Reaction Stages of Feather Hydrolysis: Factors That Influence Availability for Enzymatic Hydrolysis and Cystine Conservation during Thermal Pressure Hydrolysis
Goerner-Hu, Xinhua | Scott, Elinor L. | Seeger, Thorsten | Schneider, Oliver | Bitter, Johannes H.
The vast amount of feathers generated (>1 Mtons/a in Europe) in the poultry industry is an opportunity of upcycling by-product materials and improving sustainable practices. Feathers are potentially interesting materials as feed protein ingredients due to their high protein (>85 wt%) and cystine content (>7 wt%). However, due to their challenging recalcitrant nature, they have to be processed to make feather protein suitably digestible. The objective was to investigate the effects of temperature (120ᵒC–160ᵒC) and time (10, 30, and 60 min) in thermal pressure hydrolysis of feathers on availability for enzymatic hydrolysis (AEH) and cystine conservation. AEH is defined as degree of degradation of processed feather protein by two digestive enzymes pepsin and pancreatin (Boisen). The present study identified and assessed four temperature stages that take place during feather processing. The four temperature stages are 120ᵒC–135ᵒC, 140ᵒC–155ᵒC, > 160ᵒC, and the cooling-down phase. The second stage has the greatest influence on AEH. As well as temperature, hydrolysis time is also an essential parameter that had a major impact in the second stage (140ᵒC–155ᵒC). Both temperature and time influence negatively cystine content and stability. The present study demonstrates for the first time the importance of four reaction stages during feather hydrolysis and the impact of four stages on AEH of the obtained products.
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