By Susan Elrod, PhD
You may have heard that fruit skins contain some of the best nutrients. Much of this is fiber, but other nutrients are present in fruit and vegetable skins as well. In some cases this is interesting but irrelevant information; you wouldn’t want to eat your orange peel, no matter how many more polyphenols and other nutrients you’d be getting.1Antioxidant capacity and mineral content of pulp and peel from commercial cultivars of citrus from But what about fruits and vegetables with edible skins? What does the evidence say about consuming the whole fruit, skin and all, as opposed to using juices or extracts?
First, let’s review the definition of some commonly used terms for purposes of our scientific discussion. A whole fruit (a single berry or pomme fruit, for example) is comprised of skin (epicarp, or the outer edge of the fruit), mesocarp (which contains both flesh and juice inside), endocarp (a membrane inside that covers the seeds) and the seed. In scientific experiments, we can separate these different parts, but in everyday life, such as in juicing, you would be separating the juice from everything else (called the mash). One additional term that you will hear is pulp. Pulp is what remains after the skin is removed.
So what is the evidence about elderberries? There haven’t been studies looking at the skin versus fruit (or “pulp,” the term most frequently used in literature to distinguish the skin from the whole fruit). However, multiple studies looking at other berries and fruits have found that in general, skins tend to be higher in fiber and polyphenols.2Chemical characterization of the jabuticaba fruits (Myrciaria cauliflora Berg) and their fractions. Baori, Lime Ade 3Inhibition of low-density lipoprotein oxidation by Nagano purple grape (Vitis viniferaxVitis labrusca). Kamiyama, Masumi, et Like a lot of food research, this varies according to circumstances; polyphenols and other compounds vary according to the environment and conditions of growing4Irrigation and Rootstock Effects on the Phenolic Concentration and Aroma Potential of Vitis vinifera L. 5Determination of Anthocyanins and Total Polyphenols in a Variety of Elderberry Juices by UPLC-MS/MS and and according to the fruit itself. A study of jamun (also known as Java plum), jackfruit, and mulberry found whole mulberry fruit was the highest in resveratrol (that compound so often cited for red wine’s benefits), whereas janum seeds had the highest phenolic and antioxidant content.6Resveratrol content and antioxidant properties of underutilized fruits. Shrikanta, Akshatha, Kumar, Anbarasu and Govindaswamy, Vijayalakshmi. That’s not unusual, either; often seeds and skins of fruit are cited as excellent but often discarded sources of phenols and other nutrients. A study of grapes found that, while the skins had higher phenolic and antioxidant content than the pulp, the seeds were higher than both skin and pulp in these concentrations.7 Identification and quantification of phenolic compounds in berry skin, pulp, and seeds in 13 grapevine On the other hand, a study of chilto (or “tree tomato”) found the skin to have the highest phenolic content, over pulp and seeds, whereas the pulp had the highest vitamin C content.1Antioxidant capacity and mineral content of pulp and peel from commercial cultivars of citrus from 8Chemical and functional characterization of seed, pulp and skin powder from chilto (Solanum betaceum), an A study of Amazonian berry found that not only did skins and seeds have a much higher phenolic content compared to pulp, but the specific polyphenols varied according to fruit part: both pulp and seeds/skins parts had myricetin and ellagic acid, but cyanidin and quercetin were found only in the pulp, and proanthocyanidins found only in the seeds/skin portion.
So does that mean you should start consuming fruits whole, seeds, skin and all? Not necessarily. When we report phenolic and antioxidant content, it’s done on the basis of amount of polyphenols per weight (or volume) of fruit. So if you’re told that the phenolic content of fruit skin is 1 mg/g, and the content for fruit pulp is 0.5 mg/g, you might believe that you’d be getting twice as much phenolic content by eating the skin. However, consider the amount of skin as a portion of the whole fruit: it’s a very small percentage. So if we assume that a 100 g fruit contains 90% pulp and 10% skin, the skin would contain only 10 mg polyphenols compared to 45 mg in the pulp. Furthermore, a large volume of fruit (or pulp) goes into preparing juices, and the juice product will be more concentrated than the constituent fruits, typically yielding a higher concentration of polyphenols and other nutrients per volume.9Effects of elderberry juice on fasting and postprandial serum lipids and low-density lipoprotein oxidation in
Leaving aside considerations of what part of the fruit generates what and how many polyphenols, we can also consider research into health benefits of fruits. Particularly in human studies, it’s important to know what form the fruit was given to the patients. That is, was the study on an apple a day? A glass of apple juice a day? A dried apple preparation given in a capsule a day? Looking at the original research will tell you what form of fruit was used to elicit the benefits seen by researchers.
Elderberry consumption has been studied in humans for benefit in a few different conditions, including cardiovascular disease. In such studies, elderberry juice and extract (a preparation of fruit made by passing a solvent through the dried fruit to separate out the active ingredients) appeared to have no effect on improving serum lipids or biomarkers of cardiovascular disease.9Effects of elderberry juice on fasting and postprandial serum lipids and low-density lipoprotein oxidation in 10Cardiovascular Disease Risk Biomarkers and Liver and Kidney Function Are Not Altered in Postmenopausal Women Another study found an herbal tea made of four different plants, including elderberry, was efficacious against chronic constipation.11 Randomized clinical trial of a phytotherapeutic compound containing Pimpinella anisum, Foeniculum vulgare, Sambucus nigra, and
The bulk of human research on elderberries, however, is on its effect against viruses, specifically the cold and flu. Although more research has been conducted on the effect of elderberry against viruses in vitro (that is, in cells, not in animals or humans), there is some limited evidence of elderberry’s effect on viruses in human patients. These studies all involve commercial preparations of elderberry. In the influenza studies, adults with influenza A or B taking four tablespoons of the elderberry extract daily for 3 or 5 days showed improvement 2 to 4 days sooner than those taking a placebo, depending on the study.12Inhibition of several strains of influenza virus in vitro and reduction of symptoms by an 13Randomized Study of the Efficacy and Safety of Oral Elderberry Extract in the Treatment of In a study regarding cold symptoms, air travelers were given two capsules containing 300 mg of elderberry extract for ten days before their trip and three capsules daily during and up to 5 days after travel. Travelers taking the elderberry extract reported significantly shorter and less severe cold symptoms compared to the placebo group.14Elderberry Supplementation Reduces Cold Duration and Symptoms in Air-Travellers: A Randomized, Double-Blind Placebo-Controlled Clinical Trial.
So in summary, if you can consume whole fruits with the skin, that’s great but may not be strictly necessary, given the weight by which whole fruits are consumed compared to juices. For elderberries specifically, the bulk of the research has been conducted using extracts, so the juices and concentrates should be just fine in terms of imparting any potential benefit.
Related article: How Should I Think About Polyphenol Loss During Processing