Enzymatic modification of pectin to increase its calcium sensitivity while preserving its molecular weight.
A commercial high-methoxy citrus pectin was treated with a purified salt-independent pectin methylesterase (PME) isozyme isolated from Valencia orange peel to prepare a series of deesterified pectins. A series of alkali-deesterified pectins was also prepared at pH 10 under conditions permitting beta-elimination. Analysis of these pectins using high-performance size exclusion chromatography (HPSEC) with on-line multiangle laser light-scattering, differential viscometer, and refractive index (RI) detectors revealed no reduction in weight-average molecular weight (M(w); 150000) in the PME-treated pectin series, whereas a 16% reduction in intrinsic viscosity (IV) occurred below a degree of esterification (DE) of 47%. In contrast, alkali deesterification rapidly reduced both M(w) and IV to less than half of that observed for untreated pectin. PME treatment of a non-calcium-sensitive citrus pectin introduced calcium sensitivity with only a 6% reduction in the DE. Triad blocks of unesterified galacturonic acid were observed in (1)H nuclear magnetic resonance spectra of this calcium-sensitive pectin (CSP). These results demonstrate that the orange salt-independent PME isozyme utilizes a blockwise mode of action. This is the first report of the preparation of a CSP by PME treatment without significant loss of the pectin's M(w) due to depolymerization.
Hotchkiss
Arland T
AT
Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, USA. ahotchkiss@arserrc.gov
Savary
Brett J
BJ
Cameron
Randall G
RG
Chau
Hoa K
HK
Brouillette
Janine
J
Luzio
Gary A
GA
Fishman
Marshall L
ML
D002118:Calcium / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D002957:Citrus / Q000737:chemistry / Q000201:enzymology; D004951:Esterification; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008970:Molecular Weight; D010368:Pectins / Q000737:chemistry* / Q000378:metabolism*; D053830:Plant Viral Movement Proteins; D014764:Viral Proteins / Q000378:metabolism; D014783:Viscosity
D007527:Isoenzymes; D053830:Plant Viral Movement Proteins; D014764:Viral Proteins; D010368:Pectins; D002118:Calcium