Talk to today's medical scientists studying the disease-prevention properties of plant foods and most would tell you that a fast-rising star is the black raspberry, one of Nature's most powerful antioxidant fruits.
Particularly in the prevention of cancer, black raspberries are revealing remarkable effects as anti-tumor agents in laboratory research. In pursuit of this important finding, over the past six years no other fruit has had as much progress toward human clinical trials as the black raspberry.
Let's have a look at the scientific and health foundations for the benefits of including black raspberries in your diet.
How many species of black raspberries are commonly available to the general consumer?
In Canada and the US, there are two main species called Rubus occidentalis L. and Rubus eucodermis L. Rubus (a genus of plants in the family Rosaceae, subfamily Rosoidea). The Rubus is characterized by rose-like thorns along vines forming brambles that grow as irregular canes ranging from one to four meters in length. It is conventional to include black raspberries among other Rubus berries (red raspberries, blackberries, boysenberries, loganberries) as "brambleberries" or "caneberries" that have grown native in North America since recorded time.
How is the black raspberry different from other Rubus species?
Often called "blackcaps" by berry farmers, black raspberries are the smallest and bluest of the Rubus berries. Scientific assays of blackcap phytochemicals reveal the densest and most avid pigmentation among North American plants--so strong that the US Department of Agriculture used black raspberry juice as stamp dye on meats for several decades. Scientific tests have described blackcaps with the richest contents of pigment antioxidants among North American berries (as described further below).
Where do blackcaps grow and what markets are served?
Black raspberries grow primarily in the western US and in British Columbia. They prefer wet, mild winters and humid, warm summers and are harvested over the month of July. Oregon's Willamette Valley, especially, is noted for black raspberries accounting for 95% of total US production or about 4 million pounds per year. Only 5% of black raspberries are sold fresh. The market for processing to provide year-round supplies of frozen (immediately quick frozen, IQF), pureed or concentrated juice products makes up the rest.
What qualities of black raspberries appeal to consumers?
The intense pigmentation qualities mentioned above derive from a rich concentration and diversity of phenolic acid antioxidants in blackcaps. Phenolics give black raspberries several distinctive taste and chemical qualities, including high acidity (pH of about 3.5), semi-sweet taste (brix of about 10 in IQF fruit, 17 in puree) and a special tangy full-bodied taste that appeals to most people, including children. Blackcaps are very versatile regular in dessert recipes.
Over the past few years, research primarily at Ohio State University by Dr. Gary Stoner and colleagues has shown exciting - even astonishing - results of black raspberry phenolic extracts and whole berries themselves on colon and esophageal cancers in experimental animals. The focus has been on the antioxidant qualities particularly of ellagic and ferulic acids (both phenolic antioxidants) from blackcaps.
Black raspberries are one of the world's most promising tools from plant foods in the fight against cancer. They are now entering human clinical trials supervised by Dr. Stoner.
What are oxidants and antioxidants?
Moment by moment throughout the cells of our bodies, free radicals (i.e., oxidants or radical oxygen species) are continuously being generated by normal metabolism. Exposure to toxins in the environment, or irradiation, increases free radical production. Free radicals are unstable atoms having potential to damage cells and alter genes if not quickly neutralized.
Our bodies defend against oxidation through enzymes called dismutases, catalases, reductases and peroxidases. Also, our diet provides a host of chemicals serving antioxidant roles. These chemicals include: vitamins A, C and E; minerals like selenium, manganese and zinc; and pigments from the plant foods we eat.
In black raspberries, phenolic pigments like ellagic and ferulic acids are the major antioxidant source.
What are other pigments present in black raspberries?
The rich color of black raspberries comes from numerous chemicals of the phenolic super-family that is a class of several thousands of members serving plants as pigments. Black raspberry antioxidant strength is proportional to the intensity of the dye from its pigments.
A major subgroup of pigment phenolics is the flavonoid group that is densely populated in blackcaps. One flavonoid class in particular - anthocyanins - accounts for most of the blue-red-black pigmentation of black raspberries. In addition to anthocyanins, however, are ellagic acid, ferulic acid, gallic acid, rutin and cyanidin glycosides (phenolics identified by Dr. Stoner and colleagues as important anticarcinogens in blackcaps). Vitamin C, a universal antioxidant, is also well concentrated in black raspberries (about 2 mg per 100 grams of fruit), as is calcium (32 mg per 100 grams).
Is there a way to measure antioxidant quality of a plant food and how well do black raspberries perform?
Yes, a test called ORAC (oxygen radical absorbance capacity) is performed on a food sample in a test tube. Then, the strength of antioxidant is measure by how well it neutralizes free radicals.
At Oregon State University, black raspberries have been tested for ORAC against other berries and plant foods (first analyzed in a 2004 ORAC report by US Department of Agriculture scientists). Black raspberries had the highest ORAC among other caneberries, fruits or vegetables analyzed measuring 3 times higher ORAC than blackberries or red raspberries.
Plants with pale skins and white pulps like pears and some apples have low ORAC whereas dark fruit like black raspberries, blueberries and cranberries have relatively high ORAC.
What does a high ORAC from black raspberries mean for health protection?
The answer to this question requires actual clinical research in humans (being performed but still preliminary) but the scientific evidence points to widespread protection against numerous diseases by having a diet rich in high-ORAC foods like black raspberries.
What are some diseases that evolve from free radicals and what can we do to counter oxidative stress?
Growing scientific evidence shows that nearly every disease involves free radicals to some extent. Cancer, heart and vascular disease, diabetes, inflammation and neurological disorders all have strong components of oxidative stress. Premature aging and diseases of the elderly such as macular degeneration are thought to result from oxidative damage to cells as well.
The laboratory studies by Dr. Stoner point to the importance of oxidative factors in colon and esophageal cancer, and to the potential protective role of phenolics from black raspberries or other antioxidant-rich plant foods.
Consumers can enjoy the pleasures of dark berries in their diets while likely gaining antioxidant protection from berry phenolics. Why wait for positive results from the years of clinical research ahead? The preliminary evidence and pleasurable eating qualities of black raspberries should be enough to warrant including these berry treasures in your diet now.