Part of what provides blueberries with their spectacular flavors, aromas, and colors is their unique combination of phytonutrients. These berries provide us with 260-460 milligrams of total phenols in just two-thirds of one cup and at a cost of only 50-60 calories. Many of these phenols come in the form of flavonoids. Within this flavonoid group, blueberries provide us with flavonols like quercetin, myricetin, and kaempferol. But blueberries are best known for their anthocyanin flavonoids. Included in this anthocyanin list are cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin. Up to one third of all phenolic compounds in blueberries can consist of flavonoids.
In addition to other phytonutrients including phenolic acids and carotenoids, blueberries provide us with two unique anti-inflammatory and antioxidant phytonutrients belonging to the group of compounds known as stilbenoids. These two members of the stilbenoid family are resveratrol and pterostilbene. Resveratrol is the better known of these two stilbenoids due to a good bit of publicity about its concentration in red wine. (Red wine gets its resveratrol from the skin of red grapes.) Blueberries do contain resveratrol, yet in much smaller amounts than red wine. However, blueberries do have a strong suit in this stilbenoid category of phytonutrients, and that strong suit is pterostilbene.
You may sometimes hear stilbenoids being referred to as "phytoalexins." This name describes a group of molecules that can be synthesized by plants in response to the threat of infection by bacteria, other microbes, or environmental stressors. Because of their antioxidant, anti-inflammatory, and antimicrobial properties, stilbenoids like resveratrol and pterostilbene are a perfect fit in plant defense systems.
Pterostilbene has been shown to display many of the same properties as resveratrol in recent studies. It not only acts as an anti-inflammatory and antioxidant nutrient, but it also has antidiabetic, cardioprotective, neuroprotective, and chemopreventive (anti-cancer) properties. (Resveratrol has been shown to have all of these same properties.) Recent studies have shown that pterostilbene may be more bioavailability than resveratrol when we eat foods, including blueberries, that contain both stilbenoids. One study has shown pterostilbene to spend as much as five times longer in our body (once absorbed) before being metabolized into other compounds. This longer-lasting nature of pterostilbene may give it more time to provide us with its many health benefits. It's worth noting here that pterostilbene is present in grape plants as well as blueberries, but unlike its presence in the blueberries themselves, pterostilbene it is found primarily in the vine portion of the grape plants rather than the grapes.
The list below provides a summary of key photonutrients provided to us by blueberries:
With a nutrient-rich fruit like blueberries, we would typically expect to be present you with a list of chronic diseases and clear evidence for the ability of blueberries to decrease risk of those diseases when enjoyed in an everyday meal plan. Several research limitations prevent us from providing you with such a list, even though we are confident that we will eventually be able to do so. What we can tell you with certainty is where the research stands at present.
In the area of cardiovascular problems, the best research we've seen shows a consistently favorable impact of blueberry consumption on blood pressure, especially in persons with already elevated blood pressure. Participants in most of these studies have consumed blueberries in the form of freeze-dried blueberry beverages rather than blueberries in their fresh form. In general, however, we simply don't have a sufficient number of human studies in this cardiovascular area to document blueberry benefits. Although we would expect the unique collection of antioxidant and anti-inflammatory phytonutrients found in blueberries to provide cardiovascular benefits well beyond blood pressure regulation (including decreased risk of atherosclerosis), we need large-scale human studies to document these benefits. We also need studies on the consumption of whole, fresh blueberries as well as studies that analyze low, medium, and high intake of blueberries among healthy persons. And finally, we need studies that look specifically at blueberries rather than lumping them together with other berries.
Animal research on blueberries and cardiovascular problems provides us with more definitive results. In animal studies, blueberry extracts have fairly consistently shown an ability to decrease risk of oxidative stress and unwanted inflammation in blood vessels. And like human studies, animal studies have also shown blueberry extracts to have favorable effects on blood pressure regulation.
In the area of blood sugar regulation, a fairly substantial number of animal studies have looked at intake of blueberry extracts (or isolated blueberry phytonutrients) on blood sugar levels, insulin secretion, insulin resistance, and insulin sensitivity. For the most part, the results have shown improved insulin sensitivity, decreased insulin resistance, and improved blood sugar levels following intake of extracts by rats and mice. However, benefits have not been shown in all animal studies. The best studies that we have reviewed on human consumption of blueberries haven't focused on blueberries per se but have included them among other fruits. In one of these studies, blood sugar regulation was improved through consumption of three low-GI (glycemic index) fruit servings per day. While we are encouraged by this result, we would still like to see blood sugar-related studies that focused specifically on blueberries.
In this context of glycemic index, we would also like to note that blueberries are classified as a low-GI fruit based on studies showing their GI value to fall between 40-53. (At WHFoods, we consider all foods to be low GI if their glycemic index value falls at 55 or below.) Blueberries also rank as a good source of fiber, providing about 3.5 grams per fresh cup. When you combine their low GI value with their ability to provide us with a good amount of fiber, it should not be surprising that blueberries might help us improve our blood sugar regulation, even though they have enough sweetness to feel like a delicious treat.
Two other health research areas are important to mention with respect to blueberries. The first involves cognitive function. Preliminary studies have shown an ability of blueberry intake to improve nervous system responses, most likely by helping to protect nerve cells from oxidative damage. In one study involving older adults (with an average age of 76 years), 12 weeks of daily blueberry consumption was enough to improve scores on two different tests of cognitive function including memory. While participants in the study consumed blueberries in the form of juice, three-quarters of a pound of blueberries were used to make each cup of juice. When converted into cups, this amount represented between 2 and 2-1/2 cups per day. While this amount is likely to be more than most people would consume on a daily basis, it is still encouraging to see improvement in cognitive function (including memory) being linked to intake of blueberries in food form. We would also like to note that improved neural responses following intake of blueberry extracts has been shown in several animal studies. In addition, decreased impact of reactive oxygen species (ROS) on the central nervous system has been observed in animal studies involving intake of blueberry extracts.
A final area of health research we want to touch on is research on cancer risk. Both of the stilbenoids present in blueberries—pterostilbene and resveratrol—have been shown to have chemoprotective (cancer-preventing) and tumor suppressing properties. In addition, we know that the combination of chronic oxidative stress and chronic low level inflammation can increase the likelihood of cancer initiation. This unwanted combination leaves blueberries in a very likely position to lower cancer risk by supplying us with a unique combination of antioxidant and anti-inflammatory phytonutrients. Lab studies on several cancer cell lines have already shown the ability of blueberry extracts to inhibit proliferation (increase in cancer cell numbers) and to induce apoptosis (cell death) in several cancer cell types. This area of blueberry intake and decreased cancer risk is one we expect to see gaining attention in future research studies.
While we don't typically think about blueberries as a fruit of great diversity, these remarkable berries are found in many different varieties and many regions of the world. Their flavors can range from mildly sweet to tart and tangy, and their colors can vary from many subtle shades of blue to maroon to very dark purple. Many blueberry varieties feature a white-gray waxy "bloom" that covers the berry's surface and helps serve as a protective coat. The skin surrounds a typically semi-transparent flesh that encases tiny seeds.
From a science perspective, all blueberries belong to the Ericaceae family of plants, as well as to the Vaccinium genus found within this plant family. Cranberries, bilberries, huckleberries, and lingonberries are also members of this plant family.
Once we look inside this Vaccinium group at different varieties of blueberries, we start to see their amazing diversity. Traditionally, blueberry varieties have been subdivided into three basic groups: highbush, lowbush, and rabbiteye. Like their names suggest, "highbush" and "lowbush" differ in the height reached by the blueberries bushes themselves. Lowbush berries usually stop two feet or less above the ground, while highbush varieties can reach heights of eight to nine feet. However, an even bigger difference between highbush and lowbush involves their wild versus cultivated status. Most of the cultivated blueberries that we enjoy in the grocery are highbush varieties. Lowbush varieties are primarily found growing in the wild, and when they are "cultivated" for commercial production, growers manage wild stands (blueberries growing in the wild) rather than directly planting or sowing seeds. The underground stems of wild lowbush blueberries (called rhizomes) can be selectively propagated to increase the size and spread of the blueberry plants. However, for the most part, growers rely on the many varieties of highbush blueberries for commercial production throughout the world.
Particularly within the U.S., where blueberries are not only a native plant but widely enjoyed in many home gardens in many states, you will find the terms "northern highbush" and "southern highbush" being used to describe blueberries. Northern varieties actually need a certain number of "chill hours" to thrive, and so they do best in areas that witness a true winter season. Southern varieties require fewer chill hours and are better adapted to warmer climates. In the native state, northern highbush blueberries can be found growing in the mid-Atlantic and northeastern regions of the U.S., as well as the state of Washington. Northern highbush varieties belong to the genus species of plant called Vaccinium corymbosum. Southern highbush blueberries are more commonly found in Florida, along the Gulf Coast, and along the West Coast up through Oregon. Southern highbush are typically a cross of two blueberry species: Vaccinium corymbosum and Vaccinium darrowii. While rabbiteye blueberries are less commonly cultivated than highbush varieties, they are native to the southeastern U.S and belong to the genus/species Vaccinium virgatum (also called Vaccinium ashei.) Worldwide, northern highbush blueberries are the most widely planted varieties and the ones you are mostly like to find in U.S. supermarkets.
When thinking about the diversity of blueberries, it's also worth noting the significant diversity in their phytonutrient contents. While all varieties of blueberries contain flavonoids—including the important flavonoid subgroup called anthocyanins—the amount of total flavonoids, total anthocyanins, individual flavonoids and individual anthocyanins can vary substantially. Therefore, if you are seeking to increase your intake of one specific phytonutrient—for example, peonidin or malvidin in the anthocyanin group, or in the flavonol group, quercetin or myricetin—you cannot be guaranteed to do so simply by choosing "blueberries." However, we never recommend selection of any whole food—including blueberries—for the sake of obtaining one or two specific nutrients. The amazing benefits of blueberries and other whole foods come from their unique combination of many nutrients, not from a mere handful. Our general recommendation is not to worry about these phytonutrient details, and simply allow yourself to enjoy a wide variety of fresh blueberries in your meal plan. You can trust the natural development of the berries to do the rest!
Some popular varieties of northern highbush blueberries include Berkeley, Bluecrop, Bluehaven, Blueray, Jersey, and Patriot. Popular southern highbush varieties include Biloxi, Gulf Coast, Misty, O'Neal, and Sunshine Blue. Examples of rabbiteye varieties include Bonita and Climax.
Blueberries hold a special place in the foods of North America since more species of blueberries are native to North America than any other continent. Blueberries have become naturalized to many regions of the world, including Europe, Australia, and New Zealand, and temperate regions in Asia. They have also been widely cultivated, and are commercially grown, in other regions including South America (Argentina and Chile) and Northern Africa (Morocco).
From a history standpoint, what's quite remarkable about blueberries are the many hybrids that have expanded our agricultural options for cultivating this fruit. Many of these hybrids have involved blueberry varieties from the highbush category. "High chill" highbush blueberries are varieties that can thrive in climates with cold winters, sending the plants into dormancy. These varieties do quite well in regions as far north as Scandinavia and as far south as the southernmost regions of Chile and Argentina that extend quite close to the Antarctic. On the other hand, "no chill" highbush blueberries can thrive in much milder climates and do not go into dormancy, allowing them to thrive in other regions of the world including Indonesia, Southeast Asia, Mexico and Peru. The net result of these versatile blueberry hybrids is greater importing and exporting of the berries and increasing availability of blueberries in U.S. supermarkets.
Within the U.S., Michigan, Washington, Georgia, and Oregon are the top four states for production of highbush blueberries. About 60% of the highbush berries grown in those states eventually get sold as fresh blueberries, and the other 40% undergo further processing (for example, conversion into juices, jams, or dried additions to cereals). The largest producer of wild lowbush blueberries in the U.S. is Maine. In total, more than a dozen U.S. states grown blueberries for commercial sale, and collectively they produce over 550 million pounds of berries each year. Despite the large-scale production of these berries within the U.S., however, the majority of blueberries consumed in the U.S. come from imports rather than from domestically grown fruit. Chile and Canada supply the U.S. with the majority of these blueberry imports.
One a worldwide basis, more acreage is planted with blueberries in the U.S. than in any other country, and the U.S. produces more pounds of blueberries than any other country. Total world production of blueberries is approximate 1.5 billion pounds; following after the U.S. in total commercial blueberry production are Chile, Canada, China, Spain, Poland, Argentina, Germany, Mexico, and Morocco.
Choose blueberries that are firm and have a lively, uniform hue colored with a whitish bloom. Shake the container, noticing whether the berries have the tendency to move freely; if they do not, this may indicate that they are soft and damaged or moldy. Avoid berries that appear dull in color or are soft and watery in texture. They should be free from moisture since the presence of water will cause the berries to decay. When purchasing frozen berries, shake the bag gently to ensure that the berries move freely and are not clumped together, which may suggest that they have been thawed and refrozen. Blueberries that are cultivated in the United States are generally available from May through October while imported berries may be found at other times of the year.
At WHFoods, we encourage the purchase of certified organically grown foods, and blueberries is no exception. Repeated research studies on organic foods as a group show that your likelihood of exposure to contaminants such as pesticides and heavy metals can be greatly reduced through the purchased of certified organic foods, including blueberries. In many cases, you may be able to find a local organic grower who sells blueberries but has not applied for formal organic certification either through the U.S. Department of Agriculture (USDA) or through a state agency. (Examples of states offering state-certified organic foods include California, New York, Oregon, Vermont, and Washington.) However, if you are shopping in a large supermarket, your most reliable source of organically grown blueberries is very likely to be blueberries that displays the USDA organic logo.
Before storing remove any crushed or moldy berries to prevent the rest from spoiling. Don't wash berries until right before eating as washing will remove the bloom that protects the berries' skins from degradation. Store ripe blueberries in a covered container in the refrigerator where they will keep for up to 3 days. If kept out at room temperature for more than a day, the berries may spoil.
Here is some background on why we recommend refrigerating blueberries. Whenever food is stored, four basic factors affect its nutrient composition: exposure to air, exposure to light, exposure to heat, and length of time in storage. Vitamin C and carotenoids are good example of heat-susceptible nutrients, and their loss from food is very likely to be slowed down through refrigeration.
Blueberries can be frozen. Before freezing, wash, drain, and remove any damaged berries. To better ensure uniform texture upon thawing, spread the berries out on a cookie sheet or baking pan, place in the freezer until frozen, then put the berries in a sealed plastic bag or sealed container for storage in the freezer. You can expect to see slight changes in texture and flavor after freezing.
The impact of freezing on blueberry phytonutrient content has been a topic of special interest in food research. One recent study on frozen versus fresh blueberries suggests that while frozen blueberries may still provide us with great nutrient benefits, there may be some important nutritional advantages related to consumption of blueberries in their fresh form. When comparing the total antioxidant capacity of fresh versus frozen blueberries, 6 months of freezing (0°F/-18°C) were found to result in no decrease in overall antioxidant potential in this fruit. However, changes were found to occur in the phytonutrient composition of the berries after freezing. Among all of the phenolic phytonutrients present in fresh blueberries, between 18-34% consist of flavonoids. Among these flavonoids are anthocyanins that contribute to the gorgeous deep colors of this fruit. After six months of freezing, total anthocyanins in the berries were found to be degraded by about 59%. Some of the anthocyanins—for example, pelargonidin—remained almost completely intact. But other anthocyanins like delphinidin were found to be overwhelmingly degraded. So how did the blueberries still retain their overall antioxidant capacity despite this degrading of certain anthocyanins? The authors speculated that the anthocyanins most likely reacted with other phenolic phytonutrients in the blueberries (resulting in the creation of new compounds) or were simply degraded through oxidation. Since the total antioxidant potential was well-retained in the frozen berries, we can see how this form of the fruit might be a good option when fresh berries are not available (or when the convenience of frozen berries is a top priority). However, since the health benefits of anthocyanins like delphinidin are well-documented in research studies, fresh berries may still be providing us with some key benefits that aren't as robust in frozen berries.
If you'd like even more recipes and ways to prepare blueberries the Nutrient-Rich Way, you may want to explore The World's Healthiest Foods book.
|vitamin K||28.56 mcg||32||6.8||very good|
|manganese||0.50 mg||25||5.3||very good|
|vitamin C||14.36 mg||19||4.1||very good|
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