Phenolic compounds constitute a substantial group of phenylpropanoids which are produced by plants as secondary metabolites with antioxidant properties. The spectrum and concentrations of phenolic acids serve as a convenient marker of plant resistance to biotic stresses. Phenolics form also an important component of animal diet. Apples are a widely available fruit exhibiting significant concentrations of antioxidants, especially phenolics and carotenoids. Generally, the concentrations and composition of antioxidants vary during ripening and subsequent handling of harvested fruits.