3. Extraction, Purification, and Modification of Natural Polymers

Natural polymers gelatine, chitin, chitosan, cellulose, starch, and pectin are reviewed here with focus on their extraction methods, looking at how they are purified and the extent of modifications in their extraction and utilization. Various techniques exist for the extraction of these polymers from their natural sources which are mainly plants, insects, or fish. Within the chapter the acid and the alkaline processes usually used to extract gelatine are discussed. The gelatin prepared by the acid process is called type A gelatin, whereas that prepared by the alkaline process is called type B gelatine. Sorghum and melon bugs provide an alternative source acceptable for Halal products and serve as an alternative for markets concerned about bovine spongiform encephalopathy (BSE). Chitin extraction involves demineralization and deproteinization steps, which can be conducted by chemical or biological method. The chemical extraction requires the use of acids and bases, while the biological method involves microorganisms. Chitosan is synthesized by deacetylation of chitin using sodium hydroxide to remove the proteins in the source followed by demineralization to remove the carbon and other salts present in crude form. These and others are discussed within the chapter.