Optimization of Pectin Extractions from Walnut Green Husks and Characterization of the Extraction Physicochemical and Rheological Properties

Walnut is a nutrient with green husks containing pectin. Extraction of this pectin is valuable due to economic and environmental aspects.

Effects of three variables of pH values (1, 1.5 and 2), extraction temperatures (60, 70 and 80 °C) and process times (60, 90 and 120 min) were assessed on extraction efficiency rate, esterification degree and galacturonic acid of pectin extracted from walnut wastes using response surface statistical method. Furthermore, total ash, MW, emulsifier, rheological and Fourier transform infrared spectroscopy assessments were carried out on optimum samples.

Based on the results, optimum conditions for pectin extraction from walnut green husks with the highest extraction efficiency rate (25.76%), esterification degree (54.28%) and galacturonic acid (64.49%) were associated to pH 1.75, process temperature of 80 °C and extraction time of 120 min. The most emulsion stability of the walnut waste of pectin was seen at 4 °C and on the first day of storage. Under optimal extraction conditions, MW of the walnut green husks was 38.88 kD. Optimum sample solution of the extracted pectin exhibited viscous and pseudoplastic behaviors.

Fourier transform infrared spectroscopy spectral diagrams of the optimal pectin samples have shown presence of galacturonic acid; thus, walnut wastes can be used as a rich source of pectin.