Solvent selection and effect of extraction conditions on ultrasound-assisted extraction of phenolic compounds from galangal (Alpinia officinarum)

This study aimed to identify the appropriate extraction solvent and investigate the effect of temperature (20-70 degrees C), time (5-60 min), solvent/solid ratio (5-40), ethanol/water concentration (10-90%) and ultrasoundassisted extraction conditions (ultrasound power of 10-90% and ultrasound cycle of 1-9) on total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2 '-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and total flavonoid content (TFC) of galangal extracts. All extraction conditions studied had significant effect (p <= 0.05) on TPC, DPPH, ABTS and TFC. Ethanol/water (50%) binary solution was found as the most appropriate extraction solvent. Temperature of 25 degrees C, extraction time of 20 min, ethanol/water concentration of 50%, solvent/solid ratio of 10, ultrasound power of 50% and ultrasound cycle of 5 were determined to be the most efficient extraction conditions which yielded TPC of 66.89 mg GAE/g, DPPH of 49.01% inhibition, ABTS of 147.43 mM TE/ml and TFC of 148.22 QE/g. Significantly positive or negative, very high, strong and moderate Pearson correlation coefficients were obtained among TPC, DPPH, ABTS and TFC values. Pearson correlation analysis revealed that very high correlations (r >= 0.90) existed between DPPH and ABTS (r = 0.907, p <= 0.01), and TPC and TFC (r = 0.939, p <= 0.01) for the ethanol/water concentration, and between DPPH and ABTS (r = 0.944, p <= 0.01) for the ultrasound power. The current study showed that phenolic compounds with high antioxidant activity could be extracted from galangal using the ultrasound-assisted extraction conditions determined.

Automated summary

This study aimed to identify the appropriate extraction solvent and investigate the effect of various extraction conditions on the content of phenolic compounds in galangal extracts. The study found that ethanol/water (50%) was the most suitable solvent for extraction. The optimal extraction conditions were determined to be temperature of 25 degrees C, extraction time of 20 min, ethanol/water concentration of 50%, solvent/solid ratio of 10, ultrasound power of 50% and ultrasound cycle of 5. The study also revealed significant correlations between the content of phenolic compounds and antioxidant activity in galangal extracts.