Physicochemical properties of pectin from Malus domestica 'Falticeni' apple pomace as affected by non-conventional extraction techniques

Six non-conventional techniques (microwave-assisted extraction, ultrasound-assisted extraction, enzyme-assisted extraction - with cellulase and Celluclast 1.5L, ultrasound-assisted extraction - heating treatment, and enzyme-assisted extraction - ultrasound treatment) and conventional citric acid extraction were applied to extract pectin from Malus domestica 'Falticeni' apple pomace, and were compared in terms of extraction yields and physicochemical properties of the pectins. Microwave extraction led to the highest extraction yield and the lowest pectin recovery was found for the extraction with Celluclast 1.5L. Pectin samples obtained by microwave extraction showed color parameters comparable to commercial apple and citrus pectin, and had high galacturonic acid content, increased equivalent weight and high degree of esterification and molecular weight. High galacturonic acid content, molecular weight and degree of esterification were also found for pectin extracted by ultrasonication. On the opposite side, enzymatically extracted pectins had high equivalent weight, but lower degree of esterification that classified pectin extracted with cellulase as low-methoxylated pectin. Pectins obtained by ultrasound-assisted extraction - heating treatment and microwave extraction showed thermal properties that were similar to that of commercial pectins. The rheological characterization of pectin samples highlighted the high viscosities of solutions prepared with pectin from the ultrasound- and microwave-assisted extractions, which were correlated with their molecular weight and galacturonic acid content.