Effects of phytosanitary irradiation treatment and refrigerated storage on the physicochemical properties of three pectin types isolated from mandarin pulp

The impact of fruit exposure to ionizing energy as phytosanitary treatment on pectin properties has received little attention, especially on that from the flesh of citrus fruit other than oranges. In this study, hot-water, chelating agent and alkali soluble pectins (HWSP, CASP and ASSP) were extracted from juiced segments of mandarins that were treated with γ-irradiation (0, 0.15, 0.4 and 1 kGy) and stored (3 wks at 6 °C + 1 wk at 20 °C). Irradiation increased the recovery of HWSP and CASP and decreased the molecular weight (MW), the degree of methyl esterification (DME) and the protein content of the pectins. Storage further enhanced the recovery and the reduction of DME and MW of all tested pectins. The sum of the contents of arabinose, galactose, mannose and xylose was always lower in pectin from stored fruit as compared to pectin from non-stored fruit, independent of irradiation. Irradiation influenced the viscosity of the tested pectins from non-stored fruit. It did not impact the viscosity of pectins from stored fruit, which had a lower viscosity than that of pectins from non-stored fruit. Irradiation increased the hysteresis of pectins, independent of storage. Overall, irradiation and storage impacted the physicochemical properties of the pectins, negatively affecting their functionality.