Substrate conditions that influence the assays used for determining the β‐glucosidase activity of cellulolytic microorganisms

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Abstract
Culture filtrates from Trichoderma harzianum E58, T. reesei CL 847 and Penicillium sp. C 462 were assayed for β‐glucosidase activity using a range of substrates and sugar analysis methods. Although sugar analyses by the dinitrosalicylic acid (DNS) and Nelson–Somogyi methods gave a similar profile, when increasing concentrations of salicin were assayed, considerably higher values were obtained with the DNS assay. The salicin concentration used for the assay greatly influenced the final β‐glucosidase values with higher values obtained for T. harzianum E58 and T. reesei CL 847 at substrate concentrations of 1 mg/mL while optimum values for Penicillium sp. C 462 were obtained at substrate concentrations greater than 3 mg/mL. Low concentrations of salicin and p‐nitro‐phenyl‐β‐D‐glucopyranoside (PNPG) gave the same response as cellobiose. Cellobiose should be used at concentrations greater than 3.74 mg/mL to avoid substrate limitation of the β‐glucosidase assay.