Extraction of pectin from Premna microphylla turcz leaves and its physicochemical properties

Premna microphylla turcz leaves (PMTL) have been used for preparing a "green tofu" by Chinese for a long history. Chemical composition analysis indicated alcohol insoluble solids (AIS) of PMTL contained high amount of pectin. Water, ammonium oxalate, hydrochloric acid and sodium hydroxide were used to extract different pectic fractions sequentially. Ammonium oxalate was found to be the most effective extracting agent, reflecting on a high yield (20.61%) and a significant change of morphology of AIS. The resulted oxalate-soluble pectin (OXSP) showed high galacturonic acid content (76.15%) and average molecular weight (980.67kDa), low neutral sugar content (6.41%) and degree of methoxylation (14.90%). All of the characteristics have contributed excellent gelling and thickening properties of OXSP. These results may allow an improved use of PMTL as a resource of low-methoxyl pectin, and observation of the morphology of residues can be helpful for evaluating the efficiency of extracting agents.