FSB1 – 2004 Food Science and Biotechnology in Developing Countries Results and Discussion The DE of pectin was reduced to about 62-63% DE by PME. Based on uronic acid results after IEX, the elution profile of the unmodified pectin was polydisperse (Figure 1). The main component eluted at low salt concentrations and smaller fraction eluted at higher ionic strength. The elution profile of pectins modified by either of the PME fractions eluted near the same ionic strength as the second, smaller fraction of the unmodified pectin. The elution profile of the modified pectins was similar, even though the PME peptide fraction was different. The molecular weight of the modified pectins was not different from the original pectin and was near 134,000 (Figure 3). There was greater variation in the pectins at low molecular weight of the modified pectin and this is reflected in the higher polydispersity values (Table 1). All pectins were negatively charged as measured by the zeta potential and the modified pectins were more negatively charged than the original pectins (Table 1). The gelling profile as evaluated by TPA indicated that the two modified pectins gelled in the presence of calcium even though at 63 %DE, the pectins are high methoxyl pectins (Table 2). Typically, only pectins with %DE less than ~50% DE gel with calcium. The original pectin did not gel in the presence of 35mM CaCl2 at 2% pectin. There was no significant difference in hardness between the two modified pectins. Interactions of original and modified pectins with isolated milk proteins indicated that there were unique effects of pectins depending on the proteins. A mixture of milk caseins with any of the pectins reduced particle size from over 100 µm to about 5-6 µm (Fig. 4). Based on the comparison with dispersion systems of individual casein fractions, αS1,2 -, β-, and κ-casein, in the presence of charge modified pectins, each casein fractions interacted uniquely depending on modified pectins (Fig. 5). In most cases, pectins increased particle size and modified pectins increased particle size more than original pectins, but particle size distribution was more monodisperse. Conclusions Slight modification of pectin charge can dramatically changed functional properties of pectins. Ultimately, interactions of charge modified pectins with cations in dispersed systems gives an idea for the development of tailored pectins as gelling and stabilizing agents. References 1. Voragen A.G.J., Pilnik W., Thibault J-F., Axelos M.A.V., and Renard C.M.G.C. (1995) Pectins. pp. 287- 339 In A.M. Stephen (Ed.), Food polysaccharides and their applications. Marcel Dekker, New York. 2. Hotchkiss, A.T., Savary B.J., Cameron, R.G., Chau, H.K., Brouillette, J., Luzio, G.A., and Fishman, M.L. (2002) Enzymatic modification of pectin to increase its calcium sensitivity while preserving its molecular weight. Journal of Agricultural and Food Chemistry 50: 2931-2937. 3. Limberg G., Korner R., Buchholt H.C., Christensen T.M.I.E. Roepstroff P., and Mikkelsen J.D. (2000) Analysis of different de-esterification mechanisms for pectin by enzymatic fingerprinting using endopectin lyase and endopolygalacturonase II from A. Niger, Carbohydrate Research 327 (3): 293-307 4. Joye D.D. and Luzio G.A. (2000) Process for selective extraction of pectins from plant material by differential pH. Carbohydrate Polymers 34: 337-342. 5. Willats W.G.T., Orfila C., Limberg G., Buchholt H.C., Van Alebeek G-J. W.M., Voragen A.G.J., Marcus S.E., Christensen T.M.I.E., Mikkelsen J.D., Murry B.S., and Knox J.P. (2001) Modulation of the degree and pattern of methyl-esterification of pectic homogalacturonan in plant cell walls. The Journal of Biological Chemistry. 276 (22): 19404-19431. 6. Ralet M.C., Crėpeau M.J., Buchholt H.C., and Thibault J.F. (2003) Polyelectrolyte behaviour and calcium binding properties of sugar beet pectins differing in their degrees of methylation and acetylation. Biochemical Engineering Journal. 16: 191-201.
FSB1 – 2004 Food Science and Biotechnology in Developing Countries PME Chromatography (Valencia pulp) Bound PME (BP++) Heparin (Bound PME: hep) (Bound PME: Con A) 30-70% Am. sulfate cut Crude PME SP Cation exchange column Unbound PME SP Cation exchange column Bound PME (BP+) Unbound PME (UBP-) Figure 1. Model flow diagram of PME purification. UBP- and BP+ represented U PME and B PME, respectively. Uronic Acid (mg/ml) 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 5 10 15 20 25 30 Elution Time (min) Figure 2. Analytical ion exchange chromatography elution of unfractionated pectin samples. (O-Pec): original pectin. (B-Pec): SP-unbound and HP bound PME modified pectin. (U-Pec): SP-unbound and HP unbound PME modified pectin. (O-Pec): original pectin; (U-Pec): UBP- PME; (B-Pec): BP+.
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