Effect of temperature and pressure on the activity of purified tomato polygalacturonase in the presence of pectins with different patterns of methyl esterification

Abstract

Apple pectin was deesterified by plant pectinmethylesterase (tomato) or fungal pectinmethylesterase ( Aspergillus aculeatus) yielding two pectin solutions with the same degree of esterification of 35% but different patterns of methyl esterification (blockwise or random distribution of methyl ester groups). The optimal temperature for initial tomato polygalacturonase activity in the presence of pectin deesterified by tomato pectinmethylesterase (blockwise) and pectin deesterified by A. aculeatus pectinmethylesterase (random) at atmospheric pressure and at pH 4.4 (pH of tomato-based products) is situated around 50 and 45 °C, respectively. The catalytic activity of tomato polygalacturonase during combined pressure–temperature treatments is always higher on pectin deesterified by tomato pectinmethylesterase (block) as compared to pectin deesterified by A. aculeatus pectinmethylesterase (random) as substrate. A decreasing enzyme activity on both types of pectic substrates at the same degree of esterification of 35% is observed with increasing pressure at all temperatures tested and this decrease is more pronounced at higher temperatures. At all temperatures tested, more monomer is formed and at a higher rate using pectin deesterified by tomato pectinmethylesterase as compared to pectin deesterified by A. aculeatus pectinmethylesterase. Initially, a larger oligomer (e.g. degree of polymerisation of 7) is formed at a higher rate and in larger amounts, but was further degraded to smaller oligomers when using the former substrate as compared to the latter substrate, from which this oligomer was formed continuously within the 24-h reaction period. Industrial relevance The presented research data clearly indicates that during thermal and high pressure processing the activity of tomato PG is always higher in the presence of blockwise deesterified pectin than in the presence of randomly deesterified pectin. Moreover, by the action of tomato PG the former substrate gives rise to more and smaller oligomers as compared to the latter substrate. Hence, as a fungal PME produces randomly deesterified pectins, it better protects the deesterified substrate to plant PG action breakdown than a plant PME, yielding blockwise deesterified pectins. So, concerning the need to preserve the texture/rheology of processed fruit- and vegetable-based products, it is better to use a fungal PME.