Performance of Commercial Fungal Preparations at Elevated Temperatures

The activities of commercial reference preparations were first measured at higher temperatures in order to evaluate their general performance and to es­timate the role of the background activities originating from the production strain. The hydrolysis of the pretreated spruce substrate by the commercial preparations (with and without added в-glucosidase, BG) at various tempera­tures from 50 to 70 °C was estimated during the first 24 h of the hydrolysis. The native Trichoderma cellulases and the Aspergillus BG were rapidly inac­tivated during the first 2 h of hydrolysis of the pretreated spruce substrate at temperatures above 60 °C (Fig. 2). The hydrolysis ceased after 24 h at 60 °C and after 48 h at 55 °C (results not shown). As expected, the effect of the added BG on the sugar yield was significant. The relative inactivation of BG was more pronounced even at 60 °C (Fig. 2b). The hydrolytic effect of the rather high loading (about 20 FPU g-1 cellulose) of T. reesei and Aspergillus enzymes was obviously due to the initial stage of hydrolysis during which the enzymes remained active. The hydrolysis yield of sugars from spruce dur­ing the first 2 h was 15% of the theoretical maximum at 70 °C, 22% at 65 °C and 33% at 60 °C. There were indications that the temperature optimum of the commercial T. reesei enzymes in the hydrolysis of the pretreated spruce substrate was about 5 °C lower than on pure cellulose (results not shown).

Fig. 2 Hydrolysis of washed, steam pretreated spruce substrate (cellulose content 18.3 gL-1) with Celluclast 1.5 L FG alone (A) or supplemented with Novozym 188 (B) at various temperatures at pH 5. The dosage of Celluclast was 22 FPU g-1 cellulose and the Novozym 188 P-glucosidase 550 nkatg-1 cellulose. И50 °C, Ш55 °C, ♦бО °C, <>65 °C and • 70 °C

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