HerbalEGram: Volume 13, Issue 5, May 2016
|Editor’s Note: Each month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medicinal research. We also feature a nutritious recipe for an easy-to-prepare dish with each article to encourage readers to experience the extensive benefits of these whole foods. With this series, we hope our readers will gain a new appreciation for the foods they see at the supermarket and frequently include in their diets.|
The basic materials for this series were compiled by dietetic interns from Texas State University in San Marcos and the University of Texas at Austin through the American Botanical Council’s (ABC’s) Dietetic Internship Program, led by ABC Education Coordinator Jenny Perez. We thank Krissy Lines (TSU, 2016) for her research and work on sorrel.
History and Traditional Use
Range and Habitat
Garden sorrel (Rumex acetosa, Polygonaceae) is a wild, perennial herb characterized by slender stems supporting bright green, spear-shaped leaves, with distinctive backward-reaching lobes.1,2 Sorrel grows in patches that average in height from 20-36” and produce small red-brown flowers, which bloom in early summer and produce tiny, hard fruits.3 Sorrel is easy to cultivate, and grows best in cool, temperate climates, as well as grasslands, coastal dunes, and cliffs.1 In addition to R. acetosa, another species of sorrel, French sorrel (R. scutatus), is used for culinary purposes.4 This article will profile the history, uses, and components of R. acetosa.
Sorrel is native to Europe and northern Asia, and evidence of cultivation dates back to 4,000 BCE.2 In the Middle Ages, sorrel was a prominent vegetable throughout Europe and was also cultivated by ancient Egyptians, Greeks, and Romans. Often referred to as the lemon of the leaf crops, the sour-tasting leaves are the most commonly consumed part of the plant.2,5 Sorrel’s stem and flower were also used in medicinal applications.2 Sorrel’s species name, acetosa, is Latin for “vinegary,” indicating the plant’s acidic taste.6
Phytochemicals and Constituents
Sorrel is a nutrient-dense green, containing important vitamins and minerals, such as vitamin A, vitamin C, sodium, potassium, magnesium, calcium, and iron.2Vitamin A is a fat-soluble vitamin that supports healthy vision, bone growth, and a strong immune system.7Vitamin C is a water-soluble vitamin, essential for its role in collagen synthesis and its antioxidant properties. Sodium, potassium, and magnesium are the most abundant minerals within human cells, and each plays a role in electrolyte and fluid balance. Calcium is a structural component of the skeletal matrix, and iron is necessary for oxygen delivery and DNA synthesis.
Flavan-3-ols and other phenolic compounds in sorrel leaves provide additional benefits.8-10 Phenolic compounds have protective effects against inflammation and cell damage, and interfere with tumor and estrogen receptor activities.10 The main phenolic compounds present in R. acetosa include resveratrol (41.27 µg/g), vanillic acid (130.29 µg/g), sinapic acid (5,708.48µg/g), and catechin (75.46 µg/g). Sorrel leaves also contain beta-carotene, though not in therapeutic levels.11
Historical and Commercial Uses
Documented uses of sorrel include domestic remedies, and extend to complex medicinal therapies.2 Sorrel leaf juice has been used in fragrances and for stain removal, and sorrel leaves are a popular ingredient in French cuisine.
Sorrel leaves are considered acidic, astringent, and cooling.6 Sorrel has been used as a laxative and a topical treatment for skin disorders, sore throats, and warts.11 Sorrel leaf also was used for its diuretic properties to induce water excretion and to manage fevers.1,5,12 Due to its high concentration of vitamin C, sorrel has been used as a therapeutic food for conditions caused by vitamin C deficiencies, such as scurvy.1Furthermore, common garden sorrel was used as a treatment for constipation, cramping, and diarrhea, since the plant demonstrates soothing effects on the stomach and intestines.8,9 The astringent properties of the seeds were used to treat hemorrhages.12
Currently, sorrel is used as an ingredient in herbal medicinal remedies, such as Sinupret (Bionorica SE; Neumarkt, Germany), a proprietary blend of botanicals, indicated for sinusitis and bronchitis.7 Tablets contain 18-36mg of sorrel leaf and stem extract, in addition to four other herbs: elder flower (Sambucus nigra, Adoxaceae), primrose flower and calyx (Primula veris, Primulaceae), European vervain leaf and stem (Verbena officinalis, Verbenaceae), and yellow gentian root (Gentiana lutea, Gentianaceae).
Currently, studies on sorrel offer promising results in the areas of digestion, infection prevention, topical skin treatments, and anti-proliferative activity.10,12,13
A recent in vivo and in vitro study evaluated the traditional use of R. acetosa to treat stomach discomforts and distress in animal models.12 A 70% methanol extract from sorrel leaves was found to have a high acute toxicity dosage (i.e., large amounts were well tolerated and exhibited no adverse effects), relaxed the gastrointestinal tract or produced gastrointestinal contractions depending on the dose, and exhibited anti-emetic properties. These findings support the traditional use of sorrel as a constipation aid that stimulates bowel movement.
Anti-diarrheal properties may be linked to the presence of calcium-binding components and tannins in sorrel.8,9,12Oxalic acid binds with and thereby reduces available free calcium for receptor stimulation. This leads to reduced muscle contraction and may alleviate diarrhea.12Tannins exert an astringent effect, which may help alleviate not only conditions such as diarrhea, but also chronic upper respiratory infections, by reducing excess fluid.9
Phytochemical extracts from other buckwheat family (Polygonaceae) members exhibit antiviral and anticancer effects, specifically extracts from R. acetosella, or sheep sorrel. Sheep sorrel has a history of use as an ingredient in the formula known as Essiac tea, which purportedly is based on the traditions of the indigenous Ojibwa Native American tribe.11 Garden sorrel shows similar antiviral and anticancer effects. An in vivo trial discovered that an extract of R. acetosa reduced influenza A viral invasion of host cells, and further reduced viral growth.14 Antiviral reactions are primarily effects of rich polyphenol concentration. In sorrel, these polyphenols mainly include flavonols, proanthocyanidins, and hydrolysable tannins. These compounds may prevent the assembly and maturation (growth and development) of certain viruses, an important step in infection control.
Additional documentation supports anti-proliferative (tumor cell growth preventing) activities seen with R.acetosa preparations.10,13 Prevention of cell growth, specifically tumor cells, was found at concentrations of 75 and 100 µg/mL of a 90% aqueous methanol extract.10
In vitro and in vivo trials displayed antimicrobial and antiviral properties. Sinupret was able to reduce viscosity, or thickness, of mucus in animal models and produce an anti-inflammatory response. Sorrel’s contributions to anti-inflammation are credited to an increased response by immune cells. Few adverse side effects related to sorrel have been reported, and include gastrointestinal disorders and correlated allergic reactions.7
Oxalic acid within sorrel produces a bitter taste, which makes sorrel a valuable ingredient for adding a tart, lemony flavor to various dishes. However, oxalic acid is a potential cause for concern in regard to renal function.11 Crystalized calcium oxalate (which forms when oxalic acid combines with calcium) can lead to the formation of kidney stones and may also accumulate in the heart, circulatory vessels, and lungs.15 In addition, oxalic acid’s ability to bind to micronutrients, such as iron and calcium, decreases its absorption.11,13 Furthermore, oxalates may irritate the digestive system when consumed in large amounts.16 For these reasons, consumption of sorrel should be monitored for special populations affected by renal and arthritic conditions, as well as those with gastrointestinal disorders.1,11
Oxalic acid is concentrated at 300mg per 100 grams of sorrel.11 The majority is found within the leaves, followed by marginal amounts in stems.13 The concentration of oxalates depends on the plant’s growing conditions, such as soil and climate.8 Moreover, tannins in sorrel leaves are concentrated between 7-15%.11When consumed in large amounts, tannins may cause stomach upset and/or kidney and liver damage.
Fortunately, oxalic acid concentration decreases to negligible amounts with light cooking.11 For example, sorrel soup has a lower oxalic acid concentration compared to pesto made with fresh sorrel leaves.13 Also, the oxalic acid concentration increases proportionately to the size and length of the leaf, making young, tender leaves a better choice for those people affected by these conditions.
Macronutrient Profile: (Per 1 cup chopped raw sorrel)
3 g protein
4 g carbohydrate
1 g fat
Secondary Metabolites: (Per 1 cup chopped raw sorrel)
Excellent source of:
Vitamin A: 5320 IU (106.4% DV)
Vitamin C: 63.8 mg (106.3% DV)
Magnesium: 137 mg (34.3% DV)
Manganese: 0.5 mg (25% DV)
Very good source of:
Iron: 3.2 mg (17.8% DV)
Dietary Fiber: 4 g (16% DV)
Potassium: 519 mg (14.8% DV)
Vitamin B6: 0.2 mg (10% DV)
Good source of:
Phosphorus: 83.8 mg (8.4% DV)
Thiamin: 0.1 mg (6.7% DV)
Calcium: 58.5 mg (5.9% DV)
Riboflavin: 0.1 mg (5.9% DV)
Folate: 17.3 mcg (4.3% DV)
Niacin: 0.7 mg (3.5% DV)
DV = Daily Value as established by the US Food and Drug Administration (FDA), based on a 2,000-calorie diet.
Recipe: Green Potato Salad
Adapted from Blue Apron18