Earlier studies suggested that traditional apple varieties have quality traits well accepted by consumers and beneficial effects on human health. The aim was to collect 25 traditional apple varieties grown in Croatia and to determine, for the first time in so many details, their external (weight, height, width, shape, color), internal quality traits (firmness, starch decomposition index, maturity index, soluble solid concentration, total acids, soluble solid/total acids ratio, pH), and seed characteristics. In addition, individual polyphenols were determined in the flesh and peel, by using RP-HPLC. All was compared to the commercial variety ‘Idared’. Quality parameters of these varieties were similar to those of the commercial variety. The flesh and peel contained flavan-3-ols, dihydrochalcones, phenolic acids, and flavonols, while anthocyanins were additionally found in the peel. Total polyphenols in the peel (536–3801 mg kg−1 fresh weight (FW)) and in the flesh (79–1294 mg kg−1 FW) of the majority of varieties were higher than in the commercial variety. Principal component analysis showed possible clustering according to polyphenol amounts. According to the observed diversity of quality traits and bioactive polyphenol contents, the traditional varieties have potential for consumer acceptance and increased cultivation.

Beneficial effects of aronia phenolics are determined by their interactions with dietary fibers, such as β-glucan. The aim of this research was to study interactions between aronia phenolics and β-glucan by investigating the adsorption process. Phenolic compounds were extracted from aronia, analyzed using high-performance liquid chromatography, and adsorbed onto β-glucan at pH 1.5. The adsorption data were modeled by using Langmuir, Dubinin-Radushkevich, and Hill isotherms with a novel non-linear regression developed especially for adsorption isotherms. Aronia phenolics adsorbed onto β-glucan in amounts 31-250 mg/g (individual anthocyanins), 44-123 mg/g (individual flavonols), and 51 mg/g (neochlorogenic acid). The correlation between adsorption capacities and phenolic content was high (r 2 =0.94), which suggested that the adsorption might be concentration dependent. Modeling with a novel non-linear regression allowed more precise determination of adsorption isotherm parameters. Furthermore, there was a correlation between maximum adsorption capacities predicted by models and measured adsorption capacities (r 2 =0.76, r 2 =0.81 and r 2 =0.34 for Langmuir, Dubinin-Radushevich, Hill isotherms, respectively). The suggested bonds involved in interactions are non-covalent bonds (H bonds, Van der Waals forces). Principal component analysis showed that anthocyanins, flavonols, and phenolic acids could differently behave in the adsorption process, which could be due to differences in the chemical structures (ionic nature of anthocyanins, nonionic nature of flavonols and phenolic acids at low pH). In conclusion, aronia phenolics interacted with β-glucan by adsorbing onto its surface, and the novel modeling developed by our team was helpful in the interpretation of this process. Interactions should be further studied due to their importance for the beneficial effects of aronia.

Apple polyphenols have been studied for various beneficial bioactivities. Especially interesting are traditional, old varieties of apples for which some initial studies have suggested significant bioactivities, but they are still not completely understood. Polyphenol bioactivities can be affected by interactions with dietary fibers such as β-glucans. The aim of this study was to investigate for the first time interactions between individual polyphenols from traditional, old apple varieties (“Božićnica” and “Batulenka”) and β-glucans by studying the adsorption process. Polyphenols were extracted from the peel and flesh of traditional apples by using an ultrasonic bath and characterized with high-performance liquid chromatography. The amounts of adsorbed (qe) and un-adsorbed (ce) polyphenols were modeled with adsorption isotherms (Langmuir, Dubinin–Radushkevich, and Hill) by using improved non-linear fitting in a novel R algorithm, developed specifically for the modeling of adsorption isotherms. Polyphenols adsorbed onto β-glucan from 9 to 203 (peel, “Božićnica”), 1 to 484 (peel, “Batulenka”), 5 to 160 (flesh, “Božićnica”), and 19 to 28 mg g−1 (flesh, “Batulenka”). The adsorption was concentration dependent (polyphenols present in higher amount adsorbed in higher amounts). Physical sorption can be suggested. Polyphenols from traditional apples adsorb onto β-glucan and should be further studied.

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Apples are an important source of polyphenols in the human diet. They have also shown many potentially beneficial effects on human health. Old, traditional apple varieties grown in the past could also be valuable varieties but little is known about their polyphenolic compounds and characteristics in general. The aim of this study was to collect 25 old, traditional apple varieties, to determine their polyphenolic profile and the amounts of total polyphenols in the peel and flesh, and to compare them with a commercial variety. To the best of our knowledge, some of those varieties have never been studied before (‘Mašanka’, ‘Bobovac’, ‘Batulenka’, ‘Krastavka’). Total polyphenols were determined by using the Folin-Ciocalteu method and individual polyphenol identification was done by using an RP-HPLC. The flesh contained 170 to 941 mg kg-1 fresh weight (FW) of total polyphenols, and the peel contained 931 to 3791 mg kg-1 FW. In comparison to the commercial variety, the peel of all old varieties had higher polyphenol content, while the flesh of only some old varieties was richer in polyphenols. Principal component analysis showed possible clustering. Eighteen individual polyphenols were distributed in apple peel and flesh. The dominant polyphenol subgroups in the peel were flavonols (18 to 80 %) and flavan-3-ols (6 to 66 %), and in the flesh those subgroups were phenolic acids (41 to 85 %) and flavan-3-ols (3-49 %).