Monovalent salt-induced gelation of enzymatically deesterified pectin.
Pectin gels were induced by monovalent salts (0.2 M) concurrently with deesterification of high methoxy pectin using a salt-independent orange pectin methylesterase (PME). Constant pH was maintained during deesterification and gelation. If salt or PME was absent, the pectin did not form a gel. The gel strength was influenced by both pH and species of monovalent cation. At pH 5.0, the pectin gel induced by KCl was significantly stronger than the NaCl-induced gel. In contrast, a much stronger gel was produced in the presence of NaCl as compared to KCl at pH 7.0. LiCl did not induce pectin gelation at either pH. Molecular weights of pectins increased from 1.38 x 10(5) to 2.26 x 10(5) during NaCl-induced gelation at pH 7. One proposal to explain these pectin molecular weight changes is a hypothetical PME transacylation mechanism. However, these pectin molecular weight changes can also be explained by metastable aggregation of the enzymatically deesterified low methoxy pectin. We postulate that gelation was induced by a slow deesterification of pectin under conditions that would normally salt out (precipitate) low methoxy pectin in the absence of PME.
Yoo
Sang-Ho
SH
Crop Conversion Science and Engineering, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038.
Fishman
Marshall L
ML
Savary
Brett J
BJ
Hotchkiss
Arland T
AT
D005782:Gels / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D018021:Lithium Chloride / Q000494:pharmacology; D008970:Molecular Weight; D010368:Pectins / Q000737:chemistry* / Q000378:metabolism*; D053830:Plant Viral Movement Proteins; D011189:Potassium Chloride / Q000494:pharmacology; D012492:Salts / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology; D014764:Viral Proteins / Q000378:metabolism*
D005782:Gels; D053830:Plant Viral Movement Proteins; D012492:Salts; D014764:Viral Proteins; D012965:Sodium Chloride; D011189:Potassium Chloride; D010368:Pectins; D018021:Lithium Chloride