蜂巢中多酚的提取动力学

采用二级速率法则模拟蜂巢多酚提取过程的动力学。采用Origin8.0软件中的功能模型来预测动力学参数起始提取速率(h)、总多酚的平衡浓度(Ce)和提取率常数(k),采用Arrhenius公式描述提取率常数(k)和提取温度(Ta)的关系,建立了用于预测在提取时间tmin时提取液中总多酚的浓度(Ct)随时间(t)变化的动力学模型。这些数学模型是合理和可信的,能够很好的拟合在不同提取时间下原料粒度、提取温度和液料比对多酚的提取过程,得到多酚的提取活化能为9.26kJ/mol。      

大米陈化过程中表面油脂变化特征初探

研究了糙米和精米在人工陈化过程中表面油脂的变化情况。结果表明:糙米和精米陈化过程中游离脂肪酸值的含量和增加速率不同,精米游离脂肪酸占总脂肪质量百分比比糙米要高且增幅也比糙米大;丙二醛含量检测后发现,精米的含量达到峰值时,其含量占总脂肪质量百分比比糙米高。在37℃和25℃下储藏后期丙二醛含量出现下降。精米丙二醛含量下降幅度也较糙米大。可见精米陈化过程中油脂过氧化程度比糙米大且对丙二醛的耐受性较差;对游离脂肪酸值变化进行动力学分析后显示,零级动力学模型能够很好地反应这个指标的变化趋势,并且陈化过程中脂肪酸值的增加随绝对温度的倒数的变化符合Arrhenius方程,糙米表面油脂发生水解反应的活化能要高于精米,可见糙米相比精米稳定性高。      

Sunflower Leaf Structure Affects Chlorophyll a Fluorescence Induction Kinetics In Vivo

Chlorophyll a fluorescence induction kinetics (CFI) is an important tool that reflects the photosynthetic function of leaves, but it remains unclear whether it is affected by leaf structure. Therefore, in this study, the leaf structure and CFI curves of sunflower and sorghum seedlings were analyzed. Results revealed that there was a significant difference between the structures of palisade and spongy tissues in sunflower leaves. Their CFI curves, measured on both the adaxial and abaxial sides, also differed significantly. However, the differences in the leaf structures and CFI curves between both sides of sorghum leaves were not significant. Further analysis revealed that the differences in the CFI curves between the adaxial and abaxial sides of sunflower leaves almost disappeared due to reduced incident light scattering and refraction in the leaf tissues; more importantly, changes in the CFI curves of the abaxial side were greater than the adaxial side. Compared to leaves grown under full sunlight, weak light led to decreased differences in the CFI curves between the adaxial and abaxial sides of sunflower leaves; of these, changes in the CFI curves and palisade tissue structure on the adaxial side were more obvious than on the abaxial side. Therefore, it appears that large differences in sunflower leaf structures may affect the shape of CFI curves. These findings lay a foundation for enhancing our understanding of CFI from a new perspective.     

DNA Penetration into a Lysozyme Layer at the Surface of Aqueous Solutions

The interactions of DNA with lysozyme in the surface layer were studied by performing infrared reflection–absorption spectroscopy (IRRAS), ellipsometry, surface tensiometry, surface dilational rheology, and atomic force microscopy (AFM). A concentrated DNA solution was injected into an aqueous subphase underneath a spread lysozyme layer. While the optical properties of the surface layer changed fast after DNA injection, the dynamic dilational surface elasticity almost did not change, thereby indicating no continuous network formation of DNA/lysozyme complexes, unlike the case of DNA interactions with a monolayer of a cationic synthetic polyelectrolyte. A relatively fast increase in optical signals after a DNA injection under a lysozyme layer indicates that DNA penetration is controlled by diffusion. At low surface pressures, the AFM images show the formation of long strands in the surface layer. Increased surface compression does not lead to the formation of a network of DNA/lysozyme aggregates as in the case of a mixed layer of DNA and synthetic polyelectrolytes, but to the appearance of some folds and ridges in the layer. The formation of more disordered aggregates is presumably a consequence of weaker interactions of lysozyme with duplex DNA and the stabilization, at the same time, of loops of unpaired nucleotides at high local lysozyme concentrations in the surface layer.     

Investigation on Purification of Saturated LiNO3 Solution Using Titanium Phosphate Ion Exchanger: Kinetics Study

Lithium compounds are of high interest to many industries. The presence of undesirable impurities in Li precursors leads to uncontrolled change in the functional properties of final compounds. Therefore, the development of reliable methods for lithium salt purification is considered a key factor for their application in various industries. This work focuses on the application of a titanium phosphate ion exchanger (Li-TiOP) toward Cu²⁺, Co²⁺, Mn²⁺, Ni²⁺, and Cr³⁺ ions in the purification of a saturated LiNO₃ solution. The sorption kinetics of the selected ions, considering external and internal mass transfer, as well as chemical interaction, were deeply studied. The kinetic study showed that the values of intraparticle diffusion rate and effective diffusion coefficients for the studied ions decreased in the following order: Cr(III) ˃ Cu(II) Mn(II) ˃ Co(II) ˃ Ni(II). For all the selected ions, chemical interaction was described with a pseudo-second-order reaction model. The sorption kinetics were controlled by the size of the solvated metal ion, its effective charge, the electronic structure of the adsorbed ion, and the interaction with the functional groups of the sorbent. Due to fast kinetics, the high degree of removal of trace quantities of the impurities this material gives it consideration as a promising sorbent for the deep purification of lithium salts.     

Biochemical Characterization of Pyranose Oxidase from Streptomyces canus—Towards a Better Understanding of Pyranose Oxidase Homologues in Bacteria

Pyranose oxidase (POx, glucose 2-oxidase; EC 1.1.3.10, pyranose:oxygen 2-oxidoreductase) is an FAD-dependent oxidoreductase and a member of the auxiliary activity (AA) enzymes (subfamily AA3_4) in the CAZy database. Despite the general interest in fungal POxs, only a few bacterial POxs have been studied so far. Here, we report the biochemical characterization of a POx from Streptomyces canus (ScPOx), the sequence of which is positioned in a separate, hitherto unexplored clade of the POx phylogenetic tree. Kinetic analyses revealed that ScPOx uses monosaccharide sugars (such as d-glucose, d-xylose, d-galactose) as its electron-donor substrates, albeit with low catalytic efficiencies. Interestingly, various C- and O-glycosides (such as puerarin) were oxidized by ScPOx as well. Some of these glycosides are characteristic substrates for the recently described FAD-dependent C-glycoside 3-oxidase from Microbacterium trichothecenolyticum. Here, we show that FAD-dependent C-glycoside 3-oxidases and pyranose oxidases are enzymes belonging to the same sequence space.     

High Monocyte Count Associated with Human Cytomegalovirus Replication In Vivo and Glucocorticoid Therapy May Be a Hallmark of Disease

Cytomegalovirus (CMV) syndrome and infectious disease are defined as pathogen detection with appropriate clinical symptoms, but there are not pathognomonic signs of CMV disease. Although the prodrome of acute minor viral infections leukopenia (lymphopenia and neutropenia) is noted with onset of fever, followed by monocytosis, the role of monocytosis in CMV disease has not been described. Furthermore, under influence of corticosteroid therapy, CMV reactivation and monocytosis are described, but without a strict relationship with steroids dose. In the study, the monocyte level was investigated during the CMV infectious process. Regrettably, a non-selected group of 160 patients with high CMV viremia showed high dispersion of monocyte level and comparable with the median value for healthy subjects. Therefore, we investigated monocyte level in CMV-infected patients in relation to the logarithmic phase of the infectious process. Samples from patients with active CMV replication (exponential growth of CMV viremia) were tested. Significant monocytosis (above 1200/µL) during the logarithmic phase of CMV infection (with exponent between 3.23 and 5.77) was observed. Increased count and percentage of monocytes correlated with viral replication in several clinical situations except when there was a rapid recovery without relapse. Furthermore, glucocorticoids equivalent to 10 and 20 mg of dexamethasone during a 2–3-week period caused monocytosis—significant increase (to 1604 and 2214/µL, respectively). Conclusion: In light of the logarithmic increase of viral load, high monocytosis is a hallmark of CMV replication. In the COVID-19 era, presence of high virus level, especially part of virome (CMV) in the molecular technique, is not sufficient for the definition of either proven or probable CMV replication at any site. These preliminary observations merit additional studies to establish whether this clinical response is mediated by monocyte production or by decrease of differentiation to macrophages.     

Property and Stability of Astaxanthin Emulsion Based on Pickering Emulsion Templating with Zein and Sodium Alginate as Stabilizer

Astaxanthin loaded Pickering emulsion with zein/sodium alginate (SA) as a stabilizer (named as APEs) was developed, and its structure and stability were characterized. The encapsulation efficiency of astaxanthin (Asta) in APEs was up to 86.7 ± 3.8%, with a mean particle size of 4.763 μm. Freeze-dried APEs showed particles stacked together under scanning electronic microscope; whereas dispersed spherical nanoparticles were observed in APEs dilution under transmission electron microscope images. Confocal laser scanning microscope images indicated that zein particles loaded with Asta were aggregated with SA coating. X-ray diffraction patterns and Fourier transform infrared spectra results showed that intermolecular hydrogen bonding, electrostatic attraction and hydrophobic effect were involved in APEs formation. APEs demonstrated non-Newtonian shear-thinning behavior and fit well to the Cross model. Compared to bare Asta extract, APEs maintained high Asta retention and antioxidant activity when heated from 50 to 10 °C. APEs showed different stability at pH (3.0–11.0) and Na⁺, K⁺, Ca²⁺, Cu²⁺ and Fe²⁺ conditions by visual, zeta potential and polydispersity index measurements. Additionally, the first order kinetics fit well to describe APEs degradation at pH 3.0 to 9.0, Na⁺, and K⁺ conditions. Our results suggest the potential application of Asta-loaded Pickering emulsion in food systems as a fortified additive.     

不同大豆原料形成蛋白纤维聚合物的比较

4种通过不同加工处理得到的大豆蛋白,在低pH条件下90℃加热10h所形成的聚合物形态存在很大不同。利用硫磺素T（Th T）荧光强度、差量扫描仪（DSC）和SDS-PAGE凝胶电泳分析了来自不同原料大豆蛋白的聚合动力学和组成差异。结果表明,4种大豆原料因其加工工艺不同,蛋白质组成存在差异,在本实验的条件下,11S的存在尤其是碱性亚基会抑制纤维聚合物的形成。此外,离子强度也是纤维形成的一个必要条件。      

含硅聚氨酯的制备及其动力学研究

以3-氨基丙基三乙氧基硅烷（KH550）、丙烯酸羟乙酯（HEA）、2,4-甲苯二异氰酸酯、对甲酚为原料,制备含硅聚氨酯。用红外光谱对反应合成过程进行跟踪测定,发现端-NCO的聚氨酯预聚物和对甲基苯酚的封端反应在无催化剂条件下为二级反应,当加入催化剂三乙胺后该反应在发生初期为一级反应。无催化剂条件下该反应的活化能为46.96 kJ/mol,催化剂加入量为0.1%时反应的活化能为30.28 kJ/mol,催化剂加入量为0.3%时反应的活化能为18.16 kJ/mol,反应的活化能随催化剂加入量的增加而降低。