Protein preparations, water binding

Figure 2. Water binding (grams of unfrozen water/gram of solids) by soy protein preparations, each containing 1 g of water/g of solids, as a function of protein content, where % protein (on a solids basis) = % N X 6.25 (O) soy protein isolate B (9) soy protein concentrate (/ ) soy flour (defatted) fCJl carbohydrate-enriched fraction of soy concentrate f32j.

Despite some conflicting evidence (Kinsella and Fox, 1986), it appears that denaturation has little influence on the amount of water bound by whey proteins. However, other factors which may accompany denaturation (e.g. Maillard browning, association or aggregation of proteins) may alter protein sorption behaviour. Drying technique affects the water sorption characteristics of WPC. Freeze-dried and spray-dried WPC preparations bind more water at the monolayer level than do roller-, air- or vacuum-dried samples, apparently due to larger surface areas in the former. As discussed above, temperature also influences water sorption by whey protein preparations. The sorption isotherm for /Mactoglobulin is typical of many globular proteins. 

Water-binding agents. Preparations of protein hydrolysates containing amino acids and peptides obtained from marine raw material, particularly fish fractions, presently represent a very interesting area of research. As with the above-mentioned extracts, these preparations may find use in foods, particularly seafoods, because of their typical fish or shellfish taste. In addition, the peptides may have special effects when added to frozen fish, retaining some of the muscle juiciness and perhaps also yielding a better taste characteristic of the frozen fish. 

Hydrazide groups can react with carbonyl groups to form stable hydrazone linkages. Derivatives of proteins formed from the reaction of their carboxylate side chains with adipic acid dihydrazide (Chapter 4, Section 8.1) and the water-soluble carbodiimide EDC (Chapter 3, Section 1.1) create activated proteins that can covalently bind to formyl residues. Hydrazide-modified enzymes prepared in this manner can bind specifically to aldehyde groups formed by mild periodate oxidation of carbohydrates (Chapter 1, Section 4.4). These reagents can be used in assay systems to detect or measure glycoproteins in cells, tissue sections, or blots (Gershoni et al., 1985). 

---