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.

This research is focused on comparing the compositions of juice produced from old and commercially grown apple cultivars. We examined factors such as pH, total acids, soluble dry matter, polyphenol profile, and antioxidant activity, which impact the attributes, safety, shelf life, and nutritional value of the juice. Our analysis revealed differences between these two groups of cultivars. For instance, pH values ranged from 3.04 (in ‘Bobovec’) to 3.69 (in ‘Fuji’). The proportions of acids varied from 0.07 g/100 mL (in ‘Fuji’) to 0.19 g/100 mL (in ‘Wagener’). Soluble dry matter content ranged from 14.10% (in ‘Fuji’) to 18.50% (in ‘Kraljevčica’). We also observed variations in sugar content and composition among cultivars; for example, sucrose levels varied from 16.11 g/L (‘Fuji’) to 39.36 g/L (‘Golden Delicious). Glucose levels ranged from 4.95 g/L (‘Jonagold’) to 19.18 g/L (‘Fuji’), while fructose levels spanned from 50.78 g/L (‘Austrougarka’) to 427.97 g/L (‘Ilzer Rosenapfel’). Furthermore, old apple cultivars exhibited higher concentrations of phenols and flavonoids compared to commercial ones; we also noted significant variations in flavonol levels among different cultivars. The ‘Wagener’ and ‘Božićnica’ apple varieties had levels of myricetin measuring 0.53 and 0.52 µg/mL, respectively. On the other hand, ‘Bobovec’ stood out for its content of procyanidin B2 with a concentration of 422.61 µg/mL. When examining non-flavonoid compounds, it was found that old apple cultivars had higher concentrations of gallic acid, trans-ferulic acid, and chlorogenic acid. However, commercial cultivars showed dominance in caffeic and p-coumaric. Comparisons of antioxidant capacity using DPPH and ABTS assays clearly demonstrated the superiority of old apple cultivars. Overall, this study highlights the importance of utilizing apple cultivars for juice production. Their distinct compositions and higher antioxidant capacities contribute to potential health benefits. Preserving these cultivars for enhanced juice quality and nutritional value is encouraged. Further research could explore cultivation practices’ impact on composition and health benefits.

Apples and apple-based products are particularly interesting due to being a good source of polyphenols in an everyday diet. Recently there has been increased interest in the preservation of traditional apple varieties due to studies that suggest that traditional apple varieties have a higher content of polyphenols and antioxidant activity compared to commercial varieties. This study shows that traditional apple varieties contain higher concentration of polyphenolic compounds than conventional ones, such as chlorogenic acid (1.29–456 mg/kg dw), catechin (0.70–312 mg/kg dw), epicatechin (1.75–244 mg/kg dw), procyanidin B1 + B2 (4.08–358 mg/kg dw) and quercetin-3-glucoside (0.96–231 mg/kg dw). This research underlies the great potential of traditional apple varieties as a source of natural antioxidants and polyphenolics.

Apples and apple-based products are among the most consumed fruits around the world. However, they are susceptible to infection with the fungi Penicilium expansum. In addition to the reduction of apple quality, secondary metabolism of this fungus produces a mycotoxin patulin that has a negative effect on human health. Currently, there is no available research in the literature on the resistance of Croatian traditional apple cultivars to contamination with P. expansum, and consequently, on the patulin content in apples and apple juice produced from those apples. Although the mechanism of apple resistance to fungal diseases has not yet been sufficiently investigated, some studies have shown that polyphenolic compounds have some impact on fungi growth. In order to contribute with new knowledge, this research deals with monitoring the growth of P. expansum on apples, patulin detection by LC/MS-MS, determination of polyphenol profile by validated HPLC method, and determining the effect of polyphenolic compounds on fungi growth and patulin production during apple storage. The results of this study have shown that Croatian traditional apple cultivars harvested from family farm Horvatić contain higher concentration of polyphenolic compounds and higher antioxidant activity. At the same time, they showed more resistance to infection by P. expansum than conventional ones. The higher content of dihydrochalcones and flavanols encouraged the biosynthesis of patulin in examined cultivars. However, the higher content of non-flavonoids such as 2-6 dimethoxybenzoic acid, 4-hydroxycinnamic acid and chlorogenic acid leads to decrease in content of patulin. In conclusion, it seems that content of polyphenols and patulin production are correlated.

This study investigates the impact of polyphenols on the susceptibility of traditional and conventional apple varieties to Penicillium expansum infection and subsequent patulin biosynthesis during cold storage. Traditional varieties, notably ‘Bobovec’, exhibit significantly higher levels of total polyphenols (650.56 ± 9.85 mg/L) and flavonoids (184.11 ± 1.48 g/kg dw) compared to conventional ones after six months of storage, accompanied by the identification of key polyphenols such as chlorogenic acid, epicatechin, phloridzin, quercetin and procyanidins B1 and B2. These traditional varieties demonstrate enhanced resistance to P. expansum infection, as evidenced by prolonged periods for colony formation, particularly ‘Bobovec’ with an average of 384 h. Furthermore, the traditional variety ‘Winter Banane’ and conventional varieties ‘Idared’ and ‘Fuji’ showed increased patulin biosynthesis postinoculation, indicating higher susceptibility to fungal infection. The findings underscore the potential of polyphenols from traditional apple varieties as natural defences against fungal infections, suggesting the importance of selecting or breeding varieties with higher polyphenol content to improve resistance to postharvest pathogens, thereby enhancing the quality and safety of stored apples.

This study aimed to detect, quantify and compare the amounts of chlorogenic acid, phloridzin and quercetin in Croatian traditional and conventional apple varieties by HPLC-PDA. The results showed that Croatian traditional apple varieties had significantly higher amounts of chlorogenic acid (30.29 ± 0.34 mg/100 g dw), phloridzin (3.12 ± 0.01 mg/100 g dw) and quercetin (11.68 ± 0.09 mg/100 g dw) detected for varieties Božičnica, Mašanka and Petrovnjača, respectively. The highest contents of the total phenolic acids, dihydrochalcones and flavonols were detected in Božićnica (31.94 ± 0.65 mg/100 g dw), Mašanka (3.52 ± 0.52 mg/100 g dw) and Fuji (19.11 ± 0.56 mg/100 g dw). These results present the beginning of the research on the resistance of Croatian traditional apple varieties to plant diseases.