Apple polyphenols released during oral digestion from peel and flesh
What it found
In lab tests, 63 to 82 percent of polyphenols were released from apple flesh and 42 to 58 percent from peel during simulated oral digestion.
The release was similar whether human saliva or a lab-made saliva fluid was used.
What they found
Animal and lab studies
Polyphenol release from flesh
Between 63 and 82 percent of polyphenols were released from apple flesh during oral digestion. The variety Santana had the lowest release at 63 percent.
Polyphenol release from peel
Between 42 and 58 percent of polyphenols were released from apple peel. This was significantly lower than from flesh.
Different polyphenol groups
Hydroxycinnamic acid derivatives were released almost completely from flesh, while flavanols were released less. In peel, all groups had lower release, with flavonols and anthocyanins the lowest.
Procyanidin size effect
Larger procyanidins were released less than smaller ones. This trend was seen in both peel and flesh.
Saliva comparison
The release of polyphenols was similar when using lab-made saliva fluid or real human saliva. The difference was only 3 to 7 percent for flesh and 2 to 4 percent for peel.
Polyphenol content in apples
The peel had 2.6 to 4.5 times more polyphenols than the flesh. Commercial varieties like Braeburn and Holstein Cox had lower polyphenol levels than older varieties like Gewürzluiken and Goldparmäne.
What the authors conclude
“The data reveal a considerable polyphenol release during the oral digestion; however, differences among the varieties as well as flesh and peel were obvious.”
Also in their conclusions
- They say the data show a considerable release of apple polyphenols during oral digestion, which might allow some absorption through the mouth.
- They support eating fresh apples with the peel because the peel has more polyphenols and a wider variety of them.
- They point out the importance of chewing well, as it helps release polyphenols from the apple cells.
How it was done
The authors wanted to understand how much of the polyphenols in apples are released from the food matrix during the first step of digestion, because only released polyphenols can be absorbed by the body. They also wanted to see if a simple lab-made saliva fluid could replace human saliva in these experiments.
They studied seven apple varieties, using both lab-made saliva fluid and real human saliva from two women. They measured polyphenol release from freeze-dried flesh and peel after 2 minutes of simulated oral digestion.
What it can’t tell you
- This was a lab study using simulated digestion, so it cannot show what happens in the human body after eating an apple.
- The release was measured only during the oral phase, not during later digestion in the stomach or intestines.
- The study used freeze-dried apple samples, not fresh apples, so the results might differ from eating a whole apple.
Who paid
- Conflicts
- The authors declare no competing financial interest.
- Authors work at
- University of Stuttgart, Germany
The paper
- Title
- Bioaccessibility of Apple Polyphenols from Peel and Flesh during Oral Digestion
- Type
- Study
- Evidence
- Animals and lab studies
- Summarised from
- Full text
- Cite
- Kaeswurm JAH, Burandt MR, Mayer PS, Straub LV, Buchweitz M (2022). Bioaccessibility of Apple Polyphenols from Peel and Flesh during Oral Digestion. Journal of agricultural and food chemistry. doi:10.1021/acs.jafc.1c08130Free full textPubMed 35357186DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error