Pectins gelation properties

The importance of the degree of esterification (%DE) to the gelation properties of pectins makes it desirable to obtain a fast and robust method to determine (predict) the %DE in pectin powders. Vibrational spectroscopy is a good candidate for the development of such fast methods as spectrometers and quantitative software algorithms (chemometric methods) becomes more reliable and sophisticated. Present poster is a preliminary report on the quantitative performance of different instrumentations, spectral regions, sampling techniques and software algorithms developed within the area of chemometrics. 

The gelation process is considered a very specific process. This specificity is interpreted on a structural basis. Therefore some relationships between the chemical constitution and gelation properties of pectins and some related polysaccharides are outlined. 

Morris, E. R., Gidley, M. J., Murray, E.J., Powell, D. A., and Rees, D. A. (1980). Characterization of pectin gelation under conditions of low water activity, by circular dichroism, competitive inhibition and mechanical properties. Int. J. Biol. Macromol. 2 327-330. 

Matthew, J.A., Howson, S.J., Keenan, M.HJ. and Belton, P.S. 1990. Improvement of the gelation properties of sugar-beet pectin following treatment with an enzyme preparation derived from Aspergillus niger comparison with a chemical modification,... 

The HM and LM pectins give two very different types of gels the mechanisms of stabilization of the junction zones in the two cases are described and few characteristics given. The different molecular characteristics (DE, distribution of methoxyl or acetyl substituents, neutral sugar content or rhamnose content) play an important role on the kinetic of gelation, mechanical properties of the gel formed and also on the experimental conditions to form the stronger gels. All these points were briefly discussed. 

Enzymes can be used to specifically modify the pectins. Pectin methyl esterase is already widely used to adjust the gelling properties of commercially available pectins. The acetyl esters also strongly affect the gelation [2,3] and removal is important for the upgrading of sugar beet pectin, extractable from a by-product of the sugar industry. 

Micard V and Thibault JF. 1999. Oxidative gelation of sugar-beet pectins use of laccases and hydration properties of the cross-linked pectins. Carbohyd Polym 39 265-273. 

Substantial research efforts have been made to relate molecular properties to the structures of the junction zones and provide mechanisms for gel formation. Thus we have models for the formation and alignment of double helices for kappa-carrageenan, formation of triple helices for gelatin and egg box models for calcium induced gelation of alginate and pectin to mention a few examples (Morris 1986 Djabourov... 

As with other viscous polyanions such as carrageenan, pectin may be protective towards milk casein colloids, enhancing the properties (foam stability, solubility, gelation and emulsification) of whey proteins whilst utilizing them as a source of calcium. 

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