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The influence of alkaline extraction on some keratin hydrolysates properties

Keratin is a fibrous protein abundant in nature, being the component of wool, hair, hooves, horns, feathers, and claws. Keratin is one of the most valuable natural biopolymers due to its chemical versatility and biological performance. At the molecular level, keratin is distinguished from other biopolymers by its high concentration of cysteine-containing sulfur. Two keratin hydrolysate batches were obtained in alkaline medium, at a constant concentration of 8% NaOH and 75°C (KerNa875), 85°C (KerNa885), and 95°C (KerNa895), and at a fixed temperature of 99°C and different concentrations of NaOH, i.e. 3% (KerNa399), 5% (KerNa599), and 8% (KerNa899), respectively. Physical-chemical analyses showed that the protein content ranging between 83.60% for KerNa875 and 88.88% for KerNa399, while the total nitrogen was found 13.83% and 14.67% in the case of KerNa875 and KerNa399, respectively. Dynamic light scattering analysis showed that the particle sizes decreased with the increased concentration in the reaction medium. The average particle size was between 1352 nm and 1771 nm for the samples obtained at a temperature of 99°C and with lower values between 463.3 nm and 571.6 nm for the samples obtained with 8% NaOH. The Fourier transform infrared (FT-IR) spectra evidenced the specific bands of keratin-specific proteins and sulfur compounds. Experiments were also performed to evaluate the antioxidant activity and the growth of Tamino and Mirastar wheat plants by applying the treatments with 3% and 5% concentrations of KerNa899 on wheat seeds. These experiments showed an improvement in the wheat plant growth during 10 days of observation compared to control sample. The results recommend the potential use for keratin hydrolysates in the medical, pharmaceutical, cosmetics fields, and also as fertilizers in agriculture.