PRODUCT INHIBITION OF WHEY LACTOSE HYDROLYSIS

In the present study, glucose and galactose inhibition effects for β-galactosidase hydrolyzing lactose recovered from whey were investigated. The experiments were carried out in 250 mL of 25 mM phosphate buffer solution containing 1, 1.5, 2, 4, and 6% (w/v) lactose recovered from whey by using a commercial β-galactosidase produced from Kluyveromyces marxianus lactis at a constant temperature of 37°C, pH 6.5, and enzyme concentration of 1 mL/L, in a batch reactor system. The amounts of glucose and galactose added to the reaction solution were 6.25, 12.5, and 25 g/L. A second-order kinetic expression effectively simulated the data of residual lactose concentration with respect to processing time for each experimental condition examined. The Lineweaver-Burk plots showed that the inhibition effects of glucose and galactose were uncompetitive. The inhibition constants (K_i) obtained for glucose and galactose (10.32 g/L and 13.03 g/L, respectively) showed that the glucose was the most effective inhibitor for β-galactosidase.     

EFFECT OF IMPELLER SPEED AND VISCOSITY ON WHEY LACTOSE HYDROLYSIS AND β-GALACTOSIDASE STABILITY

In the present work, the effects of impeller speed and viscosity on the enzymatic hydrolysis of whey lactose and enzyme inactivation were studied. The experiments were carried out in 250 mL of 25 mM phosphate buffer solution containing 50 g/L whey lactose by using a commercial β-galactosidase produced from Kluyveromyces marxianus in a batch reactor system. The degree of lactose hydrolysis (%) and residual enzyme activity (%) was investigated versus impeller speeds from 100 to 600 rpm and viscosities from 1.005 to 13.43 cp for 30 minutes of processing time. The mathematical models depending on these process parameters were derived using the experimental data of residual lactose concentration and residual β-galactosidase activity. The predicted models have been confirmed with the experimental results.     

EFFECT OF IMPELLER SPEED AND VISCOSITY ON WHEY LACTOSE HYDROLYSIS AND β-GALACTOSIDASE STABILITY

In the present work, the effects of impeller speed and viscosity on the enzymatic hydrolysis of whey lactose and enzyme inactivation were studied. The experiments were carried out in 250 mL of 25 mM phosphate buffer solution containing 50 g/L whey lactose by using a commercial β-galactosidase produced from Kluyveromyces marxianus in a batch reactor system. The degree of lactose hydrolysis (%) and residual enzyme activity (%) was investigated versus impeller speeds from 100 to 600 rpm and viscosities from 1.005 to 13.43 cp for 30 minutes of processing time. The mathematical models depending on these process parameters were derived using the experimental data of residual lactose concentration and residual β-galactosidase activity. The predicted models have been confirmed with the experimental results.     

A MODELING STUDY ON HYDROLYSIS OF LACTOSE RECOVERED FROM WHEY AND β-GALACTOSIDASE STABILITY UNDER SONIC TREATMENT

In the present study, the aim was to investigate the effect of ultrasonication on the kinetics of hydrolysis of lactose recovered from whey. The effects of the duty cycle, acoustic power of sonifier, reaction volume, and the hydrolysis products on hydrolysis degree as well as on enzyme stability were studied. The hydrolysis reactions were carried out in 25 mM phosphate buffer solution by using a commercial β-galactosidase produced from Kluyveromyces marxianus lactis under the conditions of 37°C, pH 6.5, and processing time of 30 min. Under ultrasonic treatment, 92% of lactose charged was hydrolyzed and the residual enzyme activity was 77% under the optimum operational conditions: acoustic power of 20 W, duty cycle rate of 10%, and reaction volume of 250 mL. The corresponding values of hydrolysis degree and residual enzyme activity without ultrasonic irradiation were 81% and 68%, respectively. These results show that sonication was beneficial for hydrolysis of lactose recovered from whey. The mathematical models were derived by using the experimental data of residual lactose concentration and residual enzyme activity depending on the operating conditions. In addition, an exponential equation was used for reflecting the ultrasonic energy regarding the hydrolysis and enzyme inactivation. After evaluation of the data, the activation energy required for hydrolysis of lactose recovered from whey (E _H ) and the inactivation energy for β-galactosidase enzyme (E _D ) were found as 0.0489 and 0.0804 J mL^?1, respectively.     

FLAVOR ENCAPSULATION AND RELEASE CHARACTERISTICS OF SPRAY-DRIED POWDER BY THE BLENDED ENCAPSULANT OF CYCLODEXTRIN AND GUM ARABIC

The flavor inclusion powder was prepared by spray drying, using the combined encapsulation method of inclusion by β-cyclodextrin (β-CD) and emulsified by gum arabic (GA). d-Limonene and ethyl n-hexanoate were used as model flavors. The application of high pressure by Microfluidizer to the mixture of flavors and β-CD slurry was an effective means of forming inclusion complex. Flavor retention during spray drying under various compositions of the encapsulants was investigated. The flavor retention using the blended encapsulant was increased by adding GA in the encapsulant. The characteristics of release of encapsulated flavor during storage were evaluated at 50°C and 75% of relative humidity. The release rate of flavor in spray-dried powder depended on kinds of the flavors and composition of the encapsulant. The blending MD and β-CD in the feed liquid decreased the release rate of flavors. The rate of release of flavor was analyzed by Avrami's Equation.     

THE EFFECT OF TEMPERING-INTERMITTENT DRYING ON QUALITY AND ENERGY OF PLANT MATERIALS

Squash slices were dried in a laboratory scale vibro-fluidized bed in batch operation. The optimal drying condition and degradation mechanism of β-carotene was investigated. A mathematical model was established to simulate and predict the quality protection. The changes of other tissue parameters, such as appearance and rehydration ability of the dried product, were analyzed and discussed. Tempering-intermittent drying is proved to reduce degradation of β-carotene, shorten drying time, and reduce energy consumption.     

REACTOR MODELING OF AN INNOVATIVE LIQUID-SOLID CIRCULATING MOVING BED FOR THE SYNTHESIS OF LINEAR ALKYL BENZENES

The circulating moving bed is an innovative coupled reactor for producing linear alkyl benzenes. It can be used with shorter life span catalysts compared to traditional fixed bed reactors. A model is developed in which the effect of catalyst deactivation on the reaction is simulated using infinitesimal balance equations. The results of step changes between steady states and unsteady states have been calculated with the model.     

HYDROLYSIS OF ETHYL-2-BROMOISOBUTYRATE ESTER IN AN ALKALINE SOLUTION

The hydrolysis of ethyl-2-bromoisobutyrate in an alkaline solution/organic solvent two-phase medium as well as the effect of quaternary ammonium salt (e.g., tetrabutylammonium bromide) on the hydrolysis of ethyl-2-bromoisobutyrate were investigated in this work. The proposed mechanism for the hydrolysis of ethyl-2-bromoisobutyrate was verified based on experimental analysis. Both the bromo-alkyl (Br-C bond) and ester (-COOR) functional groups of ethyl-2-bromo-isobutyrate hydrolyze into alcohol and acid. Several reaction steps for the hydrolysis of these bromo-alkyl and ester functional groups were developed and discussed. A kinetic model of each reaction step was developed in which the rate expression was derived. The intrinsic rate constants of the reactions were determined from the experimental hydrolyzing data of ethyl-2-bromoisobutyrate using curving fitting. The effects of the reaction conditions on the conversion of reactants were investigated in detail. The results indicated that the conversion of reactants is highly dependent on the concentration of alkaline compound in the aqueous solution. An optimum value of alkaline concentration to produce a maximum conversion of reactant was obtained. Moreover, the conditions for reducing the hydrolysis of halo ester by adding sodium carbonate are recommended.     

HYDROLYSIS OF ETHYL-2-BROMOISOBUTYRATE ESTER IN AN ALKALINE SOLUTION

The hydrolysis of ethyl-2-bromoisobutyrate in an alkaline solution/organic solvent two-phase medium as well as the effect of quaternary ammonium salt (e.g., tetrabutylammonium bromide) on the hydrolysis of ethyl-2-bromoisobutyrate were investigated in this work. The proposed mechanism for the hydrolysis of ethyl-2-bromoisobutyrate was verified based on experimental analysis. Both the bromo-alkyl (Br-C bond) and ester (-COOR) functional groups of ethyl-2-bromo-isobutyrate hydrolyze into alcohol and acid. Several reaction steps for the hydrolysis of these bromo-alkyl and ester functional groups were developed and discussed. A kinetic model of each reaction step was developed in which the rate expression was derived. The intrinsic rate constants of the reactions were determined from the experimental hydrolyzing data of ethyl-2-bromoisobutyrate using curving fitting. The effects of the reaction conditions on the conversion of reactants were investigated in detail. The results indicated that the conversion of reactants is highly dependent on the concentration of alkaline compound in the aqueous solution. An optimum value of alkaline concentration to produce a maximum conversion of reactant was obtained. Moreover, the conditions for reducing the hydrolysis of halo ester by adding sodium carbonate are recommended.     

PREDICTION OF EQUILIBRIUM PHASE COMPOSITIONS AND β-GLUCOSIDASE PARTITION COEFFICIENT IN AQUEOUS TWO-PHASE SYSTEMS

Artificial neural networks (ANN) and Flory-Huggins (F-H)-type models were implemented to simulate the binodal curve of an aqueous two-phase, system (ATPS) composed of poly(ethylene glycol), potassium phosphate, and water. The ANN model outperformed the F-H model in predicting the equilibrium compositions of the PEG-rich phase (average percent deviation: 10.0 versus 56.6). However, the estimation of interaction parameters was feasible only in the thermodynamic framework. Beta-glucosidase was introduced into the system under various temperature (25°-50°C) and pH conditions (6.5-8.0). The β-glucosidase partition coefficient increased with the temperature and pH over a range of 0.11-1.18. The network was better suited to predict the partitioning behavior of the enzyme because of the increased number of interaction parameters. The artificial intelligence-guided approach for isolating the enzyme has the potential to reduce costs, improve performance, and identify the most favorable purification conditions.     

ALKYLATION OF BENZENE USING BATCH AND CONTINUOUS FIXED-BED REACTORS

Alkylation reactions of benzene with propylene using heterogeneous catalysts H⁺-β zeolite, MCM-22, and ZSM-5 were studied for their affinity for cumene production. This work focused on the gas-phase reaction using different crystalline catalysts at several temperatures and amounts of reactants using both batch and continuous fixed-bed reactors. The properties of baseline commercial H⁺-β catalysts versus versions modified with Ga, La, and Pt were studied. Quantitative analysis of product mixture was performed by gas chromatography. For the batch reactor, β-zeolite produced the highest cumene yield and selectivity of 72% and 92%, respectively, at 225°C. At this temperature, a benzene:propylene dilution of 7:1 molar ratio was the optimum. For the continuous system, cumene production is favored at lower space velocities, higher benzene-to-propylene ratio, and temperatures close to 225°C. Ga modification of the H⁺-β zeolite significantly enhanced cumene yield in the continuous fixed-bed reactor at 225°C, from 27% of the unmodified β-zeolite to 36% for the Ga-modified one. The life span of modified β-catalysts was studied in the fixed-bed reactor for the first eight hours of reaction.     

THE BULK AND SURFACE STRUCTURE OF γ-ALUMINA

Despite its widespread use, the composition and structure of γ-alumina have been the subject of controversy for decades. In this article we review the historical attempts to resolve two principal questions that have each been extensively debated, but in independent communities: (1) What is the distribution of vacancies over the two cation sublattices in the nominal spinel structure, and (2) what is the hydrogen content of γ-alumina, if any? We then review how recent investigations have shown that these two questions are, in fact, related, and have a single resolution. The experimental study of γ-alumina surfaces has long been dominated by IR spectroscopy of the hydroxylated surfaces, and ²⁷AI NMR. Both techniques have produced perplexing results. Here we review the development of these surface studies and parallel computational studies. Finally, we review recent computational results that explain the puzzling experimental findings.     

Linking mechanical properties of silanes to their chemical structure: an analytical study of γ-GPS solutions and films

The effects of hydrolysis and condensation processes on the molecular structure of γ-glycidoxypropyltrimethoxysilane (γ-GPS) in aqueous solutions were investigated using Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy. Hydrolysis was characterized by monitoring the production of methanol and the decrease in concentration of SiOCH₃ groups in 1% solutions of deuterium oxide using proton NMR. Hydrolysis was found to be a very rapid process, whose rate could be increased or decreased by altering the pH of the solution. NMR spectroscopy showed that hydrolysis was completed in a 1% γ-GPS solution in deuterium oxide after 34 minutes. Condensation, on the other hand, took a relatively long time to occur. In the NMR spectra, condensation was observed by the broadening of peaks due to the protons on the carbon atom adjacent to the silicon atom. In addition to proton NMR, Si-29 NMR was used to characterize the siliane in 10% solutions of γ-GPS in water. The Si-29 NMR showed oligomer growth with respect to time . The oligomer growth was correlated to mechanical test results. Infrared spectroscopy was used to characterized the structure of the γ-GPS as a deposited film on aluminium during drying cycles at elevated temperature. The drying cycles caused increased oligomerization in the silane network and oxidation of the epoxide groups in the film.     

Effect of β,β-Dimethylacrylshikonin on Inhibition of Human Colorectal Cancer Cell Growth in Vitro and in Vivo

In traditional Chinese medicine, shikonin and its derivatives, has been used in East Asia for several years for the prevention and treatment of several diseases, including cancer. We previously identified that β,β-dimethylacrylshikonin (DA) could inhibit hepatocellular carcinoma growth. In the present study, we investigated the inhibitory effects of DA on human colorectal cancer (CRC) cell line HCT-116 in vitro and in vivo. A viability assay showed that DA could inhibit tumor cell growth in a time- and dose-dependent manner. Flow cytometry showed that DA blocks the cell cycle at G(0)/G(1) phase. Western blotting results demonstrated that the induction of apoptosis by DA correlated with the induction of pro-apoptotic proteins Bax, and Bid, and a decrease in the expression of anti-apoptotic proteins Bcl-2 and Bcl-xl. Furthermore, treatment of HCT-116 bearing nude mice with DA significantly retarded the growth of xenografts. Consistent with the results in vitro, the DA-mediated suppression of HCT-116 xenografts correlated with Bax and Bcl-2. Taken together, these results suggest that DA could be a novel and promising approach to the treatment of CRC.     

Understanding Hydrolysis and Condensation Kinetics of γ-Glycidoxypropyltrimethoxysilane

Monitoring the kinetics of hydrolysis and condensation of γ-glycidoxypropyltrimethoxy-silane (γ-GPS) was carried out by NMR spectroscopy (²⁹Si-, ¹³C-, and ¹H-). The course of these reactions was followed in 2 wt% aqueous dilution conditions (26% D₂O/74% H₂O), pH 5.4, and temperatures of 26, 50, and 70°C. At ambient temperature, hydrolysis and condensation proceed at very different time scales: a few hours for the hydrolysis versus several weeks for the condensation. Distortionless Enhancement by Polarization Transfer (DEPT) sequences by ²⁹Si- and ¹³C-NMR spectroscopy were optimized for determining the complete spectral assignment for each hydrolysis step, i.e., RSi(OMe)_3-n(OH)_n (with R = (CH₂OCH)CH₂OCH₂CH₂CH₂-;andn = 1, 2, 3). A pseudo-first order rate constant for the first hydrolysis step, T0^(OMe)3 + H₂O → T0^(OMe)2OH + MeOH, was calculated to be 0.026 min^-1. Simultaneously to the condensation reactions, we have observed epoxy ring opening of the glycidyl- group. All three processes (hydrolysis, condensation, and epoxy ring opening) are dramatically accelerated with temperature increases from 26 to 70°C. The activation energy of the epoxy ring opening leading to the formation of a diol structure at the extremity of the glycidoxypropyl- chain was estimated to be 68.4 kJ/mol.     

Synthesis of bulk and alumina-supported γ-Mo2N catalysts by a single-step complex decomposition method

A single-step complex decomposition method for the synthesis of bulk and alumina-supported γ-Mo₂N catalysts is described. The complex precursor (HMT)₂(NH₄)₄Mo₇O₂₄·2H₂O (HMT: hexamethylenetetramine) is converted to γ-Mo₂N under a flow of Ar in a temperature range of 823–1023 K. Furthermore, decomposition of the precursor in a NH₃ flow forms γ-Mo₂N in a temperature range of 723–923 K. Compared with direct decomposition of the precursor in Ar, the reaction in NH₃ shows obvious advantages that the nitride forms at a lower temperature. In addition, alumina-supported γ-Mo₂N catalysts with different nitride loadings can be prepared from the alumina-supported complex precursor in the Ar or NH₃ flow. The resultant catalysts exhibit good dibenzothiophene HDS activities, which are similar to the γ-Mo₂N/γ-Al₂O₃ prepared by traditional TPR method. The catalyst prepared by decomposition in an Ar flow exhibits highest activity. It proves that such a single-step complex decomposition method possesses the potential to be a general route for the preparation of molybdenum nitride catalysts.     

Effect of Processing Variables on the Solution Characteristics of γ-Glycidoxypropyltrimethoxysilane (γ-GPS)

The effects of the hydrolysis and condensation processes on the molecular structure of γ-glycidoxypropyltrimethoxysilane (γ-GPS) in aqueous solutions were investigated using Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy and FT-Raman spectroscopy. Hydrolysis was characterized by monitoring the production of methanol and the decrease in concentration of SiOCH₃ groups in 1% solutions of deuterium oxide using proton NMR. The production of methanol and loss of methoxy groups in 25% solutions of γ-GPS in water was characterized using Raman spectroscopy. Hydrolysis was found to be a very rapid process, whose rate could be increased or decreased by altering the pH of the solution. NMR spectroscopy showed that hydrolysis was complete in a 1% γ-GPS solution in deuterium oxide after 34 minutes. Raman spectroscopy also showed hydrolysis to be rapid and complete in a 25% solution of γ-GPS in water after 1 hour. Condensation, on the other hand, took a relatively long time to occur. In the NMR spectra, condensation was observed by the broadening of peaks due to the protons on the carbon atom adjacent to the silicon atom. In the Raman spectra, condensation was characterized by the disappearance of the SiOH band near 725 cm^-1 and the development of an SiOSi band near 600 cm^-1. In addition to the proton NMR, Si-29 NMR was used to characterize the silane in 10% solutions of γ-GPS in water. The Si-29 NMR showed oligomer growth with respect to time. The oligomer growth was correlated with mechanical test results.     

SCALE-UP OF HOLLOW FIBER REACTOR SYSTEMS

Hollow fiber reactors have been developed for many biochemical and biomedical applications. In the study of these reactor systems, we have used single fiber reactors as a prototype for the larger hollow fiber cartridges. Experiments using single fibers have been conducted to obtain conversion data for reactor scale-up. We present a model for predicting conversions in bench-scale hollow fiber cartridges using these single fiber data. The model is compared to experimental conversion data and is shown to be a valuable design tool.     

Evaluation of β-diketone-containing Polymeric Coupling Agents for Enhancing the Adhesion of Epoxy to Aluminum

β-diketone-containing polymeric coupling agents (PCA) were evaluated as potential adhesion enhancers for an epoxy/aluminum bond system. Torsional shear joint measurements revealed that the β-diketone-containing PCA did not influence the joint strength and durability, positively or negatively, as compared with untreated controls. Grazing angle infrared spectroscopy revealed that despite reactivity of the β-diketone-containing monomer with aluminum substrates, no reactivity of the β-diketone was observed once the monomer was incorporated into the polymer. Deposition studies showed that the resulting PCA coating thickness following treatment and solvent rinsing was not a function of solvent solubility parameter, solution concentration, or immersion time. It was hypothesized that preferential physisorption of the phenyl and/or epoxy functionalities in the PCA inhibited reactivity of the β-diketone functionality.