Abstract:Pectinesterase from lemon was separated into seven fractions by chromatography on CM-Sephadex C-50. Purification was hindered by the presence of pectin, for which the pectinesterase had a high affinity. Two major pectinesterases were purified: one was located solely in the peel and the other in the endocarp. They possessed similar molecular weights (35 kDa and 33 kDa, respectively) and high isoelectric points (> 11, and c 9). They required the presence of cations for optimal activity, the peel pectinesterase requiring a higher concentration of cations than the endocarp enzyme. Both enzymes were completely inactivated at temperatures above 88°C. Although neither enzyme destabilised the cloud of lemon juice or of comminuted lemon beverages, they caused cloud destabilisation of orange juice.

Continuous-flow electrophoresis was used to separate pectin and coloured substances from extracts of lemon pectinesterase. Two minor lemon pectinesterases were subsequently separated from two major pectinesterases, using chromatography on Sephadex G-75 and CM-Sephadex C-50. One minor pectinesterase was stable at low pH, showed the same initial pectinesterase activity at 88°C as at 25"C, and was active at 85°C for 9 min. This enzyme destabilised the cloud of single-strength lemon juice. It is suggested that the minor pectinesterases might not be true isozymes, but could arise from association of a major enzyme with pectin.