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.
