo, G. H., Jung, W. J., Kuk, J. H. et al. 2008. Screening of protease-producing Serratia marcescens FS-3 and its application to deproteinization of crab shell waste for chitin extraction. Carbohydr. Polym. 74 504—508. 

Polysaccharides are natural polymers that are highly diverse and used widely as they are or after modification in the biomedical and pharmaceutical fields. Among the polysaccharides, cellulose is the most abundant, as it represents about one-third of all plant matter. Cellulose fibres have been used for centuries without major modification, but for many uses cellulose has been chemically modified to be easily manufactured. Chitin, the major constituent of crab shells, is probably the second most abundant polysaccharide. Before being used, chitin has to be de-acetylated, resulting in chitosan, as shown in Figure 3.11. Chitin de-acetylated over 70% is water-soluble. 

Nanometric monocrystals of chitin, commonly referred to as whiskers, are prepared by acid hydrolysis of chitin obtained from various sources such as squid pen chitin, riftia tubes, crab shells and shrimp shells. The surface of crab shell whiskers was chemically modified with alkenyl succinic anhydride (ASA) and phenyl isocyanate (PI). TEM images in Figure 14.3 show that after surface chemical modification the chitin fragments seem to be entangled, and individual whiskers are difficult to observe. 

As shown in Table 2, the xerogels prepared by these methods were hydrolyzed at almost the same rate by hen egg-white lysozyme, and the rate was about 6 times higher than that of crab shell chitin. The hydrolysis rate by lysozyme was slightly inhibited by the presence of 0-acetyl group in chitin xerogel, probably because of the steric hindrance of the 0-acetyl group at Ce for forming an enzyme substrate complex. The increase in the rate of enzymic hydrolysis also proves the formation of the same chitin gel by three independent methods. 

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