Proanthocyanidins: Food Sources, Cranberries & What Research Shows

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What Are Proanthocyanidins?

Proanthocyanidins are a structurally diverse group of plant flavonoids composed of linked flavan-3-ol units.

Common building blocks include:

• catechin;
• epicatechin;
• gallocatechin;
• epigallocatechin; and
• related flavan-3-ol structures.

When these units join together, they can form:

• dimers — two flavan-3-ol units;
• trimers — three units;
• oligomers — relatively short chains; and
• polymers — longer chains with a higher degree of polymerization.

The exact terminology used for oligomeric versus polymeric proanthocyanidins varies somewhat among researchers, so the number of units and analytical method should be checked when comparing studies.

Proanthocyanidins are described as condensed tannins because they differ structurally from hydrolyzable tannins such as gallotannins and ellagitannins.

Why Are They Called Proanthocyanidins?

The name has a historical chemical basis.

Under strongly acidic conditions and heat, proanthocyanidins can undergo reactions that produce colored anthocyanidin-related compounds.

This does not mean proanthocyanidins are simply stored anthocyanins inside fruit.

Anthocyanins and proanthocyanidins are distinct flavonoid families with different structures, physical properties, metabolism, and roles in plants.

Proanthocyanidins vs. Anthocyanins

The similar names can cause confusion.

Anthocyanins are glycosylated pigments responsible for many red, purple, blue, and violet colors in fruits and vegetables.

Proanthocyanidins are oligomers and polymers of flavan-3-ols and are commonly classified as condensed tannins.

Proanthocyanidins can contribute to bitterness and astringency but are not responsible for fruit color in the same way anthocyanins are.

A fruit can contain both families at the same time.

Cranberries and aronia berries, for example, contain anthocyanins as well as proanthocyanidins. The presence of both compounds does not mean they have identical chemistry or biological effects.

Explore the pigment family separately in our Anthocyanins guide.

Proanthocyanidins vs. Procyanidins: What Is the Difference?

Procyanidins are a subgroup of proanthocyanidins.

The term proanthocyanidin describes the broader family.

Procyanidins are proanthocyanidins built primarily from catechin and epicatechin units.

Other proanthocyanidin families can be formed from different flavan-3-ol building blocks.

Examples include:

• Procyanidins — derived primarily from catechin and epicatechin units.
• Prodelphinidins — contain gallocatechin or epigallocatechin-related units.
• Propelargonidins — contain afzelechin or epiafzelechin-related units.

Procyanidins are particularly widespread in common foods and are frequently the compounds being discussed when food articles use “proanthocyanidins” more broadly.

A-Type vs. B-Type Proanthocyanidins

Another important distinction involves the chemical bonds joining individual flavan-3-ol units.

B-Type Proanthocyanidins

B-type proanthocyanidins contain a single carbon-to-carbon interflavan linkage between neighboring flavan-3-ol units.

B-type structures are widely distributed throughout plant foods and are particularly common in foods such as grapes, cocoa, apples, and many other fruits and seeds.

A-Type Proanthocyanidins

A-type proanthocyanidins contain the carbon-to-carbon linkage plus an additional ether linkage involving oxygen.

This additional bond changes the three-dimensional structure and physicochemical behavior of the molecule.

Cranberries are one of the best-known dietary sources of proanthocyanidins containing A-type linkages.

However, A-type proanthocyanidins are not unique to cranberries. They have also been identified in foods and plants such as lingonberries, peanuts, lychee, persimmons, avocado, and other botanical sources.

The unusually prominent A-type PAC profile of American cranberry is one reason cranberry proanthocyanidins have received substantial research attention.

What Are Oligomeric Proanthocyanidins (OPCs)?

The abbreviation OPC commonly means oligomeric proanthocyanidins.

The term is frequently encountered in supplement marketing and research involving grape seed or pine bark extracts.

OPCs generally refer to relatively short proanthocyanidin chains, often dimers, trimers, and tetramers.

Longer proanthocyanidin chains are usually described as polymeric proanthocyanidins.

The boundary between “oligomeric” and “polymeric” is not defined identically in every publication, which is another reason to examine the analytical definition used in a study rather than relying only on the term OPC.

What Foods Contain Proanthocyanidins?

Proanthocyanidins occur in many plant foods.

Common dietary sources include:

• Apples
• Grapes
• Cranberries
• Aronia berries
• Blueberries and other berries
• Cocoa and dark chocolate
• Plums
• Peaches
• Nuts
• Legumes
• Certain grains
• Tea and wine

A U.S. food-composition study found that apples, chocolate, and grapes were major contributors to estimated proanthocyanidin intake in the American diet.

That does not mean those three foods always contain the highest concentration per gram. Dietary contribution depends on both concentration and how much of a food people consume.

Which Foods Are Highest in Proanthocyanidins?

There is no single permanent ranking of the “highest proanthocyanidin foods.”

Measured values depend on:

• plant species;
• cultivar;
• growing conditions;
• fruit maturity;
• skin, seed, pulp, or other tissue analyzed;
• fresh versus dry weight;
• degree of polymerization included in the analysis;
• extraction procedure;
• processing and storage; and
• analytical method.

Foods such as cocoa, certain grape seeds and skins, aronia berries, cranberries, apples, and several other deeply pigmented or tannin-rich fruits can provide substantial amounts of particular proanthocyanidin fractions.

But a concentration measured in a seed extract should not be directly compared with the concentration in a whole fruit serving without accounting for the sample basis.

Proanthocyanidins in Fruit

Proanthocyanidins are relevant to several fruits used by FruitFast, but each fruit has its own composition.

Cranberries

Cranberries contain a distinctive mixture of flavonoids that includes anthocyanins, flavonols, and proanthocyanidins.

The cranberry PAC profile is particularly notable for the presence of A-type interflavan linkages.

Cranberries can contain procyanidin dimers, oligomers, and larger polymers rather than one single “cranberry PAC” molecule.

Different cranberry juices, concentrates, powders, extracts, and supplements can differ considerably in their PAC concentration, degree of polymerization, and proportions of A-type and B-type linkages.

Aronia Berries

Aronia berries contain substantial quantities of polymeric proanthocyanidins alongside anthocyanins, flavonols, and phenolic acids.

One USDA-associated analysis of several berry species reported especially high total proanthocyanidin concentrations in chokeberry compared with the other berries evaluated in that study.

However, the exact amounts vary by cultivar and analytical method, and whole-aronia research should not automatically be attributed to its proanthocyanidins.

Explore our Aronia educational guide →
That guide covers aronia as a fruit and juice ingredient; it should not be interpreted as evidence that proanthocyanidins alone explain whole-aronia research.

Grapes

Grapes contain proanthocyanidins in several tissues, particularly skins and seeds.

Grape proanthocyanidins are predominantly associated with B-type structures built from catechin- and epicatechin-related units.

Grape seed extracts can be manufactured to contain concentrated proanthocyanidin fractions, making them very different research materials from whole grapes or grape juice.

Blueberries

Blueberries can contain proanthocyanidins in addition to their better-known anthocyanin pigments.

Blueberries also contain flavonols and phenolic acids, and their polyphenol profile differs among species and cultivars.

Research involving whole blueberries therefore should not automatically be described as research on proanthocyanidins.

Apples

Apples are an important dietary source of procyanidins and other flavan-3-ols.

Proanthocyanidin concentrations can differ substantially among cultivars and among peel, flesh, and processed apple products.

The importance of apples in population-level PAC intake reflects both their composition and their widespread consumption.

Are Proanthocyanidins Antioxidants?

Proanthocyanidins demonstrate antioxidant and redox activity in laboratory chemical systems.

The multiple hydroxyl groups present in their flavan-3-ol structures can participate in reactions involving reactive chemical species and metal ions.

However, this does not establish that intact proanthocyanidins circulate throughout the body and directly “neutralize free radicals” after they are eaten.

Higher-molecular-weight proanthocyanidins have limited absorption in intact form.

Some lower-molecular-weight compounds can be absorbed and metabolized, while larger structures primarily continue through the gastrointestinal tract and can be transformed by intestinal microorganisms.

For that reason, modern research increasingly considers:

• degree of polymerization;
• digestive transformations;
• microbial metabolism;
• phenolic metabolites;
• interactions within the gastrointestinal tract; and
• the food matrix in which PACs are consumed.

Learn more about this distinction in our Antioxidants, Free Radicals & Oxidative Stress guide.

How Are Proanthocyanidins Absorbed and Metabolized?

Proanthocyanidin metabolism is strongly influenced by molecular size.

Small flavan-3-ols and some lower-degree oligomers can be absorbed and undergo transformations such as methylation, glucuronidation, and sulfation.

Larger oligomeric and polymeric proanthocyanidins have much lower direct absorption.

A substantial portion can reach the colon, where gut microorganisms can break the compounds down into smaller metabolites.

Reported microbial products include:

• phenyl-γ-valerolactones;
• phenylvaleric acids;
• phenylpropionic acids;
• phenylacetic acids; and
• other smaller aromatic metabolites.

These compounds can subsequently be absorbed and further metabolized by the body.

This means that the substances circulating after consumption of a proanthocyanidin-rich food can look very different chemically from the large proanthocyanidin molecules originally present in the food.

What Role Does the Gut Microbiome Play?

The gut microbiome is especially important in proanthocyanidin research because many PAC structures reach the large intestine.

Microorganisms can transform proanthocyanidins into smaller compounds, while researchers are also investigating whether proanthocyanidin-rich foods influence microbial composition and activity.

Most mechanistic evidence in this area comes from laboratory, animal, or short-term experimental research.

Human responses can vary according to:

• proanthocyanidin structure;
• degree of polymerization;
• food source;
• dose;
• food matrix;
• individual gut microbiota;
• dietary pattern; and
• individual metabolism.

The gut microbiome therefore provides an important research framework, but broad claims that proanthocyanidins “improve gut health” go beyond what can be concluded from every study.

Cranberry Proanthocyanidins & Urinary Tract Research

Cranberry is the fruit most strongly associated with human proanthocyanidin research involving the urinary tract.

An important proposed mechanism involves bacterial adhesion.

Laboratory and ex vivo studies have examined whether cranberry preparations containing A-type proanthocyanidins influence the ability of certain Escherichia coli strains with P fimbriae to adhere to urinary-tract epithelial cells.

Controlled studies using PAC-standardized cranberry preparations have reported increased anti-adhesion activity in urine after consumption.

What Have Clinical Trials of Cranberry Products Found?

A 2023 Cochrane review evaluated 50 randomized or quasi-randomized studies involving 8,857 participants and many different cranberry preparations.

The review reported evidence that cranberry products probably reduced the risk of symptomatic, culture-verified urinary tract infections in some groups, including women with recurrent UTIs, children, and people susceptible to UTIs following certain interventions.

The review did not find similar evidence of benefit in every group studied, including elderly institutionalized adults, pregnant women, and adults with neuromuscular bladder dysfunction and incomplete bladder emptying.

The authors also found that evidence was insufficient to determine whether different PAC doses or juice-versus-tablet formulations reliably produced different clinical outcomes.

Therefore:

• a cranberry clinical-trial result should not automatically be attributed solely to proanthocyanidins;
• a PAC dose used in an experimental preparation is not automatically a recommended daily intake;
• results from one standardized cranberry extract do not automatically apply to cranberry juice or concentrate; and
• this research does not establish that an untested FruitFast cranberry product prevents or treats urinary tract infections.

What Does “36 mg PAC” Mean in Cranberry Research?

Some cranberry studies and supplement labels discuss a daily amount such as 36 mg of proanthocyanidins.

This number comes from specific research traditions involving standardized cranberry preparations and anti-adhesion testing.

It should not be treated as a universal recommended dietary allowance.

Proanthocyanidin measurements also depend on the laboratory method used.

For example, some cranberry research reports PAC values measured using a BL-DMAC colorimetric method.

A PAC value produced by one analytical method is not necessarily interchangeable with a value obtained using a different assay or standard.

The 2023 Cochrane review also reported that available clinical evidence did not demonstrate a clear relationship between low, moderate, and high PAC doses and UTI outcomes.

Proanthocyanidin Research: What Has Human Research Studied?

Human research involving proanthocyanidins is complicated by the fact that many interventions are not purified PACs.

Studies frequently use:

• cranberry juice or cranberry extracts;
• grape seed extracts;
• grape products;
• cocoa products;
• berries;
• pine bark extracts; or
• supplements containing mixtures of oligomeric proanthocyanidins.

These products can contain compounds other than proanthocyanidins, and their PAC profiles can differ substantially.

Grape Seed Extract & Vascular Measurements

Grape seed extract is one of the most common proanthocyanidin-rich preparations used in controlled human studies.

A systematic review and meta-analysis of 19 controlled trials examined flow-mediated dilation, systolic and diastolic blood pressure, and heart rate.

In the pooled analysis, grape seed extract was associated with a modest reduction in diastolic blood pressure and heart rate.

However, the analysis did not find statistically significant overall effects on systolic blood pressure or flow-mediated dilation, and substantial heterogeneity existed among studies.

These findings apply to the grape seed extracts that were studied.

They should not automatically be interpreted as evidence that proanthocyanidins alone produce the results, nor should they be transferred directly to grapes, grape juice, or FruitFast Concord Grape Juice Concentrate.

Blood Lipids

Another meta-analysis of randomized trials examined grape seed extract and blood lipid measurements.

The pooled results reported differences in LDL cholesterol and triglycerides, while total cholesterol and HDL cholesterol did not significantly change overall.

Again, grape seed extract is a complex and concentrated preparation and should not be equated with ordinary grape foods or isolated PACs.

Other Areas of Research

Proanthocyanidins have also been studied in relation to inflammatory signaling, glucose metabolism, gastrointestinal physiology, cognition, skin biology, and other areas.

Much of this literature consists of laboratory studies, animal models, extracts containing numerous compounds, or mechanistic research.

Direct controlled human evidence using well-characterized individual proanthocyanidin structures is much more limited.

For that reason, broad statements that proanthocyanidins improve cognition, preserve collagen, control inflammation, or improve metabolism are not supported simply by the existence of preclinical research.

Proanthocyanidin Research vs. Whole-Fruit Research

This distinction is especially important for FruitFast.

If a study investigates cranberries, aronia berries, blueberries, or grapes, the food contains many compounds besides proanthocyanidins.

Depending on the fruit, these may include:

• anthocyanins;
• flavonols;
• phenolic acids;
• organic acids;
• other tannins;
• vitamins and minerals;
• sugars;
• fiber in whole fruit; and
• many other naturally occurring constituents.

A finding involving a whole cranberry product does not automatically establish that A-type proanthocyanidins alone caused the result.

Likewise, a laboratory finding involving a purified procyanidin dimer should not automatically be applied to cranberry juice, aronia concentrate, grape juice, or another complex food.

How Processing Affects Proanthocyanidins

Food processing can alter both the amount and measurable profile of proanthocyanidins.

Important factors include:

• pressing and extraction;
• skin and seed contact;
• clarification;
• filtration;
• heat;
• oxygen exposure;
• pH;
• fermentation;
• storage time and temperature;
• interactions with proteins and polysaccharides; and
• the molecular size of the PACs involved.

Higher-molecular-weight proanthocyanidins can interact strongly with proteins, cell-wall material, and other components of the food matrix.

This means juice production, clarification, filtration, and other processing steps can produce a different PAC profile from that measured in whole fruit.

Does Fruit Juice Concentrate Contain Proanthocyanidins?

A juice concentrate produced from fruit containing proanthocyanidins can contain PACs derived from the starting fruit.

However, the amount and structural distribution in a finished concentrate depend on factors such as:

• fruit species and cultivar;
• starting-fruit PAC composition;
• skin and seed contact;
• pressing;
• clarification and filtration;
• processing conditions;
• degree of concentration;
• storage;
• molecular size of the PAC fraction; and
• analytical method.

How Are Proanthocyanidins Measured?

Proanthocyanidins are analytically challenging because they consist of many structures with different chain lengths and linkages.

Methods can include:

• colorimetric assays such as DMAC-based methods;
• normal-phase high-performance liquid chromatography;
• liquid chromatography coupled with mass spectrometry;
• thiolysis or phloroglucinolysis approaches used to characterize polymer composition; and
• other chromatographic and spectrometric methods.

Different methods may quantify different fractions or report values using different standards.

For example, one laboratory may report total PACs as catechin equivalents while another reports cranberry PACs using a specific reference standard and DMAC method.

Those values should not automatically be compared as if they represented identical measurements.

Do Proanthocyanidins Cause Astringency?

They can.

Proanthocyanidins are tannins, and tannins can interact with proteins in saliva.

These interactions contribute to the dry, puckering sensation commonly described as astringency.

The effect depends on factors such as molecular size, concentration, food matrix, acidity, sugars, proteins, and other compounds.

Fruits such as aronia and cranberries can therefore have noticeable astringency partly because of their polyphenol and tannin composition.

Are Proanthocyanidins Safe?

Proanthocyanidins occur naturally in many commonly consumed foods.

Normal dietary exposure should be distinguished from concentrated extracts and supplements that can provide much larger or differently standardized amounts.

Human studies have used numerous formulations, doses, and botanical sources.

Safety information from one grape seed extract, cranberry powder, or purified preparation should not automatically be generalized to every supplement.

People considering concentrated proanthocyanidin supplements—particularly those who are pregnant, breastfeeding, managing a medical condition, or taking medications—should discuss individual questions with an appropriate healthcare professional.

Frequently Asked Questions About Proanthocyanidins

How to Evaluate Proanthocyanidin Research

When reading a study about proanthocyanidins, first determine exactly what researchers tested.

A study may involve:

• an individual procyanidin dimer;
• an oligomeric PAC mixture;
• A-type PACs;
• B-type PACs;
• cranberry juice;
• a PAC-standardized cranberry powder or extract;
• grape seed extract;
• whole grapes or berries;
• cocoa; or
• a supplement containing multiple polyphenols.

These preparations should not be treated as equivalent.

It is also useful to consider:

• Linkage type — Were the PACs predominantly A-type, B-type, or a mixture?
• Degree of polymerization — Were researchers studying dimers, oligomers, or large polymers?
• Analytical method — How was PAC content measured?
• Dose — How much food, extract, or measured PAC was consumed?
• Population — Who participated in the study?
• Duration — Was the intervention acute or long term?
• Other compounds — Did the preparation contain anthocyanins, flavonols, phenolic acids, vitamins, minerals, caffeine, sugars, or other constituents?
• Outcome — Was the study measuring chemical antioxidant activity, bacterial adhesion, blood pressure, a biomarker, symptoms, or a clinical event?

An in vitro anti-adhesion experiment, a urinary ex vivo assay, detection of microbial metabolites, a change in blood pressure, and a reduction in clinically diagnosed infections represent very different levels of evidence.

Strong conclusions require examining the specific intervention tested rather than assigning every result to “proanthocyanidins” as one interchangeable compound.