Production and characterization of protein hydrolysates from walnut by-products

Walnut (Juglans regia) is a strategic agricultural product distinguished by its rich nutritional content, nutraceutical properties, and wide range of applications, serving as a significant economic resource for many countries worldwide. Walnut kernel is a biologically and chemically valuable food material, representing the edible part of the walnut fruit and holding a prominent place in the scientific literature due to its composition. In recent years, besides the direct consumption of walnut kernels, the importance and demand for their processed forms have been steadily increasing. This rise is crucial for promoting sustainable food production and enhancing the agricultural economic value of walnuts. Walnut flour is a by-product obtained by drying the walnut meal remaining after oil extraction from walnut kernels. Utilizing these by-products, which are often considered waste and not effectively valorized, for the production of protein hydrolysates offers an opportunity to create high-value-added products. In this thesis, hydrolysis was performed using alcalase, Favourzyme®, and savinase enzymes, and the effects of the hydrolysis process on the structural, functional, and bioactive properties of walnut protein were investigated. During the hydrolysis process, savinase exhibited the highest degree of hydrolysis (22.59%). Favourzyme® demonstrated the best performance in terms of emulsification activity (282.16 m²/g) and foaming capacity (77.67%), while savinase and alcalase enhanced fat-binding capacity. Regarding antioxidant capacity, the Cizo fraction stood out with a high DPPH inhibition rate (61.39%-67.54%). This study demonstrates that enzymes such as savinase, alcalase, and Favourzyme® provide an effective technology for producing bioactive and multifunctional hydrolysates from walnut proteins. Furthermore, it highlights the potential of samples like Cizo, which exhibit high antioxidant capacity, to be utilized in functional food and pharmaceutical products. Keywords: Walnut protein, Enzymatic hydrolysis, Functional properties, Antioxidant activity