皂土、硫酸处理对苹果汁发酵过程中果胶甲酯酶活性以及苹果蒸馏酒甲醇含量的影响

新鲜苹果汁分别采用皂土、硫酸处理后,经酿酒酵母（Saccharomyces cerevisiae）发酵获得苹果基酒,经二次蒸馏制备苹果蒸馏酒。研究苹果汁发酵过程中果胶甲酯酶（PME）活性及甲醇含量的变化,探究皂土、硫酸处理对苹果蒸馏酒中甲醇含量、风味物质及感官品质的影响。结果表明,皂土和硫酸处理苹果汁PME活性在发酵4 d后分别降低90.48%、91.75%,均未检出甲醇。与对照相比,皂土和硫酸处理的苹果基酒PME活性分别降低33.18%与24.71%,甲醇含量分别降低37.76%与30.88%;皂土和硫酸处理的苹果蒸馏酒甲醇含量分别降低47.46 mg/L、34.86 mg/L;酯类物质总含量分别提高145.73 mg/L、38.51 mg/L;醇类物质总含量分别提高144.04 mg/L、降低530.79 mg/L;总挥发酸含量分别降低50.18 mg/L、61.90 mg/L。皂土处理蒸馏酒感官评分最佳（91.3分）。综上,2种处理均可有效降低苹果蒸馏酒甲醇含量,皂土处理可以显著提高苹果蒸馏酒的品质。     

外源乙烯和茉莉酸甲酯对鲜切甘蓝活性氧代谢的影响

为研究鲜切果蔬活性氧代谢以及不同外源信号分子对鲜切果蔬活性氧代谢的影响,以鲜切甘蓝为材料,利用外源乙烯和茉莉酸甲酯（MeJA）处理鲜切甘蓝,于4℃条件下贮藏,测定了活性氧H2O2和O2-·的变化,超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）以及抗坏血酸过氧化物酶（APX）等酶活性。结果表明,乙烯和MeJA两种处理抑制了鲜切甘蓝活性氧H2O2含量的增加及O2-·的生成速率,外源乙烯处理提高了鲜切甘蓝中具有防御功能的SOD和APX活性,而抑制了POD和CAT的活性;MeJA处理后鲜切甘蓝的SOD、POD、CAT活性均受到抑制,对整个贮藏过程中的APX活性的作用效果有所不同,贮藏前期促进但贮藏后期起到一定程度的抑制作用。在两种处理中,乙烯提高鲜切甘蓝的抗氧化活性作用明显。      

茉莉酸甲酯对鲜切苹果生理生化变化的影响

为研究茉莉酸甲酯(MeJA)对鲜切苹果生理生化变化的影响,将1cm3的鲜切富士苹果分别放入100、400、1600μmol/L的茉莉酸甲酯溶液中浸泡30min,包装后放入5℃冷库中贮藏。每2d测定各类酶活性以及与成熟衰老相关的指标等的变化。结果表明,经茉莉酸甲酯处理后,鲜切苹果的APX活性降低,但LOX、PAL、CAT、PPO、POD活性增加,相对电导率和丙二醛含量降低,说明茉莉酸甲酯处理启动了鲜切富士苹果的防御反应,导致相关防御反应的关键酶活性升高,从而降低机械伤害引发的自由基对细胞膜产生的伤害。研究认为,鲜切苹果贮前经适当浓度的茉莉酸甲酯溶液浸泡,可显著延长贮藏期和保持新鲜品质。     

茉莉酸甲酯和乙烯利处理对鲜切苹果膜质过氧化反应的影响

为研究外源信号分子茉莉酸甲酯(Me JA)和乙烯(Eth)对鲜切果蔬膜脂过氧化反应的影响,本实验以鲜切富士苹果为实验材料,经10μmol/L Me JA和10μL/L乙烯利处理,分析贮藏过程中与膜脂过氧化反应相关物质及酶类的变化。结果表明,Me JA和乙烯利可显著提高脂氧合酶(LOX)活性(p<0.05),降低细胞膜的渗透率和丙二醛(MDA)的含量,同时颜色的损失减少,乙烯利处理鲜切苹果的过氧化氢酶(CAT)活性提高,超氧化物歧化酶(SOD)活性降低,但Me JA对SOD和CAT活性无显著影响,说明Me JA和乙烯利启动了鲜切富士苹果的防御反应,导致膜脂过氧化反应系统的关键酶活性升高,从而降低机械胁迫对细胞膜产生的伤害,从而显著延长贮藏期和保持新鲜品质(p<0.05)。      

Molecular differences of low methoxy pectins induced by pectin methyl esterase I: Effects on texture,release and perception of aroma in gel systems

Six types of low methoxy pectins (two commercial and four modified pectins treated with pectin methyl esterase from Valencia orange) with different degrees of esterification (DE), molecular weights (MW), and degrees of amidation were prepared. Pectin gels containing five aroma compounds were produced and their texture properties, release of aromas, and sensory flavour intensities were investigated. Regarding the gels made with lower MW pectins (<2.1 × 10⁵), only headspace concentration of isoamyl acetate was increased, according to the de-esterification of the pectins. In the pectin gels of higher MW (>3.7 × 10⁵), however, significantly higher concentrations of aromas in the headspace were shown in the gel with DE value of 6 than the gel with DE value of 40. Perceived flavour intensity was highest in the pectin gel with higher DE (∼40) and lower MW. The sensory texture analysis indicated that the pectin methyl esterase-modified pectin gels had increased hardness, coarseness of mass, springiness, and chewiness. The perceived flavour intensities of the gels showed strong negative correlations with firmness.     

茉莉酸甲酯和乙烯利处理对鲜切富士苹果抗氧化酶活力和苯丙烷代谢的影响

为研究外源信号分子茉莉酸甲酯(Me JA)和乙烯(Eth)对鲜切果蔬抗氧化酶活力和苯丙烷代谢的影响,以鲜切富士苹果为实验材料,利用Me JA和乙烯利浸泡处理,在10℃下贮藏,分析贮藏期间抗氧化酶类多酚氧化酶(PPO)、过氧化物酶(POD)和抗坏血酸过氧化物酶(APX)以及苯丙氨酸解氨酶(PAL)活性的变化。结果表明:与空白对照相比,Me JA和乙烯利可以显著提高鲜切富士苹果PPO和POD活性(p<0.05),降低APX活性下降速率。两种处理都可以提高PAL的活性,乙烯利对增强PAL活性效果更显著(p<0.05)。两种外源信号分子可以提高鲜切苹果的抗氧化能力及苯丙烷代谢能力,启动鲜切苹果的防御反应,提高果实抗性。      

Effect of CaCl2 on 2 heat-induced whey protein concentrate fibrillation pathways: Spontaneous and nuclear induction

Amyloid fibrils have many excellent functional properties that facilitate their applications in the food industry. There are 2 pathways for whey protein concentrate (WPC) to form amyloid fibril aggregates: spontaneous pathway and nuclear induction pathway. Low ionic strength is a necessary condition for the spontaneous pathway to proceed successfully. In this paper, the effect of salt ions on 2 WPC fibrillation pathways was investigated by adding CaCl₂. The results demonstrated WPC fibrils were unable to form normally through spontaneous pathway as adding CaCl₂; but still could form through nuclear induction pathway with 20 to 30 mM CaCl₂, the nuclei accelerated the fibrillation process led to the resistance to the disordered aggregation brought by CaCl₂. Moreover, divalent cations (Ca²⁺, Mg²⁺) had much stronger effects than monovalent cations (Na⁺) on fibril formation, and the results of X-ray photoelectron spectrum together with Fourier-transform infrared spectroscopy suggested that Ca²⁺ had a greater effect on the fibril formation than Cl^?.     

Combined effect of temperature and pulsed electric fields on pectin methyl esterase inactivation in red grapefruit juice (<Emphasis Type="Italic">Citrus paradisi</Emphasis>)

Pulsed electric fields (PEF) were applied to freshly prepared grapefruit juice using a laboratory scale continuous PEF system to study the feasibility of inactivating pectin methyl esterase (PME). Square wave PEF using different combinations of pre-treatment temperature, electric field strength and treatment time were evaluated in this study. Inactivation curves for the enzyme were plotted for each parameter and inactivation kinetics were calculated. Results showed that the highest level of inactivation (96.8%) was obtained using a combination of preheating to 50 °C, and a PEF treatment time of 100 μs at 40 kV/cm. Inactivation of grapefruit PME activity could be described using an exponential decay model. Calculated D-values following a 50 °C preheat were 77.5, 76.0 and 70.4 μs at 20, 30 and 40 kV/cm, respectively. The activation energy for the inactivation of PME by PEF was 36.2 kJ/mol.     

An evaluation of methyl 2-oxocyclopentanecarboxylate as an iron(III) trap: food perspectives

The 1,3‐ketoesters have great potential in the food industry, as they are suitable for trapping flavours because of their chelating effects. The results obtained for tautomerization rate constants, as a function of temperature, have allowed us to establish a fourth order enthalpic analytical equation of temperature, suggesting an overall entropic control of tautomerization. Iron, which is present as a trace element in foods and drinks, is of critical importance for the normal early growth and development of infants. The nutritional status of iron may affect the metabolism of other nutrients. In fact, iron chelates have significant beneficial effects in increasing iron bioavailability in human diets. As a result the abilities of methyl 2‐oxocyclopentanecarboxylate to chelate iron(III) in aqueous solutions was investigated. Thermodynamic and kinetic parameters associated with the double‐pathway mechanism of monochelate complexation have been determined and the advantages of kinetically and thermodynamically controlled processes are discussed.     

Effect of pH and NaCl/CaCl2 on the solubility and emulsifying properties of sweet potato protein

BACKGROUND: The effects of NaCl and CaCl₂ on the solubility and emulsifying properties, namely emulsifying activity index (EAI) and emulsion stability index (ESI) of sweet potato proteins (SPPs) at pH 1–10, were investigated. RESULTS: At lower NaCl (0.1 mol L^?1) and CaCl₂ (0.05 mol L^?1) concentrations, the solubility profiles of the SPPs were very similar to those in distilled water, and the lowest solubility occurred at pH 4. Increased NaCl and CaCl₂ concentration resulted in lower SPP solubility in most of the pH studied (P < 0.05). At pH < 3, NaCl improved the EAI of SPP while at pH > 7 it reduced the EAI of the SPP (P < 0.05). Moreover, addition of NaCl also resulted in reduction of ESI of the SPP in most of the pH studied (P < 0.05). On the other hand, the presence of 0.2 mol L^?1 CaCl₂ rendered the EAI and ESI of the SPPs independent of the influence of pH. CONCLUSION: The present studies show that pH and salts modified the emulsifying properties of the SPPs, and CaCl₂ at a certain concentration could be used to improve the emulsifying properties of the protein. Copyright © 2008 Society of Chemical Industry     

Effect of whey protein concentrate on phenolic profile and browning of fresh-cut lettuce (Lactuca Sativa)

The in vitro kinetics of lettuce PPO with respect to dissolved oxygen using catechin, chlorogenic acid, caffeic acid and gallic acid has been examined. In-vitro lettuce polyphenol oxidase (PPO) activity was determined by measuring the consumption of oxygen during the oxidation reaction. The effect of whey protein concentrate (WPC) was tested on the inhibition of lettuce PPO comparing with ascorbic acid (AA) and cysteine. A competitive model that considered inhibitors was the most appropriate model to explain reaction kinetics. Browning of lettuce was also monitored during storage for 24 h. Addition of WPC prevented loss of lightness in lettuce. Loss of identified phenolic compounds in lettuce was measured during the enzymatic browning process by high-performance liquid chromatography. Degradation of identified phenolic compounds followed first order kinetics during storage. Combination of WPC with cysteine was proposed for the protection of phenolics compounds against PPO-catalysed oxidation.     

CaCl2电解水处理提高绿豆芽品质及其机理

利用CaCl₂电解水(CaCl₂electrolyzedwater,CEW)浸泡绿豆后使其发芽,研究CEW对绿豆芽的保鲜效果及作用机制。结果表明,25 mmol/L CaCl₂浓度的电解水处理后,在贮藏5 d时,与对照组相比,其质量损失率降低,硬度和脆度约是对照组(自来水处理)的1.28倍,并且杀菌作用明显,绿豆芽表面微生物数量减少近一个对数值;低场核磁共振结果表明,绿豆芽水分状态有所改变,结合水含量增加;相对电导率、丙二醛含量和过氧化氢含量分别降低约16.5%、27.5%、36.8%,维持了细胞膜完整性,减少活性氧积累从而减轻膜脂过氧化程度。此外,CEW处理后绿豆芽贮藏期间的褐变现象得到抑制,机理与褐变底物总酚含量降低以及多酚氧化酶、过氧化物酶、苯丙氨酸解氨酶活力下降有关。由此可见,CEW处理可一定程度上延缓绿豆芽在贮藏过程中的品质劣变。     

Mechanism of interactions between Hg(II) and Demeton S: an NMR study

The chemical fate of organophosphorus pesticides (OPs) has been proven to depend strongly on the chemistry of their aquatic environment. In particular, metal ions (and metal oxide surfaces) have been known to play an important role in the hydrolytic fate of OPs. Various postulates regarding the mechanism of metal-ion-promoted hydrolysis of OPs have been made over the years. However, direct spectroscopic evidence to pinpoint the hydrolytic products and the exact interaction between metal ions and organophosphorus pesticides are still lacking. We report herein the first in-situ study of the interaction between an aqueous solution of Hg(II) and Demeton S using 1H- and 31P NMR spectroscopy. It was found that the interactions between Hg(II), a soft Lewis acid, and Demeton S tend to be a strong function of the aqueous speciation of Hg(II), and the bonding between Hg2+ and Demeton S does not involve the central P=O bond but rather Hg2+ bonds with the two sulfur atoms in the Demeton S side chain and subsequently stabilizes the Demeton S molecule, a phenomenon not previously reported for any metal ion-OP systems studied. On the basis of this study, generalizations regarding the nature of metal ion binding even within a given class of OPs (i.e., phosphorodithioates, phosphorothioates, phosphorothiolates, etc.) should be avoided or only made with extreme caution.