共查询到18条相似文献,搜索用时 46 毫秒
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海藻酸钠-琼脂混合固定化重组右旋糖酐蔗糖酶的研究 总被引:2,自引:0,他引:2
以海藻酸钠和琼脂混合物作为载体对右旋糖酐蔗糖酶固定化条件及其特性进行研究,结果表明:4%海藻酸钠和1%琼脂按1:1(V/V)混合后作为载体制备的微球固定化酶表现出持续高活力,在第6批次转化率仍在40%左右;海藻酸钠-琼脂混合载体与酶液体积比为2:1时固定化酶表现出的转化率最高;得到的固定化酶最适反应温度为40℃;最适反应pH值为5.4;最适底物质量浓度为5g/100mL蔗糖;35℃保温1h后剩余酶活力为原来的44%,固定化酶比游离酶的热稳定性好;固定化酶的动力学常数Km=0.02835mol/L。 相似文献
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研究异丙基硫代-β-D-呋喃半乳糖苷(isopropyl-β-D-1-thiogalactopyranoside,IPTG)与乳糖联合诱导重组大肠杆菌右旋糖酐蔗糖酶表达的效果。在利用IPTG和乳糖分别作为诱导剂对右旋糖酐蔗糖酶工程菌Escherichia coliBL21(DE3)/pET28-dexYG进行诱导表达的基础上,尝试将此两种诱导剂联合使用,在降低成本的同时获得较好的表达效果。在获得最佳培养基的基础上,考察菌体IPTG与乳糖的联合加入量、菌体浓度、诱导时间对右旋糖酐蔗糖酶表达的影响。在菌浓(OD600 nm)达到3.0时,加入0.1 mmol/L IPTG 95 μL+2.5 g/L乳糖,25 ℃混合诱导培养4 h,酶活力最高,达到40.44 U/mL。IPTG与乳糖联合诱导重组大肠杆菌右旋糖酐蔗糖酶表达可行。 相似文献
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酶促反应合成蔗糖棕榈酸酯的研究 总被引:6,自引:0,他引:6
讨论了以Novozym 435脂肪酶为催化剂,以蔗糖和棕榈酸为底物的糖酯合成反应及其影响因素.考察了在丙二醇和正己烷存在下,底物酸糖摩尔比、含水量、温度、脂肪酶浓度、时间以及摇床速度对转化率的影响.实验结果表明,底物棕榈酸与蔗糖的摩尔比为1.2∶1.0、含水量为4%,反应温度为65℃、脂肪酶浓度为棕榈酸质量的4%、反应时间为4.5 h、摇床速度为200 r/min时,棕榈酸的转化率可达到86.94%. 相似文献
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Interactions between acidified dispersions of milk proteins and dextran or dextran sulfate 总被引:1,自引:0,他引:1
Polysaccharides are often used to stabilize cultured milk products, although the nature of these interactions is not entirely clear. The objective of this study was to investigate phase behavior of milk protein dispersions with added dextran (DX; molecular weight = 2 × 106 Da) or dextran sulfate (DS; molecular weight = 1.4 × 106 Da) as examples of uncharged and charged polysaccharides, respectively. Reconstituted skim milk (5–20% milk solids, wt/wt) was acidified to pH 4.4, 4.6, 4.8, or 4.9 at approximately 0°C (to inhibit gelation) by addition of 3 N HCl. Dextran or DS was added to acidified milk samples to give concentrations of 0 to 2% (wt/wt) and 0 to 1% (wt/wt) polysaccharide, respectively. Milk samples were observed for possible phase separation after storage at 0°C for 1 and 24 h. Possible gelation of these systems was determined by using dynamic oscillatory rheology. The type of interactions between caseins and DX or DS was probed by determining the total carbohydrate analysis of supernatants from phase-separated samples. At 5.0 to 7.5% milk solids, phase separation of milk samples occurred after 24 h even without DX or DS addition, due to destabilization of caseins in these acidic conditions, and a stabilizing effect was observed when 0.7 or 1.0% DS was added. At higher milk solids content, phase separation was not observed without DX or DS addition. Similar results were observed at all pH levels. Gelation occurred in samples containing high milk solids (≥10%) with the addition of 1.0 to 2.0% DX or 0.4 to 1.0% DS. Based on carbohydrate analysis of supernatants, we believe that DX interacted with milk proteins through a type of depletion flocculation mechanism, whereas DS appeared to interact via electrostatic-type interactions with milk proteins. This study helps to explain how uncharged and charged stabilizers influence the texture of cultured dairy products. 相似文献
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Comparison of PEG/fractionated dextran and PEG/industrial grade dextran aqueous two-phase systems for the enzymic hydrolysis of starch 总被引:2,自引:0,他引:2
The aqueous two phase systems of polyethylene glycol (PEG)/fractionated dextran (DEX500) and PEG/industrial grade dextran (DEXI) were examined for the semi-continuous hydrolysis of starch. DEXI coagulates immediately as agitation stops and forms a biphasic system promptly whereas DEX500 forms clearer phases at a slower rate though. The partitioning of DEXI in the PEG phase is considerably lower compared to that for DEX500. Addition of starch in the biphasic systems was found to increase phase separation rate and dextran partition to dextran phase. Viscosities of the DEXI systems were only 10% higher than those of DEX500. Semi-continuous hydrolysis in the two phase systems exhibit steady performance for five cycles with 123.5% and 100.2% conversion of the initial starch load, for DEX500 and DEXI, respectively. The PEG/DEXI system presents almost equivalent performance to PEG/DEX500 system and has considerable lower cost than the latter. 相似文献
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以橄榄叶为原料,运用酶法提取叶片中多酚类物质,并对其加工稳定性进行探讨。在优化复合酶配比的基础上,采用单因素和均匀试验设计方法,考察酶解时间、酶解温度、pH值、酶用量和料液比5个因素对橄榄叶粗多酚得率的影响。并在此基础上,研究甜味剂、防腐剂、氧化剂和还原剂对油橄榄叶粗多酚加工稳定性的影响。结果表明:复合酶的最佳配比为纤维素酶∶果胶酶∶中性蛋白酶为1∶1∶2;橄榄叶粗多酚的最佳提取方案是酶解时间40 min,酶解温度72℃,pH值4.2,酶用量7.1%,料液比1∶52(g/mL);粗多酚在葡萄糖、蔗糖、阿斯巴甜和木糖醇溶液中的稳定性依次降低;低浓度山梨酸钾中多酚稳定性较好,山梨酸钾对多酚稳定性整体优于苯甲酸钠;高浓度氧化剂和还原剂对多酚稳定性均有较大影响。 相似文献
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比较正交设计和均匀设计对酪蛋白酶水解参数的优化效果。结果表明:当采用三氯乙酸沉淀法测定水解度时,正交设计的最高水解度高于均匀设计的最高水解度,分别为79.27%和59.81%,此时的参数组合分别为底物浓度6%和4%、酶:底物比4%和4%、温度58℃和56℃、pH8.0和8.0、水解时间3h和2.33h;当采用甲醛滴定法测定水解度时,正交设计与均匀设计的最高水解度非常接近,分别为10.82%和10.73%,此时的参数组合分别为底物浓度8%和10%、酶:底物比6%和7%、温度56℃和58℃、pH7.5和8.0、水解时间3h和3h。在本实验参数水平数较少的情况下,正交设计的优化效果优于均匀设计。 相似文献
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水溶性葡聚糖亲和-超滤载体对溶菌酶吸附分离特性的研究 总被引:1,自引:0,他引:1
亲和-超滤载体决定了亲和-超滤膜分离蛋白质的效率。以溶菌酶为对象,探讨了pH、离子浓度、反应时间等操作条件对葡聚糖亲和-超滤载体吸附溶菌酶的影响,随pH增加,亲和-超滤载体对溶菌酶的吸附量呈增长趋势,而随着离子浓度的增加,其吸附作用受到了抑制,此外亲和-超滤载体与溶菌酶的吸附能够在短时间内达到吸附平衡。应用Langmuir方程拟合了等温条件下亲和-超滤载体对溶菌酶的吸附曲线,得到最大理论吸附量为13.65mg/g,解离常数为3.019mg/mL。用醋酸缓冲溶液对载体进行洗脱,测得溶菌酶的平均洗脱率为91.74%。 相似文献