By Vaios T.
By Vaios T. Karathanos, Ph.D., Professor of School of Nutrition & Dietetics, Harokopion University of Athens
Currants (black Corinthian raisins) are a unique dried vine product that is produced mainly in southern Greece and in smaller quantities in California, South Africa and Australia. Especially in the region around the town of Aeghion is produced the world-known Vostizza currants, a PDO product (Product of Designated Origin). The cultivation of currants in the Greek South is referred in Homer’s Odyssey almost three thousand years ago and by philosopher Aristotle. The currants are produced mostly in high-altitude, mountainous area and are sun-dried without addition of any additive, such as accelerating drying agent or infused sugars. The product, which is fully traceable to the farmer, is then washed by potable water and cleaned in modern food factories. The area of Aeghion has made in recent years several new developments in agriculture, such as the first implication of certified organic agriculture in Greece more than three decades ago. Also the main Agricultural Cooperative of the area has assisted researchers from Greek and several European Universities to participate in collaborative research projects, such as the food quality and safety and nutritional value of the product.
Recent research performed in Universities has assisted to disclose the high nutritional value of currants:
- Currants are an excellent source of antioxidants and polyphenol compounds (1) (flavonoids, anthocyanins, proanthocyanidins, procyanidins, resveratrol) and it has a very high antioxidant content (2). The currants have some advantages over several other fruits because they are coming from black/deep blue grapes, which are considered as better phenolic source than white grape in antioxidants and anthocyanins (3). The drying of currants under low relative humidity and in moderate temperatures allows the preservation of antioxidants and vitamins of grapes when they are turned to currants.
- A basic advantage of currants (and several other fruits, such as raisins) is that they are consumed along with their skin. Their skin, being deep blue/black, is full of antioxidants. Also due to their small size, currants have a very high specific surface area (area of skin/mass of product), therefore a higher concentration of antioxidants but also dietetic fiber than several other fruits. The contained fiber of currants is very high (about 7%). Fiber acts as a substrate of useful bacteria in the colon, thus they give to the currants (and other similar fruits) prebiotic properties. Thus they assist the good health of gastrointestinal system and prevent the cholesterol biosynthesis.
- Currants are excellent source of minerals, such as zinc, magnesium, iron and especially potassium. The latter is very important in several functions in mammals but especially in the sodium/potassium equilibrium in body and depression of high blood pressure. The potassium content of currants is 0.8% per weight on the average.
- Clinical studies, which took place in humans under the guidance of the Department of Nutrition of Harokopion University and the Athens Medical School, showed that there is bioavailability (4) of the currants’ antioxidants in blood after intervention and a high antioxidant activity.
- The glycaemic index (GI) of currants is moderate in healthy humans while in people suffering from diabetes the effect of currant sugars is also moderate and much better than other even less sweet fruits, which make currants as suitable for consumption by several categories of humans when they are consumed in moderation, even by those suffering from metabolic diseases (5). The sweetness of currants is due to their high content (35% by weight) in the very sweet sugar fructose which, however, has a low GI (19) in comparison to glucose (100). Therefore currants are very sweet and contribute to the satiety.
- Body weight in human volunteers who consumed currants daily did not increase, but rather decrease. This was attributed to the sweetness of the product, the satiety that resulted in, and the high fiber content of the product.
- In published research in vitro it was found that currant juice resulted in significant apoptosis of gastric cancer cells (6) and colon (7) while more research is underway for the effect of cancer on other cancer cells.
- Currants were provided, under continuous medical guidance, to people with Diabetes Mellitus II. It was shown that moderate daily consumption of currants (two tablespoons per day, 36 g) did not result in any glucose elevation in the blood. The antioxidant activity of blood was increased significantly and blood pressure decreased significantly (8). Thus currants may be a constituent of our diet that may lead to a healthier diet style that may protect from cardiovascular diseases.
- In a clinical study in healthy humans that due to their life-style or environmental reasons were subjected to strong oxidative stress, the consumption of a normal daily dose of two tablespoons resulted in the reverse of oxidative stress phenomenon and a better health. Oxidative stress has been accused of causing diseases such as cardiovascular or cancer.
- The strong antioxidant content of currants remains quite constant during the grapes’ drying (9) but also during further processing (10) of the product, i.e. during baking, production of biscuits, etc.
The nutritional research for the health benefits of currants is continued for other metabolic diseases, such as Non-Alcoholic Fatty Liver Disease or effects on healthy humans. The studies are performed within a project of the Agricultural Cooperatives’ Union of Aeghion, Harokopion University, Academy of Athens and Athens Medical School, as well as in collaboration with other European Research Institutes.
The research which is underway but especially the already published research, may help to uncover the high nutritional value of this sweet dried fruit. A fruit that comes from the old times, related to the homemade tradition of old Europe and still an important constituent of the Mediterranean Diet.
- Chiou, A., Karathanos, V.T., Mylona, A., Salta, F.N., Preventi, F. & Andrikopoulos, N.K., 2007. Currants (Vitis vinifera L.) content of simple phenolics and antioxidant activity, Food Chemistry, 102(2): 516-522.
- Kaliora, A.C., Kountouri, A.M., Karathanos, V.T., 2009. Antioxidant Properties of Raisins (Vitis vinifera L.). J. Med. Food, 12(6), 1302–1309.
- Chiou, A., Panagopoulou E.A., De Marchi, S., Gatzali, F. & Karathanos, V.T., 2014. Anthocyanins content and antioxidant capacity of Corinthian currants (Vitis vinifera L., var. Apyrena). Food Chem., 146, 157-165.
- Kanellos, P.T., Kaliora, A.C., Gioxari, A., Christopoulou, G.O., Kalogeropoulos, N., & Karathanos, V.T., 2013. Absorption and Bioavailability of Antioxidant Phytochemicals and Increase of Serum Oxidation Resistance in Healthy Subjects Following Supplementation with Raisins. Plant Foods Hum. Nutr., 68(4), 411-415.
- Kanellos, P.T., Kaliora, A.C., Liaskos, C., Tentolouris, N.K., Perrea, D., & Karathanos, V.T., 2013. A Study of Glycemic Response to Corinthian Raisins in Healthy Subjects and in Type 2 Diabetes Mellitus Patients. Plant Foods Hum. Nutr., 68(2), 145-148.
- Kaliora, A.C., Kountouri, A., & Karathanos, V.T., Koumbi, L., Papadopoulos, N.G. & Andrikopoulos, N.K., 2008. Effect of Greek raisins (Vitis vinifera L.) from different origins on gastric cancer cell growth. Nutrition & Cancer, 60(6), 792-799.
- Kountouri, A., Gioxari, A., Karvela, E., Kaliora, A.C., Karvelas, M., & Karathanos, V.T., 2013. Chemopreventive properties of raisins originating from Greece in colon cancer cells. Food & Function, 4(3), 366-372.
- Kanellos, P.T. Kaliora, Α.C, Tentolouris, N.K., Argiana , V., Perrea, D., Kalogeropoulos, N., Kountouri, A.M. & Karathanos, V.T. A pilot randomized controlled trial to examine the health outcomes of raisin consumption in diabetic subjects. Nutrition, 30, 358-364.
- Karathanos, V.T. & Belessiotis, V.G., 1999. Application of a thin-layer equation to drying data of fresh and semi-dried fruits. Journal of Agricultural Engineering Research (νέος τίτλος: Biosystems Engineering), 74: 355-361.
- Karvela, E., Makris, D. Kalogeropoulos, N., Karathanos, V.T., & Kefalas, P., 2009. Factorial design optimisation of grape (Vitis vinifera) seed polyphenol extraction. Eur. Food Res. Technol., 229, 731-742.