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.

No abstract

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.

No abstract

Pectinesterase from apple was separated into two fractions by chromatography on Sephadex G‐75. The major pectinesterase was purified by cation‐exchange chromatography on CM‐Sephadex C‐50. It had a molecular mass of 36 kDa, and isoelectric point of about 9, similar to one of the major pectin‐esterases of lemon. The enzyme required the presence of cations for optimum activity and was completely inactive at temperatures above 75°C. Although the major pectinesterase had no effect on the cloud stability of apple juice, a fraction containing a minor pectinesterase caused cloud clarification.