Relationships between the blacking phenomenon and norlignans of Sugi (Cryptomeria japonica D. Don) heartwood II. On blacking heartwood containing two main norlignans, sugiresinol and hydroxysugiresinol

The first paper of this series reported on the relationship between the blacking phenomenon of Sugi (Cryptomeria japonica D. Don) heartwood and the norlignan contents by using a partially black heartwood. In this study, the relationship was investigated further by using blacking heartwood, mainly consisting of sugiresinol and hydroxysugiresinol, and the results were as follows: (1) The moisture content, amount of methanol extract, and the pH value of the black heartwood portion were greater than those of the normal reddish heartwood part. (2)In the black heartwood part, the K+ cation content and the HCO3- anion content showed extremely highter values. This case especially indicated a greater content of potassium hydrogencarbonate. (3) In the methanol extract of the black heartwood part, considerable amounts of sugiresinol and hydroxysugiresinol were found, whereas seuirin-C was found rarely in this part. This difference of main norlignans indicates a difference in structure stability. (4)In the black heartwood part, mainly norlignans containing considerable amounts of agatharesinol, sugiresinol, and hydroxysugiresinol were extracted by the treatment of acid-methanol (0.1% AcOH in methanol), but it was possible to extract sequirin-C by the treatment of reductive methanol (0.1% ascorbic acid in methanol). It was found that norlignans extractions differed by these treatments. (5)The four main norlignans, agatharesinol, sequirin-C, sugiresinol, and hydroxysugiresinol, were determined from their extraction from the intermediate wood to the outermost heartwood. These norlignans showed different accumulation patterns. These patterns made it possible to determine successively agatharesinol, seuirin-C, and sugiresinol= hydroxysugiresinol. It is concluded from the above results that the black coloration of sugi heartwood, whose main contents are sugiresinol and hydroxysugiresinol, might be due to the rapid changes of sequirin-C because these main norlignans are stable in the black heartwood part.