Optimizing the microwave-assisted extraction of phenolic antioxidants from apple pomace and microencapsulation in cyclodextrins
Abstract
Apple pomace is the skin, seeds and flesh leftover after juice extraction, and is rich in polyphenols that have demonstrated high antioxidant activity both in vivo and in vitro. Despite this fact, apple pomace remains an underutilized agricultural waste product. To add value and increase the commercial applicability of the pomace, efficient methods for the extraction of phenolics from apple pomace are needed. Traditional solvent extraction is both solvent and time intensive, leading to the consideration of alternate extraction techniques such as microwave-assisted extraction (MAE). MAE of phenolic compounds from pomace of four apple cultivars (Red Delicious, Golden Delicious, Winesap and Jonathan) was optimized for various extraction parameters (microwave power, extraction time, solvent volume to sample ratio and solvent type) using response surface methodology. Optimum conditions were based on maximizing two responses: total polyphenol content (TPC) and antioxidant activity as measured by the percent inhibition (%IP) of the DPPH free radical. Response surface models were developed by regression, taking into consideration significant model parameters (p<0.05). Each solvent system showed similar optimum extraction conditions independent of apple cultivar. Red Delicious pomace variety had the highest TPC (15.8 mg GAE/g DW) and DPPH radical scavenging activity (94.4% inhibition) obtained under the optimum conditions of 735 W and 149 s, with 10.4 mL of 60% ethanol and 5.65 mL of 70% acetone, respectively. Catechin, phloridzin, caffeic acid, chlorogenic acid and quercetrin were some of the major phenolic compounds identified by HPLC in the extracts. Stabilization of the extracted phenolics obtained under optimized conditions was carried out by encapsulation in α-, β-, and 2-hydroxypropyl-β-cyclodextrin. Inclusion complex formation was confirmed by differential scanning calorimetry for all the three CD types. Complexes were also found to be stable to oxidation up to temperatures of 250°C. Phase solubility studies indicated an A L type diagram and established the formation of a 1:1 complex of the extract with β-CD, with a moderate binding constant (Kc = 1.02 mg GAE/g extract-1) The overall results of this research indicate that MAE is an efficient method for extraction of valuable antioxidant compounds from apple pomace. Further, their encapsulation in β-CD results in the formation of stable inclusion complexes with enhanced solubility for potential use as functional food ingredients. Keywords: apple pomace, microwave-assisted extraction, encapsulation, cyclodextrin, inclusion complex.
Degree
M.S.
Advisors
Ballard, Purdue University.
Subject Area
Food Science
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