Exploring the Functional Properties of Hydrolyzed Keratin: Filling the Knowledge Gap on Surface Active, Emulsifying, and Thickening Properties

Hydrolyzed keratin (HK) refers to any hydrolysate of keratin of a different origin derived by acid, alkali, enzymatic, or other methods of hydrolysis. HK is water soluble and has distinct chemical-physical properties compared to fibrous keratin. Although HK is employed across various technological sectors, there is a notable gap in the literature regarding the detailed chemical-physical properties of commercially available HKs. This study aims to address this gap by providing a thorough analysis of the surface-active, emulsifying, and thickening properties of three commercially available HKs. The results reveal relevant differences among HKs marketed under the International Nomenclature Cosmetic Ingredient (INCI) name "Hydrolyzed Keratin," with variations in their chemical-physical properties, primarily influenced by molecular weight. Specifically, HKs with a higher average <i>M</i> _w (>3000 Da) and protein content demonstrate enhanced emulsifying and thickening capabilities. Conversely, HKs with low <i>M</i> _w (<1000 Da) do not show surface-active properties suitable for the preparation of emulsions. Therefore, this study underscores the need for the standardization of commercially available HK products to obtain biomaterials with tailored and specific chemical-physical properties, enhancing their potential applications in cosmetic and pharmaceutical topical formulations.