Leaves of Invasive Plants—Japanese, Bohemian and Giant Knotweed—The Promising New Source of Flavan-3-ols and Proanthocyanidins

Abstract

This is the first report on identification of all B-type proanthocyanidins from monomers to decamers (monomers—flavan-3-ols, dimers, trimers, tetramers, pentamers, hexamers, heptamers, octamers, nonamers, and decamers) and some of their gallates in leaves of Japanese knotweed (Fallopia japonica Houtt.), giant knotweed (Fallopia sachalinensis F. Schmidt) and Bohemian knotweed (Fallopia × bohemica (Chrtek & Chrtkova) J.P. Bailey). Flavan-3-ols and proanthocyanidins were investigated using high performance thin-layer chromatography (HPTLC) coupled to densitometry, image analysis, and mass spectrometry (HPTLC–MS/MS). All species contained (−)-epicatechin and procyanidin B2, while (+)-catechin was only detected in Bohemian and giant knotweed. (−)-Epicatechin gallate, procyanidin B1 and procyanidin C1 was only confirmed in giant knotweed. Leaves of all three knotweeds have the same chemical profiles of proanthocyanidins with respect to the degree of polymerization but differ with respect to gallates. Therefore, chromatographic fingerprint profiles of proanthocyanidins enabled differentiation among leaves of studied knotweeds, and between Japanese knotweed leaves and rhizomes. Leaves of all three species proved to be a rich source of proanthocyanidins (based on the total peak areas), with the highest content in giant and the lowest in Japanese knotweed. The contents of monomers in Japanese, Bohemian and giant knotweed were 0.84 kg/t of dry weight (DW), 1.39 kg/t DW, 2.36 kg/t, respectively, while the contents of dimers were 0.99 kg/t DW, 1.40 kg/t, 2.06 kg/t, respectively. Giant knotweed leaves showed the highest variety of gallates (dimer gallates, dimer digallates, trimer gallates, tetramer gallates, pentamer gallates, and hexamer gallates), while only monomer gallates and dimer gallates were confirmed in Japanese knotweed and monomer gallates, dimer gallates, and dimer digallates were detected in leaves of Bohemian knotweed. The profile of the Bohemian knotweed clearly showed the traits inherited from Japanese and giant knotweed from which it originated.

Innovative Extraction Techniques Using Deep Eutectic Solvents and Analytical Methods for the Isolation and Characterization of Natural Bioactive Compounds from Plant Material

“…Maceration (heating and stirring method) and Soxhlet extraction are the oldest types of extraction techniques and usually uses organic solvents such as methanol (MeOH), ethanol (EtOH), propanol, acetone, ethyl acetate and their mixtures with varying proportions of water [23][24][25]. The extraction solvent, the solid/solvent ratio and the process temperature are the most important parameters when it comes to extraction efficiency [26]. However, these conventional techniques have numerous drawbacks, the most important of which are: long extraction time, high extraction costs (associated with the use of large quantities of organic solvents and energy), non-selective extraction, possibility of degradation/isomerization of analytes due to prolonged heating, negative environmental effects and inappropriate recycling practices for the solvents used [27].…”

“…In the long term, would their use lead to a shortened lifetime of the extractors and the analytical tools needed for their identification and quantification? All the above questions remain open and certainly offer many possibilities that can be answered in the future [26,168,169].…”

Flavan-3-ols and Proanthocyanidins in Japanese, Bohemian and Giant Knotweed

“…Post-chromatographic derivatization with 4-dimethylaminocinnamaldehyde (DMACA) reagent [ 17 ] enabled the detection of flavan-3-ols and proanthocyanidins, which was more selective than the detection before derivatization. We previously used this method in two studies: (1) an HPTLC/MS/MS study on flavan-3-ols and proanthocyanidins in rhizomes of Japanese knotweed [ 9 ]; and (2) an HPTLC study on flavan-3-ols and proanthocyanidins in leaves of Japanese, Bohemian and giant knotweed [ 18 ]. In this study, the following twelve standards were used for analyses: (+)-catechin, (−)-epicatechin, (−)-catechin gallate, (−)-epicatechin gallate, (−)-gallocatechin, (−)-epigallocatechin, (−)-gallocatechin gallate, (−)-epigallocatechin gallate, procyanidin B1, procyanidin B2, procyanidin B3 and procyanidin C1 ( Figure 1 ).…”

“…Additionally, from the peak heights in vid eodensitograms of all STSs it is evident that Japanese knotweed is the richest source of proanthocyanidins ( Figure 5 ). The chromatographic fingerprints of rhizomes of Japanese, Bohemian and giant knotweed were also compared with the chromatographic fingerprints of leaves obtained from the respective plant species and collected at the same locations [ 18 ] as the rhizomes. The STSs of leaves were prepared as described in our previous study [ 18 ].…”

“…Im ages of the chromatograms were converted to videodensitograms, which were integrated using VideoScan software. Limits of detection (LOD), limits of quantification (LOQ) and the stability of the derivatized standards of (−)-epicatechin (100 ng) and procyanidin B2 (100 ng) on the HPTLC silica gel plates were described in our previous study [ 18 ]. STSs from rhizomes were analyzed on an HPTLC silica gel plate ( Figure 4 ) using equal amounts (30, 40, 60, 80, 100, 120 and 150 ng per plate) of (−)-epicatechin and procyanidin B2 standards for the calibration curves.…”