Nutritional Composition of Stevia rebaudiana Bertoni Leaf: Effect of Drying Method

Purpose: To determine the effect of three methods of drying, viz, sun, oven and microwave, on Stevia rebaudiana Bertoni leaf’s nutritional composition. Methods: Fresh Stevia rebaudian bertoni leaves were dried separately by sun, oven and microwave. The chemical composition was determined by Association of Official Agricultural Chemists (AOAC) method. Tannin content was measured by titrimetric method while heavy metals were analyzed by atomic absorption spectrometry. Results: The following data were obtained for the plant when the three drying methods were employed: moisture content, 4.45 – 10.73 %; ash, 4.65 – 12.06 %; protein, 12.44 – 13.68 %; fat, 4.18 – 6.13 %; total dietary fiber, 4.35 – 5.26 % and total carbohydrates, 63.10 – 73.99 %. The pH value was 5.96, 5.95 and 6.24 for sun, oven and microwave drying, respectively. Total energy of the plant material was in the range 362.3 – 384.2 kcal/100 g while tannin content was in the range 5.43 – 5.91 %. Moreover, reducing sugar was 4.5, 4.8 and 5.3 %, respectively, for sun, oven and microwave drying. Heavy metals content varied in stevia leaves, with lead was detected in high concentration in sun-, ovenand microwave–dried materials with values of 4.77, 0.14 and 2.16 μg/g, respectively, while the corresponding values for cadmium were 0.49, 0.44 and 0.33 μg/g, Arsenic level was 0.30, 0.09 and 0.10 μg/g for sun, oven and microwave drying, respectively. Mercury level was the same (0.1 μg/g) irrespective of the drying method. Conclusion: The results obtained indicate that Stevia leaves is a good source of carbohydrate and other nutrients and hence a substitute for sugar in processed drinks. Furthermore, drying reduces nutritional values with the exception to fiber content.