Influence of environmental conditions on thermal stability of recombinant Aspergillus aculeatus pectinmethylesterase

The thermal stability of purified recombinant Aspergillus aculeatus pectinmethylesterase (PME) in different media was studied. The influence of pH, ionic strength and additives (salts and polyols) was evaluated. At pH 5.0 and a high ionic strength (0.50 M), the enzyme showed a high thermostability (inactivation at temperatures ⩾60 °C). Interestingly, an enhancement of its heat stability was observed at pH 7.0 and temperatures above 55 °C, this behaviour was reflected in an atypical evolution of structural changes in the overall conformation of the enzyme, according to FTIR spectroscopy results. Recombinant A. aculeatus PME thermal inactivation at pH 7.0 could be described by a fractional-conversion model. Addition of NaCl increased the thermal stability at pHs 5.0 and 7.0, while addition of CaCl2 had no influence. With regard to sugars (sucrose, trehalose, glucose and maltose) and polyols (sorbitol, lactitol and glycerol) addition, at the same concentration and pH, the polyols showed a higher protective effect than sugars. Also, the thermostability of recombinant A. aculeatus PME increased with the additive concentration, although the source of OH groups was the main parameter involved.