Effect of solvents and extraction methods on total anthocyanins, phenolic compounds and antioxidant capacity of Renealmia alpinia (Rottb.) Maas peel

The effect of different solvents and extraction methods on total anthoc yanins, phenolic compounds, and antioxidant capacity from x´kijit (renealmia alpinia Rottb. Maas) peels was evaluated. In order to evaluate the effect of solvents on the bioactive compounds extraction efficienc y and antioxidant capacity, a special cubic mixture design model was implemented with ethanol, methanol, and acetone as solvents and conventional (agitation - 1 and 6 h; Soxhlet - 2 and 4 h), novel (power ultrasound - 2.5 and 5 min) methods, and combination of extraction methods. Acceptable correla - tions between predicted and experimental data were obtained for total anthoc yanins ( r2 = 0.95), phenolic compounds (r2 = 0.78), and antioxidant capacity (r2 = 0.97), with methanol exhibiting the highest extraction yield of bioactive compounds and resultant antioxidant capacity. Although the extraction of total anthocyanins (82.2-85.8 mg cyanidine/ kg) and phenolic compounds (183.6-207.0 mg GAE/kg) was best carried out through Soxhlet, the ultrasonic treat- ment showed similar antioxidant capacity values (27.4-34.3 mg Trolox/kg) to those of 2-h Soxhlet. Moreover, a 5-min ultrasound pretreatment significantly increased (p < 0.05) phenolic compounds by 11, 21 and 12% when combined with agitation 1, 6, and 2-h Soxhlet treatments, respectively ; while the antioxidant capacity increased by 26, 48, and 22% for the same treatments. Ultrasound might be used as a valuable, green alternative procedure for improving the solvent extraction of bioactive compounds.