The effect of low pH precipitation on the functional properties of orange peel pectin

Abstract

The citrus industry produces some of the most important consumer products annually, paralleled by generation of biomass, such as pulp and peels. This biomass is an untapped natural resource that is typically discarded or used as animal feed. The current study aimed at assessing the effect of low acid precipitation of pectin from orange peels on its techno-functional properties. Four low pH points (1.0, 1.5, 2.0, and 2.5) of citric acid were used to extract pectin followed by the evaluation of water and oil holding, and emulsifying capacities, thermal and pasting properties, and spectral and antioxidant properties. The water and oil holding properties and emulsifying capacity had marginal and negligible differences, while the peak and setback viscosities of pectin were greatly affected by extractive pH, with the highest viscosities (8,746 and 7,208 cP, respectively) observed for pectin extracted at pH 1.5. Similarly, the gelation enthalpy temperature was higher for pectin extracted at pH 2.0 and 2.5 (1,810.78 and 1,678.67 J/g), which implies a higher degree of polymerisation. For spectral properties, a common peak at 2,500–3,000 cm−1 indicating the stretching of C-H bonds was observed with lower transmittance at pH 1.5 and 2.0, which potentially relates to decreased methyl esterification. The study provides evidence that low acid precipitation of pectin has an effect albeit marginal on gelling and pasting properties. Thus, different low pH points could be used based on desired end application, such as stabilising or gelling. The leverage on low acid precipitation as an extraction method provide an impetus to driving circular and sustainable economies in biomass value addition.