As our 5th best source of vitamin C among all 100 WHFoods, strawberries might logically be expected to provide antioxidant benefits. But the scope of strawberry antioxidants extends far beyond vitamin C. What we're talking about in the case of strawberries is a collection of polyphenol antioxidants that includes flavonoids, phenolic acids, lignans, tannins, and stilbenes. Each one of the polyphenol categories contains an enormous variety of antioxidants, most of which have also been shown to have anti-inflammatory properties. We have compiled the list of polyphenols below to give you a better idea about the antioxidant and anti-inflammatory phytonutrients present in strawberries.
|Cyanidins||Ellagic acid||Sangulin H-6|
Alongside of vitamin C and their diverse polyphenol content, strawberries provide us with other key antioxidants and anti-inflammatory nutrients. Strawberries are an excellent source of manganese—a mineral which plays a key antioxidant role as a cofactor for the enzyme superoxide dismutase. And while strawberries are not a high-fat food, they do contain seeds and those seeds serve as a good source of the omega-3 fatty acid alpha-linolenic acid. You are also going to find small amounts of carotenoids in strawberries, especially lutein and zeaxanthin.
We would like to add a special note here about the ellagitannins in strawberries. These beneficial antioxidant and anti-inflammatory polyphenols change in concentration along with the ripening of the berries. In research studies on strawberries, four stages of ripening are usually taken into account: (1) the green stage, which is the least ripe; (2) the veraison stage, in which the berries are basically pinkish in appearance with some yellowish and greenish hues; (3) the ripe stage, which we are quite familiar with because of its bright anthocyanin reds; and (4) the overripe stage. While it can be difficult to see color differences in the ripe versus overripe stage, overripe strawberries are more mushy to the touch (at least in spots) and duller in appearance. Their vibrant reds have "lost their shine." Interestingly, the ellagitannin content of strawberries appears to decrease from stage to stage across the lifespan of the strawberries. While this is not a reason to choose unripe strawberries (since some of their health-benefitting qualities do not develop until they increase in ripeness, and also because they also have yet to develop their full delicious taste and aroma), it is a reason not to choose overripe strawberries in order to preserve as many ellagitannin benefits as possible.
Not surprisingly, the rich antioxidant and anti-inflammatory content of strawberries can pave the way for impressive cardiovascular benefits. Research on the antioxidant content of strawberries is providing us with more and more evidence about decreased lipid peroxidation in our blood vessel linings following strawberry consumption, and less malondialdehyde formation as well. Strawberry intake has also been shown to result in better free radical scavenging activity. Of special interest in this area of research has been the effect of strawberry consumption on the activity of an enzyme called paraoxonase-1 (PON-1). This enzyme is able to help break down lipid hydroperoxides (LOOH), and this process can help protect our blood vessels since excessive presence of LOOH can increase our risk of blood vessel damage due to the highly reactive nature of LOOH. In studies to date, strawberry intake has ranged from 2–4 cups per day over a period of 10–30 days. Within this context, it can also be helpful to know that about eight whole large strawberries will fit into one measuring cup. In terms of pint containers, you will usually find roughly 3 cups of whole large strawberries per pint, or 24 large strawberries. While these amounts are obviously not precise, they can give you a ballpark for understanding the amounts used in studies of strawberries and cardiovascular health.
In this "other" category we would like to mention two other areas of ongoing health research on strawberries. The first area involves regulation of blood sugar, and the second area involves cognitive processes, especially as they can change during later life.
Improved regulation of blood sugar is a health benefit that appears more and more likely based on the findings from recent studies on strawberry consumption. Especially following consumption of a meal, researchers are finding better regulation of insulin and blood sugar levels in connection with strawberry intake. Numerous mechanisms are under investigation here, including release of incretin hormones like GLP-1 (glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic polypeptide) and alterations in the activity of carb-related enzymes like alpha-glucosidase and alpha-amylase. At this point in time, however, much of the research on strawberries and blood sugar regulation has been conducted on animals only, and we have yet to see any large-scale human studies on these aspects of strawberry intake.
Most assessments of strawberries show a glycemic index (GI) value of approximately 40. This GI for strawberries would not only be considered low, but is also considerably lower than the GI for many other fresh fruits, including apricots, bananas, cantaloupe, pineapple, and watermelon (and, of course, dried fruits like figs which have a more concentrated sugar content after being dried). The low GI of strawberries seems to match up well with new research studies on their blood sugar impact. We would also like to note that among our Top 25 food sources for folate at WHFoods, there are only two fruits: papaya and strawberries. The fact that 1 cup of these berries provide roughly 10% of our daily recommended folate (400 micrograms) might play an important role in their blood sugar impact since folate deficiency has been associated with increased risk of type 2 diabetes and since improvements in type 2 diabetes have been shown with increased intake of folate. Coupled with the substantial number of animal studies that show improved blood sugar regulation following strawberry intake, as well as the low GI value for strawberries and their provision of nutrients like folate, we expect to see future studies that document the benefits of strawberries for lowering risk of type 2 diabetes in humans, and also perhaps also for improved blood sugar regulation in persons already diagnosed with this condition.
The strong antioxidant and anti-inflammatory benefits provided by strawberries make this fruit a natural candidate for research in the area of cognitive function. Research on female participants 70 years and older in the Nurses Health Study (conducted jointly by Brigham and Women's Hospital, Harvard Medical School, and Harvard School of Public Health) has shown reduced cognitive loss in women who consumed at least 1–2 servings of strawberries per week. This finding is encouraging, especially due to the very feasible amount of strawberries involved. (At 8 large strawberries per cup, we are talking about 8–16 strawberries during the course of an entire week.) Research on rats in the area of cognitive function and strawberry intake has demonstrated a phenomenon technically referred to as "hippocampal neurogenesis." This term refers to new nerve generation in the area of the brain known as the hippocampus, which is often involved in the learning and recall of new information. Researchers have hypothesized that the benefits of strawberries in this regard might be due to increased expression of the gene for insulin-like growth factor 1 (IGF-1), a peptide (protein-based) hormone involved in growth and tissue building. More research is needed before we can draw any firm conclusions about strawberries and cognitive function. However, these preliminary study findings suggest that the benefits of strawberry intake extend into this area of our health.
Strawberries are among the most popular berries consumed worldwide. As a wild fruit, strawberries are native to regions of the earth known as "temperate" regions. These regions include most of Europe, Asia, North America, and the lower half of South America, including Chile. Not only do strawberries grown wide throughout these many regions of the world, they have also been cultivated for hundreds of years. In the United States, which is the world's largest commercial producer of strawberries at approximately 3 billion pounds per year, strawberry varieties are often divided by growers into categories like "early season," "mid-season," "late-season," "June-bearing," or "day neutral" (which typically produce during July, August, and September). Another popular variety is "everbearing," which contrary to its name, typically bears fruit 2–3 times per year in different seasons.
The strawberry plant is unusual in its ability to flower in "flushes" during different seasons of the year, including spring, summer, and fall. During warmer summer months, it can invest a good bit of its energy in "runner" formation and eventually establish roots in new areas for the growth of new plants. It is also capable of "wintering over" with some helpful protection by growers.
So as you can see, both wild and cultivated strawberries can be quite versatile and adaptive, and this versatility is reflected in their many different growing regions and varieties. Over 100 different varieties of strawberries are grown commercially worldwide.
Strawberries belong to the rose family of plants (Rosaceae). This remarkable family contains a large number of familiar foods, including many popular berries. Alongside of strawberries, other berries found in this plant family include blackberries, boysenberries, loganberries, and raspberries. Apples and loquats are members of the rose family, as are almonds, apricots, cherries, peaches, plums, and prunes. The strawberries we enjoy from the grocery store all belong to the genus Fragaria. Given the spectacular fragrance of this unique berry, this genus name makes perfect sense to us!
The aroma of wild and cultivated strawberries is legendary worldwide. Scientists now know that esters (including methyl anthranilate), alcohols, and furanones (including mesifurane) are included in the volatile substances that help provide strawberries with their fragrance. In fact, researchers have even identified a gene called SAAT (strawberry alcohol acyltransferase) which helps strawberries generate their aroma and flavor during ripening. Fragaria moschata—sometimes called the must strawberry or hautbois strawberry—is native to Europe and sometimes regarded as one of the most fragrant varieties of this berry. The most common species of strawberry found in supermarkets throughout the U.S. is Fragaria ananassa. Within this genus/species you will find many popular varieties of strawberry including Alba, Clery, Darselect, Elsanta, Eva, and Portola. Fragaria vesca, Fragaria virginiana, and Fragaria chiloensis are other popular species of commercially grown strawberries.
As mentioned in the Description section above, strawberries have grown wild throughout Europe, Asia, North America, and the lower half of South American for thousands of years. And for hundreds of years they have been cultivated in these and other locations across the globe. Countries currently producing strawberries on a commercial basis include the United States, Mexico, Spain, Korea, Poland, Turkey, and Egypt, with lesser amounts grown in Morocco, Chile, other countries throughout Europe, Japan, and the Russian Federation. The United States produces by far the most strawberries worldwide, at well over 1 million metric tons (very close to 3 billion pounds) annually. This amount is approximately 30% of strawberries commercially produced worldwide.
Within the U.S., California is by far the country's largest strawberry-growing state, with about 41,500 planted acres. Florida ranks second, with approximately 11,000 acres. While a good way back in total volume, Oregon ranks as the third largest strawberry-producing state. U.S. adults average about 7.5 pounds of fresh strawberry consumption per year. About 80% of all strawberries produced in the U.S. are sold as fresh market strawberries, and about 20% are sold in frozen form.
As strawberries are very perishable, they should only be purchased a few days prior to use. Choose berries that are firm, plump, free of mold, and which have a shiny, deep red color and attached green caps. Since strawberries, once picked, do not ripen further, avoid those that are dull in color or have green or yellow patches since they are likely to be sour and of inferior quality. Full ripe berries have the peak flavor and texture. "Full ripe" in this case means optimally ripe, not overripe. We believe that the surprisingly fragile and perishable nature of strawberries is especially important!
Medium-sized strawberries are often more flavorful than those that are excessively large. If you are buying strawberries prepackaged in a container, make sure that they are not packed too tightly (which may cause them to become crushed and damaged) and that the container has no signs of stains or moisture, indication of possible spoilage. Strawberries are usually available year round, although in greatest abundance from the spring through the mid-summer.
At WHFoods, we encourage the purchase of certified organically grown foods, and strawberries are 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 strawberries. In many cases, you may be able to find a local organic grower who sells watermelon 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 strawberries is very likely to be strawberries that display the USDA organic logo.
In the case of strawberries, we would like to add that pesticides have been shown to be of special concern. According to results from the 2015 Pesticide Data Program administered by the U.S. Department of Agriculture (USDA), well over half of all strawberry samples (706 total) contained pesticide residues. Over 30% contained residues from five different pesticides, and 3.5% contained residues that exceeded established Environmental Protection Agency (EPA) tolerances. One strawberry sample also contained residues from 20 different pesticides among the 38 different types of pesticide residues found on the strawberry samples. While certified organic strawberries are definitely not guaranteed to be free of pesticides, the rate of detection on organic strawberries has been far lower than the rate on conventional produce. A 2010&ndashl2011 pilot program at the USDA, for example, performed 5,022 analyses on 26 strawberry samples and failed to detect pesticide residues in 5,012 of the 5,022 analyzed. So, you can see why we have decided to place special emphasis on the purchase of certified organic strawberries.
Food scientists have recently taken a close look at storage time, storage temperature, storage humidity, and degree of strawberry ripeness and found significant differences among their impact upon nutrient retention. On average, studies show 2 days as the maximal time for strawberry storage without major loss of vitamin C and polyphenol antioxidants. It's not that strawberries become dangerous to eat or invaluable after 2 days. It's just that more storage time brings along with it substantially more nutrient loss. In terms of humidity, 90-95% has been shown to be optimal. Most refrigerators will average a much lower humidity (between 80-90%). Because air circulation inside the fridge can lower humidity, you may want to give your strawberries more storage humidity by putting them in your refrigerator's cold storage bins (if available). Those cold storage bins will help boost humidity by reducing air circulation. If your refrigerator does not have storage bins, you can use a sealed container for refrigerator storage of your strawberries. Optimal temperature for strawberry storage over a 2-day period has been found to be relatively cold—36F (2C). All public health organizations recommend refrigerator temperatures of 40F (4.4C) as the maximum safe level for food storage.
However, if you are storing sizable amounts of fruits and vegetables—including strawberries—in your refrigerator, you may want to consider setting your refrigerator to a lower-than-maximum temperature setting in the range of 36°-38°F (2°-3°C).
Here is some background on why we recommend refrigerating strawberries. 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, vitamin B6, and carotenoids are good examples of nutrients highly susceptible to heat, and for this reason, their loss from food is very likely to be slowed down through refrigeration.
The very fragile nature of strawberries means that great care should be taken in their handling and storage. Before storing in the refrigerator, remove any strawberries that are molded or damaged so that they will not contaminate others. Place the unwashed and unhulled berries in a sealed container to prevent unnecessary loss of humidity. Strawberries will maintain excellent nutrient content if properly stored in a refrigerator for two days. Make sure not to leave strawberries at room temperature or exposed to sunlight for too long, as this will cause them to spoil.
To freeze strawberries, first gently wash them and pat them dry. You can either remove the cap and stem or leave them intact, depending upon what you will do with them once they are thawed. Arrange them in a single layer on a flat pan or cookie sheet and place them in the freezer. Once frozen, transfer the berries to a heavy plastic bag and return them to the freezer where they will keep for up to one year. Adding a bit of lemon juice to the berries will help to preserve their color. While strawberries can be frozen whole, cut or crushed, they will retain a higher level of their vitamin C content if left whole.
Commercial food processing can dramatically lower the nutrient content of strawberries, especially their phytonutrient content. The strong impact of some processing methods may be to do heat, pH (changes in acidity during processing), oxygen exposure, light exposure, the physical and mechanical impact of processing, or a combination of these factors. In any case, a much safer bet in terms of strawberries and nourishment is to stick with fresh berries or carefully frozen berries, and in the case of baby food or the feeding of young children, to purée the berries in a blender so that overall processing is kept to a minimum.
If you'd like even more recipes and ways to prepare strawberries the Nutrient-Rich Way, you may want to explore The World's Healthiest Foods book.
|vitamin C||84.67 mg||113||44.1||excellent|
|fiber||2.88 g||12||4.5||very good|
|iodine||12.96 mcg||9||3.4||very good|
|folate||34.56 mcg||9||3.4||very good|
|vitamin B6||0.07 mg||4||1.6||good|
|omega-3 fats||0.09 g||4||1.5||good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%