Improving and Characterizing the Nutritive Value of Feather Meal Using Rainbow Trout (Oncorhynchus mykiss) as a Biological Model: Insights into Determinants of Digestibility of Proteins

Feather meal (FeM) is a high-protein and cost-effective feed ingredient, made from the steam-hydrolysis of keratin waste products generated by the animal processing industry. Keratins are composed of ~90% indigestible protein highly cross-linked with disulphide bridges. Steam-hydrolysis promotes the disruption of disulphide, peptide, and hydrogen bonds, allowing peptides to become digestible and amino acids absorbable. The variability of the nutritional value of FeM is the result of the use of different raw materials and processing conditions during the production of this ingredient. Variations of heat processing conditions create disparities of disulphide conformers, D-amino acids, and cross-linked amino acids contents, and these affect the nutritional value of protein ingredients. Better understanding of the chemical interactions occurring during the processing of FeM would enable the development of methods to improve and estimate the nutritional value of this ingredient, which could assure the quality of FeM to feed stakeholders. FeMs were hydrolyzed using a novel enzymatic pre-treatment with the aim of better understanding the effects of peptide and disulphide bonds on the digestibility of amino acids and bioavailability of test amino acids (arginine) in this ingredient by rainbow trout. In a first study, a bench-scale trial was carried out to determine the potential of incubating FeM with sodium sulfite and proteases to cleave disulphide and peptide bonds, respectively. Subsequently, a pre-treatment to improve the nutritional value of FeMs was developed. In a second study, the bioavailability of arginine in two FeMs and in their pre-treated counterpart (PTFeM) were assessed through a growth trial using rainbow trout. In follow up studies, the apparent digestibility of amino acids in the same FeMs and PTFeMs were assessed in rainbow trout. The disulphide and cross-linked amino acid contents in the four ingredients were quantified in an attempt to determine the factors affecting their digestibility and bioavailability. Results from this thesis demonstrate that a simple treatment targeting the disruption of disulphide and peptide bonds effectively improves the bioavailability of arginine and the digestibility of amino acids in FeMs. Furthermore, this thesis gives insight on the effect of structural and chemical characteristics of protein on the nutritional value of FeM.