The structure of high-methoxyl sugar acid gels of citrus pectin as determined by AFM

Authors: Fishman, Marshall; Cooke, Peter

Submitted to: Carbohydrate Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2008
Publication Date: 11/19/2008
Citation: Fishman, M., Cooke, P.H. 2009. The structure of high-methoxyl sugar acid gels of citrus pectin as determined by AFM. Carbohydrate Research, 344, p.1792-1797.

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 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 native high methoxyl sugar acid gels (HMSAG) were obtained by atomic force microscopy (AFM) in the Tapping ModeTM. Electronic thinning of the pectin strands to one pixel wide allowed the pectin network to be viewed in the absence of variable strand widths related to preferentially solvated sugar. Thinned images revealed that HMSAG of pectin are comprised of a partially cross-linked network in that many of the cross-linking moieties are attached at only one end. Based on their structural similarities, aggregated pectin in water appears to be a fluid precursor of a HMSAG of pectin. Furthermore, 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.