Submitted to: Biomacromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2006
Publication Date: 1/6/2007
Citation: Fishman, M.L., Cooke, P.H., Chau, H.K., Coffin, D.R., Hotchkiss, A.T. 2007. Global structures of high methoxyl pectin from solution and in gels. Biomacromolecules 8,No. 2, p.573-578. Interpretive Summary: The need to increase utilization of low valued co-products derived from the processing of fruit has prompted us to investigate the structure of pectin from solution and in gels. Pectin is a polysaccharide found in orange peels. In this work we show the potential of a new kind of molecular imaging, i.e. atomic force microscopy, for determining the batch quality of pectin from orange peels as a food grade gelling agent. This research should be of help to fruit growers and processors by increasing the demand and value of their by-products without increasing the cost of the basic commodity to the consumer.
Technical Abstract: Images of high methoxyl orange pectin deposited from solution and sugar acid gels (HMSAG) were obtained by atomic force microscopy in the Tapping Mode (TM). 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 ug/mL and 13.1 ug/mL. At 6.5 ug/mL, shapes imaged included rods, segmented rods, kinked rods, rings, branched molecules and dense circular areas. At 13.1 ug/mL, all of these shapes were integrated into networks. These same structures were discernable in pectin high methoxyl sugar acid gels. Thus one might consider pectin networks in water at concentrations in excess of 10ug/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 than gels in which strands were non-uniformly distributed and were separated by large and small spaces.