Guarana powder polyphenols and alpha-glucosidase inhibition in lab tests
What it found
In lab tests, polyphenols released from the insoluble part of guarana powder blocked the enzyme alpha-glucosidase more strongly than the soluble polyphenols did.
The insoluble fraction contained 14 proanthocyanidins, mostly dimers to tetramers.
What they found
Animal and lab studies
Enzyme blocking strength
The insoluble-bound fraction needed a 5.8-fold lower concentration than the soluble fraction to block half of the alpha-glucosidase activity. Its value was 1.624 µg GAE/mL, compared with 9.50 µg GAE/mL for the soluble fraction.
Comparison to acarbose
The insoluble-bound fraction's half-blocking value was lower than that reported for acarbose, which ranged from 36.0 to 107.3 µg/mL in other studies. It was also in the same range as green, oolong and black tea.
How they block the enzyme
Both fractions blocked alpha-glucosidase in a mixed reversible way, meaning they can bind to the free enzyme and to the enzyme-substrate complex. Both bound more effectively to the free enzyme than to the enzyme-substrate complex.
Proanthocyanidin profile
Fourteen proanthocyanidins, from dimers to tetramers, were tentatively identified in the insoluble-bound fraction. They included propelargonidins and procyanidins, with mostly type-A linkages, and no galloylated compounds were found.
Afzelechin presence
Afzelechin was found in the insoluble-bound fraction but has never been identified in the soluble fraction of guarana powder. A recent study found a positive link between afzelechin units in proanthocyanidins and their ability to block alpha-glucosidase.
Other findings
Phenolic content
The soluble fraction had 65.16 mg GAE/g of guarana powder, while the insoluble-bound fraction had 3.97 mg GAE/g. The insoluble-bound fraction made up 6% of the total phenolic content.
What the authors conclude
“Insoluble-bound polyphenols showed a higher efficacy (lower IC 50 ) in inhibiting alpha-glucosidase compared to that of soluble phenolics.”
Also in their conclusions
- They say the insoluble-bound polyphenols were more effective at inhibiting alpha-glucosidase than the soluble ones.
- They suggest that other processes, such as enzyme-assisted extraction or fermentation, should be used to release more of these compounds from the cell wall.
- They say the results may help in finding nutraceuticals and functional ingredients for managing or preventing type 2 diabetes.
How it was done
The authors wanted to see whether polyphenols bound to the cell walls of guarana powder, which are usually thrown away, could also block alpha-glucosidase. They say no previous study had looked at this insoluble-bound fraction.
They extracted soluble polyphenols from guarana powder bought in São Paulo, Brazil, then released the insoluble-bound polyphenols from the leftover residue using alkali and ultrasound. They measured total phenolics, tested both fractions against alpha-glucosidase in the lab, and used MALDI-TOF mass spectrometry to identify compounds in the insoluble-bound fraction.
What it can’t tell you
- These are lab tests using an enzyme from yeast, not studies in people. They cannot show what happens to blood sugar in someone who eats guarana powder.
- The study did not feed guarana to anyone, so it cannot show whether the insoluble-bound polyphenols reach the small intestine or affect diabetes in real life.
Who paid
- Funding
- Funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior; Fondo Nacional de Desarrollo Científico y Tecnológico; Natural Sciences and Engineering Research Council of Canada; Fundação de Amparo à Pesquisa do Estado de São Paulo; Conselho Nacional de Desenvolvimento Científico e Tecnológico (from the PubMed record).
- Conflicts
- The authors declare no conflict of interest.
- Authors work at
- University of Sao Paulo, Brazil; Memorial University of Newfoundland, Canada
The paper
- Title
- Insoluble-Bound Polyphenols Released from Guarana Powder: Inhibition of Alpha-Glucosidase and Proanthocyanidin Profile
- Type
- Study
- Evidence
- Animals and lab studies
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Pinaffi ACDC, Sampaio GR, Soares MJ, Shahidi F, de Camargo AC, Torres EAFS (2020). Insoluble-Bound Polyphenols Released from Guarana Powder: Inhibition of Alpha-Glucosidase and Proanthocyanidin Profile. Molecules (Basel, Switzerland). doi:10.3390/molecules25030679Free full textPubMed 32033416DOI
Summary written 29 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error