Prevention of Sugi (<i>Cryptomeria Japonica</i> D. Don) from Turning Black by Smoke Heating
Keywords:<i>Cryptomeria japonica</i> D. Don, blackening heartwood, smoke heating, pH, norlignans
AbstractGreen sugi logs (tree A, normal heartwood color; tree B, heartwood color gradually turned to black after harvesting) were smoke-heated for 5, 10, 20, and 40 h to investigate the influence of smoke heating on the color change of heartwood. After the treatment, changes in color, pH, and content of norlignan were examined. The heartwood was also saturated with KHCO3 in order to examine the relationship between pH and changes in heartwood color. The results revealed that smoke heating the logs for at least 5 h prevented the heartwood from turning black; instead, the treated heartwoods turned yellowish-white. The pH value of the tree B decreased significantly from 7.4 to 6.5 after a 5-h smoke heating; from then on, the pH remained nearly constant with additional exposure. When smoke-heated, tree A- and tree B-heartwood specimens were saturated with a KHCO3 solution (pH 8.6), the brightness decreased, and the color turned black, suggesting that the blackening substances did not deteriorate when exposed to smoke heating. In the tree A heartwood, on the other hand, the contents of sequirin-C and agatharesinol barely changed before and after smoke heating. In the tree B heartwood, however, the amounts of agatharesinol and sequirin-C decreased significantly compared with those in the fresh heartwood before it turned black, whereas a large amount of norlignans, in particular, sequirin-C, was found in the smokeheated heartwood. The results obtained in the present study suggest that the chemical changes of norlignans accompanied with pH changes are closely involved in color changes in the sugi heartwood.
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