There is no doubt that citrus fruits contain a variety of polyphenols – anti-oxidant rich compounds found in many plants. There is also a lot of evidence that links the consumption of citrus fruits with many health benefits, including protection from disease.
Polyphenols in citrus
Polyphenols are the most abundant phytochemicals found in citrus fruits. A mixture of polyphenols creates the unique flavor and odor profile for each specific fruit. In addition, citrus peels often contain different concentrations, and in some cases, the largest, of polyphenols. More than 60% of citrus polyphenols are flavanoids; the most common includes the flavanones;
- hesperidin 3,
- narirutin 4, and
- naringin 7
Taking absorption, metabolism, and bioavailability into account are crucial to determining the potential for polyphenols in human health. All three are very complex processes.
- The polyphenols are released from the food matrix (i.e. molecular attachment to the rest of the fruit or juice);
- Enzymes and microbes in the gut continue the breakdown;
- The liver also plays a role in absorption and metabolism;
- The compounds are then transported to the cells or tissues that require them.
Polyphenols, bioavailability, bioaccesibility & absorption
But – just how do those polyphenols get into the bloodstream?
The mechanism by which polyphenols are absorbed into the body is not yet fully understood. A recent study in the academic journal Comprehensive Reviews in Food Science and Food Safety by researchers at Monash University in Australia analyzed the data from just under 150 in vitro, animal, and human studies.
They note that several factors come into play, and underscored the importance of taking those variables into considerations in any future studies.
- While citrus polyphenols are absorbed into the body via specific pathways, the pathways vary greatly from one individual to another.
- Absorption is affected by: age, sex, gut microbiota, current metabolic state, genetics;
- Other factors affect bioavailability and bioaccessibility, including: lifestyle, type of processing, solubility, the food matrix (i.e. molecular structure, which is affected by cooking, for example), dose or amount, and the other foods you eat with citrus.
Since most citrus polyphenols, and the catabolites (or products of metabolism), are absorbed in the large intestine, gut microbiota are crucial. With their help, polyphenol absorption can reach 100%.
The deficiencies and inconsistent results of some earlier studies most likely resulted in underestimating flavanoid absorption by up to 20% or more. What you eat with citrus fruits also affects how much polyphenols end up in your bloodstream to help the body’s work.
- Fats from dairy only seem to have a minor effect on bioavailability, delaying it for some time after consumption;
- Citrus polyphenols seem to bind to starches, which may reduce the bioaccessibility and bioavailability of both;
- Sucrose seems to increase bioaccessibility and improve absorption of naringenin 2 to 100%, and improves bioavailability of polyphenols in general;
- Dietary fibres can affect the composition and activity of gut microbes.
Of all the studies they analyzed, only four had examined metabolites, or the compounds that are created by the metabolism process. The metabolites themselves have specific properties that have yet to be established.
The researchers point out shortcomings in previous studies, noting that polyphenol metabolism in humans differs from person to person. Blood analysis reveals that peak levels of flavanone absorption occurs about six hours after consuming the fruits.
It’s a complex process that clearly needs future study.
Photo by Bicanski (CC0C/Pixnio)