Rapid and non-destructive discrimination of pecan cultivars by oil unsaturation using portable Raman spectroscopy

Pecan is a commercially important tree nut whose quality and shelf life depend strongly on its oil composition. The ratio of oleic acid to linoleic acid varies among cultivars and governs oxidative stability. However, standard reference methods for measuring oil unsaturation, including gas chromatography of fatty acid methyl esters and iodine value titration, are destructive, slow, and reagent-intensive. This study evaluated portable 785 nm Raman spectroscopy as a rapid, non-destructive method for discriminating pecan cultivars by oil unsaturation. Spectra were acquired from oil extracted from the stored kernels of four cultivars (Desirable, Moneymaker, Schley, Stuart) and from intact kernels of four others (Cape Fear, Creek, Desirable, Sumner). After baseline correction and normalization, three unsaturation indices centered at 1656, 3010, and 1265 cm -1 were computed. In the extracted oil, the cultivars formed a reproducible unsaturation gradient (Desirable, Schley, Stuart, Moneymaker), significant for all three markers (F between 68 and 75; p < 10 -20 ), and ANOVA-simultaneous component analysis attributed 62 % of the spectral variance to cultivar (p < 0.001), while storage condition and time were not significant. The same ordering was confirmed non-destructively in the intact kernels (F between 21 and 27). An independent peroxide-value assay confirmed the oils oxidized substantially over 79 days (3.1 to 17.5 meq/kg). However, this oxidation was not reflected in the Raman spectra, and the cultivar fingerprint tracked each cultivar’s intrinsic oil unsaturation and remained stable across storage. Raman spectroscopy offers a rapid, reagent-free, oxidation-tolerant basis for distinguishing pecan cultivars in both extracted oil and intact kernels.