The increasing generation of keratinic wastes by the poultry industry stimulated research on novel, costeffective methods of keratin protein management respecting current environmental regulations. Enzymatic treatment of feather waste with microbial keratinases appears to be one of the most promising methods to obtain valuable products. Nevertheless, the action of keratinolytic proteases requires the support of disulfide bond-reducing agents to reveal their full potential. The presented study was aimed at evaluating effects of moderate thermo-chemical feather pretreatment, preceding hydrolysis with two crude microbial keratinases from Bacillus cereus B5esz and B. subtilis P22. Keratinases of both tested strains exhibited capability for degradation of native feathers, but substrate pretreatment resulted in significant improvement of the process. Application of 10 mM sulfite in the pretreatment remained to be the most appropriate option, leading to 160% or 95% activity enhancement of keratinases from B. cereus and B. subtilis, respectively. Pretreatment with 10 mM NaOH also gave a satisfactory effect. Pepsin digestibility was mostly influenced either by 1 mM sulfite pretreatment or by sole autoclaving. Crude keratinase from B. cereus, a potent keratinase producer, expressed only four times lower specific activity against raw feathers in comparison to purified commercial proteinase K, and the action of both enzyme preparations was influenced by sulfite pretreatment of the substrate. Additionally, the concentrated culture broth of B. cereus B5esz proved to be highly applicable in degradation of raw feathers, especially in the presence of sulfite or sulfite-pretreated feathers.
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