Capillary electrophoresis analysis of orange juice pectinesterases

Pectinesterase (PE) was extracted from orange juice and pulp with 1 M NaCl, desalted, and separated using capillary electrophoresis (CE) gel procedure s (CE-SDS-CGE) and isoelectric focusing (CE-IEF). PE resolved as a single p eak using noncoated fused silica columns with CE-SDS-CGE. CE-IEF separation of PE required acryloylaminoethoxyethanol-coated columns, which had limite d stability. Thermal stability of PE extracts before and after heating at 7 5 degreesC for 30 min and at 95 degreesC for 5 min established heat labile and heat stabile fractions with identical PE migration times by CE-SDS-CGE or CE-IEF. Peak magnitude decreased to a constant value as heating time inc reased at 75 degreesC. Regression analysis of CE-SDS-CGE peak migration tim es of molecular weight (MW) standards estimated both heat labile and heat s table PE at MW approximate to 36 900. Traditional SDS-PAGE gel separation o f MW standards and active PE isolated by IEF allowed estimation of MW appro ximate to 36 000. CE-SDS-CGE allowed presumptive, but not quantitative, det ection of active PE in fresh juice.