July 3, 2013
Freeze Them Or Cook Them, Blueberries Are Still Packed Full Of Nutrients
April Flowers for redOrbit.com - Your Universe Online
Thanks to widely reported health benefits of blueberries - including the potential to decrease cardiovascular risk factors, enhance insulin sensitivity, improve cognition and more - the little deep blue berries have never been more popular. A recent study led by the USDA/ARS Children's Nutrition Research Center at Baylor College of Medicine and Texas Children's Hospital questioned what happens to the health benefits of blueberries after they are cooked in a variety of different ways.
Dr. Michael Grusak and his colleagues measured the levels of the beneficial phytochemicals in blueberries after cooking the berries in a variety of ways. Using a cell-based culture assay, the team also examined the bioactive potential of wild blueberry extract after cooking.
"The point of the study was two-fold," Grusak said. "Because blueberries are touted as such a health-beneficial food, we wanted to know the nutrient content of blueberries after consumers cook them in a number of ways. But researchers are also beginning to use blueberries in clinical trials, so the information we gained from this study will be important to help researchers design better studies."
The phytochemicals in blueberries that are known to have beneficial health impacts - anthocyanin (ANC), proanthocyanidin (PAC) and chlorogenic acid (CA) - were measured after exposing the blueberries to common postharvest handling practices and culinary preparation methods. The team used quick-frozen blueberries available in the freezer section of grocery markets. These blueberries are commonly used in processed foods.
The team also measured the same phytochemicals in individually quick frozen wild blueberries that had been subjected to temperature fluctuations, which are frequently encountered during distribution and handling for retail sales. The levels of ANC, PAC and CA levels dropped by about 8, 43 and 60 percent, respectively, when compared to quick-frozen berries stored continually from harvest at -80 degrees Celsius. The levels were also reduced by baking, boiling and microwaving. Longer cooking times, 3-5 minutes of microwaving for example, caused the biggest declines in the concentrations of these blueberry components.
The team performed cell-based assays to measure the antioxidant activity of blueberry extract after cooking in various ways. Antioxidants are known to combat oxidative stress, which is a contributor to certain human diseases. The team only saw a decline in antioxidant properties after microwaving the extract for five minutes. Boiling, baking or shorter microwaving times did not have an adverse effect.
"What we can say from this study is that cooking and heating, especially longer microwaving, does decrease the amount of beneficial compounds in the berries," Grusak said. "Minimal cooking would be ideal, but there are still measurable levels of health-beneficial components in blueberries, even after a variety of preparations."
The results, published in the Journal of Berry Research, suggest the need for conducting future health-related studies involving blueberries to consider the methods by which blueberries are prepared and the effects they have on the compositional attributes of the fruit at the time it is eaten.