Changes in kernel chemical composition during nut development of three Italian hazelnut cultivars

This research focused on the variation of the kernel and pellicle (seed coat) constituents during nut growth, from early development to maturity.Material and methods. Nuts of three hazelnut cultivars widely grown in Italy: \u2018Tonda Gentile Romana\u2019, \u2018Tonda di Giffoni\u2019 and \u2018Nocchione\u2019. were randomly sampled weekly, from the same trees, starting from the first week of July 2007 (day of the year: DOY = 186) until the beginning of September (DOY = 249), at harvest time. Oil content increased continuously during the development of the kernel, from 30\u201335 g 100 g 121 dry weight (DW) at the beginning of July, to 61\u201368 g 100 g 121 DW in the first week of September. Total monounsaturated fatty acids were the main group of fatty acids in the oil and oleic acid was the most predominant one, showing slight variations depending on the cultivar and kernel growth stage. Nitrogen content in the kernel decreased continuously during development, from 4.2 g 100 g 121 DW to 2.9 g 100 g 121 DW on average among the cultivars. Soluble sugars, mainly sucrose, showed a wide fluctuation until late July, and the content observed in the mature seed was about 5 g 100 g 121 DW in all cultivars. The organic acids, mainly represented by malic acid, showed a large decrease during the early stages (July), and reached on average a content of about 0.3\u20130.4 g 100 g 121 DW at the mature stage. Starch content for all cultivars was highest at the first sampling date, then decreased rapidly, coinciding with the initial kernel expansion stage. Starch levels then increased to a second peak in early August, then rapidly decreased again, followed by a gradual decline up to the time of nut ripening. The total phenol content was mainly concentrated in the pellicle and showed wide variation during the nut development both in the kernel and pellicle. The complexity of these dynamics can explain the different kernel taste in immature and mature states, and highlights the possibilities of optimizing the orchard management and harvesting time