Structural characterization of red beet fiber and pectin

Abstract

Detailed composition, fine structure, and functional relationships of multiple red beet fiber fractions were determined. Red beet pomace, the fraction remaining after commercial puree extraction, contained dietary fiber (50.8%), that was largely insoluble (40.1% vs. 10.7% soluble dietary fiber) with pectin as the major polysaccharide; sucrose (8.07%), fructose (1.14%) and glucose (2.33%) free sugars; protein (10.2%), and fat (3.02%). Malto-oligosaccharides and methyl-esterified, acetylated and feruloylated rhamnogalacturonan I oligosaccharides with branched arabinogalacto-oligosaccharide side chains were detected by MALDI-TOF MS and NMR analysis. Red beet pectin, acid-extracted with a microwave using 10 min and 80 °C conditions, had high molar mass (1036 kDa) with viscosity that was similar to sugar beet pectin extracted under the same conditions. A random coil shape was confirmed for red beet pectin microwave extracted under 3 min and 120 °C conditions. Longer microwave extraction times and microwave extraction at pH 1 produced compact spherical red beet pectin with lower molar mass and viscosity. The structural properties of these red beet pomace and fiber fractions suggest that they can function to thicken and stabilize food systems, and the structure of the pectin fractions indicate strong potential as a prebiotic food ingredient.