Optimization of Ultrasound-Assisted Extraction of Phenolic Antioxidants from Tectona grandis Leaves, Using Experimental Design

Aims: This study aims to apply central composite design to optimize ultrasound-assisted extraction conditions in order to maximize simultaneously total polyphenols and antioxidant activity from aqueous leaves extract of Tectona grandis.

Study Design: Young teak leaves were collected in June 2011 from teak plantations in the center of Côte d’Ivoire. After harvesting, the dried leaves were packed and shipped to CIRAD laboratory (Montpellier, France), where they were stored until processed and analyzed.

Place and Duration of Study: This study was carried out during season 2011-2012 in the CIRAD laboratory (Montpellier, France).

Methodology: Central composite design was used to simultaneous maximize ultrasound-assisted extraction of total polyphenols and antioxidant activity from Tectona grandis leaves. The design independent variables selected for this study were vegetal to liquid ratio (X1, leaves: citric acid; w:v), extraction time (X2, min) and solvent concentration (X3, citric acid concentration).

Results: Optimal condition obtained includes 10-2 N citric acid concentration, 16.25 g/L vegetal to citric acid ratio and 37.5 min for extraction. Under the above-mentioned condition, the experimental content of total polyphenols and antioxidant activity from aqueous leaves extract of T. grandis were 1,310 µmol.g-1 GAE and 431 µmol.g-1 TE, respectively. These results were well matched with their predicted values which are 1,300 µmol.g-1 GAE and 429 µmol.g-1 TE for polyphenols and antioxidant activity, respectively.

Conclusion: Ultrasound-assisted extraction was successfully optimized using central composite design to obtain an aqueous leaves extract of Tectona grandis, with optimized polyphenol content and antioxidant activity. Results indicated that this extraction method is a promising technique for extraction of phenolic antioxidants from T. grandis, as compared as infusion and decoction, and aqueous extracts of T. grandis leaves could be explored as a potential antioxidant agent for use in medicine against cardiovascular and cancer diseases.