Collagen, gelatin’s parent molecule, is a fibrous protein found abundantly in all
multicellular animals, as the main component of their connective tissues (Swatschek
et al. 2 002; Zhou and Regenstein 2007; Boran et al. 2010; Zhu et al. 2010). The
molecular weight of the collagen molecule is around 330 kDa. Gelatin is the colla-
gen fraction after heat hydrolysis that exceeds an arbitrary minimum molecular
weight of 30 kDa (Boran et al. 2010). To date, 27 variants of collagen have been
identified (Gómez-Guillén et al. 2011 ). According to the nature of their aggregated
forms or their morphological differences, the majority of collagens can be divided
into four major groups: thick striated fibers, non-fibrous networks collagen, non-
striated filamentous collagen, and fibril-associated collagen. These collagen mole-
cules consist of closely related but genetically distinct proteins, possessing a basic
structure of three polypeptide chains, each with a glycine-X-Y repeat (where X is
mostly proline and Y is mostly hydroxyproline), forming tightly bound triple heli-
ces (mainly stabilized by intra- and interchain hydrogen bonding), which subse-
quently aggregate to form various types of supporting structures (Bailey et al. 1998;
Gómez-Guillén et al. 2011 ). Although there are some differences in the amino acid
composition of collagens derived from different sources, the composition of collagen encompasses all 20 amino acids (Gómez-Guillén et al. 2002). The amino acid composition of gelatin is closer to that of its precursor gelatin (Karim and Bhat 2009 ). The molecular structure of gelatin is shown in Fig. 23.1 .
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