**2. Characteristics of jumbo squid as fishery**

20 Recent Advances in Plasticizers

where X and Y are often proline and hydroxyproline. Each collagen type varies in the length of

Collagen *per se* is regarded as one of the most useful biomaterials. The excellent biocompatibility and safety due to its biological characteristics, such as biodegradability and weak antigenicity, have made collagen one of the primary resources in medical applications. In addition, other uses include gelatin production, nutritional supplements, sausage casings, and in cosmetic products it claims anti-ageing benefits (Kim & Mendis, 2006; Lee et al., 2001). Recently, the use of fish collagen in the manufacture of biopolymer films has been reported. Collagens from different species of fish have been extracted using acetic acid, which were used later to produce biodegradable films (Venugopal, 2009). Studies on the production and characterization of films using fish gelatins are quite recent, and all fish gelatins have been observed to exhibit good film-forming properties, yielding transparent, nearly colorless, water soluble, and highly extensible films (Avena-Bustillos et al., 2006; Benjakul et al., 2006;

On the other hand, chitosan is a polysaccharide that is produced by deacetylation of naturally occurring chitin, and it has a great potential for a wide range of applications due to its versatile properties, such as in food and nutrition, biotechnology, material science, drugs and pharmaceuticals, agriculture and environmental protection, and recently in gen therapy as well (Venugopal, 2009; Dutta et al., 2009; Shahidi et al., 1999; Shahidi et al., 2002). Nonetheless, pure chitosan, as a film material, does not form films with adequate mechanical properties due to its low percentage of elongation (Butler et al., 1996). For this reason, one of the current trends in designing biodegradable materials for packaging is to combine different biopolymers (Bawa et al., 2003; Bertan et al., 2005; Colla et al., 2006; Le-Tien et al., 2004; Lee et al., 2004; O'Sullivan et al., 2005; Tapia-Blacido et al., 2007; Yu et al., 2006).

Chitin and chitosan belong to a group of natural polymers produced by the shells of crab, shrimp, and lobster. In addition to be nontoxic, chitin and chitosan are inexpensive, biodegradable, and biocompatible. Regarding to film-forming properties, chitosan is more versatile as compared to its precursor chitin. Chitosan has the capacity to form semipermeable coatings which, when used in foods, prolong their shelf life by acting as

Furthermore, since collagen in acid solution exhibited positively charged groups, it has a molecular interaction with chitosan with high potential to produce biocomposites (Liang et al., 2005; Lima et al., 2006; Sionkowska et al., 2006; Wang et al., 2005; Wess et al., 2004),

In the first part of this chapter, the most important characteristics of jumbo squid as fishery, as well as the most recent scientific literature dealing with chitosan and collagen films made from seafood by-products, are reviewed. In the second part, thermal, mechanical and morphological properties of chitosan and acid soluble collagen (ASC) produced by casting films are discussed. As-cast films dried in relation to the molecular interaction of ASC by using differential scanning calorimetry (DSC), scanning electron microscope (SEM), and infrared spectroscopy are also discussed in this chapter. Thermal properties by DSC, SEM images, mechanical properties, water vapor barrier properties, and water solubility characteristics of the chitosan/ASC blends are analyzed as a function of ASC content in

the helix and the nature and size of the non-helical portions (Lee, C. R. et al., 2001).

Carvalho et al., 2008; Gomez-Guillen et al., 2007; Zhang et al., 2007).

barriers against air and moisture (Agulló et al., 2004).

terms of the individual properties of chitosan and ASC.

acting as a possible plasticizer agent.

Squid or calamari are cephalopods which comprises a group around 300 species, being the jumbo squid or *Dosidicus gigas* one of them (Figure 1). Jumbo squid is a member of the flying squid family, Ommastrephidae (Nesis, 1985), and are known to eject themselves out of the water to avoid predators. Jumbo squid are the largest known mollusks and the most abundant of the nektonic squid. They can reach up to 2 m in length and weigh up to 45 kg. This specie is characterized by its large, tough, thick-walled mantle and long tentacles. These organisms are aggressive predators. Jumbo squid earned the nickname of "red devils" because of their red hue when hooked, which they use to camouflage from predators in deep waters where most animals cannot see the red color. This coloration is due, like other cephalopods, to the presence of chromatophores. Also, squid possess the ability to squirt ink as a defense mechanism (Nigmatullin et al., 2001).

Fig. 1. Jumbo squid (*Dosidicus gigas*).

Jumbo squid is an endemic species to the Eastern Pacific, ranging from northern California to southern Chile and to 140 degrees W at the equator. Exploratory commercial fishing for *Dosidicus gigas* began in the 1970s off the Pacific coast of America. The catches of this fishery increased from 14 tons per year in 1974 to over 250,000 tons in 2005. Since then, it has become an extremely important fisheries resource in the Gulf of California, Costa Rica Dome and Peru (Marakadi et al., 2005).

The commercial fishery of jumbo squid consists of a multinational jigging fleet, which fish at night using powerful lights to attract squid (Waluda et al., 2004). The caught of this organism depends of the season and the region. In the Gulf of California for example, this organism enter to the Gulf from the Pacific in January, to reach their northernmost limit by April, and to remain in the central Gulf from May through August; the highest aggregations of specimens are found along the western (Baja California) coast. From September squids appear to migrate onward the eastward to the Mexican mainland coast and then southwards, to the Gulf back into the Pacific (Ehrhardt et al., 1983). Whereas, in Peruvian waters the highest squid concentrations occur along the coast of northern Peru, from Puerto Pizarro to Chimbote, with low to medium squid concentrations off Pisco and Atico. The highest catches occur during autumn, winter, and spring, since squid tend to be dispersed in summer (Taipe et al., 2001).

Although the growth of this fishery has been spectacular, great contrasts have characterized it. Of the total catch, a major portion remains unused or minimally used. In Mexico for instance, no more than 11% of the resource is used for human consumption, regardless of its low price and high nutritional value (De la Cruz et al., 2007). Moreover, only the mantle

By-Products From Jumbo Squid (*Dosidicus gigas*): A New Source of Collagen Bio-Plasticizer? 23

The most abundant and widespread family of collagens, it is represented by the fibril-forming collagens, especially types I, III and V (Sato et al., 1989). Their basic structure consists of three protein chains that are supercoiled around a central axis in a right-handed manner to form a triple helix, called tropocollagen, which is a cylindrical protein of about 280 nm in length and 1.5 nm in diameter. Each chain, called α chain, contains about 1000 amino acids and it has a molecular weight of 100 kDa, depending on the source. Tropocollagen molecules may be formed by three identical chains (homotrimers) as in collagens II and III, or by two or more

The three α chains are perfectly intertwined throughout the tropocollagen molecule to form the tripe helix except for the ends, where helical behavior is lost, since in these regions, called telopeptides, globular proteins that are involved with intermolecular crosslinking with other adjacent molecules are found (Engel & Bachinger, 2005). A structural prerequisite for the assembly of a continuous triple helix, the most typical conformation of collagen, is that every third position along the polypeptide chain is occupied by a glycine residue. Being glycine the smallest amino acid and lacking of a side chain, the collagen α chains can coil so tightly because glycine can be easily accommodated in the middle of a steric smooth superhelix and form stable packed structures; this would be very difficult with the bulkier residues. Further stabilization of the triple helix is attained by the formation of hydrogen bonds that are formed between the amino groups of glycine residues and the

The structural constraints that make the collagen triple helix unique among proteins are given by its unusual amino acid content. Besides glycine as the major residue, a repeated sequence that characterizes the collagenous domains of all collagens is the triplet (Gly-X-Y), where X and Y are often proline and hydroxiproline, respectively (Figure 2). Depending on the collagen type, specific proline and lysine residues are modified by post-translational enzymatic hydroxylation. These imino acids permit the sharp twisting of the collagen helix and are associated with the stability and thermal behavior of the triple helical conformation.

The main sources of industrial collagen are limited to the skin and bones of pigs and cattle. However, as a possible alternative to the problems associate to transmissible bovine

different chains (heterotrimers) as in collagen types I, IV, and V.

carbonyl groups of residues from other chains.

Source: Branden & Tooze, 1999; Voet & Voet, 1995.

**3.1 Sources and extraction** 

Fig. 2. Spatial conformation of a typical tropocollagen molecule.

(42%) is usually used, which is later primarily marketed fresh, frozen or pre-cooked (Luna-Raya et al., 2006). Some of the by-products produced after filleting, like fins and heads, are utilized but huge amounts are wasted. Fortunately, a number of studies have reported that this waste is an excellent raw material to obtain important by-products with high commercial value, such as collagen (Gómez-Guillen et al., 2002; Kim et al., 2005, Shahidi, 2006; Torres-Arreola et al., 2008; Gimenez et al., 2009).
