Abstract
Micro matrix solid phase dispersion (micro-MSPD) was optimized by response surface methodology for the extraction of polyphenols from the peel of twelve traditional and eight commercial apple varieties grown in Croatia. The optimized micro-MSPD procedure includes the use of 0.2 g of sample, 0.8 g of dispersant, a 57% solution of methanol in water as the solvent and 5 mL of extract volume. The total polyphenolic index (TPI) and antioxidant activity (AA) were measured by spectrophotometric assays. Eighteen polyphenolic compounds were identified in all investigated apples by HPLC-DAD and LC-(ESI)-MS. The peel of traditional apple varieties had higher contents of all investigated polyphenols. Calculated relative contribution of polyphenol groups indicated non-flavonoids (28.6%) and flavanols (46.2%) as the major contributors to the total polyphenolic content in traditional and commercial apple varieties, respectively. The most abundant polyphenol in traditional apple peel was chlorogenic acid, procyanidin B2 and epicatechin (1143 ± 755 µg/g dw, 954 ± 343 µg/g dw and 560 ± 362 µg/g dw, respectively). The peel of varieties ‘Apistar’, ‘Bobovac’ and ‘Božićnica’ could be highlighted as an important source of polyphenols.
Highlights
There has been a growing interest in the preservation of traditional apple varieties, which can still be found in individual orchards
Studying the sample (0.2 g and 0.5 g) and dispersant (0.4 g and 1.0 g) masses at the same ratio (1:2), in terms of total polyphenolic index (TPI), showed that the elution time considerably decreased at low mass values and that the contact time between the sample and the solvent was more regular
Significant differences in terms of TPI were observed and the sample:dispersant ratio was included as a factor in the experimental design
Summary
There has been a growing interest in the preservation of traditional apple varieties, which can still be found in individual orchards. Due to favorable differences in their adaptive characteristics that developed through many years, many of these traditional varieties should be preserved for the modern fruit-culture, such as the shape of their fruit, their taste, peel and pulp colors and their higher resistance to diseases [1,2]. In Croatia, many of these varieties still exist in locations where they have adapted well to the environmental and geographic features, which make them desirable for breeding. Fruit from these varieties is often commercially unattractive, due to undesirable organoleptic properties. Apples are generally considered “healthy food”; one of the most important features of apples, the one that makes them interesting for researchers, is their polyphenol content, especially flavan-3-ols, phenolic acids, flavonols, dihydrochalcones and anthocyanins [1,2,4,5,6]
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