Enhanced acid phosphatase yield by polyhydroxyethylmetacrylate gel-immobilized Humicola lutea cells

Aim The aim of the present study was to immobilize by entrapment the filamentous fungus Humicola lutea 1205 spores in polyhydroxyethylmetacrylate gel and to use them for acid phosphatase production under the control of the inoculum level. Methods. Control on gel inoculum volume was made by its reduction in half when inoculum/medium ratio in fermentation flask reached 50/50 ml. The distribution of the growing fungal cells in the whole interior of the gel blocks and some specific changes of the surface cell. morphology were observed by scanning electron microscopy investigations. Results. The effect of the control of inoculum amount on acid phosphatase production is evident: approximately two-fold longer half-life times - 10 runs for 10% polymer and 16 runs for 20% gel matrix; significant enhancemcnt of relative acid phosphatase activities (over 150 and 200% in the case of 10 and 20% gel, respectively); almost two-fold higher enzyme yield was obtained compared to the maximal values in reuses without reduction of inoculum. A clear advantage of using immobilized H.. lutea is the absence of free mycelium in the medium or on particle surface, therefore whole acid phosphatase detected in culture filtrates is a result of the growing immobilized cells in gel blocks. Conclusion. All results obtained confirm the importance of inoculum size control during the cultivation of immobilized fungus for acid phosphatase production. The advantages of polyhydroxyethyhnetacrylate biocatalyst make it an attractive source of fungal acid phosphatases and allow their use in food technology for mild hydrolysis of casein.