甘露聚醣結構差異對其化學降解之影響

Abstract

甘露聚醣為植物及酵母中含量豐富且結構複雜的多醣，並在食品領域中有著廣泛的應用價值。為提升益生元活性與加工特性，常將聚醣降解為寡醣，然而因其結構複雜性且具側鏈的立體阻礙性質，達到高效且選擇性的解聚反應仍具挑戰性。本研究於50、65、80℃ 三種溫度下，採用0.1 M硫酸對四種植物來源甘露聚醣，包含：葫蘆巴膠、關華豆膠、刺槐豆膠、蒟蒻膠進行水解反應，結果顯示蒟蒻膠具有最高的活化能 (60.30 kJ/mol)。進一步於統一條件(0.1 M硫酸、80℃) 下，針對反應時間0、1、2、4、12、24小時的水解產物，結合運用Somogyi-Nelson法、高效陰離子交換層析－脈衝安培檢測法 (HPAEC-PAD) 及高效粒徑篩析層析法 (HPSEC) 進行系統性的分析。假一級動力學擬合結果顯示，蒟蒻膠的寡醣還原醣生成速率最低，反映其初期還原端釋放較為緩慢；然而，以乘冪函數及韋伯分佈描述整體多醣分子量下降趨勢時，卻顯示蒟蒻膠整體多醣鏈斷裂速率並非最慢，同時HPAEC-PAD證實其能生成高度多樣化的甘露寡醣片段。此一結果推論源於多醣的多階段降解特性，反應初期因半乳糖側鏈水解速率較高，能使還原端較快形成，而直至反應中後期推論因蒟蒻膠主鏈乙醯基脫落產生自催化效應或非結晶區初步水解而使膠體結構趨於鬆散，進而提升整體的酸水解反應速率。本研究由活化能切入，結合多尺度動力學指標，證實甘露聚醣的化學降解並非典型的一級動力學反應，而是呈現多階段水解機制。透過系統性解析甘露聚醣結構－降解機制－反應速率之整合視角，為功能性甘露寡醣製備與多醣水解工程提供具體且可量化的參考依據。

Mannans are abundant and diverse polysaccharides in plants and yeasts with numerous applications in food products. To improve their prebiotic effects and ease processing, mannans are often converted into manno-oligosaccharides (MOS) through depolymerization. However, achieving efficient and selective depolymerization of mannans is challenging due to their complex structure and steric hindrance from side chains. In this study, four plant-derived mannans - fenugreek, guar, locust bean, and konjac gum - were hydrolyzed with 0.1 M sulfuric acid at three different temperatures (50, 65, and 80℃). Among them, konjac gum exhibited the highest activation energy (60.30 kJ/mol). Further hydrolysis were conducted under standardized conditions (0.1 M H2SO4, 80℃) at 0, 1, 2, 4, 12, and 24 hours. The hydrolysates were determined by the Somogyi-Nelson method, high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), and high-performance size-exclusion chromatography (HPSEC). Pseudo-first-order kinetic fitting revealed that konjac gum had the lowest rate of reducing sugar formation from oligosaccharides, indicating a slower release of reducing ends in the early stage of reactions. Nevertheless, fitting the overall molecular weight reduction trend to the power function and Weibull distribution revealed that konjac gum did not exhibit the slowest polymer chain scission rate. HPAEC-PAD analysis further confirmed its ability to generate a diverse MOS profile. These results suggested the multi-phase degradation mechanism: in the early stage of the reaction, the higher hydrolysis rate of the galactose side chains led to a rapid release of reducing ends; in the mid-to-late stages, it was hypothesized that the deacetylation of konjac glucomannan induced the auto-catalytic effect or the initial hydrolysis in the amorphous regions caused structural loosening, thereby accelerating main chain depolymerization and enhancing the overall reaction rate. By examining activation energy and multi-scale kinetic models, this study confirmed that the chemical degradation of mannans did not follow classical first-order kinetics; instead, it proceeded via the multi-phase hydrolysis mechanism. This integrated analysis of mannan structure, degradation mechanism, and reaction kinetics provided concrete and quantifiable insights for the production of functional manno-oligosaccharides and the design of polysaccharide hydrolysis processes.