Abstract
Sugar beet pectin is rich in rhamnogalacturonan-I (RG-I) region, which is a potential source of prebiotics. RG-I pectin cannot be extracted the same way as commercial homogalacturan-rich pectin using hot acid. Therefore, this study has explored several alternative methods, including microwave-assisted extraction (MAE) and conventional-solvent extraction (CSE) at atmospheric pressure using different solvents, and microwave-assisted hydrothermal extraction (MAHE) under pressure using water. No conclusive differences in microwave and conventional heating were found with heating rate controlled. The optimum treatment times of both MAE and CSE at 90 °C atmospheric pressure and regardless of the solvents used were 120 min; however, MAHE at 130 °C under pressure can dramatically reduce the time to 10 min. Alcohol-insoluble solids (AIS) extracted using pH13 solvent by MAE had both the highest RG-I yield at 25.3% and purity at 260.2 mg/g AIS, followed by AIS extracts using water by MAHE with 7.5% and 166.7 mg/g AIS respectively.
Highlights
Pectins are complex heteropolysaccharides found in the primary cell wall and middle lamella of terrestrial plants
Sugar beet pectin is rich in rhamnogalacturonan-I (RG-I) region, which is a potential source of prebiotics
They consist of two major structural domains, homoglacturonan (HGA) and rhamnogalacturonoan-I (RG-I), which are covalently linked to one another (Ishii & Matsunaga, 2001)
Summary
Pectins are complex heteropolysaccharides found in the primary cell wall and middle lamella of terrestrial plants. They consist of two major structural domains, homoglacturonan (HGA) and rhamnogalacturonoan-I (RG-I), which are covalently linked to one another (Ishii & Matsunaga, 2001). HGA is a linear homopolymer of α-1,4-linked-Dgalacturonic acid (GalA) which can be methylesterified and acetylated to various degrees (Zhan, Janssen, & Mort, 1998) and is regarded as “smooth” pectin. Many of the rhamnose residues have side chains containing linear and branched α-L-arabinofuranosyl (Araf), and/or β-D-galactopyranosyl (Galp) residues. Due to its highly branched nature, RG-I is often referred to as “hairy” pectin (Willats, McCartney, Mackie, & Knox, 2001). HGA-rich pectin are most widely used as hydrocolloids due to their ability to trap or bind water to form gels at low concentration
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