麻竹稈纖維素酶解木質素萃取方法及其木質素特性分析

Abstract

麻竹（Dendrocalamus latiflorus）為臺灣分布最廣之竹種，生長快速，單一生長季即可達最大高度，可達25 m，由於上述特性，在材料加工或生質能源利用上相當具有潛力。纖維素酶解木質素（cellulolytic enzyme lignins, CELs）為研究植物木質素之優良材料，但傳統萃取所耗時間長。故本研究分析超音波萃取對於麻竹稈CELs之影響，結果顯示其酸可溶木質素略多、分子量稍大，但並不影響CELs之其他性質，所以將超音波用於萃取不同生長階段麻竹稈之CELs，並進一步分析CELs其之性質。 在麻竹稈生長過程中，木質素隨著生長階段而累積，接近成熟時，木質化較高時，木質素含量變化趨於穩定。試驗結果顯示麻竹稈木質素為H-G-S type lignin，為典型草本植物木質素。其中，S unit在不同生長階段之變化最為顯著，以2.5個月生麻竹稈中段之S/G ratio最高，顯示S unit在木質化前中期的生合成速度相對G unit較快，之後稍微減緩，而在接近成熟時（6個月生基部）又相對增加。H/G ratio變化趨勢逐漸下降，顯示H unit植物生長初期較為重要。麻竹稈木質素含有p-coumaric acid與ferulic acid，其ferulic acid以生長初期的含量最多（5%），在植物成熟時逐漸減少，顯示ferulic acid在植物木質化的初期扮演著重要的角色。而p-coumaric acid的含量在2.5個月生麻竹稈中隨著生長階段而增加，可高達21.4%，變化趨勢與全細胞壁核磁共振（nuclear magnetic resonance, NMR）木質素單體分析相同，但與CELs之趨勢相反。 NMR分析結果顯示，麻竹稈CELs主要鍵結為-O-4，隨生長階段而逐漸增加。值得注意的是，.-O-4鍵結含量為4-4.6%，顯示麻竹木質素之醚鍵比起其他竹類相對含量較多，降解可能相對較為容易。

Dendrocalamus latiflorus is the most widely distributed bamboo species in Taiwan. It grows rapidly and reaches its maximum height (about 25 m) in a growing season. Due to the characteristics, it has great potential for material processing and bioenergy. Cellulolytic enzyme lignins (CELs) is a good material for plant lignin research, but the traditional extraction of CELs takes long times. This study analyzed the effect of sonication for D. latiflorus culm CELs extraction. The results show that the CELs extracted with sonication have more acid soluble lignin, and the molecular weight of these CELs are larger. Except the properties mentioned earlier, sonication does not affect others properties of CELs in this study. So we used the sonication to extract CELs, and analyzed the properties of CELs from different portions of D. latiflorus culm. During the growth of D. latiflorus culm, the lignin accumulated with the growing stages. And D. latiflorus culm’s lignin is a H-G-S type lignin, which is the typical herbaceous lignin. The change of S unit was the most significant in different growth stages. The highest S/G ratio was in the mid-section of 2.5-month-old D. latiflorus culm, indicating that the S unit accumulates faster than G unit in the early stage of lignification, then slows down. When the bamboo culm approachs maturity (6-month-old basal), the S unit accumulation rate rises again. The trend of H/G ratio decreased gradually, indicating that H unit is more important at the initial stage of plant growth. D. latiflorus culm’s lignin contains p-coumaric acid and ferulic acid. Ferulic acid in the early stage is the most abundant (5%) during lignification, and reduces when plants mature gradually, indicating that ferulic acid play an important role in early lignification. However, the content of p-coumaric acid increased with the growing stage in 2.5-month-old D. latiflorus culm, up to 21.4%. The trend is the same as the whole cell wall NMR analysis but opposite to that of CELs NMR analysis. NMR analysis showed that the main linkage of D. latiflorus culm CELs is -O-4, which gradually increased with growing stage. It is important to note that that the content of .-O-4 linkage is 4-4.6%, indicating that the content of ether bond of D. latiflorus culm CELs is higher than other bamboos, and this might make the lignin degradation more easily than others.