DOI: 10.34810/data1724
title: Stable isotope ratio values (bulk δ18O, and δ13C and δ2H of various fatty acids) of hazelnuts

description: Dataset containing stable isotope ratio values (bulk δ18O determined by EA-IRMS, and δ13C and δ2H of various fatty acids determined by GC-IRMS) of hazelnuts obtained and used by Torres-Cobos et al. Data correspond to the values of 207 authentic and traceable ‘Tonda di Giffoni’ hazelnut samples from various geographical origins and harvest years, obtained in the framework of the TRACENUTS, PID2020-117701RB-I00. 
Samples were analyzed in duplicate, and reported values correspond to the means.
description: Briefly, bulk isotopic analysis (δ18O, in ‰) was determined by Elemental Analysis-Isotope Ratio Mass spectrometry (EA-IRMS) as described by Torres-Cobos et al., (Food Chemistry, 2024, 449: 139083; https://doi.org/10.1016/j.foodchem.2024.139083). An aliquot of 0.3 mg of the ground and lyophilized sample was placed into silver capsules (Lüdi Swiss, Flawil, Switzerland) and analyzed in a TC/EA-IRMS Delta Plus XP (Thermo Fisher Scientific) equipped with an autosampler (Sample Tray, N° 2, MAS200R autosampler) and a 450 mm ceramic pyrolysis reactor, heated to 1445 °C. Helium was the carrier gas (pressure 62 kPa), and carbon monoxide (CO) was the reference gas with a δ18O value of −8.68 ‰ (pressure 180 kPa). The certified standard IAEA-601 (benzoic acid, δ18O= +23.3 ‰) and the internal secondary standards, UB-YCEM (δ18O = +17.6 ‰) and UB-ASC (δ18O = +13.2 ‰), both barium sulphates, were used fitting the range of the samples. 
The isotopic values of fatty acid methyl esters were determined by GC-IRMS. Samples were prepared and analyzed as described by Torres-Cobos et al., (Food Chemistry, 2024, 449: 139083; https://doi.org/10.1016/j.foodchem.2024.139083). Briefly, fatty acid methyl esters were obtained by extracting the lipid fraction of hazelnuts with diethyl ether and transesterifying it with a solution of methanolic potassium hydroxide. The H and C isotopes of individual fatty acid methyl esters were determined using a Trace GC Ultra gas chromatograph with a Triplus Autosampler, coupled to an Isotope Ratio Mass Spectrometer Delta V Advantage through a GC Isolink interface (Thermo Fisher Scientific, Waltham, Massachusetts, USA). A capillary column (VF-23ms, 60 × 0.32 mm I.D., 0.15 μm; Agilent Technologies, Santa Clara, California, USA) was used for the separation, with the following oven temperature program: start at 60 °C; hold for 1 min; increase at 6 °C/min up to 160 °C; hold for 10 min; increase to 240 °C at 6 °C/min. Helium (1.8 mL/min) was the carrier gas. The injector temperature was 240 °C (1 μL injected, split ratio of 1:5). The commercial NiO/CuO-NiO-Pt combustion reactor (P/N 1255321, Thermo Fisher Scientific, Waltham, Massachusetts, USA) operated at 1000 °C for CO2. For the analysis of H2, the commercial high temperature reactor (P/N 1255330, Thermo Fisher Scientific, Waltham, Massachusetts, USA) was used and adjusted to 1400 °C. The certificated standards used for the analysis of δ2H were Androstane, USGS76, Coumarin, and a secondary standard, FAME C19. For the analysis of δ13C, the standards used were Icosane, FAME C16, USGS76, FAME C19, USGS72, phenanthrene 16/0020.