板栗仁中多酚氧化酶活性的研究

采用分光光度法对板栗仁中多酚氧化酶的活性进行了研究.结果表明,酶液加入量与吸光度值成正比关系,多酚氧化酶的最适反应温度为30～40 ℃,最适反应pH值为5.4,板栗仁表层多酚氧化酶的活性显著高于心部的活性.同时,对酶的热稳定性以及抑制剂亚硫酸钠、抗坏血酸对酶活力的影响进行了探讨.     

鸭儿芹多酶氧化酶特性的研究

以鸭儿芹多酚氧化酶的基本性质为研究目标,考察了鸭儿芹多酚氧化酶的反应进程及温度、pH、底物浓度以及酶浓度对其活性的影响.结果表明:鸭儿芹多酚氧化酶在反应过程中催化速率并不随时间的增加而增大,鸭儿芹多酚氧化酶的最适活性温度为40℃,pH为6.4,酶反应底物浓度为0.1 mg·mL-1,酶浓度为0.5Iμg·mL-1.     

几种抑制剂对水蜜桃多酚氧化酶的抑制效应

目的:研究几种抑制剂对水蜜桃多酚氧化酶酶促反应的抑制效应。方法:对水蜜桃多酚氧化酶底物特异性进行分析,在确定最适底物的基础上,采用酶动力学方法研究谷胱甘肽、L-半胱氨酸、氟化钠对水蜜桃多酚氧化酶活性的抑制效应。结果:谷胱甘肽、L-半胱氨酸、氟化钠均能抑制水蜜桃多酚氧化酶活性,3者导致酶活力下降50%的浓度(IC50)分别为0.22,0.06,4.57 mmol/L,其中前两者表现为竞争性抑制,后者为非竞争性抑制;3者对水蜜桃多酚氧化酶的抑制常数分别为0.2435,0.4974,0.43 mmol/L。在降低水蜜桃多酚氧化酶酶活的同时,谷胱甘肽和L-半胱氨酸对酶促反应有延滞作用。结论:谷胱甘肽、L-半胱氨酸、氟化钠均可有效抑制水蜜桃多酚氧化酶酶促反应速率,L-半胱氨酸的抑制效果最强,氟化钠抑制效果最差。本试验可为水蜜桃等果蔬深加工过程中抑制剂的应用提供一定参考。     

芦荟多酚氧化酶特性的研究

研究了芦荟多酚氧化酶的基本性质。以邻苯二酚为底物,采用分光光度法在4 10nm处测定芦荟多酚氧化酶的活性,研究了温度、pH值、底物浓度以及酶浓度对其活性的影响,并建立了酶促褐变反应动力学方程。实验结果表明,芦荟多酚氧化酶的最适温度为4 0℃,最适pH值为6 5 ,其酶促褐变反应动力学符合米氏方程所描述的单底物酶促反应动力学,相应的动力学参数Km=0 2 8mol/L ,Vmax=2 32×10 -2 U/min。文中还研究了利用蛋白酶抑制褐变的方法,以芦荟多酚氧化酶液(mL)∶木瓜蛋白酶(mL ,浓度0 5mg/mL) =5∶1的比例向芦荟多酚氧化酶粗酶液中添加木瓜蛋白酶,在5 5℃、pH5 7条件下,水解10min可较好地抑制多酚氧化酶的活性,从而抑制芦荟的酶促褐变。     

佛手瓜多酚氧化酶酶学特性研究

以佛手瓜中的多酚氧化酶为研究对象,对其酶学特性的研究表明：佛手瓜果实多酚氧化酶的最适pH 值为7.5,最适温度为30℃,底物浓度与酶活性呈正相关;该酶迅速催化焦性没食子酸的酶促氧化反应,但对邻苯二酚、对苯二酚和间苯二酚的催化活性较低。抗坏血酸、柠檬酸、四硼酸钠、MgCl2 和EDTA-2Na 对佛手瓜多酚氧化酶的抑制作用依次减弱,抗坏血酸、柠檬酸对佛手瓜多酚氧化酶的抑制作用随着浓度的升高而加强。     

雪莲果多酚氧化酶活性及褐变控制的研究

以雪莲果为原料,采用丙酮酸缓冲液提取、硫酸铵提纯法,得到一种活性较高的多酚氧化酶,并对其活性进行了研究。研究发现:环境温度、介质pH值、抑制剂和底物浓度对多酚氧化酶的活性有一定的影响,反映了多酚氧化酶对反应介质的依赖关系,提出在雪莲果加工过程中,可通过钝化酶活性、抑制酶促反应、驱氧处理和复合抑制等途径控制雪莲果酶促褐变。     

龙眼果肉中多酚氧化酶和过氧化物酶性质研究

测定了10个不同品种龙眼果肉中的多酚氧化酶活性.结果表明:华路广眼的多酚氧化酶活力最强,为25440U/(g·min),而罗伞木最弱,为9120U/(g·min).以石硖为试材,对其多酚氧化酶的性质进行研究时发现:龙眼多酚氧化酶酶促褐变反应动力学符合米氏方程所描述的单底物酶促反应动力学,相应的动力学参数Km=0.64mol/L,Vmax=0.12U/min;且底物过量时,多酚氧化酶活性随其加入量的增大而迅速增大,但底物逐渐饱和时其活性增加减缓直至饱和值.在灭酶条件研究中发现:多酚氧化酶粗酶液在100℃水浴中处理1min即完全失活;而果浆中的多酚氧化酶在100℃水浴中处理5min才能完全失活.实验还测得石硖中过氧化物酶活力为4440 U/(g·min),且其果浆中过氧化物酶在100℃水浴中处理7min完全失活.     

烟草酶促棕色化反应及调控技术研究进展

由多酚氧化酶(PPO)介导的酶促棕色化反应是烟草调制、醇化过程中普遍存在的问题,严重影响烟叶质量。本文介绍了影响酶促棕色化反应的因素,对农学、物理、化学和生物学等酶促棕色化反应调控技术进行了综述,探讨了各种调控方法的优缺点。     

低频超声对丰水梨多酚氧化酶酶活的影响研究

研究低频超声对丰水梨多酚氧化酶(PPO)的影响,探讨超声功率、超声时间、超声温度、pH等因素对其酶活的影响,同时对多酚氧化酶的酶反应动力学进行研究。研究表明,多酚氧化酶经超声波处理后,酶活性均比未经超声波处理的酶活力有所下降,而超声对过氧化物酶酶活的最适温度和最适pH影响不大。经过超声处理后PPO的K_m值变大,可见超声处理使PPO和底物的亲和力有所降低。     

西葫芦多酚氧化酶酶学特性研究

以邻苯二酚为底物,采用分光光度法对西葫芦多酚氧化酶(PPO)的酶学特性及不同抑制剂对多酚氧化酶活性的影响进行研究。结果表明,西葫芦多酚氧化酶最适pH为6.6,最适温度为35℃,90℃处理5min可使该酶失活。多酚氧化酶催化的酶促褐变反应动力学符合米氏方程,动力学参数为Km=0.0417mol/L,Vmax=208.33U。四种抑制剂对PPO的抑制效果由强到弱依次为:亚硫酸氢钠>L-半胱氨酸>抗坏血酸>柠檬酸。     

Development of hydrogel patch for controlled release of alpha-hydroxy acid contained in tamarind fruit pulp extract

Synopsis The aim of this study was to develop hydrogel patch using crosslinked chitosan-starch as polymeric matrix for controlling the release of the natural alpha-hydroxy acid (AHA) contained in the extract of tamarind's fruit pulp. The chitosan (MW 100 000) was blended with corn, tapioca or rice starch in various ratios and then crosslinked with glutaraldehyde. The physical characteristics, mechanical resistance, bio-adhesion property and surface morphology of the prepared hydrogel patches with and without the extract were investigated. The release patterns of the hydrogel patches containing the extract were investigated by measuring the amount of tartaric acid, a major AHA present in the tamarind's fruit pulp extract, accumulated in the receptor medium of the vertical diffusion cell at various time intervals over a period of 6 h. The results indicated that the formulations of chitosan : corn starch 4.5 : 0.5 with glutaraldehyde 0.02% w/w (C(4.5)C(0.5)G(0.02)) or 0.04% w/w (C(4.5)C(0.5)G(0.04)), chitosan : tapioca starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C(4.5)T(0.5)G(0.04)) or 0.05% w/w (C(4.5)T(0.5)G(0.05)), and chitosan : rice starch 4.5 : 0.5 with glutaraldehyde 0.04% w/w (C(4.5)R(0.5)G(0.04)) and chitosan : rice starch 4.0 : 1.0 with glutaraldehyde 0.03% w/w (C(4.0)R(1.0)G(0.03)) provided the flexible and elastic patches with good bio-adhesive property. The tensile strength values ranged from 5 to15 N mm(-2) and the elasticity ranged from 30 to 60%. The addition of the extract in these formulations significantly increased the tensile strength values of the obtained patches. The patch of C(4.0)R(1.0)G(0.03) formulation containing the extract showed relatively highest porosity, corresponding to its highest amount (12.02 +/- 0.33 mg) and rate (0.452 +/- 0.012 mg mm(-2) min(-1/2)) of tartaric acid released. The amounts of tartaric acid released from the developed hydrogel patches were proportional to a square root of time (Higuchi's model), particularly the release from C(4.0)R(1.0)G(0.03) (R(2), 0.9978 +/- 0.0020) and C(4.5)R(0.5)G(0.04) (R(2), 0.9961 +/- 0.0024) patches.     

Estimation of freezing storage time and quality changes in hake (Merluccius merluccius, L.) by low field NMR

The potential of low field NMR (LF NMR) as a fast monitoring technique to estimate the quality of hake (Merluccius merluccius) frozen stored at -10°C for up to 6months was evaluated. LF NMR clearly detected three populations of water: water strongly bound to macromolecules (T(2b)), trapped water (T(21)) and free water (T(22)). As storage time increased, and concomitant with an increase in the T(22) and a decrease in the T(21) water populations, the water holding capacity (WHC) and apparent viscosity values decreased and the shear strength increased, reflecting the characteristic loss of juiciness and tougher texture developed by hake during frozen storage. Two mathematical models were constructed: a simple regression using the biexponential analysis of the relaxation times (T(21), T(22)) and amplitudes (A(21), A(22)) and a partial least square regression (PLS) of CONTIN analysis. Both models seemed suitable to estimate the quality of the product.     

Photostabilization of ascorbic acid with citric acid, tartaric acid and boric acid in cream formulations

This study involves the evaluation of the effect of certain stabilizers, that is, citric acid (CT), tartaric acid (TA) and boric acid (BA) on the degradation of ascorbic acid (AH(2) ) in oil-in-water cream formulations exposed to the UV light and stored in the dark. The apparent first-order rate constants (0.34-0.95 × 10(-3) min(-1) in light, 0.38-1.24 × 10(-2) day(-1) in dark) for the degradation reactions in the presence of the stabilizers have been determined. These rate constants have been used to derive the second-order rate constants (0.26-1.45 × 10(-2) M(-1) min(-1) in light, 3.75-8.50 × 10(-3) M(-1) day(-1) in dark) for the interaction of AH(2) and the individual stabilizers. These stabilizers are effective in causing the inhibition of the rate of degradation of AH(2) both in the light and in the dark. The inhibitory effect of the stabilizers is in the order of CT > TA > BA. The rate of degradation of AH(2) in the presence of these stabilizers in the light is about 120 times higher than that in the dark. This could be explained on the basis of the deactivation of AH(2) -excited triplet state by CT and TA and by the inhibition of AH(2) degradation through complex formation with BA. AH(2) leads to the formation of dehydroascorbic acid (A) by chemical and photooxidation in cream formulations.     

第一过渡金属对槲皮素的化学改性及抗氧化活性

通过对槲皮素的化学改性,合成了槲皮素的第一过渡系生命元素的配合物,并对槲皮素配合物的溶解性、总抗氧化能力、清除O2·自由基和DPPH·自由基的活性进行了比较研究.研究结果表明,槲皮素配合物的在水中的溶解性优于槲皮素;槲皮素配合物的总抗氧化能力强弱为:槲皮素＜槲皮素铁(Ⅱ)＜槲皮素铬(Ⅱ)＜槲皮素镍(Ⅱ)＜槲皮素钴(Ⅱ)＜槲皮素锰(Ⅱ)＜槲皮素铜(Ⅱ)＜槲皮素锌(Ⅱ);清除O2自由基的能力为:槲皮素＜槲皮素铁(Ⅱ)＜槲皮素铬(Ⅱ)＜槲皮素镍(Ⅱ)＜槲皮素锰(Ⅱ)＜槲皮素铜(Ⅱ)＜槲皮素钴(Ⅱ)＜槲皮素锌(Ⅱ);清除DPPH·自由基的能力为:槲皮素＜槲皮素铁(Ⅱ)＜槲皮素镍(Ⅱ)＜槲皮素铬(Ⅱ)＜槲皮素铜(Ⅱ)＜槲皮素钴(Ⅱ)＜槲皮素锰(Ⅱ)＜槲皮素锌(Ⅱ).槲皮素经化学改性的产物比槲皮素有更好的生物活性.     

Combination of NMR and MRI quantitation of moisture and structure changes for convection cooking of fresh chicken meat

This study demonstrates that a combination of bulk NMR and magnetic resonance imaging measurements of the T(2)-values of water protons can be used to determine the heat-induced changes in the structure and moisture content of fresh chicken meat which had been cooked in a convection oven at 200°C for a range of times. The gravimetric moisture content was also determined for both the raw and cooked meat. Multi-exponential fitting of the bulk NMR T(2) relaxation time data demonstrated three distinct water populations T(21) (39-43ms), T(22) (82-99ms) and T(23) (2-3ms) for raw meat which changed to 18-31ms (T(21)), 61-208ms (T(22)) and 3-7ms (T(23)) after the meat had been cooked. The T(1) and T(2) values obtained by MRI for cooked meat decreased progressively with increased heating time. There are highly significant correlations between the T(2) values from MRI and the T(21) values from bulk NMR measurements of cooked meat (r=0.986; p<0.01), and also between the normalised M(0) values from MRI and the gravimetric moisture content (r=0.953; p<0.01).     

云杉鞣质级分的分子量测定及鞣革性能的研究

云杉树皮(P.Likangensis Pritz)粉碎后,经丙酮水浸提去脂,依次用乙醚、乙酸乙酯萃取,得到乙醚级分,乙酸乙酯级分和水级分。对各级分进行试验:1.采用蒸气压渗透法,测定各级分的数均分子量Mn;2.鞣革试验。结果表明: 1.乙醚级分的Mn=350,主要由鞣性小的小分子非鞣质组成;乙酸乙酯级分的Mn=860,具有显著的鞣性;水级分的Mn=1550,主要由属于大分子的鞣质组成。 2.各级分与皮蛋白质结合的顺序依次为:水级分、乙酸乙酯级分、乙醚级分。而渗透性顺序依次为:乙醚级分、乙酸乙酯级分、水级分。 3.云杉栲胶鞣性差的原因,除了树皮单宁含量低(8.91％)外,其中脂类物质(二氯甲烷萃取物)含量高(2.44％),也是其渗透极慢的原因之一。本文对云杉鞣料的开发利用提供了一些理论数据。     

Impact of a pulsed electric field on damage of plant tissues: effects of cell size and tissue electrical conductivity

Efficiency of pulsed electric field (PEF) induced permeabilization at 293 K in selected fruit and vegetable plant tissues (apple, potato, carrot, courgette, orange, and banana) at electric field strength (E) of 400 V·cm(-1), 1000 V·cm(-1) and pulse duration (t(p)) of 1000 μs was studied experimentally. The mean cell radius (〈r〉) was within 30 to 60 μm, and the ratio of electrical conductivities of the intact and damaged tissues (σ(i)/σ(d)) was within 0.07 to 0.79 for the studied tissues. Electroporation theory predicts higher damage for tissue with larger cells; however, the direct correlation between PEF damage efficiency and size of cell was not always observed. To explain this anomaly, a theoretical Monte Carlo model was developed and checked for parameters typical for potato tissue. The model showed a strong dependence of PEF damage efficiency and power consumption (W) on σ(i)/σ(d) ratio. The optimum value of electric field strength (E(opt)) was an increasing function of σ(i)/σ(d), and plant tissues with high σ(i)/σ(d) ratio (σ(i)/σ(d) ≈ 1) required application of a rather strong field (for example, E(opt) ≈ 3000 V·cm(-1) for σ(i)/σ(d) ≈ 0.8). However, the PEF treatment at a lower field (E ≈ 400 V·cm(-1)) allowed regulation of the selectivity of damage of cells in dependence of their size. A good qualitative correspondence between experimental data and simulation results were observed.     

The effects of modified atmosphere gas composition on microbiological criteria, color and oxidation values of minced beef meat

This paper reports the effects of modified atmosphere gas compositions with different concentrations of CO(2)/O(2)/N(2) on color properties (L*, a* and b* values), oxidation stability (TBARS value) and microbiological properties of minced beef meat stored at +4 °C. Sampling was carried out on the 1st, 3rd, 5th, 7th, 9th, 11th and 14th day of storage. The gas mixtures used were as follows: (i) %30O(2) + %70CO(2) (MAP1), (ii) %50O(2) + %50CO(2) (MAP2), (iii) %70O(2) + %30CO(2) (MAP3), (iv) %50O(2) + %30CO(2) + %20N(2) (MAP4), and (v) %30O(2) + %30CO(2) + %40N(2) (MAP5). Control samples (AP) were packaged under atmospheric air. Pseudomonas, lactic acid bacteria, Brochothrix thermosphacta, and Enterobacteriaceae members were monitored. Among these five modified atmosphere gas compositions, the best preservation for minced beef meat was in MAP4 gas combination maintaining acceptable color together with oxidation stability and acceptable microbial loads until the end of storage period of fourteen days.     

Essential oil composition,phenolic compound,and antioxidant potential of Inulaviscosa as affected by extraction process

The purpose of this study was to compare the essential oil composition of Inula viscosa leaves by hydrodistillation (HDE), ultrasonic (UDE) and solvent (SE) extractions followed by hydrodistillation. The total polyphenol and flavonoid contents and their antioxidant effects were studied by different solvent of extraction: ethanol (ET), ethyl acetate (EA), methanol (ME) and aqueous (AE). The principal compounds for HDE were: 2-hexenal (3.70%), caryophyllene oxide (3.11%), γ-selinene (3.09%), 3-hexen-1-ol (2.00%), eugenol (1.70%) and trans-caryophyllene (1.34%), while for UDE were: γ-selinene (5.68%), caryophyllene oxide (4.87%), trans-caryophyllene (1.99%) and nerolidol (1.74%). The oil obtained by SE was shown to contain tridecane (3.89%), dodecane (3.08%), trans-caryophyllene (2.94%), caryophyllene oxide (2.56%) and nerolidol (2.53%). Significant changes on phenolic contents were found between the different solvent of extraction. ME and AE extracts led to the highest total polyphenol (PHL) and flavonoid (FL) amounts. The anti-radical activity and reducing power were maximal in AE and ME extract. HPLC examination established that the ferulic acid as major phenolic acid in ME and AE fractions, whereas luteolin was the main compound of EA and ET fractions.     

DNJ对正常小鼠脂代谢的影响及作用机理初探

本文为探索DNJ对脂代谢的影响及作用机理,给正常小鼠灌胃DNJ 40 d后,用试剂盒测定各实验动物脂代谢相关生化指标、酶活及抗氧化指标。结果显示与阴性对照组比较,8.0 mg/(kg bw?d)剂量DNJ使雌、雄小鼠的体重增加率分别降低59.40%和9.15%;腹腔脂肪系数降低38.30%和15.18%;肝脏脂肪含量降低18.42%和36.66%;血清TC降低27.40%和28.57%,TG降低0.89%和15.03%,HDL增加42.19%和6.80%;肝脏SOD活性上升29.24%和25.17%,GSH增加16.29%和15.00%,8-isoprostane下降18.53%和15.19%;雌鼠FAS、ACO活性下降14.02%和9.67%,雄鼠ACO活性上升21.63%。说明适量DNJ主要通过抑制雌鼠脂肪酸合成、加速雄鼠脂肪酸氧化来减少脂肪蓄积,且对雌鼠具有更好的预防肥胖作用;同时可增强小鼠机体抗氧化能力,预防脂代谢异常。