It is neutralized with salts or gypsum which may result in a product with a high salt content. Acid hydrolysisĪcid hydrolysis of keratin can be done with hydrochloric acid (HCl) or sulphuric acid (1% hydrochloric acid solution, sodium thioglycolate). However, it was suggested that sulfur content and bulk density (respectively positively and negatively correlated to nutritive value in poultry) should be used to monitor feather meal quality as there was no indication that high pressure was detrimental to feather meal quality ( Moritz et al., 2001). Increasing steam pressures of 204, 276 or 345 kPa during 30 min, at pH 5.7 or 9, have resulted in increasing pepsin digestibility but also in a lower cystine content of feather meal ( Latshaw, 1990). Feathers are first cooked under steam pressure (for instance for 30-40 min at 143 ☌ under 3 atm) and then dried (90-110☌ for 5 h) ( Strzetelski et al., 1999). Pressurized cooking is the primary method of processing used to make feather meal. A unfavourable effect of thermal and chemical methods of keratin hydrolysis is the destruction of some amino acids, including cystine ( Papadopoulos, 1985 Papadopoulos et al., 1986). There are several ways to hydrolyze feather keratin and many patents have been registered. Variability of feather meal between batches and between plants can be quite high due to differences in processes. All feather meals produced within the EU are reported to be hydrolized ( Crawshaw, 2019). Hydrolized feathers are then dried to 8% moisture and ground to produce a valuable uniform hydrolized feather meal. A thorough hydrolysis under controlled conditions (see processes below) destroys disulphur bonds between amino acids and convert feathers into hydrolized feathers. While this makes raw feathers light, durable, and unable to stretch (unlike hair), it also makes feather keratin undigestible (digestibility < 5%) ( Papadopoulos, 1985 Kornillowicz-Kowalska et al., 2011).įor that reason, it is necessary to hydrolyze feather meal in order to transform it into a valuable source of protein in animal feeding ( El Boushy et al., 1990 Papadopoulos, 1985). This highly polymerized protein contains about 8% cysteine, a sulphur amino acid that makes strong disulphur bonds between each other within the primary structure and contributes to the folding of the chain into secondary structures (alpha-helix and beta-sheet in a ratio of 2:1). Another issue is that keratin, the main component (80-100%) of feather proteins, is poorly digestible when raw ( Moran et al., 1967). Feathers represent 3-7% weight of the live bird, therefore producing a considerable mass of protein ( Soni et al., 2017 Collins et al., 2014).įeather meal is a protein source of poor quality because its protein is deficient in amino acids that essential in many livestock species, notably lysine, methionine, histidine and tryptophan ( Crawshaw, 2019 Baker et al., 1981). Feathers are a byproduct of broiler, turkey and and other poultry processing operations. Feather meal is used as a source of protein for farm animals and as a fertilizer. Feather meal results from the processing of the feathers obtained after poultry slaughtering.
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