Pectinesterase activity in the component parts of different Israeli citrus fruit varieties*

Abstract

SummaryPectinesterase activity in whole fruits and single fruit components was established for grapefruit and orange (shamouti and valencia) varieties. It was found to range, in terms of pectinesterase units per gram of test material, from PE.u. x 104=5·1 for hand‐reamed or 11·2 for commercially extracted juice to PE.u. x 1044=821 for pulp and rag. Enzyme activity in each of the different components was highest in valencia. The comparative distribution of component activity was similar for all three fruit varieties. When test materials of low pH were allowed to stand even for short periods prior to examination, partial inactivation occurred, whereas at pH 3·5 and above, pectinesterase activity remained stable for 8 hr or more. Therefore, in order to obtain reproducible results, stabilization of the more acid samples by raising the pH level to at least 3·5 was necessary.