Characterization of pectins extracted from pomegranate peel and their gelling properties

• Pomegranate peels from four varieties yielded between 6.8% and 10.1% pectins.
• The recovered pectins were low methylated.
• Homogalacturonan regions predominated in pomegranate pectins.
• FT-IR spectra allowed to discriminate samples by their methylation.
• The extracted pectins formed gels in presence of calcium at pH3 and pH7.

The composition of pomegranate peel, the main by-product during pomegranate processing, and some of the characteristics of the water-soluble pectins were investigated. Four tunisian pomegranate peels were subjected to hot aqueous extractions (86 °C, 80 min, 20 mM nitric acid). Pomegranate peels yielded between 6.8% and 10.1% pectins. The extracted pectins were low methylated and were characterized by the predominance of homogalacturonan regions. Principal component analysis applied on FT-IR spectral data in the region between 4000 and 650 cm−1 differentiated the samples according to their degree of methylation. At pH 3, in the presence of 0.7% pectin, all solutions showed a rapid gel formation with G′ > G″. With decreasing temperature from 90 °C to 10 °C, G′ increased to reach a plateau at 10 °C. The variation in the pectin gel formation between varieties was attributed to difference in pectin characteristics particularly the hydrodynamic volume and the neutral sugar content.