Comparison of four feed proteases for improvement of nutritive value of poultry feather meal

Feed industries are seeking new ways to cope with increased raw material costs, and one approach is to apply enzymatic treatment in the production of feed ingredients from animal by-products. Keratinases, a group of proteases, are capable of hydrolyzing keratin-rich material and have been applied in the production of cost-effective feather by-products for use as feed and fertilizers. The current study examined 4 commercial feed proteases from Bacillus subtilis, Bacillus licheniformis PWD-1, Aspergillus niger, and Serratia proteamaculans HY-3 used to hydrolyze chicken feather under different conditions. The degree of keratinolysis was monitored by measuring the release of NH(2) groups using o-phthalaldehyde (OPA) and by scanning electron microscopy. All 4 feed proteases were able to degrade feather at pH 5.5 and 7.0. The degree of hydrolysis was stimulated by the addition of reducing reagents such as dithiothreitol (DTT) and Na(2)SO(3). In general, the protease from B. subtilis was more efficient in degrading feather keratin compared to the other 3 feed proteases at both pH 5.5 and 7.0. For commercial production, the application of protease from B. subtilis is even more advantageous considering the lower cost-in-use.