Márcia Regina Simões

The effect of temperature and flow rate on the clarification of the aqueous stevia-extract in a fixed-bed column with zeolites

Stevia is being used as a sweetener due to its low calorific value and its taste, which is very similar to that of sucrose. After extraction from dried leaves, stevia extract is dark in colour so needs to be clarified for better acceptance by consumers. Adsorption is one of the most important processes in this clarification. In this work the clarification of extract stevia extract in fixed-bed columns with calcium zeolites was studied. Two temperatures (10oC and 30oC) and six different flow rates (2, 5, 9, 12, 16 and 19 mL/min) were studied. The results showed that the mass-transfer coeffcient increases with an increase in flow rate and the length of unused bed reaches a maximum at 9 mL/min for both temperatures. The fit of the Thomas model with the breakthrough data was not very good.

Chitosan as flocculant agent for clarification of stevia extract

Stevia is used as a sweetener due to its low calorific value and its taste, which is very similar to that of sucrose. After extraction from dried leaves, stevia extract is dark in colour, and therefore needs to be whitened to increase acceptance by consumers. In this study we tested chitosan, a cationic polyelectrolyte, as flocculant agent for the whitening of the Stevia extract. Positive charges of chitosan can interact electrostatically with a counter-ion, sodium tripolyphosphate (TPP), and then chitosan precipitates. A factorial design was used to study the whitening process, in which Glycosides Removal, Colour Removal, Turbidity Removal and Soluble Solids Removal were evaluated. The studied factors were Chitosan Mass and pH of the TPP solution. The results showed that chitosan is a good flocculant agent, being able to flocculate both the glycosides and the pigments that make the extract coloured.

Clarification of Aqueous Stevia Extract Using Alginate Beads — Evaluation by Factorial Design Methodology

Stevia is used as a sweetener due to its low calorific value and its taste, which is very similar to that of sucrose. Stevia extract is dark in colour and needs to be clarified for better acceptance by consumers. The adsorption processes widely used in clarification do not use organic solvents. Alginate beads have been used as the adsorbent material in the present work. Experiments were carried out in batch mode in which the aqueous stevia extract was mixed with the alginate beads prepared previously by ionotropic gelation. A factorial design was used to study the process of clarification, in which colour removal and the percentage of stevioside adsorbed were evaluated. The studied factors were temperature, pH of the aqueous stevia extract and adsorption time. The results showed that alginate beads are capable of adsorbing both the steviosides and the pigments that give colour to the extract. The experimental design showed that only the pH and contact time were important variables in determining the percentage clarification, in contrast to the other responses which were not affected by the various factors studied. An equation describing the percentage clarification as a function of pH and time is proposed.

Effect of pH on the Clarification of Stevia rebaudiana Bertoni Extract Using Alginate Beads

Stevia rebaudiana Bertoni is plant used for producing a natural sweetener. After extraction from leaves, stevia extract is dark in colour and must be clarified for better acceptance by consumers. Adsorption processes are widely employed in the clarification because they do not use organic solvents. In the present work, the use of alginate beads as an adsorbent was investigated. Experiments were carried out in a batch system in which the aqueous stevia extract was mixed with the alginate beads previously prepared by ionotropic gelation. The effect of pH on the adsorption process was evaluated and the performance of the beads was examined by colorimetric analysis (colour removal, turbidity removal and adsorption of stevia steviol glycosides), as well as by refractive analysis for determining the adsorption of soluble solids. The results showed that the alginate beads were capable of adsorbing both the stevia steviol glycosides and the pigments that colour the extract. The best results were observed at a pH value of 2.0.