Optimization of Ultrasonic-Assisted Extraction of Phenolic Compounds from Apples
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Optimization of Ultrasonic-Assisted Extraction of Phenolic Compounds from Apples Lidija Jakobek 1 & Martina Boc 1 & Andrew R. Barron 2
Received: 20 October 2014 / Accepted: 18 March 2015 # Springer Science+Business Media New York 2015
Abstract 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.
Keywords Ultrasonic extraction . RP-HPLC . Apples . Old varieties . Phenolic compounds
* Lidija Jakobek [email protected] 1
Department of Applied Chemistry and Ecology, Faculty of Food Technology Osijek, J. J. Strossmayer University of Osijek, Kuhačeva 20, 31000 Osijek, Croatia
2
Department of Statistics, Yale University, 24 Hillhouse Ave., New Haven, CT 06511, USA
Introduction Apples are a type of fruit used commonly in the human diet due to their availability during the whole year, pleasant taste, and presence of many nutrients like vitamins and other bioactive compounds. Many studies have associated apples and their nutrients with the positive influence on the human health. Bioactive polyphenols from apples have shown antiviral properties (Suárez et al. 2010), the inhibition of Helicobacter pylory (Pastene et al. 2009), and anticarcinogenic properties (Veeriah et al. 2007). Due to many positive effects, apples are studied intensively. Polyphenolic compounds are found in apples in high amounts (Escarpa and González 1998; Tsao et al. 2003; Veberic et al. 2005; Khanizadeh et al. 2008; Wojdylo et al. 2008). The major polyphenolic groups are polimeric proanthocyanidins composed of several flavan-3-ol molecules, monomeric flavan-3-ols (flavanols), flavonols, anthocyanins, dihydrochalcones, and hydroxycinnamic acids (Escarpa and González 1998; Tsao et al. 2003; Veberic et al. 2005; Khanizadeh et al. 2008; Wojdylo et al. 2008). Flavonols and anthocyanins are usually found in the peel, although some red fleshed apples can have anthocyanins in the flesh as well (Jakobek et al. 2013). Proanthocyanidins/flavan-3
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