3.2. Kinetic parameters of beta-amylase immobilized onglutaraldehyde-agarose beadsThe moderate activity recovered even in the case of the glu-taraldehyde support may be due to the three reasons explainedin introduction: enzyme distortions, external diffusion limitationsor steric problems to the enzyme-substrate interaction generatedby the support surface. Immobilization procedure raised the Kmvalue by about 15 times, while decreasing the Vmax by only a30% (Table 2). The apparent increase in Km and the relative goodconservation of Vmax for the glutaraldehyde derivative (Table 2)suggested that the main problem is just diffusion problems forthe entry of the substrate inside the biocatalyst particle. In fact,the milling (just by magnetic stirring) of the catalyst particle per-mitted to increase the observed activity. The negative effects ofimmobilization on both kinetic constants decreased the catalyticefficiency of beta-amylase (Vmax/Km values showed in Table 2)by a 20 fold factor. Chang and Juang [30] also observed a decreasein apparent affinity between beta-amylase and starch when theenzyme was immobilized on chitosan-clay composite, althoughthe Km increase was only about 2.5 times. The Km for the freeenzyme was very near to our study (2.4 mg mL−1). In Roy and Edge’s[33] study, when the enzyme was immobilized on polystyrenecation exchange resin equilibrated with Al3+íons, its Km increasedabout 6 times. Differences on the particles size, pores diameter andenzyme loading may drastically influence the effect of diffusionallimitations on the expressed activity of immobilized enzymes[15,22].