Pectins from food waste: Characterization and functional properties of a pectin extracted from broccoli stalk

Abstract

Currently about 60–75% of world broccoli production is wasted during harvesting. The aim of the present study was to extract and characterise the pectin present in broccoli stalks and to evaluate its functional properties. The stalks were initially treated with boiling ethanol to remove compounds such as pigments and free sugars and then the pectin (FB) was extracted with 0.1 M nitric acid for 30min. The pectic fraction FB (18% yield) was found to contain 75% galacturonic acid with a degree of methyl-esterification of 56%, and an acetyl content of 1.1%. Rhamnose and galactose were the main neutral sugars present. NMR analyses showed that FB was composed of homogalacturonan and rhamnogalacturonan I substituted with β-1,4-D-galactan. The molar mass of FB was 72.2 × 103 g/mol and the viscosity of a 5% (w/w) solution in 0.1M NaCl at pH 4 showed shear thinning behaviour with a low shear Newtonian plateau of ~100 Pa s at 25 °C. At the same concentration FB showed a weak gel like behaviour. FB (0.5–4%, w/w) was also able to stabilize medium chain triglyceride oil in water emulsions. The results suggest that broccoli stalk could be used as an alternative source of commercial pectins.