Optimization of Ultrasonic-Assisted Extraction of Phenolic Compounds from Apples

In order to optimize conditions for the extraction of polyphenols from apples, peel and flesh of apples were subjected to an extraction process with different solvents consisting of various ratios of methanol and water (40, 60, 80 %), 100 % methanol, or with methanol acidified with hydrochloric acid (0.1 %). Extractions were performed using an ultrasonic bath with time periods from 5 to 15 min. Total polyphenols and total anthocyanins were analyzed using the Folin-Ciocalteau or the pH differential method, respectively. Individual polyphenols were analyzed with reversed-phase high-performance liquid chromatography with photodiode array detection (RP-HPLC-PDA). The differences in polyphenol content were statistically analyzed using t tests, associated with a regression model. The results showed that an efficient extraction from the peel could be performed with 80 % methanol to extract flavonols, anthocyanins, dihydrochalcones, and flavan-3-ols. Acidified methanol could also be useful for the extraction of anthocyanins and flavonols from the peel. For the flesh, 80 % methanol could be a solvent of choice for flavan-3-ols, dihydrochalcones, and hydroxycinnamic acids.