Pectins rich in RG-I and galactose extracted from garlic pomace: Physicochemical, structural, emulsifying and antioxidant properties

Abstract

Pectins are highly sought after as food additives, functional ingredients, and structural polymers. So far, no study has been performed on the extraction, characterization, and application of pectins from garlic pomace. In this study, a medium-sized low-methoxyl pectin rich in rhamnogalacturonan-I (RG-I) and galactose was prepared from garlic pomace (termed “GP”; molecular weight, Mw, 324.08 kDa; degree of methyl esterification, DM, 48.10%; RG-I, 35.20%), via citric acid-water extraction at 65 °C for 120 min and ethanol precipitation. GP contained six neutral monosaccharides (fucose, rhamnose, arabinose, galactose, glucose, and xylose) and two acidic monosaccharides (galacturonic acid and glucuronic acid), and could protect zebrafish against metronidazole-induced oxidative damage. Compared with commercial citrus pectin, GP had a comparable Mw, much more RG-Is and homogalacturonans, higher protein and phenolic contents, higher degree of branching, lower crystallinity, higher thermal stability (over 30–377 °C), higher in vitro and invivo antioxidant capacities, higher viscosity, and higher emulsifying and emulsion-stabilizing abilities. Accordingly, garlic pomace was a good source of RG-I-rich and galactose-rich pectins with high emulsifying and antioxidant capacities. GP can be used for making foods and pharmaceuticals possessing simultaneously high emulsifying, emulsion-stabilizing, and antioxidant capacities. This study demonstrates a sustainable garlic waste valorization approach.