Production of Extracts Composed of Pectic Oligo/Polysaccharides and Polyphenolic Compounds from Cranberry Pomace by Microwave-Assisted Extraction Process

Abstract

Using cranberry (Vaccinium macrocarpon L.) pomace as a starting material, the microwave-assisted production of extracts and their structural characterization were investigated. Three methods (acidic, alkaline, and sequential acid/alkaline) and two microwave power settings (36 and 72 W/g) were compared in terms of total yield and recovery of oligo/polysaccharides and phenolic compounds. Acid extraction led to the lowest yields of 3.4–4.9% (w/w), while alkaline extraction at 32 W/g resulted in a yield of 12.6% (w/w). Higher microwave power favored the release of high molecular weight polysaccharides (200–700 kDa). As compared to acidic and alkaline extractions, sequential one yielded pectic polysaccharides with the highest arabinan (Ara:Rha, 6.6:1) and galactan branching chains (Gal:Rha, 5.2:1) and the lowest proportion of monosaccharides (Glu, Xyl/Man) from hemicellulosic polysaccharides. Response surface methodology was used to optimize the microwave-assisted sequential extraction as it was identified as the most appropriate method for the production of highly branched pectic polysaccharides. Variables included pomace concentration (3.33–50.00 mg/ml solvent), sodium hydroxide concentration (0–2 M), time (1–6 min), and microwave power (35–80 W/g cell wall material). The sequential extraction conditions for the optimal extract yield (28.65%) were determined to be 0.1 M HCl/1.51 M NaOH, 65 W/g, 16.33 mg pomace/ml, and 4.73 min, at which polyphenols and oligo/polysaccharides recovery of 57.0% and 10.56%, respectively, were obtained. The composition and the molecular weight distribution confirmed the isolation of arabinan-rich RGI (GalA:Rha of 15.8:1; Ara:Rha of 5.7:1) type pectic polysaccharide extracts enriched with polyphenolic compounds.