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

Abstract

-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 (10 º C and 30 º C) 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.

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

“…lower than the 80% obtained by Moraes and Machado (2001) with CaX zeolite. Mantovaneli et al (2004) and Moraes and Machado (2001) observed that temperature had a negative effect on colour removal using zeolites. However, in the present work, temperature has been found to have a positive effect on colour removal using alginate beads.…”

“…According to Peretz and Cinteza (2008), the removal efficiency towards cationic molecules is strongly dependent on the pH value. With increasing pH, the charged sites on the surface of calcium alginate become more negative.…”

“…However, these solvents are usually toxic to humans and, after clarification, have to be totally removed from the sweetener. Others processes have been used in the clarification, such as filtration (Silva et al 2007;Reis et al 2009), coagulation with polyelectrolytes (Fernandes et al 2001;Bunhak et al 2002) and adsorption (Mantovaneli et al 2004;Silva et al 2007;Goto 2004).…”

“…In this context, many adsorbents have been examined for the clarification of stevia extract, such as zeolites (Mantovaneli et al 2004;Silva et al 2007;Moraes and Machado 2001) and ion-exchange resins (Goto 2004).…”

“…Alginate beads are capable of adsorbing compounds such as proteins (Roy et al 2004) and heavy metal ions (Papageorgiou et al 2008) and have even been used for the clarification of stevia (Mahl et al 2010). For this reason, they could be tested as adsorbents for clarifying stevia extract.…”