Some chemical and nutritional properties of feather protein isolates containing varying half-cystine levels.

Abstract

Feather (keratinous) protein isolates containing 2.8 and 7.2% half-cystine were prepared. Solubility of the former increased to 100% between pH 6 and 12, whereas, that of the latter reached only 2.5% at pH 12. Tests showed that mixtures of sodium dodecyl sulfate and 2-mercaptoethanol were needed to completely solubilize the high half-cystine protein, and that sodium dodecyl sulfate alone or in combination with urea and/or 2-mercaptoethanol increased solubilization of the low half-cystine product. The rates of these reactions are further increased by heat. Dry heat denatured the low half-cystine isolate more readily than the high half-cystine product; moist heat denatured both at a similar rate. Gel electrophoretic properties were unique for each keratinous product. Only the low half-cystine isolate ahd desirable functional properties in that it formed thick, viscous mayonnaise-like emulsions and desirable foams. Functional properties of this isolate were improved dramatically by adjusting the pH from 5.0 to 8.2 or by a two-step change from pH 5.0 to 4.0 to 8.2. Apparent nitrogen digestibility of the two keratinous isolates was greater than 90% as measured by rat growth and by pepsin-HCl digestion.