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 would like to acknowledge Perez, ABC Special Projects Director Gayle Engels,
and ABC Chief Science Officer Stefan Gafner, PhD, for their contributions to
this project.
By Hannah Baumana and Mindy Greenba HerbalGram Assistant Editor b ABC Dietetics Intern (UT, 2014)
History
and Traditional Use
Range and Habitat
Vitis vinifera means “the vine that bears
wine” and belongs to the Vitaceae family. Grapes are perennial climbers that
have coiled tendrils and large leaves. They contain clusters of flowers that mature
to produce small, round, and juicy berries that can be either green (“white”)
or red.1 There are seed and seedless varieties, although the seeds
are edible and packed with nutrition. The juice, pulp, skin, and seed of the
grape can be used for various preparations.2
Grapes are a vine and
must be trained to grow along a fence, wall, or arbor.3 The fruit
does not ripen after harvesting; therefore, it is important to harvest
well-colored and plump berries that are wrinkle-free and still firmly attached
to the vine. They are best stored in the refrigerator since freezing will
decrease their flavor.1,4 Pesticide use is common in vineyards, and
careful washing is recommended when purchasing conventionally grown grapes.
As one of the leading commercial fruit crops
in the world in terms of tons produced, grapes are cultivated all over the
world in temperate regions. The top producers are Italy, France, Spain, the United
States, Mexico, and Chile.1,5 Annually, worldwide grape production
reaches an average of 60 million metric tons, 5.2 million of which are grown in
the United States.
Phytochemicals
and Constituents
Antioxidants are enzymes and nutrients that
prevent oxidation, meaning they neutralize highly reactive ions or molecules known
as free radicals in the human body by donating electrons, or modulating enzymes
that metabolize free radicals. Free radicals are produced naturally through
metabolism as part of normal physiological functions (e.g., a defense mechanism
against pathogens), but may be produced in excess, creating a situation where they adversely alter lipids, proteins, and DNA, and trigger a
number of human diseases. Grape and grape products are
good sources of beneficial antioxidant compounds.
Grapes contain phytochemicals called
polyphenols. Polyphenols are the most abundant source of dietary antioxidants
and are associated with numerous health benefits.2,6 The phenolic
compounds are more concentrated in the skin of the berry, rather than in the
flesh or seeds, and the content tends to
increase as the fruit ripens. Grapes contain polyphenols from the classes of flavonoids,
stilbenes, and phenolic acids. Red wine and grapes are rich in flavonoids such
as anthocyanins and catechins, stilbenes such as resveratrol, and phenolic
acids such as caffeic acid and coumaric acid. Red grapes have higher
concentrations of these phenolic compounds than red wine grapes. Different
grape varietals contain varying amounts of phenolic compounds.
Anthocyanins are flavonoids that naturally
occur in the plant kingdom and give many plants their red, purple, or blue pigmentation.
Vitis vinifera may contain up to 17 anthocyanin pigments, which are
contained in the skins.2,7 Grapes also contain other flavonoids,
including catechins, epicatechins, and proanthocyanidins. Attempts to study the
benefits of individual phytochemicals in humans has been difficult since these
phytochemicals are complex and often interact with one another to increase
their overall benefits.
There are numerous studies using animal
models in phytochemical research.8 Animal models have shown that
anthocyanins protect against oxidative stress, which can be the beginning
stages of many chronic conditions, such as cardiovascular disease, diabetes,
and cancer.
Grape
seeds are a particularly rich source of proanthocyanidins, a class of nutrients belonging to the flavonoid family. Proanthocyanidins,
also known as condensed tannins, are polymers (naturally occurring large
molecules) with flavan-3-ol monomers as building blocks. The term oligomeric proanthocyanidin (OPC), which
also is commonly used to describe these compounds, is not well-defined and is debated
among various members of the scientific community.
Grape seed
extract is available as a nutritional supplement. Partially purified
proanthocyanidins have been used in phytomedicinal preparations in Europe for
their purported activity in decreasing the fragility and permeability of the
blood vessels outside the heart and brain.9
Grapes have a high stilbene, specifically
resveratrol, content. Resveratrol, which is found in the skin and seeds of red
grapes as well as in red wine, is produced as the plant’s defense mechanism
against environmental stressors.1,2,10,11 Resveratrol first gained
attention as a possible explanation for the “French Paradox” — the observation
that French people tend to have a low incidence of heart disease despite having
a typically high-fat diet.1 The antioxidant activity of grapes is
strongly correlated with the amount of resveratrol found in the grape.10
Studies have found resveratrol to be anti-carcinogenic, anti-inflammatory, and
cardio-protective in animal models.11 However, in a human study in
which healthy adults consumed resveratrol, it was determined that the compound was
readily absorbed, but it metabolized quickly, leaving only trace amounts.12
In addition to their high resveratrol
content, grapes are also an excellent source of vitamin K and provide moderate
amounts of potassium, vitamin C, and B vitamins.
Historical and
Commercial Uses
Grapes have been consumed since prehistoric
times and were one of the earliest domesticated fruit crops.1,13 According
to ancient Mediterranean culture, the “vine sprang from the blood of humans who
had fought against the gods.”14 But according to archaeological
evidence, domestication took place about 5,000 years ago somewhere between the
Caspian and Black Seas, and spread south to modern-day Syria, Iraq, Jordan, and
Egypt before moving towards Europe.5,13 After the collapse of the
Roman Empire in the 5th century, when Christianity became dominant, wine was
associated with the Church and the monasteries soon perfected the process of
making wine.1
About 300 years ago, Spanish explorers
introduced the grape to what is now the United States, and California’s
temperate climate proved to be an ideal place for grape cultivation.1
The grape is, famously, the most common
ingredient in wine-making. A naturally-occurring symbiotic yeast grows on the
grapes, making them easier to ferment and well-suited to the wine-making
process.4 Popular wine cultivars of V. vinifera include Cabernet Sauvignon, Merlot, Chardonnay,
Sauvignon Blanc, Vermentino, and Viognier.10
Wine often has been used as a medium for
herbal remedies, due to the solvent nature of the alcohol. Both the Chinese and
Western traditions made use of medicated wines (though ancient recipes in China,
which date to the Shang Dynasty [ca 1600-1046 BCE], would have been made with
rice [Oryza sativa, Poaceae] wine
rather than grape wine).15 Many aperitifs and liqueurs originally
were digestive aids made with wine and fortified with herbs such as wormwood (Artemisia absinthium, Asteraceae) and
anise seed (Pimpinella anisum,
Apiaceae).16 Medicated wines are less potent and usually require a
higher dosage than tinctures made with higher-proof alcohol.
Grapes are generally sweet and are used as
table grapes, juice, jam, jelly, or for wine-making.13,17 About 99%
of the world’s wine comes from V. vinifera.14
Grapes can also be dried in the vineyard
and turned into raisins. To accomplish this, ripe grapes are plucked from the
vine and placed on paper trays for two to four weeks. Afterwards, they are sent
to the processing plant to be cleaned, packaged, and shipped.5
Modern Research
Grapes have been the subject of numerous
studies focused on many of their bioactive compounds, including flavonoids,
stilbenes, and phenolic acids. Researchers have observed antioxidant, anti-tumor,
immune modulatory, anti-diabetic, anti-atherogenic, anti-infectious, and
neuro-protective properties of the fruit.11 Research suggests that
grape product consumption could possibly benefit those with cancer, diabetes,
and cardiovascular disease, which are among the leading causes of death worldwide.18
However, more human studies are needed to support any of these purported
benefits.
An in vitro study showed that antioxidants
from a variety of grape product extracts performed as well as or better than
BHT, tocopherol, and trolox in radical scavenging activity, metal chelating
activity, and inhibition of lipid peroxidation.7 Water and ethanol
seed extracts had the highest amount of phenolic compounds of any of the
extracts used in the study.
Grape seed extract (GSE), which has a
growing body of study behind it, has gained attention for its possible use in
lowering blood pressure and reducing the risk of heart disease, especially in
pre-hypertensive populations.19 Unlike grape skins, where only red
grapes contain anthocyanins, seeds from both white and red grape contain
beneficial compounds. A standardized GSE made from white wine grapes recently
was studied for its effects on gastrointestinal inflammation.20
While most studies focus on GSE and cardiovascular health, the preliminary
results were promising enough to warrant a future human trial.
Cardiovascular Disease
Polyphenols have been found to protect the
body from inflammation, which is common in people with heart disease.11
In a recent meta-analysis, the acute effects of polyphenols on the endothelium
(inner lining of the blood vessels) were investigated. The analysis found that
blood vessel function significantly improved in healthy adults in the initial
two hours after consuming grape polyphenols.21 Another analysis
found that the polyphenol content in every part of the grape — fruit, skin, and
seed — had cardioprotective effects.22 In animal, in vitro, and
limited human trials, grapes showed beneficial actions against oxidative stress,
atherosclerosis (plaque build-up in arteries), high blood pressure, and
ventricular arrhythmia (irregular heartbeat).
Cancer Chemopreventive Effects
Although the causes of and treatments for
cancer are complex and multifaceted, studies have been done on the antioxidant
activity of polyphenols and their cancer chemopreventive effects. These
antioxidants demonstrate the ability to protect the body from cancer-causing
substances and to prevent tumor cell growth by protecting DNA and regulating
natural cell death.8,11,23
Diabetes
In a randomized, double-blind controlled clinical
study, healthy overweight/obese first degree relatives to type 2 diabetic
patients were given grape polyphenols to counteract a high-fructose diet. After
nine weeks of supplementation, grape polyphenols protected against
fructose-induced insulin resistance.24 In another study, diabetic
patients who consumed a dealcoholized Muscadine grape wine had reduced fasting
insulin levels and increased insulin resistance.25
Nutrient
Profile26
Macronutrient Profile: (Per 150 g
[approx. 1 cup] grapes)
104 calories
1.1 g protein
27.3 g carbohydrate
0.2 g fat
Secondary Metabolites: (Per 150 g
[approx. 1 cup] grapes)
Excellent source of:
Vitamin K: 22 mcg
(27.5% DV)
Good source of:
Potassium: 288 mg
(8.2% DV)
Vitamin C: 4.8 mg
(8% DV)
Thiamin: 0.1 mg
(6.7% DV)
Riboflavin: 0.1
mg (5.9% DV)
Dietary Fiber: 1.4
g (5.6% DV)
Manganese: 0.1 mg
(5.5% DV)
Vitamin B6: 0.1
mg (5% DV)
Also provides:
Phosphorus: 30 mg
(3% DV)
Magnesium: 11 mg
(2.8% DV)
Iron: 0.5 mg
(2.8% DV)
Vitamin A: 100 IU
(2% DV)
Niacin: 0.3 mg
(1.5% DV)
Vitamin E: 0.3 mg
(1.5% DV)
DV = Daily Value as established by the US Food and Drug Administration,
based on a 2,000-calorie diet.
Recipe: Rosemary-Roasted
Grapes and Cashew Cheese Crostini
Ingredients:
- 1 cup raw cashews
- 1-2 cloves of
garlic, minced
- 1/4 cup water
- 1/4 cup freshly-squeezed
lemon juice, divided
- 1/2 teaspoon kosher
or fine sea salt
- 1 pound seedless
red grapes, washed and removed from stem
- 3 tablespoons
olive oil, plus more for garnish
- 1 tablespoon fresh
rosemary leaves, minced
- Salt and pepper
to taste
- 1 small baguette
or other loaf, sliced diagonally in 1/4 inch thick slices
Directions:
- Soak cashews in enough water to cover by an inch for at least 4 hours.
Drain.
- Make cashew “cheese” by placing soaked cashews, garlic, water, 2
tablespoons of lemon juice, and salt into a food processor and blend until
smooth.
- Heat oven to 400°F. In a baking dish, mix grapes, olive oil, remaining
lemon juice, rosemary, salt, and pepper. Place on center rack and roast 10-12 minutes
or until skins are soft. Remove and set aside.
- Move the oven rack to the top setting and increase the heat to broil. Arrange
bread slices in a single layer on a baking sheet and place in oven to toast for
1-3 minutes, monitoring carefully to prevent burning.
- Assemble crostini by spreading each toast with a layer of cashew
cheese and topping with the grape mixture. Sprinkle with salt and drizzle with
olive oil. Serve warm.
References
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