Abstract
BackgroundAfter cellulose and starch, chitin is the third-most abundant biopolymer on earth. Chitin or its deacetylated derivative chitosan is a valuable product with a number of applications. It is one of the main components of shrimp shells, a waste product of the fish industry. To obtain chitin from Penaeus monodon, wet and dried shrimp shells were deproteinated with two specifically enriched proteolytic cultures M1 and M2 and decalcified by in-situ lactic acid forming microorganisms. The viscosity of biologically processed chitin was compared with chemically processed chitin. The former was further investigated for purity, structure and elemental composition by several microscopic techniques and 13C solid state NMR spectroscopy.ResultsAbout 95% of the protein of wet shrimp shells was removed by proteolytic enrichment culture M2 in 68 h. Subsequent decalcification by lactic acid bacteria (LAB) took 48 h. Deproteination of the same amount of dried shrimps that contained a 3 × higher solid content by the same culture was a little bit faster and was finished after 140 h. The viscosity of chitin was in the order of chemically processed chitin > bioprocessed chitin > commercially available chitin. Results revealed changes in fine structure and chemical composition of the epi-, exo- and endocuticle of chitin from shrimp shells during microbial deproteination and demineralization. From transmission electron microscopy (TEM) overlays and electron energy loss spectroscopy (EELS) analysis, it was found that most protein was present in the exocuticle, whereas most chitin was present in the endocuticle. The calcium content was higher in the endocuticle than in the exocuticle.13C solid state NMR spectra of different chitin confirmed < 3% impurities in the final product.ConclusionsBioprocessing of shrimp shell waste resulted in a chitin with high purity. Its viscosity was higher than that of commercially available chitin but lower than that of chemically prepared chitin in our lab. Nevertheless, the biologically processed chitin is a promising alternative for less viscous commercially available chitin. Highly viscous chitin could be generated by our chemical method. Comprehensive structural analyses revealed the distribution of the protein and Ca matrix within the shrimp shell cuticle which might be helpful in developing shrimp waste processing techniques.
Highlights
After cellulose and starch, chitin is the third-most abundant biopolymer on earth
Deproteination of wet and dried shrimp shells with enrichment cultures M1 and Enrichment culture and enrichment culture 2 (M2) To elucidate whether there exist relevant differences for deproteination of wet or dried P. monodon shells, protein and calcium elimination from the respective abdomen fractions with the proteolytic enrichment cultures M1 and M2 were compared (Figure 1a and b)
The proteolytic culture M2 was the more efficient of the two enrichment cultures that were used for deproteination of both wet and dried shrimp shells
Summary
Chitin is the third-most abundant biopolymer on earth. Chitin or its deacetylated derivative chitosan is a valuable product with a number of applications. It is one of the main components of shrimp shells, a waste product of the fish industry. The viscosity of biologically processed chitin was compared with chemically processed chitin. Besides cellulose and starch chitin is one of the most common biopolymers on earth. The rapid increase of the human population on earth and the resulting rising demand for raw materials requires the recycling of biological waste fractions to upgrade the major components, such as lignin, starch, cellulose or chitin. If purified from crustaceans or fungi, highly polymeric chitin or chitosan would be available in sufficient amounts for future uses
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