Whole-cell enzymes have been used as biocatalysts in a variety of reactions, such as free fatty acid production and the synthesis of fatty acid esters. In the present study, enzyme pretreatments with PEG, MES, Tween 80, Saponine, MgCl2 center dot H2O, CaCl2 and different pH values were evaluated by using the Plackett-Burman statistical design to improve both the hydrolytic and synthetic activity of an induced mycelium-bound lipase from Aspergillus niger MYA 135. Interestingly, the preincubation at pH 4 had a significant effect on both the hydrolytic and transesterification activity, demonstrating the influence of the correct ionisation state on these activities. Meanwhile, the enzyme pretreatment with MgCl2 for in situ water activity control positively affected the esterification catalyst. Thus, compared with the control without pretreatment, the hydrolytic and the transesterification activities increased to 60.1 and 60.8 %, respectively, and with respect to the esterification reaction, the conversion was improved 2.33 times. Based on these results, by applying a simple pretreatment to the biocatalyst, the catalyst's activity toward hydrolysis and synthesis was enhanced.
