MICROBIAL INULINASE SECRETION USING CHEMICALLY-MODIFIED INULINS

Caproyl and cholesteryl derivatives of native dahlia inulin were prepa red from the respective chloride donors, and the light derivatization was monitored by C-13-NMR and by FTIR. These inulin derivatives were e mployed as carbon sources and as inulinase inducers using different st rains of the inulinolytic yeast Kluyveromyces marxianus. A low but con sistent basal inulinase activity (constitutive) was expressed in contr ol cultures grown in carbon source-free and yeast extract-based media, independently of the salt supplement. A higher enzyme activity result ed from induction with native inulin. The highest inulinase activity, in U/mL of cell-free medium, was attained with the lipophilic inulin d erivatives. Caproylated inulin was superior as an inulinase inducer co mpared to the cholesteryl derivative. The native inulin-based medium w as used as reference for the induction of inulinase in the IZ-275 yeas t strain at 28 degrees C and 100 rpm for 70 h. With caproyl-inulin, a 6.8-or 4.9-fold increase of the units of inulinase/mL of cell-free med ium was observed, respectively, in the absence or presence of ammonium phosphate supplement. The corresponding values for the IZ-619 yeast s train were 4.9 and 1.8. Cholesteryl-inulin did not induce the IZ-265 s train, but IZ-619 inulinase activity experienced a 4.1-fold increase i n the ammonium phosphate supplemented medium. Thus, the induction/secr etion process of inulinase is affected by the presence of ammonium pho sphate, depending on the yeast strain and the modified inducer.