Phenolic compounds (phenylpropanoids with an aromatic ring bearing one or more hydroxyl groups and various other substituents) are produced by plants as secondary metabolites, ranging from simple monomers to very large polymers. Due to their antioxidant activity they play crucial roles in plant defences against both biotic and abiotic stressors, moreover they are an important component of animal diet and they are highly beneficial for human health.
As fruits represent the key source of antioxidants the knowledge of health-promoting substance contents in fruits affects consumers' perceptions of fruits quality. Apples are a widely available fruit exhibiting significant concentrations of antioxidants, however the concentrations and composition of antioxidants vary during ripening and subsequent handling of harvested fruits.