Jindamol, H. ; Rascher, U. ; Thiele, B. ; Wuyts, N. ; Linow, M. M. ; Mosaleeyanon, K. ; Chutimanukul, P. ; Toojinda, T. ; Junker-Frohn, L. V.

2023

Abstract: In the industrial production of essential oils from medicinal plants, the quantity of secondary metabolites is relevant the quality of the essential oil. The secondary metabolite content varies depending on several factors during cultivation. Quantification of secondary metabolites is necessary to set growing conditions and define the optimal harvesting time to obtain the desired quantity of secondary metabolites. Spectral reflectance measurements of plants are a promising technique for increasing the effectiveness of such monitoring, as they can be performed non-destructively, rapidly and in real-time. The purpose of this study is to develop a non-destructive quantification method for eugenol and methyl eugenol, the crucial constituents in the essential oil of Holy basil, using leaf-level hyperspectral data. Point measurements of spectral reflectance in the spectrum range from 350 to 2500 nm were collected from a total of 200 leaves sampled from two cultivars, a green and a red cultivar of commercial relevance. Plants were sampled at four developmental stages: vegetative, pre-flowering, flowering, and harvesting, and leaf samples differed in leaf age and position. Eugenol and methyl eugenol content of each leaf sample was analyzed by the standard method of gas chromatography-mass spectrometry (GC-MS). A wide range of eugenol and methyl eugenol concentrations was found among cultivars and stages of development between 140-7500 and 235-11000 μg/gDW, respectively. The resulting dataset including spectral data and target secondary metabolite data was analysed using partial least squares regression (PLSR). The PLSR modeling resulted in a coefficient of determination (R2) of the calibration and validation sets of about 0.5 for both secondary metabolites, with RMSEP of 1.3 and 1.13 in eugenol and methyl eugenol, respectively. The study demonstrated that a non-destructive quantification technique by detecting hyperspectral reflectance can be used for estimating the content of eugenol and methyl eugenol in Holy basil. In the future, the study will be extended to increase the number of data points and include more cultivars and stress conditions to achieve a higher accuracy needed to develop a non-destructive quantification method.

Keyword(s): Biology (2nd) ; Chemistry (2nd)