title: Global structures of high methoxyl pectin from solution and in gels.
abstract: Images of high methoxyl orange pectin deposited from solution and high methoxyl sugar acid gels (HMSAG) were obtained by atomic force microscopy (AFM) in the tapping mode. For the first time, images of pectin deposited from water revealed that the transition from pectin networks to individual molecules or aggregates thereof occurred at concentrations between 6.5 and 13.1 microg/mL. At 6.5 microg/mL, shapes included rods, segmented rods, kinked rods, rings, branched molecules, and dense circular areas. At 13.1 microg/mL, all of these shapes were integrated into networks. These same structures were discernible in pectin high methoxyl sugar acid gels. Thus one might consider pectin networks in water at concentrations in excess of 10 microg/mL to be separate fluid precursors of networks in high methoxyl sugar acid gels. Examination of AFM images revealed that gels with "uniform" distribution of strands and pores between strands had higher gel strengths as measured by a penetrometer than gels in which strands were nonuniformly distributed and were separated by large and small spaces.
authors.affiliation: Crop Conversion Science and Engineering Research Unit, Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Wyndmoor, Pennsylvania 19038, USA. mfishman@errc.ars.usda.gov
authors.forename: Marshall L
authors.initials: ML
authors.lastname: Fishman
authors.forename: Peter H
authors.initials: PH
authors.lastname: Cooke
authors.forename: Hoa K
authors.initials: HK
authors.lastname: Chau
authors.forename: David R
authors.initials: DR
authors.lastname: Coffin
authors.forename: Arland T
authors.initials: AT
authors.lastname: Hotchkiss
mesh_terms: D032084:Citrus sinensis; D005782:Gels; D019563:Mechanics; D018625:Microscopy, Atomic Force; D008968:Molecular Conformation; D010368:Pectins / Q000737:chemistry*; D012996:Solutions; D013400:Sugar Acids; D014867:Water
chemical_list: D005782:Gels; D012996:Solutions; D013400:Sugar Acids; D014867:Water; D010368:Pectins