Noninvasive Assay for Cyanogenic Constituents in Plants by Raman Spectroscopy: Content and Distribution of Amygdalin in Bitter Almond (Prunus Amygdalus)

Abstract

The ability of Fourier transform Raman spectroscopy to measure cyanogenic glycoside amygdalin was investigated using a standard addition series in which amygdalin (0–700 nmol/mg) was added to ground sweet almond. As an additional test, the method so developed, and further refined, was used to determine endogenous amygdalin in bitter almonds. Using partial least-squares regression (PLSR), the best correlation between the spectra of the standard addition series and amygdalin content exhibited a value of 0.999, while the root mean square error of cross validation (RMSECV) was found to be 4 nmol/mg using one principal component. The model was based on the first derivative of the aromatic C–H stretching band at 3060 cm−1. A less accurate but still excellent PLSR model could be developed on the vibrational band of the nitrile group, specific for the cyanogenic compound in the system. The best PLSR model obtained for endogenous amygdalin in 17 raw bitter almonds yielded a RMSECV = 13 nmol/mg and r = 0.937. In addition, the distribution of amygdalin in bitter almond was investigated in situ by obtaining spectra of an intact cross-section of the cotyledon of bitter almond using Raman microscopy. While amygdalin was found not to be present in measurable amounts in the center of bitter almond, the concentration increased towards the epidermis, but not linearly.

Cyanide and Amygdalin as Indicators of the Presence of Bitter Almonds in Imported Raw Almonds

“…However, they are similar to the 290 mg HCN per 100 g of tissue reported by Micklander et al. (12). These data are not meant to suggest that Sample 1 contained 10% bitter almonds, but merely to indicate the ability to confirm their presence.…”

“…Micklander et al. (12) report an amygdalin value of 110 nmol/mg in bitter almonds, or 50 mg/g. According to Sánchez‐Pérez et al.…”

Identification and quantification of valuable plant substances by IR and Raman spectroscopy

“…They are accumulated in several plants acting as a defense system against fungi and herbivores. Micklander et al [68] reported a development of a method assessing the content and distribution of cyanogenic glycoside amygdalin in bitter almonds [8,68]. They choose Raman spectroscopy for analysis because the nitrile group gives rise to strong Raman band near 2240 cm À1 whereas in IR spectroscopy this group can be recognized only with low intensity.…”

Investigation on Clarified Fruit Juice Composition by Using Visible Light Micro-Raman Spectroscopy

“…As a consequence of significant improvements of micro-Raman spectroscopy technology, an increasing attention has been given to the applications of Raman spectroscopy to heterogeneous systems such as those used in the food industry [2,3]. Raman spectroscopy has been successfully employed in the characterization of starch and pectin in potato [3], bitter almonds [4] and for edible oil authentication [5]. In particular, powdered pectin has been extensively investigated by means of FT-IR and FT-Raman spectroscopy [6].…”