Apple Peel Powder: What is Quercetin and What Are Its Benefits?

February 25, 2024 8 min read

Apple Peel Powder: What is Quercetin and What Are Its Benefits?

According to some, apples are the second most popular fruit in the world but how do you eat yours? Do you peel it, core it, chop it, or eat it whole? However you choose to eat an apple, it’s bursting with nutrients and if you’re removing the skin before you eat it, read on to find out why you shouldn’t (or if you do why you should get yourself a pot of Apple Peel Powder instead).

The nutritional profile of apple peel

“An apple a day can keep the doctor away” is a famous saying but here we’re specifically going to focus on the peel. It’s not to everyone’s taste but nestled inside the crunchy outside of the apple is an array of nutrients, including fibre, vitamins, and minerals.

The peel is also home to some pretty special antioxidants. Many of the protective benefits associated with fruits and vegetables can be attributed to antioxidants and phytochemicals[i].

One of those is quercetin, which has been linked to lowering the risk of diabetes, heart disease, and even cancer[ii]. Quercetin can be referred to as a phytochemical, polyphenol or flavonoid.

What is quercetin?

Quercetin is a potent antioxidant flavonoid, or more specifically a flavonol. It’s a plant pigment and is found in many foods, including:

  • Apples
  • Berries
  • Cherries
  • Citrus fruits
  • Grapes
  • Onions

The beneficial effects of flavonoids like quercetin are derived from their functions as antioxidants in the body. Antioxidants are compounds that bind to free radicals to neutralise them and stop them from causing you harm. They’re a bit like a security guard escorting a rowdy person out of a public building.

When free radicals are in a high abundance in the body, they can cause cellular damage which is linked to several chronic illnesses.

Quercetin is the most consumed flavonol in the human diet. Flavonols are a subgroup of flavonoids, natural substances that are found in deep-coloured foods. Flavonols have a ketone group and are associated with a wide range of health benefits and antioxidant potential. They are the largest and most common flavonoid subgroup[iii].

How does the body absorb quercetin?

When you eat foods containing quercetin, a small amount is absorbed in the stomach, but the major absorption site is the small intestine. Any unabsorbed quercetin passes to the colon, where it is used up by the colonocytes, the cells lining your bowel.

Bacteria, including Eubacterium ramulusClostridium orbiscindensEubacterium oxidoreducens, and the Butyrovibrio spp.transform quercetin into the following metabolites:

  • 3,4-dihydroxyphenylacetic acid
  • 3-(3-hydroxyphenyl) propionic acid
  • 3,4-dihydroxybenzoic acid
  • 4-hydroxybenzoic acid

These metabolites are then transported to tissues and cells throughout the body via the circulatory system, where they are thought to have a greater health impact than the original quercetin[iv]. For example, in a study by Vissiennon et al (2011) p-hydroxyphenylacetic acid and 3,4-dihydroxyphenylacetic acid had an anti-anxiety effect[v].

Health benefits of quercetin

Quercetin has been linked to a variety of health properties. The potent antioxidant and anti-inflammatory effects of this flavonoid have generated much scientific interest. Here, we’ll delve into some of those effects backed up by science.

Antioxidant properties

The most revered property of quercetin is its antioxidant potential. It can neutralise free radicals travelling around the body, limiting the damage they cause. When there is a build-up of free radicals, it can lead to a phenomenon called oxidative stress, so keeping them in check with antioxidants can help limit the development of chronic and age-related diseases[vi].

Research has shown that quercetin has neuroprotective benefits against chronic Alzheimer’s Disease. Specific proteins called FoxO, which are key substrates of SIRT1, are necessary for the formation of memory and cognitive function. Dysfunction in these proteins or transcription factors has been associated with numerous age-related diseases, including Alzheimer’s[vii]. Quercetin targets SIRT1 to regulate cellular senescence and age-related cellular processes[viii].

A further study by Elreedy et al (2022) found that quercetin when administered with aluminium chloride, resulted in a significant improvement in short-term memory in rodents. The study found that its benefits were linked to its ability to reduce the expression of a hallmark Alzheimer’s Disease gene[ix].

Anti-inflammatory properties

Wherever there’s a chronic disease, inflammation is never far behind. Quercetin can prevent inflammation by reducing the production of inflammatory cytokines. This can help to prevent inflammatory disease and pain associated with inflammation[x].

In a study by Kim et al. (2019) quercetin was found to reduce the clinical symptoms of arthritis by stopping the release of inflammatory cytokines, such as interleukin-17, and could have the potential to become a therapeutic agent for bone destructive processes seen in rheumatoid arthritis[xi].

A further study by El-Said et al (2022), demonstrated quercetin from Egyptian Fenugreek seeds has an anti-inflammatory effect in rodent models against rheumatoid arthritis. That’s because it can downregulate the expression of adenosine deaminase (ADA) genes. ADA is an inflammatory enzyme that causes pain and joint stiffness in rheumatoid arthritis patients[xii].

Cardiovascular health

There is a lot of research into the effect of quercetin on heart health.  A study published in 2007 investigated the effects of quercetin on high-blood pressure patients and those with prehypertension. The researchers found that quercetin reduced, systolic, diastolic and mean arterial pressure in high blood pressure patients. Blood pressure was unchanged in prehypertensive patients[xiii].

Several studies have also shown that quercetin can reduce the progression of atherosclerosis in animal models. A study by Juźwiak et al. (2005) investigated the effects of quercetin on high blood fat levels and the development of atherosclerotic plaques in animal models. It was shown that quercetin reduced triglyceride and cholesterol levels caused by eating a high-fat diet after 3 months. Quercetin also lowered the formation of plaques in the aorta and carotid artery in animals fed a high-fat diet[xiv].  

Immune function

Quercetin’s anti-inflammatory and antioxidant properties help to bolster the immune system. Animal studies have shown that quercetin may have an important role in relieving allergy symptoms.

For example, quercetin supplementation in animals has shown that this potent flavonoid could protect against immunoglobulin E-mediated food allergies, such as peanuts[xv]. As well as anti-allergic properties, quercetin is also known for its antioxidant activity and stimulation of the immune system, which means it can be used in the treatment of other illnesses such as bronchial asthma and allergic rhinitis[xvi].

Cancer prevention

An emerging area of research for quercetin is cancer prevention. Early studies are showing that quercetin can increase cell apoptosis, effectively cell suicide, and autophagy. It can also prevent metastasis of cancer cells[xvii].

Currently, this research is in its early stages, so more research is needed. However, the inclusion of quercetin could have some potent protective benefits.

Additional benefits of apple peel

Although quercetin steals the spotlight because of its numerous, and quite frankly remarkable, health benefits, apple peel in general is a treasure trove of nutrients.

One of which is fibre. The peel of an apple contains a large proportion of its overall dietary fibre content. Fibre can support the normal function of your gut microbiome and regular bowel movements, preventing constipation.

Apple peel is also packed with phenols, like polyphenols (including quercetin), that can improve digestion, cognitive function, blood sugar levels and a whole host of other wonderful things.

Zahid et al (2023) investigated the stability and bioaccessibility of freeze-dried apple peel powder in invitro digestion and colonic phases. They found that gut microbes utilised the phenolic compounds present in the apple peel powder. The fermentation of the peel caused a reduction in pH, increasing the abundance of Bifidobacteria.Therefore, the study showed that freeze-dried apple peel powder could support the growth and activity of intestinal bacteria, demonstrating its prebiotic effects, which in turn could support your health[xviii].

How to incorporate apple peel into your diet

Squeezing quercetin, and more specifically apple peels, into your diet couldn’t be easier with our Organic Apple Peel Powder. Each 4.2g serving of apple peel powder is bursting with vitamins A and C, potassium, calcium, folate and iron. It’s also bursting with polyphenols that will support the growth and activity of your gut microbiota.

Check out our prevention and repair recipes to show you how you can easily incorporate this pot of magic into your diet or combine it with our PureHMO® range for a simple gut health smoothie.

Conclusion

Despite being discarded in favour of the flesh, apple peel is a powerhouse of nutrition and health benefits. It contains an array of nutrients, including flavonols, like quercetin, which offer antioxidant and anti-inflammatory effects, as well as benefits for your heart health, immunity, and potentially even cancer protection.

Why not explore the world of apple peels and incorporate them into your diet, to give your body a nutritious boost?

Written by: Leanne Edermaniger, M.Sc. Leanne is a professional science writer who specializes in human health and enjoys writing about all things related to the gut microbiome. 

Sources

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[ii] Ansari P, Choudhury ST, Seidel V, Rahman AB, Aziz MA, Richi AE, Rahman A, Jafrin UH, Hannan JMA, Abdel-Wahab YHA. Therapeutic Potential of Quercetin in the Management of Type-2 Diabetes Mellitus. Life (Basel). 2022 Jul 28;12(8):1146. doi: 10.3390/life12081146. PMID: 36013325; PMCID: PMC9409999.

[iii] Panche AN, Diwan AD, Chandra SR. Flavonoids: an overview. J Nutr Sci. 2016 Dec 29;5:e47. doi: 10.1017/jns.2016.41. PMID: 28620474; PMCID: PMC5465813.

[iv] Hai Y, Zhang Y, Liang Y, Ma X, Qi X, Xiao J, et al. Advance on the absorption, metabolism, and efficacy exertion of quercetin and its important derivatives. Food Frontiers. 2020 Nov 2;1(4):420–34. doi:10.1002/fft2.50

[v] Vissiennon C, Nieber K, Kelber O, Butterweck V. Route of administration determines the anxiolytic activity of the flavonols Kaempferol, quercetin and myricetin — are they prodrugs? The Journal of Nutritional Biochemistry. 2012 Jul;23(7):733–40. doi:10.1016/j.jnutbio.2011.03.017

[vi] Pizzino G, Irrera N, Cucinotta M, Pallio G, Mannino F, Arcoraci V, Squadrito F, Altavilla D, Bitto A. Oxidative Stress: Harms and Benefits for Human Health. Oxid Med Cell Longev. 2017;2017:8416763. doi: 10.1155/2017/8416763. Epub 2017 Jul 27. PMID: 28819546; PMCID: PMC5551541.

[vii] Du S, Zheng H. Role of FoxO transcription factors in aging and age-related metabolic and neurodegenerative diseases. Cell Biosci. 2021 Nov 2;11(1):188. doi: 10.1186/s13578-021-00700-7. PMID: 34727995; PMCID: PMC8561869.

[viii] Cui Z, Zhao X, Amevor FK, Du X, Wang Y, Li D, et al. Therapeutic application of quercetin in aging-related diseases: SIRT1 as a potential mechanism. Frontiers in Immunology. 2022 Jul 22;13. doi:10.3389/fimmu.2022.943321

[ix] Elreedy HA, Elfiky AM, Mahmoud AA, Ibrahim KS, Ghazy MA. Neuroprotective effect of quercetin through targeting key genes involved in aluminum chloride induced alzheimer’s disease in rats. Egyptian Journal of Basic and Applied Sciences. 2023 Jan 5;10(1):174–84. doi:10.1080/2314808x.2022.2164136

[x] Li Y, Yao J, Han C, Yang J, Chaudhry MT, Wang S, Liu H, Yin Y. Quercetin, Inflammation and Immunity. Nutrients. 2016 Mar 15;8(3):167. doi: 10.3390/nu8030167. PMID: 26999194; PMCID: PMC4808895.

[xi] Kim HR, Kim BM, Won JY, Lee KA, Ko HM, Kang YS, Lee SH, Kim KW. Quercetin, a Plant Polyphenol, Has Potential for the Prevention of Bone Destruction in Rheumatoid Arthritis. J Med Food. 2019 Feb;22(2):152-161. doi: 10.1089/jmf.2018.4259. Epub 2018 Dec 31. PMID: 30596535.

[xii] El-Said KS, Atta A, Mobasher MA, Germoush MO, Mohamed TM, Salem MM. Quercetin mitigates rheumatoid arthritis by inhibiting adenosine deaminase in rats. Mol Med. 2022 Feb 22;28(1):24. doi: 10.1186/s10020-022-00432-5. PMID: 35193490; PMCID: PMC8862293.

[xiii] Edwards RL, Lyon T, Litwin SE, Rabovsky A, Symons JD, Jalili T. Quercetin reduces blood pressure in hypertensive subjects. J Nutr. 2007 Nov;137(11):2405-11. doi: 10.1093/jn/137.11.2405. PMID: 17951477.

[xiv] Juźwiak S, Wójcicki J, Mokrzycki K, Marchlewicz M, Białecka M, Wenda-Rózewicka L, Gawrońska-Szklarz B, Droździk M. Effect of quercetin on experimental hyperlipidemia and atherosclerosis in rabbits. Pharmacol Rep. 2005 Sep-Oct;57(5):604-9. PMID: 16227643.

[xv] Shishehbor F, Behroo L, Ghafouriyan Broujerdnia M, Namjoyan F, Latifi SM. Quercetin effectively quells peanut-induced anaphylactic reactions in the peanut sensitized rats. Iran J Allergy Asthma Immunol. 2010 Mar;9(1):27-34. PMID: 20548131.

[xvi] Mlcek J, Jurikova T, Skrovankova S, Sochor J. Quercetin and Its Anti-Allergic Immune Response. Molecules. 2016 May 12;21(5):623. doi: 10.3390/molecules21050623. PMID: 27187333; PMCID: PMC6273625.

[xvii] Reyes-Farias M, Carrasco-Pozo C. The Anti-Cancer Effect of Quercetin: Molecular Implications in Cancer Metabolism. Int J Mol Sci. 2019 Jun 28;20(13):3177. doi: 10.3390/ijms20133177. PMID: 31261749; PMCID: PMC6651418.

[xviii] Zahid HF, Ali A, Ranadheera CS, Fang Z, Ajlouni S. Identification of Phenolics Profile in Freeze-Dried Apple Peel and Their Bioactivities during In Vitro Digestion and Colonic Fermentation. Int J Mol Sci. 2023 Jan 12;24(2):1514. doi: 10.3390/ijms24021514. PMID: 36675061; PMCID: PMC9864335.


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