Effect of growth site type, felling season, storage time and kiln drying on contents and distributions of phenolic extractives and low molar mass carbohydrates in secondary xylem of silver birch Betula pendula

Abstract

The effect of growth site type, felling season, storage time and kiln drying on the contents and distributions of phenolic extractives and low molar mass carbohydrates in secondary xylem of silver birch Betula pendula was studied. The results indicated that the total amount of methanol-soluble extractives did not change markedly under the prevailing conditions of the study. However, the contents of phenolic compounds, (+)-catechin and (+)-catechin-7-O-β-D-xylopyranoside, and low molar mass sugars, D(+)-xylose, D(−)-fructose, D(+)-glucose, sucrose, maltose and raffinose, changed with season, storage time, radial location in the stem or growth site type. The glycosidic bond in (+)-catechin-7-O-β-D-xylopyranoside, sucrose, maltose and raffinose was hydrolysed with kiln drying, resulting in elevated contents of the monosaccharides, D(+)-xylose, D(−)-fructose, D(+)-glucose, in kiln dried boards. Surprisingly, the content of (+)-catechin did not increase simultaneously with the breakdown of (+)-catechin-7-O-β-D-xylopyranoside, indicating that (+)-catechin may polymerise or have another bonding pattern with other wood components due to elevated temperatures during kiln drying. In addition, the relative amount of phenolic compounds, (+)-catechin monomer and its glycoside, (+)-catechin-7-O-β-D-xylopyranoside, in the methanol extracts decreased with partial vacuum drying.