由脫脂芝麻粕回收製備芝麻素酚之研究

Abstract

木酚素(lignan)為一類植物次級代謝物，以芝麻與亞麻籽中含量最為豐富。研究證實木酚素具有多種生理活性，包括抗氧化、抗腫瘤、調節血脂、抗發炎與抗老化等。芝麻籽中主要的木酚素為，芝麻酚(sesamin)，芝麻酚林(sesamolin)及木酚素配醣體(lignan glucosides)。經過加工提取芝麻油後，sesamin及sesamolin主要存在於芝麻油中，而木酚素配醣體包括sesaminol glucosides 及pinoresinol glucosides則存在於芝麻粕中。Sesaminol及其異構物近來已被證實具強抗氧化性、與α-tocopherol具協同作用，並且能抑制低密度脂蛋白氧化等活性，然而芝麻中存在的形態為conjugate form，主要為sesaminol glucosides，於芝麻中含量約0.1% (w/w)。本研究建立由脫脂芝麻粕回收製備sesaminol之程序。內容分為三部分，第一部分藉由sesamolin酸轉換途徑製備sesaminol及評估其可行性。結果顯示在試驗系統下，sesamolin皆無法轉換出sesaminol。推論sesamolin酸轉換路徑，主要途徑為sesamolin水解得到sesamol及samin ; 次要途徑為sesamolin因酸催化裂解並進行結構重組得到sesamol及sesaminol。第二部分探討由sesaminol glucosides (STG)製備sesaminol的最適條件。分別進行酸水解與酵素水解試驗。以STG區分為試驗原料。分別以5%甲酸、1.2 M鹽酸級0.6 M硫酸在高溫高壓下酸水解，發現以5%甲酸可對STG進行水解並生成sesaminol，但STG水解效率不佳，於1.2 M鹽酸及0.6 M硫酸下雖然STG可完全降解但產物不安定，並無sesaminol產生。第三部分探討利用酵素水解法製備sesaminol之可行性，首先篩選可水解STG的商業化酵素，結果以Viscozyme® L及Pectinex Ultra SP-L效果最佳。分別以脫脂芝麻粕及sesaminol glucosides萃出物為原料的結果顯示，利用Viscozyme® L及Pectinex Ultra SP-L於45℃下作用48 h後的水解液含有最多量的sesaminol。其中以Viscozyme® L對sesaminol glucosides萃取物的水解效果最佳，產物約含有5% sesamin及5% sesaminol，相較於存在芝麻中的sesaminol含量提升了近5000倍。

Lignan, a class of plant secondary metabolites, occurs naturally abundant in sesame seeds and flaxseeds. Many studies revealed that sesame lignans possess multiple biological activities such as antioxidant, anti-tumor, anti-inflammatory, and anti-aging activity. Sesaminol has been shown a variety of beneficial functions to humans, including its strongly antioxidant activity, a potent inhibitor to retard the oxidation of low-density lipoproteins, anti-tumor activity by the induction of apoptosis in human lymphoid leukemia cells. However, sesaminol presents only 0.001% in sesame seeds, and glucosyl conjugates of sesaminol, particularly sesaminol triglucoside (STG), are the major form in sesame. The present study aimed to develop a promising and feasible method to produce sesaminol by hydrolyzing STG. First, we deduced the proposed pathway for acid conversion of sesamolin. We considered that sesamolin would be hydrolyzed to form sesamol and samin rather than rearranged to synthesize sesaminol based on we failed to prepare sesaminol in any cases through sesamolin by acidic-catalyzed conversion. Ont the other hand, isolation of STG from defatted sesame cake was achieved by extraction with 80% MeOH and successively HP-20 resin fractionation.Subsequently, the isolated STG fraction was hydrolyzed with individually acid solutions including 1.2 M HCl, 0.6 M H2SO4, and 5% formic acid under the condition at 121℃ and 1.5 atm. The results revealed STG was fully degraded with the treated groups of both 1.2 M HCl and 0.6 M H2SO4 within 20 min, and no sesaminol was detected in their corresponding hydrolysates. For the group of formic acid treatment, only trace sesaminol been detected and revealed 5% formic acid was not appropriate to produce sesaminol by acid hydrolysis at 121℃ and 1.5 atm with STG. For the investigation of sesaminol production through hydrolyzing STG by commercially available enzymes, eight tested groups with individual or combined enzymes were designed for evaluating the feasibility. Our results suggested that Viscozyme®L and Pectinex Ultra SP-L could catalyze the hydrolysis of STG to generate sesaminol. Futhermore, the optimal condition for preparing sesaminol concentrate by Viscozyme®L hydrolysis with ethanol extract of defatted sesame cake was also evaluated. With the optimal condition, the content of sesaminol in the product was approximately 5% (by weight) that was about 5000-fold increased with the recovery of 84% .