B. Laratta

Thermal resistance of pectin methylesterase in tomato juice

Abstract The behaviour of pectin methylesterase (PME, EC.3.1.1.11) was analysed in five new tomato cultivars for juices and tomato products. The thermal inactivation of this enzyme was evaluated in the range 73–88 °C and was found to be exponential. For each cultivar examined the logarithmic values of decimal reduction times plotted against temperature had a classic biphasic pattern featuring a sudden change in slope at temperatures exceeding 78 °C. The z values determined in the range 78–88 °C were much higher than those calculated from the log D T versus T °C in the range 73–88 °C.

Thermostability of three pectinesterase isoenzymes in tomato fruit

Abstract The thermal stability of three forms of pectin methylesterase purified from tomato was evaluated at pH 4.5. The time-dependent heat-inactivation curves for the three forms exhibit exponential behaviour in the temperature range between 70 °C and 90 °C. The determination of DT and Z parameters displays a different heat-inactivation kinetic among the three isoenzymes. In particular, two forms (PME1 and PME3) show similar behaviour with a Z value of 24 °C, whereas the third form (PME2) shows a Z value of 15 °C.

Pectin methylesterase in Citrus bergamia R : purification, biochemical characterisation and sequence of the exon related to the enzyme active site

Three forms of pectin methylesterase (PME) were purified, from bergamot fruit (Citrus bergamia R.), to homogeneity by ion-exchange and affinity chromatography. The isoforms, named PME I, PME II and PME III, according their elution order on a heparin-sepharose column, were characterized for their relative molecular mass, activity kinetic parameters and thermostability. The molecular mass was estimated to be 42kDa for the three forms, and the apparent Km values for citrus pectin were 0.9mg/ml for PME I and 0.5mg/ml for PME II and PME III. The optimum pH values lie within the range 6.5-9.0, depending on salt concentration. Thermal behaviours of the three PME isoforms were studied in a temperature range from 65°C to 80°C with the less abundant PME I isoform showing a higher heat resistance. Moreover, the complete exon 2 sequence of PME gene was acquired (GenBank accession no. DQ458770) using a PCR-based approach on well-known Citrus genomic DNA present in the NCBI database.