CAN MICROWAVE PRETREATMENT IMPROVE THE ANTIOXIDANT AND TECHNOLOGICAL PROPERTIES OF PROTEIN HYDROLYSATES OBTAINED FROM FREE-RANGE CHICKEN FEATHERS?

In the new global economy, the poultry sector has notable importance, especially regarding meat production. Within this large market niche, the creation of free-range poultry, also called “Caipira”, has emerged as an alternative to traditional poultry production to achieve the consumer's demand for animal welfare and low environmental impact in food manufacturing. However, increasing free-range chicken meat consumption worldwide has generated a large volume of by-products from slaughterhouses. The chicken feathers, rich in keratin proteins, are frequently underused, engendering economic and environmental losses. Alternatively, these feathers can be better utilized through enzymatic hydrolysis, providing valuable amino acids and peptides. Nevertheless, the biotransformation of chicken feathers through hydrolysis is difficult because of the tightly packed keratin proteins. To minimize this effect, microwave heating can weak the rigid structure of chicken feathers, improving the hydrolysis process. Thus, this study set out to investigate how microwave alkaline pretreatment (MAP) influences enzymatic hydrolysis of free-range chicken feathers using two different enzymes, and evaluate the antioxidant activity and technological properties of the obtained hydrolysates. Four protein hydrolysates were produced from treated (700 W / 10 min in NaOH 0.5 M) and untreated feathers subjected to enzymatic hydrolysis with Alcalase® or Flavourzyme® (5% for 240 min). Antioxidant activity was evaluated against DPPH and ABTS radicals. For the technological properties, the emulsifying capacity, emulsion stability, and oil holding capacity were measured. A two-way ANOVA revealed that is a marked interaction effect between MAP and enzyme type in the antioxidant activity of the hydrolysates. In fact, the DPPH and ABTS radical scavenging capacities were higher in Flavourzyme® hydrolysates obtained from treated feathers. This result confirms that MAP may be associated with structural changes in free-range chicken feathers, improving protein hydrolysis. In addition, according to the literature, hydrolytic reactions using Flavourzyme® (an exopeptidase) produces low molecular weight hydrolysates, which present a high antioxidant capacity, compared to the samples hydrolyzed with Alcalase® (an endopeptidase). Our findings suggest that the MAP facilitates the action of the enzyme in the hydrolytic cleavage and Flavourzyme® seems to have a better ability to produce greater amounts of peptides with high antioxidant capacity. The oil holding capacity of the analyzed hydrolysates appeared to be unaffected by MAP or enzyme type. For emulsifying capacity and emulsion stability of the hydrolysates, only MAP had a significant effect (P < 0.05), showing higher values in the hydrolysates obtained from treated feathers irrespective of enzyme type. In conclusion, this study has found that microwave alkaline pretreatment has a great influence on the enzymatic hydrolysis of the free-range chicken feathers, possibly facilitating the enzyme-substrate interaction. In general, we observed that hydrolysates obtained from treated feathers showed high antioxidant activity, emulsifying capacity, and emulsion stability. Furthermore, the developed technique can be a promising option for poultry solid waste management.