The comparison of antioxidant capacity and HPTLC polyphenolic profile of green fruits and leaves of walnut (Juglans regia L.) cultivars grown in Poland

Walnut (Juglans regia L.) has a wide range of applications in food, pharmaceutical and cosmetics industries, however both unripe fruits and leaves have not been widely evaluated for varietal variation so far. Due to, leaves and immature fruits of seven walnut cultivars (Lake, Mars, Franquette, U02, SK04/10, Broadview, and Resovia) grown in Poland were compared for the first time in terms of antioxidant capacity (DPPH and FRAP), total phenolic content and qualitative polyphenol profile (HPTLC). The highest phenolic content was found for the Franquette (p < 0.05), both for leaves and nuts. In general, lower variability was observed for leaves, in the case of green nuts the results were more diversified by cultivar. The rapid and cost-saving HPTLC method was used to compare the polyphenolic profiles of the extracts. Cultivar-dependent differences in phenolic acids (mainly syringic) and flavonoids (mainly derivatives of quercetin) presence were found. Despite of observed differences between cultivars, it was found that both part of walnut are abundant in polyphenols. However it has been confirmed that the selection of a phytochemically appropriate cultivar may be important in providing a particularly valuable raw material for the food, pharmaceutical and cosmetic applications, thus the further quantitative studies are required.