Blueberries contain a large amount of polyphenols – compounds with a strong antioxidant effect, preventing heart disease, cancer and civilization diseases such as metabolism disorders. They are not destroyed by cooking or baking, but by pasteurization. Currently, blueberries known from Polish forests contain the most polyphenols, but scientists from the USA have found South American blueberries, easy to grow, with the highest content of these valuable compounds currently found in fruits.
A team of scientists from the University of Maine, led by Prof. Klimis-Zacasa conducted research on an important group of antioxidants, which are polyphenols. They are organic chemical compounds from the group of phenols, found in many plants and fruits. They have a strong antioxidant effect, reducing the chances of, e.g. cardiovascular diseases or cancer. They are divided into hydrolysed tannins and phenylpropanoids, which group includes the best known antioxidants, which are flavonoids.
Blueberries are one of the greatest sources of polyphenols, researchers from the University of Maine found. A constant diet with their use enables the prevention of pathological metabolic changes, the so-called metabolic syndrome (MetS) and increases resistance to this syndrome.
The metabolic syndrome is a group of disorders that are symptoms of or lead to more serious diseases. They include: obesity, hypertension, chronic inflammatory ailments, dyslipidemia, i.e. the presence of elevated levels of triglycerides and low-LDL lipoproteins in the blood, with low concentrations of high-density HDL lipoproteins, glucose intolerance and insulin resistance. These disorders affect about 37 percent. of the US population and a slightly smaller group in Europe. Many substances in food can help prevent MetS, which again reduces the need for drugs that have side effects, Prof. Klimis-Zacas
Previous studies have documented the healing properties of polyphenols. The experiments were carried out for cardiovascular diseases on a model of obese rats, the so-called Zucker rats modeling human obesity. The blood vessel walls of these animals, like obese humans, show an abnormal reaction to dilatation and constriction, which affects blood flow and pressure, the researchers say in the study.
According to their findings, the optimal amount of polyphenols, which strengthen and elasticize the walls of blood vessels, is provided in 2 cups of blueberries a day for a person weighing 70-80 kg. In Zucker rats, the polyphenols contained in the equivalents of these 2 cups of berries made the blood vessels elastic and regulated blood pressure, while lowering it in 4-5 weeks. A similar effect in humans should be expected after approx. 8 weeks. According to researchers, an additional positive effect of the polyphenols contained in berries is the reduction of chronic inflammation, a change in the lipid profile, i.e. the reduction of LDL cholesterol in favor of HDL cholesterol and the reduction of hypertension to a level close to the normal level.
Blueberries burn fat
Meanwhile, a team of scientists from TWU in Denton, Texas, led by Dr. Shiwani Moghe, investigated the effects of blueberry polyphenols on the heart, circulatory system and obesity.
It was found in the course of the research that polyphenols derived from berries have a great influence on the differentiation of adipocytes. Adipocytes are primary fat cells that synthesize and store simple fats (triglycerides). Plant polyphenols reduce adipogenesis, i.e. the process of the production of white and yellow adipose tissue cells in which fat stores are stored. This tissue is responsible for obesity. Thanks to berry polyphenols, lipolysis is induced, i.e. the process of fat breakdown in which energy is generated.
Dr. Moghe’s team set out to investigate these processes at the molecular level. The tissue culture of the mice was treated with berry polyphenols, while in the second culture it was allowed to grow unhindered. The control group had a much higher tissue lipid content than the polyphenol-treated tissue group. The highest dose of polyphenols, corresponding to about 3 cups of pure blueberries per day per human weighing 70-80 kg, decreased the content of tissue lipids by 73%, while the lowest doses caused their decrease by 27%.
Currently, it should be checked whether there will be side effects at a high dose of polyphenols in the case of humans and whether this dose will actually be effective. The most important thing is to determine the optimal dose for humans, because current research shows that thanks to this substance it will be possible to reduce the size of adipotic tissue, i.e. potential adipose tissue – says Dr. Moghe.
Don’t know where to buy blueberries? At Medonet Market you will find freeze-dried berries that you can add to your smoothie or porridge. They are low in calories and also help lower blood sugar levels.
Baking does not destroy polyphenols
In turn, an international team of European scientists, consisting of scientists from the University of Reading, the University of Northumbria and the University of Düsseldorf, led by Dr. Ana Rodriguez-Mateos, set out to investigate the effects of feeding blueberries in the daily diet. Most often they are not served raw – they are instead an ingredient of dishes and desserts. Usually, the heat treatment process, such as cooking and baking, removes most of the desired substances. Scientists set out to investigate whether this is happening to polyphenols. It turned out that home treatment removes some of them, depending on the technology used. Making the berries juice and pasteurizing it causes the greatest damage. The longer the pasteurization temperature and its duration, the more polyphenols disappear. For short pasteurization it is 22 percent. With long-term pasteurization and juices with a lot of sugar, as much as 81 percent disappears. these ingredients. It is different when cooking or baking. Short cooking or baking of whole, not crushed fruit at a stable temperature below 200 degrees Celsius does not have significant effects on the content of polyphenols in a dish or berry dessert prepared in this way.
According to researchers, however, thermal treatment produces significant effects depending on the type and size of polyphenol molecules. Anthocyanin levels drop by 10 to 21 percent. There are more smaller procyanidin molecules as larger anthocyanin molecules break down, while the quercetin level remains unchanged. Instead, the amount of phenolic acid increases. According to Dr. Ana Rodriguez-Mateos, the yeast used in baking cakes has a stabilizing effect on polyphenols. The topic seems ridiculous, but when we think about the use of polyphenols in everyday life, we should not only consider supplements that are sometimes less digestible, but simply fruit, most often present on our menu. Due to their health-promoting properties, it is necessary to determine how the process of their preparation affects the physicochemical properties of the substances in them, Dr. Ana Rodriguez-Mateos told Science Daily.
However, blueberries don’t always have the same polyphenol content. European forest blueberries, including blueberries found in Poland, have about 1,5 times more of these valuable ingredients than farmed blueberries. However, they are difficult to harvest and availability depends on whether the weather for these berries was good in a given year. Therefore, a team of scientists from The City University of New York, led by Dr. Edward Kennelly, draws attention to two species of wild blueberries growing in Mexico, Latin America and South America: Anthopterus wardii Ball and Cavendishia grandifolia Hoerold. Often included in the food of the local Indians, they can be cultivated, and the content of polyphenols and phenolic acid is the highest among blueberries known to science. So it is possible that in a few years we will be eating South American blueberries, just like blueberries today.
Tekst: Marek Mejssner