Publisher Summary


Phospholipids (PLs) are major components of biological membranes and important biochemical intermediates in cell growth and function in both plants and animals. PLs are primarily of vegetable origin (vegetable lecithins) from commercially produced oilseeds such as soybeans, sunflower seeds and canola (rapeseed) and are used in food matrices for their emulsifying and widely used structure-enhancing properties.

 In biochemistry and medicine,

 lecithin is specifically referred to as sn-3-phosphatidylcholine. In this chapter, lecithin is described as a mixture of PLs containing glycolipids and oils. Vegetable lecithins are mainly composed of phosphatidylcholine (PC), phosphatidylthanolamine (PE), phosphatidylinositol (PI), phosphatidic acid (PA), small amounts of lyso-phosphatidylcholine (LPC) and other glycerin contains PL. Animal lecithins are derived from eggs, dairy and marine animals, including curls. Due to their superficial functional properties, PLs are used as emulsifiers in food and in pharmaceutical, cosmetic, animal feed and technical applications. PLs also have nutritional functions as they contain organic binding choline, inositol and fatty acids. Both vegetable and animal lecithin are gaining interest due to their nutritional and technical properties. The chapter summarizes the current state of industrial knowledge on the production and use of natural phospholipids and focuses on the production of rapeseed and egg lecithin.

5.5.2 Collagen protein

Collagen can be obtained from animal skins, hides, bone extracts, offal meats, and skeletal muscle. The native collagen tissue of animal carcasses is of little use in food. However, through denaturation followed by partial hydrolysis, collagen can be converted into a highly functional protein ingredient known as gelatin. Gelatin derived from young collagen, such as the skin of pigs, chicken and some fish, is called "type A gelatin" and is suitable for a wide range of food applications. A mild acid treatment is generally sufficient to extract the gelatin from the collagen material. In contrast, gelatin extracted from mature (highly cross-linked) collagen sources such as cattle hides, bones and cartilage is called "type B gelatin" and has limited use in food but more so in non-food applications. This type of gelatin requires more vigorous treatments for solubility, for example, pre-treated in an alkali-lime solution for a few days. Type A gelatin has a high isoelectric point (pH 6–9) and thus has a net positive charge in most food uses, while type B gelatin has an isoelectric point near pH 5.0 and therefore has a net positive or negative charge depending on the acidity of the food (Stainsby, 1987). Chemically, skin contains a mixture of type I and III collagen, whereas bone and cartilage have a preponderance of type I and III collagen, respectively (Weiss, 1984).

The relative independence of pH (4–9) 

for gelation makes gelatin particularly useful for a wide range of applications. However, the largest single application of gelatin in foods is cold desserts due to the protein's unique cold gelation and melt-in-your-mouth property. A typical gelation process will involve heating the gelatin solution past its denaturation point and then rapidly cooling it to allow renaturation and interaction of the gelatin molecules to form a protein gel matrix. Because hydrogen bonds are the predominant force stabilizing the gel and no interpeptide covalent bonds are present, gelatin gel is thermoreversible and melts readily at body temperature. The rapid setting of the gel is essential for the immobilization and uniform distribution of fruit pieces and other particles in the gel matrix. Gelatin is also used in frozen dairy products, such as frozen desserts, to inhibit ice crystal growth and recrystallization (graininess) as well as lactose recrystallization (gritiness) during frozen storage (Jones, 1977). In baking, gelatin is used in soft candies, such as Gummy Bears, to stabilize sucrose, corn syrup, and other ingredients through its gelling property.

In meat products, collagen is used to make edible casings

 and as an ingredient in sausage products to increase the protein content of the product. In the case of skeletal muscle collagen, it is concentrated by mechanical denervation or partial degreasing by a low-temperature extraction process. Collagen added to emulsified meats, such as turkey and beef franks, improves the emulsion stability of raw meat. However, upon cooking, significant product shrinkage may occur due to loss of water and collapse of emulsified fat droplets, resulting in increased meat toughness (Gillett, 1987). This is because collagen denaturation and consequent abrupt shrinkage occur around the final cooking temperature (65–75°C) (Davey and Gilbert, 1974), disrupting the fat globule membrane (where collagen serves as a constituent) as well as the gel. matrix made of suspended myosin and collagen fibrils.

To improve the functional performance of collagen in muscle foods,

 native collagen has been treated to increase its solubility and eliminate cooking-induced shrinkage. Heat-predenatured collagen, when added at a level of no more than 10% of product weight, was found to improve bond strength and juiciness in restructured low-fat, low-salt beef (Kenney et al. ., 1992). Recent industrial developments include low-temperature processing to produce gelatin-rich proteins. Raw collagen extracted from pork trimmings and poultry skins (chicken and turkey) can form a firm, elastic cold-setting gel when formulated into emulsified muscle foods. The gel serves as a matrix to trap fat and immobilize water, as well as to adhere part