Efficient digestion and structural characteristics of cell walls of coffee beans

Screening of effective food-processing cellulase for digestion of cell walls of coffee beans was carried out, and the cellulase from Trichoderma sp. was selected. The digestion of the cell walls of green and roasted coffee beans was carried out by sequential procedures of alkali boiling (0.1 M Na2CO3 buffer, pH 10, and 0.1 M NaOH), cellulase digestion, autoclaving with 0.1 M NaOH, and cellulase redigestion. The total digestion yields were >95 and >96%, respectively. The cell walls became thin, and the final residues of the cell walls were easily broken into small pieces. The neutral sugar analysis of the digestion or the extract and the residues and the microscopy observations with staining with toluidine blue O, Yariv reagent, and calcofluor for the residue in each step were investigated. Four structures, the galactomannan-cellulose (center part), the membrane of the arabinogalactan protein, the cellulose-rich galactomannan layer, and the arabinogalactan protein-rich layers (outer part), were found in the cell walls.