Changes of the lipid fraction during fruit development in hazelnuts (Corylus avellana L.) grown in Poland

Detailed changes in composition of fatty acids, as well as alterations in the content of triacylglycerols and tocopherols during the maturation of Kataloński hazelnuts grown in Jankowice, Poland were studied. Samples with different maturity levels were collected at weekly intervals between August and September 2013. Nineteen different fatty acids were identified. The amount of oleic acid (n9) was the greatest in all samples, the amount of linoleic acid (n6) acid was second greatest, while the amount of palmitic acid was third greatest in all samples, except during the very first stage of maturation. A decreasing trend in the amount of polyunsaturated fatty acids (PUFA) was observed from early developed to completely maturated hazelnuts (from 30.09 to 10.28 g 100 g⁻¹of oil). On the other hand, the amount of monounsaturated fatty acids (MUFA) in hazelnuts increased from early to harvest stage (from 22.03 to 79.17 g 100 g⁻¹of oil). Linoleic acid and oleic acid were the most abundant fatty acids located in sn‐2 position of triacylglycerols. Different distributions of both acids were reported during maturation. Oleic acid reported a constant distribution in an internal position, whereas linoleic acid content in sn‐2 position increased during maturation. Finally, the tocopherol content increased from early to harvest stage and the amount of α‐tocopherol was observed to be the highest among tocols. Practical applications: The composition of hazelnuts changes during maturation. Harvest timing has a strong effect on both oil yield and quality factors, such as fatty acid composition and tocopherol content. The distinguishing features mentioned have a significant impact on the hazelnut's final oxidative stability, which is an important parameter from the grower's and distributor's practical perspective. The results obtained may be applied to the specific set up of harvesting time, when the nuts contain the highest amount of desired fatty acid. At the beginning of the maturation period, hazelnut kernels are an abundant source of both MUFA and PUFA (especially essential ones) and can be perceived as beneficial additive compounds to be applied in pharmaceutical and cosmetic products. The composition of the hazelnuts' lipid fraction changes during maturation. This includes the tocopherol content, fatty acid composition and fatty acid distribution in TAG molecules. Upon the ripening of hazelnuts, the content of monounsaturated fatty acids was increased, the content of saturated fatty acids was constant and polyunsaturated fatty acids decreased significantly (p < 0.05). The α‐tocopherol concentration increased during the kernel growing season, while the content of γ‐ and β‐homologues decreased significantly (p < 0.05). Additionally, highly significant positive correlations were found between the amount of α‐tocopherol and oleic acid and between the amount of γ‐tocopherol and linoleic acid.