Ergogenic and Antioxidant Effects of Corinthian Currant

Aerobic exercise performance in events lasting more than one hour has been shown to improve with pre- or/and during-exercise consumption of carbohydrates (CHO) and athletes or recreationally exercised individuals are often advised to consume CHO before, and/or during exercise. The improvement in performance with CHO supplementation is due to the maintenance of blood glucose levels and the increased CHO availability for oxidation late in exercise that may preserve muscle glycogen. Apparently based on the above mechanisms, the dietary industry provides a wide variety of CHO supplements in different forms (sport drinks, sport gels, CHO bars, sport jellybeans, sport chews). Athletes at all levels use these supplements to optimize their performance during training or competitive events. However, these products are processed, and often expensive, in contrast with other natural foods that may provide an alternative for those preferring a healthier, though, equally effective choice.

Aerobic exercise and training relates with the production of reactive oxygen and nitrogen species (RONS), as indicated by the changes in the concentration of several by-products deriving from the oxidation of biomolecules, and the upregulation of antioxidant enzymes. Although RONS in low to moderate quantities are essential for optimized exercise performance and exercise-induced adaptations, yet, excessive production of RONS especially during exhaustive exercise, promote contractile dysfunction, muscle weakness and fatigue, and impaired recovery from exercise.Therefore, research has focused on nutritional strategies aimed at reducing these effects. There is evidence that treating with antioxidants, protects in part against free radicals-mediated damage in exercise. In regards with this prospective, the supplementation of antioxidants is a very common strategy to minimize RONS production and avoid the detrimental effects of oxidative stress in exercise. In the same way with CHO, natural foods could also provide an alternative antioxidant source for those seeking a more healthy option.

Corinthian currants or Corinthian raisins are small, dark purple colored, sun-dried vine products, produced from a special type of black grape (Vitis Vinifera L., var. Apyrena) and cultivated almost exclusively in the Southern of Greece. Corinthian currants are well known for their potential health benefits. They consist a high source of complex CHO (32.5% glucose, 32.1% fructose, 0.40% sucrose, 0.72% maltose), minerals (magnesium, iron, potassium, phosphorus, zinc) and vitamins (ascorbic acid, pyridoxine, riboflavin and thiamin) necessary for vitality, while they contain virtually no fat or cholesterol. Additionally, currants are considered as dried fruits with low to moderate glycemic index despite their high carbohydrate content. Therefore, Corinthian currant could be used as an alternative CHO source during exercise and provide a natural and healthy choice, equally effective to other commercial supplements on favorably affecting metabolism and/or improving performance.

Except for their high CHO content, Corinthian currants are also rich in polyphenols which are free radicals scavenging compounds and provide them with antioxidant properties. The rich antioxidant content renders Corinthian currant a potentially capable nutrient to boost an individual's antioxidant status in response to prolonged aerobic exercise. However, no study so far has addressed this potential role of Corinthian currants.

Therefore, the purpose of the present study was to investigate the effect of pre-exercise supplementation of Corinthian currants on metabolism and performance, as well as redox status in response to prolonged aerobic exercise. These responses were compared against glucose and water.

Eleven healthy well-trained male (n = 9) and female (n = 2) adults (18 - 45y) participated in the present cross over, randomized study. The participants visited the laboratory four times in total. During their first visit, anthropometric characteristics assessment and baseline measurements were performed (body mass, standing height, percentage body fat, VO2max). Both the protocol for the assessment of VO2max, and the exercise protocol were performed on a cycle ergometer (Cycloergometer, Monark 834, ERGOMED C, Sweeden). During their second visit, the participants were randomly assigned to either Corinthian currant (1.5 g CHO/kg BW), or glucose drink (1.5 g CHO/kg BW), or water (6ml/kg BW) condition. After the assignment of the experimental condition, the participants performed the exercise protocol which consisted of 90 min of submaximal (70 - 75% VO2max) cycling, followed by a near maximal (95% VO2max) time trial to euxhastion. Fluid intake was kept constant at 7 ml/kg BW before the start of exercise, 3 ml/kg BW every 20 min during the 90-min exercise bout and 7 ml/kg BW within 15 min after the end of exercise. During their third and fourth visits, the participants repeated the experimental procedure after they had been assigned to one of the remaining two conditions. Between the first, second and third visit, there was a wash out period of two weeks. Blood samples were collected at baseline (before the CHO or water consumption), 30 min after CHO or water consumption (pre-exercise) and at 30 min, 60 min, 90 min of submaximal trial, after exhaustion (TT), and 1 h after the end of the exercise, for the assessment of GSH, catalase, uric acid , TAC, and TBARS.