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91.
研究了超高压中温协同处理对砀山梨汁中多酚氧化酶活性的影响,实验压力为0.1~500 MPa,温度为20~60 ℃。此外,考察了不同pH值(3~7)和保压时间(2~34 min)超高压处理对酶活性的影响。实验结果分析表明:在处理温度为50 ℃、保压时间为10 min和梨汁pH值为5的条件下,200~300 MPa处理梨汁时多酚氧化酶被激活,活性表现最高;500 MPa时酶的活性下降到75.3%。协同温度为30 ℃处理梨汁时,酶的活性反而增大;30 ℃以后,酶活性随温度升高而迅速降低;有效协同高压处理的温度为40 ℃。随着保压时间的延长,梨汁中过氧化物酶的活性减小;18 min以前下降速度较快些,之后下降速度变缓。pH在5~6之间,酶的残留活性最大;pH值为6时,梨汁中多酚氧化酶最为耐压。 相似文献
92.
A metabonomic study based on the application of multivariate curve resolution and alternating least squares (MCR-ALS) to three-way data sets obtained by liquid chromatography coupled to mass spectrometry detection (LC-MS) was carried out for Rambo and Raf tomato cultivars treated with carbofuran pesticide. Samples were picked up during a 21 days period after treatment and analyzed by LC-MS in scan mode, along with the corresponding blank samples. Then, MCR-ALS was applied to the three-way data sets using column wise augmented matrices, and the evolutionary profiles as a function of the time after treatment were estimated for the metabolites present in both cultivars, as well as their corresponding pure spectra estimations. A comparative study using those estimations showed that some of these metabolites followed different behavior for the different cultivars after treatment. Since all treated and untreated Rambo and Raf samples were picked up according to the same sampling protocol and in a similar state of maturation, any difference in the behavior between profiles can be interpreted as an effect due to the presence of pesticide and to the kind of cultivar. Based on this hypothesis, several PLS-DA approaches were tested to check if it would be possible to classify samples by using the metabolites MCR estimations. Results showed that PLS-DA models for classification of treated or non-treated (blank) samples were the best ones obtained (98.44% of correct classifications for the validation set), which supports the stress effects related to carbofuran treatment. In addition, excellent discrimination among the four groups could be attained (89.06% of correct classifications for the validation set). 相似文献
93.
Twenty protein α-amino acids have been used to detect adulterations in orange juices from Spanish oranges. An analytical method based on the use of normal-phase liquid chromatography coupled to mass spectrometry has been performed for detection and quantification of these compounds in this complex matrix. MS and MS/MS parameters were optimized and most abundant product ion of each amino acid were selected to be monitorized. Method performance is improved with the use of an Allure Acidix column in which mobile phase composition and flux were optimized. Good separation was achieved using water/acetonitrile (20:80) and water/methanol (10:90) at pH 3, with elution gradient. The method has been used to assess the presence of amino acids in different kinds of orange juice: packing orange juice from both frozen concentrates and recently squeezed oranges, and fresh sweet orange juice hand-squeezed in the laboratory just before the analysis. The differences in composition between the juices and the potential adulteration practices have been evaluated and discussed. 相似文献
94.
固相萃取-高效液相色谱法同时测定噻菌灵和多菌灵在浓缩菠萝汁中的残留量 总被引:3,自引:0,他引:3
建立了一种可同时测定浓缩菠萝汁中噻菌灵和多菌灵残留量的反相高效液相色谱分析法。浓缩菠萝汁样品与水按一定比例稀释后,经过调节溶液的pH值、离心、过滤,用混合相固相萃取小柱(Mixed-mode SPE)进行提取、净化,并用配有二极管阵列检测器(DAD)的液相色谱仪检测,外标法定量。使用噻菌灵和多菌灵对照品进行添加回收率测定,结果显示,本方法对噻菌灵的检出限为0.020 mg/kg,回收率为75.7%~93.3%;对多菌灵的检出限为0.020 mg/kg,回收率为80.8%~99.2%;测定的相对标准偏差均不大于5.7%。本方法简单、快速、准确,能满足常规噻菌灵和多菌灵残留量检测的需要。 相似文献
95.
96.
97.
Derivatization yields of different esters (methyl, ethyl, n-propyl, isopropyl, n-butyl and isobutyl) of citric, malic and isocitric acids with various acylating agents, such as acetic anhydride, propionic anhydride, trifluoroacetic anhydride and heptafluorobutyric anhydride, were investigated. The formation of acylated malic and isocitric acid esters is rapid and quantitative whereas the acylation of citric acid esters was slow and partial in most instances. It was found that selective analytical conditions can be achieved with the O-heptafluorobutyryl n-butyl esters. The analytical applicability of the separation and determination of the malic, isocitric and citric acid contents of model solutions and of pressed lemon juice is discussed. Concentrations of 1.2 × 10?3 ?9.0 × 10?3g per 100 g of isocitric acid and 4.2 × 10?3 ?3.5 × 10?2 g per 100 g of malic acid in the presence of 9.3 × 10?1 g per 100 g of citric acid were measured with relative standard deviations of 7.5 and 4.2%, respectively. 相似文献
98.
99.
José Manuel López-Nicolás Estrella Núñez-Delicado Antonio José Pérez-López Álvaro Sánchez-Ferrer Francisco García-Carmona 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):219-222
Polyphenol oxidase causes enzymatic browning by catalyzing natural phenolic compounds to quinones. Subsequent nonenzymatic
oxidative polymerization reactions form brown, black, or red pigments (melanins). Many methods can be shown experimentally
to diminish or prevent browning but are not all applicable for food use. In this work, the colour of fresh apple juice was
evaluated in the presence of maltosyl-β-CD, compound that complex polyphenol oxidases substrates. The effectiveness of CD
as browning inhibitor was determined by the difference between the colours observed in the CD-treated sample and the controls,
using the colour space CIE- L, a*, b* system. We have kinetically modelled apple juice enzymatic browning in the absence and
presence of maltosyl-β-CD. The complexation constant between the mixtures of diphenols present in apple juice and maltosyl-β-CD
was calculated (Kc = 4.09 mM−1). 相似文献
100.
A coupled membrane process of membrane distillation and osmotic evaporation, where the solutions were thermostated separately
at different temperatures, was developed. Enhanced water flux was obtained since the total driving force of the coupled process
was higher than the sum of the driving forces of single processes. Apple, raspberry, sour cherry, red, and black currant juices
were concentrated by the novel, mild technique.
Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May
2006. 相似文献