Presenting ChromaQuest findings at CONECT 2026: Keeping natural colours from fading, with help from invasive plants

Photos by: Elīna Karaseva and Kristiāna Jasureviča, poster by Evelina Niedrite

At the XIX International Scientific Conference of Environmental and Climate Technologies (CONECT 2026), held 12–15 May 2026 at the Riga Technical University Auditorium Centre "Domus Auditorialis" in Riga, Latvia, Evelina Niedrite presented a poster titled "Polyphenols from invasive Reynoutria species: extraction, characterisation, application." The work was carried out at the Department of Environmental Science, University of Latvia, together with co-authors Linda Ansone-Bertina, Linards Klavins, Jorens Kviesis, Alise Zommere, and Maris Klavins.

Anthocyanins are the natural pigments behind the deep reds, purples, and blues of many berries, and they are increasingly attractive as plant-based alternatives to synthetic food colourants. Their weakness is stability: exposed to heat, light, and changes in pH, anthocyanins gradually lose their red colour and drift towards dull brown tones. That fading is the main barrier to using them in real products.

Copigmentation is a stabilisation strategy in which anthocyanins are paired with "copigment" molecules typically colourless polyphenols. Through non-covalent interactions such as π–π stacking and hydrogen bonding, the copigments wrap around the coloured form of the anthocyanin (the flavylium cation) and shield it from the water attack that would otherwise bleach it into colourless or brown by-products. The net effect is more intense, longer-lasting colour.

The novelty here is where the copigments come from. Invasive knotweed (Reynoutria) species are an environmental problem that generates large amounts of biomass when they are cleared biomass that usually has to be disposed of. But that same biomass is unusually rich in polyphenols (flavonoids, stilbenes, phenolic acids, and flavan-3-ols such as catechin). The study extracted and purified these polyphenols and put them to work as a copigment for aronia (chokeberry) anthocyanins, a natural colourant that is famously rich in pigment but quick to degrade.

Aronia anthocyanins were held at a fixed concentration and combined with knotweed polyphenol extract at a lower and a higher dose, then stored for 10 days at 4, 21, and 40 °C. Colour was tracked by UV–VIS spectroscopy (the red anthocyanin band sits near 525 nm; a rising band near 440 nm signals browning) and by CIELAB colour measurements. The key results:

• More copigment meant far better colour retention. Under heat stress at 40 °C, the lower-dose sample lost roughly 48 % of its red colour over 10 days, while the higher-dose sample lost only about 3 %.

• The benefit was clearest under stress. At a cool 4 °C everything stayed fairly stable, but as temperature rose, the extra copigment made a growing difference at 21 °C the lower dose faded noticeably while the higher dose barely changed.

• Less browning, too. The rise in the 440 nm browning band was consistently smaller at the higher copigment concentration, meaning the polyphenols not only preserved redness but also suppressed the side-reactions that turn anthocyanins brown.

• Colour measurements agreed. CIELAB data confirmed that redness (the a* value) was much better preserved at the higher copigment dose, whereas the low-dose, high-temperature sample faded markedly.

Together these results point to a clear, dose-dependent stabilisation effect, strongest at higher polyphenol concentration and lower temperature. Findings show a route to more stable natural colourants useful for food, packaging, and other applications looking to move away from synthetic dyes. Environmentally, they turn invasive-plant biomass into a high-value functional ingredient, giving an economic incentive to clear these species rather than simply paying to destroy them.

The work forms part of the Latvian Council of Science project ChromaQuest  "Biorefinery-derived Functional Ingredients for Enhanced Conjugate Stability of Natural Dyes through Co-pigmentation" (project No. lzp-2024/1–0066).