Quantification of Silymarin in Silybum marianum with near-infrared spectroscopy: a comparison of benchtop vs. handheld devices

Silybum marianum is part of the Asteraceae family and widely used for its regenerative effect on toxic liver diseases for which silymarin, a sum parameter of six flavanonol derivatives, has the main responsibility [1]. While the European Pharmacopeia suggests a Soxhlet method for silymarin extraction, the required 16 hours are excessively time-consuming [2].

As near-infrared spectroscopy (NIRS) is known for its fast and non-invasive measurements [3], [4], the aim of this study is the development of a time-saving and cost-efficient alternative for quantification of silymarin and its flavanonol derivatives in milk thistle seeds. Additionally, the quality of a handheld compared to benchtop NIR spectrometer is investigated.

Milk thistle seeds were measured in milled and ground state with one benchtop and two handheld spectrometers. Using chemometric pre-treatment partial least square regression (PLSR) models were calculated and quantified with cross validation (CV). In the example of silymarin the benchtop device NIRFlex N-500 (Büchi, Flawil, Switzerland) gave the best results both for milled and ground samples (RMSECV between 0.01 and 0.17%), though the MicroNIR 2200 (Viavi Solutions, Milpitas, USA) provided a similar performance (RMSECV between 0.01 and 0.18%). Resembling results were gained by the microPhazir (Thermo Fisher Scientific, Waltham, USA) (RMSECV between 0.01 and 0.23%), only the ground samples gave no satisfactory output.

This study proves that NIRS offers an alternative for the quantification of silymarin and its flavanonol derivatives. Soxhlet extraction cannot only be replaced by measurements with benchtop devices but even handheld spectrometers with their possibility of on-field measurements offer a good choice.

• References

• 1 Abenavoli L, Izzo AA, Milić N, Cicala C, Santini A, Capasso R. Milk thistle (Silybum marianum): a concise overview on its chemistry, pharmacological, and nutraceutical uses in liver diseases. Phyther Res 2018; 32: 2202-2213
• 2 Council of Europe. European Pharmacopoeia. Stuttgart: Deutscher Apotheker Verlag; 2013
• 3 Huck CW. Advances of infrared spectroscopy in natural product research. Phytochem Lett 2015; 11: 384-393
• 4 Kirchler CG, Pezzei CK, Be B, Mayr S, Huck CW. Critical evaluation of spectral information of benchtop vs. portable near-infrared spectrometers: quantum chemistry and two- dimensional correlation spectroscopy for a better understanding of PLS regression models of the rosmarinic acid content in Rosmari. Analyst 2017; 142: 455-464