Walnut and Co-Products: Composition, Nutritional Value, and Health-Related Properties

In addition to providing substances of high nutritional quality, regular walnut intake is associated with wellness and preventive effects on various diseases. Such benefits have been mostly attributed not only to the richness of walnuts in healthy lipids (plentiful in unsaturated fatty acids) and proteins but also to the presence of a vast array of phytochemicals, including phytosterols, tocochromanols, oxylipins, and polyphenolic compounds, among others. The overall objective of this review is to provide an up-to-date overview of the diversity of compounds with nutritional and therapeutic value present in walnuts. It was specifically intended to 1) analyze the general chemical composition of the common walnut, and those from the main-derived food by-products, with a focus on lipids, proteins, and phytochemicals; 2) provide information on processing, preservation, and uses of selected by-products; 3) review relevant scientific literature linking consumption of walnuts and some of their components, with promising effects on selected diseases; 4) examine the bioactive properties of walnut components in light of the mechanisms underlying the observed therapeutic effects; 5) unveil nutritionally valuable compounds derived from the inedible part of the fruit. The study also gives insights into walnut-derived ingredients for functional food applications and the production of targeted bio-functional compounds.