Quantitative assay of β-(1,3)–β-(1,6)–glucans from fermentation broth using aniline blue

An aniline blue fluorescence assay was constructed to quantify two fungal β-(1,3)–glucans with β-(1,6)–sidechains: scleroglucan and schizophyllan. Calibration curves were linear in the range from 30 mg/l to 6 g/l with R² > 99.8%. The assay was robust against D-glucose (50 g/l), oxalic acid (22.5 g/l), protein (0.667 g/l), and KCl (13.3 g/l). Sclerotium rolfsii and Schizophyllum commune cultures were sampled, and the test results of the assay and alcohol precipitation were compared. The correlation between assay results of samples at different stages of the purification with the values from the precipitation of the polymers was the best in the supernatant for S. rolfsii and after blending for S. commune. Using the precipitation data, correction factors of 2.46 and 3.83 for S. rolfsii and S. commune, respectively, were found. A range of other polymers were tested for their measurability with this assay. However, except for laminarin and microcrystalline cellulose no robust correlation between concentration and fluorescence intensity was found.