RESEARCH LIBRARY / EVIDENCE INDEX

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Explore selected studies on plants, brewing and quality, with clear summaries and links to the original research.

External research, not PUREXA product test reports.

Browse 7 selected studies

EXPLORE THE EVIDENCE

Plants & preparation (3)

Why the plant and preparation matter

Three Annona species / leaves, stem bark and seeds / three preparation methods.

Chemical profiles and laboratory responses differed across the Annona species, plant parts and preparations studied.

Why it matters: A finding about one plant part or extract cannot automatically describe another.

Study limits: Laboratory research on Angolan plant material—not a trial in people or a test of PUREXA tea.

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Source details

Phenolic Profile and Bioactive Prospects of Wild Annona Species From Angola

Rangel et al. / Chemistry & Biodiversity

DOI: 10.1002/cbdv.202503294

Source checked: 24 October 2026

How butterfly pea pigments respond to pH

Blue-petal extracts / pigment chemistry.

In laboratory extracts, butterfly pea pigments changed colour as pH changed, and those colour changes were reversible.

Why it matters: This helps explain why changing acidity can change the colour of butterfly pea tea.

Study limits: The experiments tested petal extracts under controlled conditions—not a health benefit or the stability of every brewed cup.

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Source details

Phenolic composition by UHPLC-Q-TOF-MS/MS and stability of anthocyanins from Clitoria ternatea L. (butterfly pea) blue petals

Escher et al. / Food Chemistry

DOI: 10.1016/j.foodchem.2020.127341

Source checked: 24 October 2026

How preparation affects hibiscus extraction

Hibiscus calyces—the fleshy structures around the flowers / water extraction.

Plant-piece size and the amount of water affected pigment extraction. Higher temperatures shortened extraction time but did not increase the final yield in this experiment.

Why it matters: Preparation can change how quickly compounds enter the water—not just the final amount extracted.

Study limits: This study measured hibiscus pigments under controlled conditions; it does not establish an ideal recipe for every herbal tea.

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Source details

Aqueous extraction of anthocyanins from Hibiscus sabdariffa: Experimental kinetics and modeling

Cissé et al. / Journal of Food Engineering

DOI: 10.1016/j.jfoodeng.2011.10.012

Source checked: 24 October 2026

EXPLORE THE EVIDENCE

Methods & quality (2)

Why the testing method matters

Testing method evaluated for 219 pesticide targets across seven herbal materials.

Changing the laboratory solvent and sample dilution changed pesticide-measurement signals, with different effects across the herbal materials.

Why it matters: A testing method needs to account for the material being measured.

Study limits: This is a method study—not evidence that these herbs or PUREXA products contain the pesticides studied.

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Source details

Influence of injection solvent and serial dilution on matrix effect in GC-MS/MS multiresidue pesticide analysis: a factorial study across seven herbal matrices

Enia et al. / Scientific Reports

DOI: 10.1038/s41598-026-72448-4

Source checked: 24 October 2026

Mycotoxins in dried herbs

91 dried-herb samples / laboratory testing and exposure modelling.

Some dried-herb samples contained measurable mycotoxins. Estimated exposure to fumonisin B2 and total zearalenone did not indicate a health concern under the study’s assumptions.

Why it matters: Finding a substance and estimating exposure answer different questions.

Study limits: The exposure assessment covered those two toxin groups, not every mycotoxin or any PUREXA batch.

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Source details

Mycotoxins occurrence in dry herbs used for tea preparation: method validation, analysis of bulk samples and dietary risk assessment

Evangelista et al. / Mycotoxin Research

DOI: 10.1007/s12550-026-00652-2

Source checked: 24 October 2026

EXPLORE THE EVIDENCE

Interpreting findings (2)

A six-week hibiscus tea trial

65 adults with prehypertension or mild hypertension / brewed hibiscus or placebo / six weeks.

Systolic blood pressure—the upper number—fell more in the hibiscus-tea group than in the placebo group. The difference in diastolic pressure was not statistically significant.

Why it matters: A human finding needs to be read alongside who took part, what they drank and what was measured.

Study limits: The result applies to the studied preparation and participants; it does not establish an effect of a PUREXA product.

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Source details

Hibiscus sabdariffa L. tea (tisane) lowers blood pressure in prehypertensive and mildly hypertensive adults

McKay et al. / The Journal of Nutrition

DOI: 10.3945/jn.109.115097

Source checked: 24 October 2026

Different laboratory tests, different responses

Water-based leaf extract / cell-free chemical tests.

A water-based soursop leaf extract produced different responses across the chemical tests: activity against some reactive molecules, but an increase in peroxynitrite.

Why it matters: One laboratory result does not describe every response to the extract.

Study limits: These tests were outside living cells and do not show a health effect in people.

View study abstract
Source details

Effect of Annona muricata aqueous leaf extract on reactive oxygen and nitrogen species

Vidová Uğurbaş et al. / European Review for Medical and Pharmacological Sciences

DOI: 10.26355/eurrev_202209_29748

Source checked: 24 October 2026

Selected for questions about plants, preparation and testing—not as a complete review of the evidence.

Terms used in these studies
In vitro
Tests outside a living organism, rather than a study in people.
Assay
A laboratory test used to measure a specific response.
Matrix
The material being tested, such as a particular herb.
Analyte
The substance a test measures.
Mycotoxins
Toxins produced by certain moulds.

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