45G-26 |
Valencia pectin methylesterase modify charge and charge distribution of pectin |
Y. KIM and L. Wicker. Dept. of Food Science & Technology, Univ. of Georgia, Food Science Bldg., Athens, GA 30602-7610 Pectin methylesterases (PME) de-esterify high methoxyl (HM) pectin, alter calcium reactivity, and influence gelling potential of pectin. Our objectives were to prepare and characterize properties of citrus PME modified pectins and to develop calcium sensitive HM pectin. Crude PME fractions were partially purified using cation exchange (Hi-Trap SP) and Heparin columns. Positive PME fractions were quantified by titration, protein analysis and SDS-PAGE. Pectin was de-esterified by PME that never bound columns (SP-unbound/HP-unbound, SPU/HPU) and bound only to heparin (SP-unbound/HP-bound, SPU/HPB). The PME reaction was terminated and pectin was washed and dried. Ion exchange chromatography (IEX) was performed to separate pectin fractions using a Q5 anion exchange column (gradient of 0.5 to 1.3 M acetate buffer, pH 5). Fractions were analyzed for uronic acid (UA) content by m-hydroxydiphenol and %DE by titration method. Calcium sensitivity of 2% modified pectins was measured using textural profile analysis of the pectin gel. The specific activity of PME was 22U/mg (SPU/HPU) and 48U/mg (SPU/HPB). SDS-PAGE analysis identified peptides at 36, 27 and 13 kDa from both PME fractions. SPU/HPB had mostly 36 kDa, however, SPU/HPU had evenly 36 kDa and 27 kDa peptide. The degree of esterification was reduced from 76% to 70%. Unmodified pectin gave two peaks after gradient elution from IEX. Both modified pectins eluted later as a single, broad peak. Unmodified pectin didn’t gel with CaCl2, but modified pectin gelled. Pectin (2%) modified by SPU/HPU or SPU/HPB PMEs had hardness values of 40.9g ,or 39.9g, respectively, in the presence of 35mM CaCl2. PME de-esterification of pectin yielded a calcium sensitive high methoxyl pectin that had similar charge distribution regardless of PME source. PME modified pectins formed calcium gels of similar hardness, and unmodified pectin did not gel with calcium.
Session 45G, Fruit & Vegetable Products: Vegetables (Fresh)
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