Two Lipoxygenases from Germinated Barley-Heat and Kilning Stability

Using ammonium sulfate precipitation followed by hydrophobic and ion exchange chromatography, two lipoxygenase isoenzymes, LOX 1 and LOX 2, were 18.3- and 44.5-fold purified from germinated barley, with 18 and 24% recovery of activity respectively. LOX 1 and LOX 2 were characterized by isoelectric points 4.9 and 6.4, and molecular weights of 90 kd and 110 kd, respectively. Apparent Km values for linoleic acid were 0.06 mM for LOX 1 and 0.18 mM for LOX 2. LOX 1 converted linoleic acid to 9 and 13 hydroperoxides at about 4:1, whereas the 13 hydroperoxide was the major product formed by LOX 2 (ratio 3:7). For both isoforms, thermal inactivation data indicated first order kinetics with activation energies influenced by ionic strength and pH. Isoenzymes composition was analyzed for three kilning schemes: the 1:3 ratio between LOX 1 and LOX 2 observed in germinated barley increased during the course of kilning.     

高静压技术对豆浆中脂肪氧合酶的钝化效果及其动力学分析

研究了高静压技术(HHP)对豆浆中脂肪氧合酶(LOX)活性的钝化作用,并进行失活动力学分析。结果表明:HHP处理能显著钝化豆浆中LOX活性。用300～600MPa压力处理5～20min,对LOX活性有显著的钝化效果(P<0.05),并且随处理压力和处理时间的增加,酶的失活率提高。当压力500MPa,保压时间0min时也有一定的钝化LOX效果;当压力600MPa处理10min以上,豆浆LOX活性被完全抑制。用500MPa处理5min,可以达到与传统巴氏杀菌相同的钝酶效果(P>0.05)。HHP技术钝化豆浆LOX的过程可用一级动力学模型拟合(R2>0.900)。随着压力的升高和处理时间的延长,k值逐渐升高,D值逐渐减小;动力学参数ZP和Va分别为125.94MPa和-45.290cm3/mol。HHP技术在钝化豆浆中脂肪氧合酶活性方面比传统巴氏杀菌彻底,效果更好。其在改善豆浆品质方面具有良好的应用前景。     

青椒果实冷害与活性氧清除酶和脂氧合酶活性变化的关系

青椒在9℃下冷藏8周,未出现冷害,膜透性变化不大。而在2℃下贮藏1周后即出现冷害症状,超过4周发生严重冷害,膜透性迅速上升。与9℃贮藏青椒相比,2℃贮藏的青椒SOD活性降低,而CAT和APX活性降低更多;POD活性也明显低于9℃贮藏青椒,但7周时骤升至峰值。9℃下青椒的LOX活性变化很小,而2℃下青椒的LOX活性2周时迅速上升,此后保持较高的水平。低温促进了膜脂过氧化产物MDA的积累,使2℃下青椒的MDA含量高于9℃的。可见青椒的冷害与低温下活性氧清除酶,特别是CAT和APX活性的降低以及LOX活性增强,导致活性氧化代谢失调和膜脂过氧化有关。     

Bread and durum wheat compared for antioxidants contents,and lipoxygenase and peroxidase activities

Potential beneficial components, including proteins, total phenolics, total flavonoids, carotenoids, tocopherols, and DPPH radical scavenging activity, were investigated in wholemeal of ten bread (T. aestivum L.) and ten durum (T. durum Desf.) novel wheat genotypes. In addition, the activity rate of lipoxygenase (LOX) and peroxidase (POD) enzymes implicated in the antioxidant metabolism was determined. The protein contnet and the antioxidant properties varied according to the two different wheat species, as well as, between the different bread and durum wheat genotypes themselves. The results indicated significant differences in proteins and antioxidant compounds between bread and durum wheat. Higher total proteins, wet gluten and antioxidants contents, combined with lower LOX and POD activities, point to a higher nutritive value of durum wheat than bread wheat.     

啤酒生产过程中氧化还原酶系的研究

啤酒生产过程中的氧化还原酶与啤酒风味陈化紧密相关。低水分下，其耐温活性远高于其它几种酶，在麦芽中酶活升高比例最大（与大麦中的酶活相比），其在糖化过程中氧化多酚的能力远大于多酚氧化酶。糖化过程中迅速失活，而脂肪酸氧化酶在糖化起始的低温阶段仍有部分酶活，影响不饱和脂肪酸的氧化。焙燥过程中适当延长50～70℃温度段时间，可有效降低麦芽中氧化还原酶的酶活。结合这些酶的性质，从部分抑制它们的活性角度出发，在糖化过程中，于50～60℃进行隔氧处理，可经济、有效的减少影响风味氧化的前驱物质的含量。同一质量等级不同品种的麦芽的氧化还原酶系差别相当大，相应制得的麦汁中与风味氧化有关的物质含量也有较大差别，这可能是造成不同批次原料酿造的成品啤酒风味保鲜期不稳定的原因之一。     

动物脂肪氧化酶及其对动物性食品的影响研究进展

脂质的氧化是导致动物性食品及其原料在加工、储运过程中营养价值和产品品质下降的重要原因之一。脂肪氧化酶(LOXs)是催化脂质,特别是不饱和脂质氧化的关键酶。它催化多不饱和脂肪酸(PUFA)氧化,导致动物性食品风味、色泽及质构劣化,营养价值降低。文章根据近几十年国内外研究资料,在详细介绍LOXs分子结构的基础上,着重阐述LOXs催化PUFA氧化的催化反应性能,并对LOXs的发现、分布、分离纯化与活性测定方法及其对动物性食品的影响等方面的重要研究进行综述。     

脱脂豆粕中不同脂肪氧合酶活力对大豆分离蛋白凝胶性质的影响

通过加热处理低温脱脂豆粕，研究了豆粕中脂肪氧合酶的热失活动力学，并以此制备不同酶活的脱脂豆粕。分别提取分离蛋白。考察了不同分离蛋白的凝胶性质，并从蛋白溶液浊度、NSI值和碱溶上清液的分子量分布角度探讨了不同脂肪氧合酶活力对上述蛋白功能性质的影响。发现随豆粕中酶活力降低，所得分离蛋白的功能性质得到提高。     

大豆脂肪氧合酶酶促合成亚油酸氢过氧化物

研究了水相体系中大豆脂肪氧合酶酶促合成亚油酸(LA)氢过氧化物的反应,最佳反应条件为底物质量浓度4 11g/L,pH=9,5℃,反应时间120min,亚油酸氢过氧化物产率80%。当m(LA)∶m(surfactant)=1∶1时,Tween系列、CTAB、AOT、AEO4、OAPCG、S8390均能加速反应,其中AEO4使反应时间缩短至30min,产率提高12%。一些盐可以明显地加快反应进程,其中柠檬酸钠使反应时间缩短至15min。外源Fe3+在反应体系中的浓度为0 5μmol/L或外源Fe2+为5nmol/L时反应速度显著提高,消除了滞后期。     

Biologically Active Components Inactivation and Protein Insolubilization during Heat Processing of Soybeans

Inactivation of lipoxygenase, trypsin inhibitor, urease and retention of protein solubility during water blanching of dehulled soybeans at 90°, 95° and 100°C were investigated. Lipoxygenase was the most heat labile, followed by urease and then trypsin inhibitor. Processing time based on “acceptable inactivation time” (AI) was proposed. AI value was longest for trypsin inhibitor, followed by urease and then lipoxygenase. The combined effect of heat on protein solubility and biologically active components inactivation was expressed as “PDI at acceptable inactivation time” (PDIAI). PDIAI value for the processing “limiting factor,” trypsin inhibitor inactivation, at the three temperatures were 36.7%, 42.5%, and 34.8%, respectively.     

Inhibition of Horse Bean and Germinated Barley Lipoxygenases by Some Phenolic Compounds

Phenolic compounds have been repeatedly implicated as potent antioxidants. Efficiency has been frequently estimated by radical scavenging activity and few reports have considered lipoxygenase (LOX) inhibition. Horse bean LOX was inhibited by a range of phenolic acids, gallates and flavonoids. All compounds tested were uncompetitive inhibitors with the exception of flavonol aglycons which were non competitive type. In each class of compounds, inhibition constants were strongly affected by structures. Inhibition patterns of (-)-epicatechin on germinated barley LOXs were detailed: (-)-epicatechin acted as an uncompetitive inhibitor while (-)-epicatechin reduced hydroperoxide formation by its radical scavenging activity and thus limited enzyme activation.