Penicillium expansum is a necrotrophic plant pathogen among the most ubiquitous fungi disseminated worldwide. It causes blue mould rot in apples during storage, transport and sale, threatening human health by secreting patulin, a toxic secondary metabolite that contaminates apples and apple-derived products. Nevertheless, there is still a lack of sufficient data regarding the resistance of different apple cultivars to P. expansum, especially ancient ones, which showed to possess certain resistance to plant diseases. In this work, we investigated the polyphenol profile of 12 traditional and 8 conventional apple cultivar and their resistance to P. expansum CBS 325.48. Eight polyphenolic compounds were detected; the most prominent were catechin, epicatechin and gallic acid. The highest content of catechin was detected in ‘Apistar’—91.26 mg/100 g of fresh weight (FW), epicatechin in ‘Bobovac’—67.00 mg/100 g of FW, and gallic acid in ‘Bobovac’ and ‘Kraljevčica’—8.35 and 7.40 mg/100 g of FW, respectively. The highest content of patulin was detected in ‘Kraljevčica’ followed by ‘Apistar’—1687 and 1435 µg/kg, respectively. In apple cultivars ‘Brčko’, ‘Adamčica’ and ‘Idared’, patulin was not detected. Furthermore, the patulin content was positively correlated with gallic acid (r = 0.4226; p = 0.002), catechin (r = 0.3717; p = 0.008) and epicatechin (r = 0.3305; p = 0.019). This fact indicates that higher contents of gallic acid, catechin and epicatechin negatively affected and boost patulin concentration in examined apple cultivars. This can be related to the prooxidant activity of polyphenolic compounds and sensitivity of P. expansum to the disturbance of oxidative status.

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Apples are one of the most popular foods around the world. However, recently there has been a growing interest in the preservation of traditional apple varieties. This interest has grown due to the studies that suggest that traditional apples contain higher amounts of polyphenolics and antioxidant activity compared to commercial ones. Polyphenolics in apples have gained much attention because of their beneficial effects on human health, and thus they became a quality trait of apples. Traditional apple varieties have the same groups of polyphenols as commercial ones and those are flavan-3-ols, phenolic acids, flavonols, dihydrochalcones, and anthocyanins. However, traditional apple varieties proved to be rich in some individual polyphenolics, such as procyanidins B1, B2, A2, epicatechin, quercetin-3-rutinoside, chlorogenic acid, etc. This chapter is underlying the great potential of traditional apple varieties as a source of some individual polyphenolics and natural antioxidants.

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