ASIAN JOURNAL OF FORESTRY Volume 4, Number 1, June 2020 E-ISSN: 2580-2844 Pages: 6-9 DOI: 10.13057/asianjfor/r040102 Steaming-caused chemical changes of sugi (Cryptomeria japonica) wood monitored by NIR spectroscopy SITI HANIFAH MAHDIYANTI 1,♥ , SATORU TSUCHIKAWA 1,♥♥ , KATSUYA MITSUI 2 , LASZLO TOLVAJ 3,♥♥♥ 1 Graduate School of Bioagricultural Sciences, Nagoya University. Nagoya 464-8601, Japan. ♥ email: siti.hanifah.m@mail.ugm.ac.id, ♥♥ st3842@agr.nagoya-u.ac.jp 2 Gifu Prefectural Human Life Technology Research Institute. Yamada, Takayama 506-0058, Japan 3 Institute of Physics and Electrotechnics, University of Sopron. HU-9400 Sopron, Hungary. Tel.: +36-99-518140, ♥♥♥ email: tolvaj.laszlo@uni-sopron.hu Manuscript received: 29 October 2019. Revision accepted: 28 January 2020. Abstract. Mahdiyanti SH, Tsuchikawa S, Mitsui K, Tolvaj L. 2020. Steaming-caused chemical changes of sugi (Cryptomeria japonica) wood monitored by NIR spectroscopy. Asian J For 4: 6-9. Sugi (Cryptomeria japonica D. Don) wood samples were steamed, applying a broad range of steaming time (0-20 days) at 90 and 110°C steaming temperatures. NIR spectroscopy was used to monitor the chemical changes caused by steaming. The difference spectrum method was applied to find the absorption increases and decreases. Before the subtraction, the spectra were normalized to one unit at 1739 nm to eliminate the parallel shift of the spectra. Steam-induced chemical changes in the wavelength range of 1300-2100 nm are related to the absorption of water and the absorption of extractives, especially phenolic contents. These chemical changes are suspected to be strongly related to color changes in steamed wood. Longer duration of steaming caused phenolic compounds to change into similar contents in all wood tissues, which cause their color to change more uniformly. Steaming caused a water bounding capacity loss of the cell wall. This change was much faster at 110°C than at 90°C. Keywords: Color change, hydroxyl groups, steaming, sugi wood, NIR spectroscopy Abbreviations: NIR: near infra-red, E: earlywood, L: latewood, H: heartwood, S: sapwood, nm: nanometre INTRODUCTION Steaming is a useful method for color modification of wood materials. Some wood species have a white-greyish color without a distinct texture (poplar, beech, hornbeam, etc.). Some other species have a strikingly inhomogeneous color (black locust, Turkey oak, beech having red heart, etc.). Disadvantageous wood texture might be turned to a more favorable and characteristic appearance using steam treatment. The color modification effect of steaming is a widely investigated phenomenon (Varga and van der Zee 2008; Straze and Gorisek 2008; Tolvaj et al. 2009, 2010, 2012; Milic et al. 2015; Geffert et al. 2017; Dzurenda 2017, 2018a, 2018b; Banadics and Tolvaj 2019). The color of a material is determined by the presence of conjugated double bond chemical systems. These systems are located in lignin and in extractives for natural wood material. The color of wood species is determined by the extractive content primarily. However, extractives are highly sensitive to heat. This phenomenon is the main basis of color modification by steaming, where wood material is subjected to the simultaneous effect of heat and moisture. Generally, the maximum steaming temperature is 120°C in industrial practice. This is the upper-temperature limit because of the high steam pressure above this temperature. Most of the main chemical substances of wood (cellulose, hemicelluloses, and lignin) are stable below 120°C. It is well known (Fengel and Wegener 1984), that mainly the thermally less stable polyoses are decomposed due to the influence of heat. Acetic acid is released by the scission of acetyl groups linked as an ester group to the hemicelluloses (Tjeerdsma and Militz 2005; Windeisen et al. 2007). The degradation products of hemicelluloses modify the initial color of wood. This phenomenon is the second-order producer of color changes during steaming. The main creators of this color change are the extractives. The chemical changes of extractives cannot be traced by middle IR spectroscopy because of their low-level quantity (Tolvaj et al. 2013). The NIR wavenumber range from 12800-7000 cm-1 is considered to be influenced by particle size and especially by visible color change, and it has proven to be useful for qualitative purposes (Schwanninger et al. 2011). The NIR wavenumbers related to extractives, 7092 and 6913 cm-1 assigned to first overtone of O-H stretching, is due to the presence of phenolic hydroxyl groups (Schwanninger et al. 2011). Phenolic compounds are suspected to be responsible for wood discoloration related to extractives (Torres et al. 2010). The change in acetyl ester in hemicellulose due to thermal degradation related to color change can be observed in the NIR second-derivative spectra between 8650-8450 cm -1 (Schwanninger et al. 2011). The NIR wavenumber, which is adjacent to the visible-light range, is supposed to be sensitive to trace visual color change, and is more suitable for the observation of chemical change related to the color in wood. The aim of this study was to investigate the chemical changes of sugi (Cryptomeria japonica D. Don) wood