Secondary metabolites are compounds that have an important ecological and protective function in plants. They are formed from primary metabolites or their intermediates. Walnut leaves contain mostly phenols. Main representative is juglone. Juglone is known by his allelopathic effect on other plants. The concentration of phenols in leaves fluctuates. Their highest concentrations are in July. In August the phenol concentration decreases. It depends on cultivar and enviromental factors. Gallic acid is the most abundant in kernels. Ellagic acid, caffeic acid, chlorogenic acid, vanillic acid, etc. are also present. Kernels are important because of fatty acids. These are not secondary metabolites. Their stability is influenced by phenols. Walnut liqueur and walnut oil are also marketable products. For walnut liqueur unripe green fruits are collected (ethanol is added). The liqueur is rich in phenols. The opposite is true for walnut oil. It mainly contains unsaturated fatty acids (linoleic, linolenic, oleic). Oil is produced from already dried kernels by pressing. Different pressing methods do not significantly affect the change in oil composition.
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