Orientador: Prof. Dr. Silvio Claudio da Costa

Data da Defesa: 17/02/2017



INTRODUTION: Stevia rebaudiana is a perennial shrub belonging to the Asteraceae family. It is native to South America, but commonly found in Paraguay, Argentina and southern Brazil. In its constitution presents several compounds already identified, however, those of greater commercial value are presented as glycosides of esteviol, which are natural sweeteners with sweetness power of on average 300-450 times greater than sucrose. Currently, several traditional and modern methods are being evaluated in order to obtain a high yield of extraction, which is one of the largest industrial problems. Also, it is increasingly sought to obtain sweeteners with high sensorial quality as well as to evaluate the composition of the extract as a whole and its connection with physiological benefits already reported in the literature.
OBJECTIVES: The aim of this study was to use two pre-treatments in Stevia leaves before extraction: an enzyme and another using ethanol. With the enzymatic, the influence on the steviol glycoside extraction yield compared to an untreated extraction was evaluated. Already with the ethanol treatment craved the characterization of the obtained byproduct and its potential as a food additive and research of changes generated by treating the sheet characteristics and yield of extraction and finally, to define a procedure for obtaining sweeteners and evaluate the sensory characteristics of the final product.
METHODOLOGY: For enzymatic pretreatment, cellulase enzyme was run at different times (15, 30, 45, 60 min) at a ratio of 1: 5 (w / v) at 50 ° C and 150 rpm. Thereafter, aqueous extraction at 1:10 (w / v), 50øC and 120 rpm was performed on both treated and untreated leaves. Total glycosides were also extracted from the leaves. The glycoside contents were analyzed by HPLC high performance liquid chromatography. For the ethanolic treatment, it was carried out by means of a chromatographic column using the force of gravity. A total of 14 ethanolic fractions were collected and analyzed for HPLC, total phenolics, antioxidant activity and identification of compounds by HPLC. Then, the leaves were dried and evaluated in both treated and untreated leaves total glycosides, ash, moisture, chlorophyll, anthocyanins, total phenolic, flavonoids, antioxidant activity and also, the lipids were extracted from the two leaves for posterior Identification and quantification of fatty acids in GC-MS. Then, to determine the optimum conditions of extraction of the glycosides was used a central composite experimental design composed of three variables and two levels. Once the conditions were optimized, the glycosides were extracted from treated and untreated leaves and a method of purification of sweeteners was suggested, consisting of extraction, vacuum filtration, ultrafiltration, nanofiltration, ion exchange, adsorption and drying. Finally, the sweetener powder was analyzed for purity, sweetness power in relation to sucrose, bitterness threshold and overall acceptance in relation to sucralose, the sweetest currently consumed in the world.
RESULTS AND DISCUSSION: In the enzymatic treatment, the evaluated time that resulted in a greater amount of sweetener achieved was of 60 min. It was observed that in only one extraction cycle 71% of the sweeteners originally present in the leaves were obtained, compared to 56% obtained from leaves without treatment. Also, with the enzymatic treatment the whole rebaudioside C of the leaf was extracted and a greater of content of rebaudiosídeo A, whereas in sheets without treatment more stevioside was obtained, that has inferior sensorial characteristics. With the ethanol treatment in stevia leaves one can obtain and characterize a potential by-product for use in drugs or as food additive, since ethanolic extracts of stevia leaves have proven both biological and industrial benefits. A new compound not yet reported in the literature on stevia leaves or extracts was reported.
Moreover, it was verified that the ethanolic treatment influences in the yield of extraction and obtaining of compounds and does not intervene negatively in the characteristics and composition of the leaves. Also, a methodology for obtaining sweeteners with the minimum use of toxic solvents was proposed, although more studies should be done to increase the purity of the obtained sweetener. Finally, by evaluating sensorial the characteristics of the sweetener obtained from the treated leaves and comparing it with the most consumed sweetener in the world, it is concluded that the product needs a high concentration for the bitterness threshold and has similar acceptance to that of sucralose, proving to be a quality product.
CONCLUSION: The enzymatic treatment and the ethanolic treatment in leaves of Stevia rebaudiana preceding the extraction process is presented as a viable, scalable and beneficial alternative since good yields of glycoside extraction are obtained and in the case of ethanolic treatment, a byproduct with commercial value and besides improving the extraction process, a final product with sensorial quality is reached.

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