Hydrolysis of beta-glucosyl ester linkage of p-hydroxybenzoyl beta-D-glucose, a chemically synthesized glucoside, by beta-glucosidases

To investigate the hydrolysis of glucosyl esters by beta-glucosidase, p-hydroxybenzoyl beta-D-glucose (pHBG) was chemically synthesized. The hydrolytic activity of some beta-glucosidases for pHBG was compared to that for p-nitrophenyl beta-glucoside (pNPG). The Clavibacter michiganense and Flavobacterium johnsonae enzymes could hydrolyze pHBG and steviol glycosides which are natural glucosyl esters. The commercial beta-glucosidase originating from Caldocellum saccharolyticum also hydrolyzes pHBG despite having no activity for steviol glycosides. The beta-glucosidase from Aspergillus niger cleaved the glucosyl ester linkage much more weakly than the glucosidic linkage. The pH-activity profile for the hydrolysis of pHBG was similar to that of pNPG by the C. saccharolyticum beta-glucosidase. The similar profiles for these substrates suggested that the active site for the glucosyl ester chemically resembles that for glucoside with respect to catalysis. Kinetic analysis of the C. saccharolyticum beta-glucosidase for mixed substrates of pHBG and pNPG showed that the hydrolysis of pHBG competed with that of pNPG. This result indicated that there is only one active site for both the glucosyl ester and glucoside. Mass spectroscopic analysis of the hydrolysates of pHBG in H218O suggested that beta-glucosidase hydrolyzes glucosyl esters between the anomeric carbon of glucose and the carbonyl oxygen, not between the carbonyl carbon and the carbonyl oxygen.     

Sterol ester production using lipase-catalyzed reactions in supercritical carbon dioxide

Synthesis of sterol and stanol esters is of importance, due to their recent recognition and application in the food and nutriceutical industries as cholesterol-lowering agents. In this study, several enzymes were evaluated to determine the best catalyst and optimal conditions for the reaction between various fatty acids and cholesterol or sitostanol in supercritical carbon dioxide (SC-CO₂). Using an analytical supercritical fluid extraction (SFE) unit, the lipase derived from Burkholderia cepacia, Chirazyme L-1, was determined to be the most selective for facilitating the desired reactions. Fatty acids C₈-C₁₈, pressures between 20.7 MPa and 31 MPa, a temperature range of 40-60 °C, along with variable flow rates, and initial static hold times were used to evaluated the feasibility of the above reaction. The yield of the cholesterol esters, as measured by supercritical fluid chromatography (SFC), ranged from 90% for caprylic acid to 99% for palmitic acid, while the corresponding reaction between sitostanol and the same fatty acids produced yields of 92% for caprylic acid and 99% for palmitic acid, respectively. The extraction apparatus was modified to provide a continuous flow of the reagent fatty acid and sterol/stanol over the enzyme bed, thereby allowing continuous production of the desired esters which averaged a 99% yield under optimal conditions.     

Impact of interactions between metal oxides to oxidative reactivity of manganese dioxide

Manganese oxides typically exist as mixtures with other metal oxides in soil-water environments; however, information is only available on their redox activity as single oxides. To bridge this gap, we examined three binary oxide mixtures containing MnO(2) and a secondary metal oxide (Al(2)O(3), SiO(2) or TiO(2)). The goal was to understand how these secondary oxides affect the oxidative reactivity of MnO(2). SEM images suggest significant heteroaggregation between Al(2)O(3) and MnO(2) and to a lesser extent between SiO(2)/TiO(2) and MnO(2). Using triclosan and chlorophene as probe compounds, pseudofirst-order kinetic results showed that Al(2)O(3) had the strongest inhibitory effect on MnO(2) reactivity, followed by SiO(2) and then TiO(2). Al(3+) ion or soluble SiO(2) had comparable inhibitory effects as Al(2)O(3) or SiO(2), indicating the dominant inhibitory mechanism was surface complexation/precipitation of Al/Si species on MnO(2) surfaces. TiO(2) inhibited MnO(2) reactivity only when a limited amount of triclosan was present. Due to strong adsorption and slow desorption of triclosan by TiO(2), precursor-complex formation between triclosan and MnO(2) was much slower and likely became the new rate-limiting step (as opposed to electron transfer in all other cases). These mechanisms can also explain the observed adsorption behavior of triclosan by the binary oxide mixtures and single oxides.     

脂肪酶水解壳聚糖作用研究

通过还原端基含量测定、粘度测定研究了脂肪酶非专一性对壳聚糖的降解作用,探索了酶反应过程中温度、pH、加酶量、底物浓度、反应时间、金属离子等因素对脂肪酶降解壳聚糖的影响,以及不同脱乙酰度和不同分子量的壳聚糖与脂肪酶降解反应的关系。结果表明,以壳聚糖为底物的脂肪酶的一些催化特性为最适温度50～55℃,最适pH5～5.5,反应时间在3～4h范围内;降解作用随着酶用量和底物浓度的增加而增加,水解反应不符合Michaelis-Menten方程;3mmol/L的Cu2 ,10mmol/L的Mg2、Ca2 对脂肪酶有一定的激活作用,10mmol/L的Ba2 、Zn2 、Fe3 对该酶有一定的抑制作用,随着底物壳聚糖脱乙酰度的提高,降解速度降低。     

纤维素酶水解玉米芯的研究

研究了影响纤维素酶水解玉米芯的各个因素(pH、温度、酶添加量、底物浓度)，得到纤维素酶水解玉米芯的最佳条件——pH4．5，温度35℃，酶添加量10U／g玉米芯，底物浓度100g／L。在最佳条件下纤维素酶水解玉米芯的葡萄糖产率为27．1％。     

Hydrolysis of N-Acetyl-L-Glutamine by Acylase I

Parenteral administration of N‐acetyl‐L‐glutamine (NAQ) produces substantial urinary losses. To evaluate enteral utility, we examined NAQ hydrolysis by acylase I, a critical first step in biological utilization. NAQ was quantitatively hydrolyzed to glutamine in vitro. Enzyme kinetic parameters were compared for NAQ (Km = 11.4 mM, Vmax = 5.54 nmole glutamine/min/μg enzyme) and an approved food additive, N‐acetyl‐L‐methionine (NAM) (Km = 1.36 mM, Vmax = 7.48 nmole methionine/min/μg enzyme). These data indicated preference for NAM in substrate recognition (Km), but similar relative catalytic ability (Vmax). While NAQ is possibly a suitable enteral glutamine source, utility will depend on intestinal acylase I levels and intestinal residence times not yet determined. Keywords: nutrition, N‐acetyl‐L‐glutamine, glutamine, acylase, bioavailability     

酸性酶对纤维素的水解性能

用酸性纤维素酶分别处理棉、粘胶和天丝织物,通过测定处理液中还原糖含量,研究了影响酶水解的各种因素.结果表明,酸性酶对粘胶的水解活力最高,纯棉次之,对天丝织物的活力最低;织物所受前处理条件、酸性酶浓度、机械搅拌条件和不同缓冲体系等对酸性纤维素酶水解性能也会产生影响.经退浆、煮练、漂白后的织物,酶水解能力较高;适当地增加机械搅动,采用HAc-NaAc缓冲体系,酶活力也较高.     

通过酶促反应制备壳寡糖

用酶降解法对壳聚糖进行降解 ,研究了温度、pH值、金属离子等对酶促反应的影响 ,降解的最佳温度和pH值分别为 5 0℃和 5 0 ,Mg2 + 和Ca2 + 对酶降解具有一定的促进作用 ,而重金属离子Cu2 + ,Ni2 + 和Zn2 + 对酶降解有强烈的抑制作用。通过降解过程中壳聚糖溶液粘度的变化可以得出 ,该壳聚糖酶是以内切方式作用于壳聚糖。采用离子交换色谱柱对降解产物进行分离 ,得到了聚合度为 2～ 9的壳寡聚糖。该酶促反应符合米氏动力学方程 ,米氏常数Km 值为 2 60 1g/L ,Vmax 值为 3 5 79× 10 - 2 g/min·L。     

植物蛋白水解复合酶的研究

在研究植物蛋白水解机理及前处理基础上,通过正交实验筛选出植物蛋白水解专用复合酶配方与使用条件,测定植物蛋白水解复合酶酶解产物结果。     

碱法水解大豆异黄酮工艺条件研究

为提高大豆总异黄酮中的染料木黄酮含量,用碱水解大豆异黄酮粗品,促使丙二酰基异黄酮转化为葡萄糖苷型异黄酮,再对其进行酸水解.单因素和正交实验研究表明,温度是主要的影响因素.由正交实验得出大豆异黄酮碱水解后再进行酸水解的最佳工艺路线为:用1.0 mol/L NaOH溶液,料液比1∶ 10,温度65 ℃,水解时间20 min,后用1 mol/L盐酸,55 ℃水解2 h,样品中以染料木黄酮计的异黄酮总含量由287.09 μg/g提高到532.76 μg/g.     

纤维素酶水解壳聚糖条件的研究

利用绿色木霉产生的纤维素酶水解壳聚糖,并对其水解条件进行了研究.在50℃、pH5.0条件下,按照8 U/g底物的酶量,将纤维素酶添加到3%壳聚糖溶液中,水解20 h可得到平均聚合度为4的低聚壳聚糖.     

纤维素酶酶解醇葛根素研究

以提取葛粉后的葛根废渣为研究对象,采用微生物和代谢物酶解提制葛根素,通过高效液相色谱法分析葛根素含量,考察影响葛根素溶出的酶解时间、酶量、pH 值、固液比等参数,探索微生物与底物葛渣间的生物交互作用。实验结果表明：葛根废渣5g,纤维素酶量为底物40%,葛根废渣与水的质量比为1:10,pH 值为5,在30℃酶解36h 后,经乙醇浸提3h,可提取葛根素33.54mg,为葛根废渣的资源化再利用提供实验基础。     

纤维素酶催化大豆异黄酮的水解

为充分发挥大豆异黄酮生物价值,采用纤维素酶催化糖苷型大豆异黄酮水解制备游离苷元型大豆异黄酮。通过考察10种纤维素酶对糖苷型大豆异黄酮总水解率和苷元型大豆异黄酮总转化率的影响,筛选得到一种成本较低且水解效果较好的纤维素酶,用于催化水解糖苷型大豆异黄酮,优化了该纤维素酶在水解工艺中底物质量浓度、酶添加量、反应体系pH、酶解温度、酶解时间等参数。结果表明：选择来源于Trichoderma viride的纤维素酶作为大豆异黄酮水解用酶;底物质量浓度0.8～2.0 mg/mL、酶添加量7%～11%、反应体系pH 5.0、酶解温度55℃、酶解时间5～6 h是较经济有效的水解工艺参数,实验优化过程中,大豆异黄酮总水解率超过90%,总转化率接近60%。因此,采用纤维素酶催化水解大豆异黄酮可显著增加游离苷元含量,提高大豆异黄酮利用价值。     

棕榈油的酸催化水解工艺研究

以棕榈油为原料进行常压酸催化水解工艺研究。考察了反应时间、反应温度、催化剂用量、油水质量比及乳化剂用量对棕榈油水解反应的影响,得出棕榈油一次酸催化水解的最佳反应条件:反应时间7 h,反应温度100℃,催化剂浓硫酸用量7.5%,油水质量比1∶1,乳化剂磺酸用量0.5%;在最佳反应条件下棕榈油水解产物酸值(KOH)为192.77 mg/g,水解率达到91.96%。并研究出一套循环水解的工艺流程,实现油脂水解产物的循环利用,提高了水相中甘油的含量。     

超声强化椰子油水解的研究

对超声强化椰子油水解进行了研究。试验表明，声强对水解效果的影响显著，探头式超声强化效果远优于槽式超声，且影响水解的主要因素为乳化剂(十二烷基硫酸钠)与酸用量、功率及作用时间。在确定主要影响因素的基础上，采用均匀设计试验法确定了各最佳参数：在乳化剂用量0．9％、酸用量0．2％、功率600W的条件下，作用5min，可使酸值达12mgKOH／g样左右。结果显示，按所提出的方法进行处理，可在温和的条件下使油脂水解的诱导期大大缩短。     

风味蛋白酶水解蛋清工艺条件的研究

为了研究出经济实用的酶解蛋清蛋白质的方法,本研究使用诺维信风味蛋白酶,对酶解工艺条件进行了探讨.结果表明,风味蛋白酶水解蛋清蛋白质最佳工艺条件为预处理温度90 ℃、时间30 min,水解温度55 ℃、pH值为6、时间8 h.     

中性蛋白酶水解花生粕的研究

选用中性蛋白酶对花生粕进行单酶水解研究.在单因素分析的基础上采用响应面分析方法对花生粕的酶解条件进行优化,得出最佳的水解条件为:底物浓度6%,反应时间3 h,反应温度44℃,pH6.7,加酶量6 500U/g底物,在此条件下理论水解度为7.63%.     

酶法水解奶油制备奶味香精的研究

选取了脂肪酶对不同类型的奶油、奶酪和牛奶等进行酶解。在非水介质下水解，得到了奶香浓郁，赋香效果明显的奶味香精。水解时以乙醇或丙酮为溶剂，在pH7．0、50℃下解4h，酶用量为1％～1．5％时得到的奶味香精香气最浓郁。经过感官评定认为此产品香气自然、柔和，可作为调配奶味香精的香基。     

风味酶酶解马氏珠母贝肉的工艺研究

对风味酶酶解马氏珠母贝肉的工艺进行了研究.结果表明,酶解最适条件为1 g底物加酶量为7200 U,底料与水的质量比为1/3,反应温度为50℃,反应pH值为7.0,反应时间为4h,此时酶解率为43.45%,1 kg马氏睐母贝肉可得118.3 gEAP干粉,产品中粗蛋白占56.6%.酶解产物经Sephadex G-15葡聚糖凝胶层析分离,获得4个组分,分子量分布范围为57543～79.其中分子量小于6026的占83.4%,是良好的食物蛋白基料.