Walnut (Juglans regia L.) Leaves and Green Husks: Their Functional Properties, Health Benefits and Potential Use in Foods

Abstract

The walnut tree (Juglans regia L.) is a well-known member of the Juglandaceae family and is widely cultivated worldwide. Since ancient times, parts of the walnut tree have been used in traditional medicine for the treatment of various diseases (such as venous insufficiency, hemorrhoids, hypoglycemia, diarrhea, asthma, eczema, stomachache, cancer, and microbial infections). Walnut leaves and green husks are important agricultural byproducts, which attract attention in terms of their chemical composition (such as protein, fat, carbohydrate, vitamin E and minerals including Ca, K, Mg, Fe, Zn and Mn) and bioactive contents (such as phenolics, flavonoids, organic acids, triterpenic acids, terpenes, terpenoids, tetralon derivatives, megastigman derivatives and juglone), and they are cheap and abundant while being in the form of waste. Walnut leaves and green husks, which have qualities that can be used in the development of high value-added products and functional foods, may provide benefits to human health with their various properties such as antioxidant, antimicrobial, antifungal, anti-inflammatory, antidiabetic, anthelmintic, antidiarrheic, antihistaminic, antiulcer, antiasthmatic, immunomodulator, antifertility, anticancer, anti-aging and hepatoprotective. In this review, general information is presented about their health benefits and potential as functional additives and/or nutraceutical in foods, by drawing attention to the phytochemical profiles and chemical properties of walnut leaves and green husks, which are agricultural wastes.