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      Gelation of high-methoxy pectin by enzymic de-esterification in the presence of calcium ions: a preliminary evaluation

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      Carbohydrate Research

      Elsevier BV

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          Abstract

          Cohesive gels have been obtained by de-esterification of 1.0wt% high-methoxy citrus pectin (degree of esterification approximately 68%) in the presence of Ca(2+) cations, using a commercial preparation (NovoShape) of fungal methyl esterase cloned from Aspergillus aculeatus. A convenient rate of network formation (gelation within approximately 30min) was achieved at an enzyme concentration of 0.2 PEU/g pectin. At a Ca(2+)-concentration of 40mM and incubation temperature of 20 degrees C, severe syneresis (>7% of sample mass) was observed, but release of fluid decreased with decreasing concentration of Ca(2+) and increasing temperature of incubation, becoming undetectable for 10mM Ca(2+) at 30 degrees C. Under these conditions, progressive development of solid-like character (storage modulus, G') was observed during 160min of enzymic de-esterification, and the mechanical spectrum recorded at the end of the incubation period had the form typical of a biopolymer gel. On subsequent heating to 70 degrees C, dissociation of the gel network (sigmoidal reduction in G' and G'') was observed. At or above the midpoint temperature of this melting process ( approximately 50 degrees C), there was no indication of gel formation on enzymic de-esterification (at 50 or 60 degrees C). At lower temperatures (20, 30 and 40 degrees C), the rate of gelation (assessed visually) showed no systematic increase as the incubation temperature was increased towards the temperature-optimum of the enzyme ( approximately 50 degrees C). This unexpected behaviour is attributed to competition between faster de-esterification and slower formation of Ca(2+)-induced 'egg-box' junctions.

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          Author and article information

          Journal
          Carbohydrate Research
          Carbohydrate Research
          Elsevier BV
          00086215
          September 2009
          September 2009
          : 344
          : 14
          : 1818-1823
          Article
          10.1016/j.carres.2008.09.029
          19100969
          aaddf6a3-69ad-4775-9d63-9249298e1ae0
          © 2009

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