Development of a fluorescence sensor to monitor lipid oxidation. II. The kinetics of chitosan fluorescence formation after exposure to lipid oxidation volatiles

Chitosan was used as a basis for a fluorescence sensor to monitor volatile malonaldehyde production during lipid oxidation. The rate of chitosan fluorescence formation during exposure to volatiles generated during lipid oxidation depended on the extent of fluorescence formation to the one half power and had an activation energy of 13 kcal/mole. Three processes were involved in the fluorescence formation. The rate of volatile malonaldehyde generation during lipid oxidation depended on the extent of malonaldehyde formation to the one half power and had an activation energy of 14 kcal/mole. Malonaldehyde sorption on chitosan powder was immediate and independent of temperature. Chitosan fluorescence formation after exposure to volatile malonaldehyde proceeded at a constant rate and had an activation energy of 13 kcal/mole.     

FLOW PROPERTIES OF TOMATO CONCENTRATES

The flow properties of over seventy concentrates made from four cultivars of tomatoes were determined with a concentric cylinder viscometer. The apparent viscosity (100 s⁻¹, 25°C) of the concentrates of each variety was proportional to the 2.5 power of the concentration (% total solids). The apparent viscosity of the Nova cultivar obeyed the Arrhenius temperature relationship; the activation energy for the concentrates was 2.3 ± 0.3 kcal/mole. The simple power law and the Casson model described satisfactorily the flow data of the concentrates but the power law gave higher correlation coefficients. The Herschel-Bulkley model with the Casson yield stress was also satisfactory but the correlation coefficients were lower than for the simple power law. The consistency index of the power law model also showed a power dependence on the concentration. The natural logarithm of the yield stress and the concentration could be correlated by a quadratic equation.     

THE β-N-ACETYLGLUCOSAMINIDASE ACTIVITY OF EGG WHITE. 2. Heat Inactivation of the Enzyme in Egg White and Whole Egg

SUMMARY– The kinetics of the heat inactivation of β-N-acetylglucosaminidase in egg white and whole egg at neutral pH is first order in the temperature range 58–62°C. Rate constants for enzyme inactivation by heat are reported for both egg white and whole egg. The activation energy for heat denaturation is 91 kcal/mole in egg white and 73 kcal/mole in whole egg. Reduction of enzymatic activity upon heating can be used as an indication of whether egg white or whole egg has been maintained at the time-temperature combinations approved for pasteurization by the U.S. Department of Agriculture. This test should be useful as a process control tool.     

Heat and Fermentation Effects on Total Nonprotein Nitrogen and Urea in Milk

Kinetic analysis was applied to the increase of NPN and the decrease in urea when milk was heated at 80, 100 and 120°C. NPN increase with heat followed zero-order kinetics with an energy of activation of 17 kcal/mole. Urea losses with heating followed pseudo first-order kinetics with an energy of activation of 20 kcal/mole. Commercial yogurt and leben fermentation processes were used to determine the effects of fermentation on NPN and urea. Yogurt and leben fermentations increased NPN by 150 mg/kg and 208 mg/L, respectively, but had no effect on urea.     

KINETICS of THERMAL SOFTENING of WHITE BEANS EVALUATED BY A SENSORY PANEL and the FMC TENDEROMETER

The temperature dependence of the rate index of thermal softening of white beans ( Phaseolus vulgaris , subsp. nanus Metz. variety Manteca de Leon ) was determined within the temperature range of 90C to 122C using an industrial FMC tenderometer and a trained sensory panel. Based on sensorial results a first order reaction was assumed, whereas the tenderometer values were described by a biphasic model. Using a multiple linear regression analysis on the sensorial data, the activation energy for the heat induced firmness degradation of beans was calculated as 130.8 kJ/mole. Activation energies of both phases of the biphasic model were obtained by a two-step linear regression on the tenderometer data. Activation energies of both phases were equal, namely 105.1 kJ/mole.     

KINETICS OF HEAT COAGULATION OF EGG ALBUMIN DETERMINED BY WATER BINDING AND RHEOLOGICAL MEASUREMENTS

Dynamic testing of heat coagulated egg albumin revealed that phase angle, a measure of the fluidity of a viscoelastic material, exhibits a first order change during heating in a similar manner as the changes in the spin-lattice relaxation time (T1) of water protons measured by a pulsed nuclear magnetic resonance instrument. The absolute modulus, on the other hand, which is an index of the elastic properties exhibited a zero order change in a similar manner as the development of gel strength measured by constant rate penetrometry using an Instron universal testing instrument. Arrhenius activation energy of 29 kcal/mole for the phase angle and 38.9 kcal/mole for the absolute modulus indicate that the process of protein-water interaction to immobilize water within the gel and that of protein-protein interaction to form the solid gel network occur simultaneously during heating, but they proceed by different mechanisms with the latter process showing greater heat sensitivity.     

Interaction of Hydrochloric Acid with Cyclodextrin

The first order rate constant for the hydrochloric acid catalyzed hydrolysis of β-cyclodextrin increases during the reaction, because the α-1,14-bonds present in the macrocycle and in linear dextrins (formed by opening of the macrocycles) are split at different rates. The activation energy for hydrolysis of the glycosidic bond of maltose is 30,5 kcal/mole, while the opening of the cyclodextrin macroring is characterized with a value of 34,2 kcal/mole. At lower temperatures and higher HCl concentrations a rather stable crystalline HCl-cyclodextrin complex is formed with good yield. This complex contains 1,8 molecules of HCl per cyclodextrin unit. After storage at room temperature for one year it still retains 1 mole of HCl. Storing the product in sealed vials for one year leads to no change in the composition.     

Thermal Degradation of Texture in Apples

Thermal degradation of texture in Cortland and Spigold varieties of apples was studied using instrumental Texture Profile Analysis. The loss of hardness was modeled as a first order reaction and the activation energy was found to be 26.5 kcal/mole and 15.6 kcal/mole for Cortland and Spigold, respectively. The z value for the loss of hardness was found to be 24.8°C and 42.2°C, respectively, for Cortland and Spigold. The temperature of processing was found to significantly change hardness, cohesiveness, and chewiness in both the varieties. In the case of Spigold, time of processing was found to significantly affect hardness and cohesiveness. And in the case of Cortland, time of processing was found to significantly change hardness, springiness and chewiness.     

Flow Behavior and Gelatinization of Cowpea Flour and Starch Dispersions

The flow behavior of a 25% cowpea slurry with 8% oil held at 70°C showed shear-thinning behavior and an Arrhenius temperature relationship. Cowpea flour (8%) and starch (2.5%) slurries heated for less than 1 min at 70–87°C exhibited shear-thickening while those heated longer times exhibited shear-thinning behavior. Maximum viscosities attained due to heat-induced gelatinization showed a power relationship with temperature of heating. Starch gelatinization kinetics followed a first-order equation and the temperature dependence of the rate constant followed the Arrhenius relationship with an activation energy of about 47.4 kcal/mol. Heating the slurries for >200 min above 80°C resulted in loss of viscosity.     

KINETIC PARAMETERS FOR THERMAL INACTIVATION OF PLASMIN

Plasmin (EC 3.4.21.7) is the principal indigenous protease in bovine milk. Kinetic parameters for thermal degradation of plasmin were determined using a miniature continuous flow pasteurizer designed for heat treatment of small quantities of liquid. Plasmin activity was measured using a pH-stat titration, which measures the release of H ⁺ from a caseinate substrate.
Heating milk at various temperatures resulted in significant difference (P > 0.01) in residual plasmin activity and linear decrease in activity at each temperature. The calculated D-values were: 105, 90, 76.5, 62, and 47 s at 72, 78, 85, 92, and 100°C, respectively. The Z-value for plasmin inactivation was estimated to be 77.5°C, and the Arrhenius activation energy was 7.04 kcal/mole.
UHT milk containing plasmin was heated for an equivalent of 5 D inactivation of the enzyme at 100°C. After storage for 30 days at 4°C, no enzyme regeneration was observed.     

Degradation Kinetics of Chlorophyll in Peas as a Function of pH

The kinetics of chlorophyll degradation in pea puree were determined in a specially designed reactor with on‐line pH control capability. Without pH control, the pH of the pea puree decreased continuously with heating due to acid formation; the pH was maintained within ±0.1 of the desired value with on‐line pH control. Chlorophyll (both a and b) degradation followed the first‐order reaction model. The temperature dependence of the rate constant was adequately modeled by the Arrhenius equation. The activation energy was independent of pH and was 17.5 kcal/mol and 17 kcal/mol for chlorophyll a and chlorophyll b, respectively. The degradation rate constant decreased log‐linearly as the pH was increased. A mathematical model was developed to predict the chlorophyll concentrations as a function of time, temperature and pH.     

Effects of Heat Treatments on the Ethylene Forming Enzyme System in Papayas

Heat inactivation studies were conducted on the ethylene-forming enzyme system (EFE) in papayas. Heat inactivation of the papaya EFE was biphasic and both phases followed first order kinetics. The activation energies E, for the thermal inactivation of the heat resistant (HR) and the heat susceptible (HS) EFEs were 68.3 and 51.2 Kcal/ mole, respectively. The thermodynamic constants for the heat inactivation of both EFEs were; enthalapy, 5 1.2 kcal/mole for HS and 66.7 kcal/mole for HR; free energy, 22.5 kcal/mole for HS and 23.3 kcal/mole for HR; entropy, 87.2 cal/deg-mole for HS and 137.8 call degmole for HR. The heat resistant EFE appeared to compromise about 25% of the total EFE activity. Commercial heat treatments used for quarantine treatments affected mainly the heat susceptible portion which comprised the remaining 75% of the total EFE activity.     

Flow Properties of Low-Pulp Concentrated Orange Juice: Effect of Temperature and Concentration

Three 65° Brix low-pulp concentrated orange juice (COJ) samples, between −19 and 30°C were shear-thinning (pseudoplastic) fluids with negligible magnitudes of yield stress. The simple power law model fit welt the shear rate-shear stress data. For one sample, the Powell-Eyring model also described the data well. The Arrhenius model described the effect of temperature on the apparent viscosity and the consistency index of the power law model. The activation energy of flow (E_a) was 10.7 ± 0.2 kcal/g mole. The models of Harper and El Sahrigi and Christiansen and Craig were suitable for describing the combined effect of temperature and shear rate. The magnitude of E_a decreased with decrease in concentration. Apparent viscosity and K increased exponeitially with concentration.     

Kinetics of Folacin Destruction in Swiss Chard During Storage

The folacin activities in fresh Swiss chard leaves stored in open air at 4, 21, 35 and 40°C were determined by a microbiological assay using Lactobacillus casei. At 21°C the leaves were also stored in plastic bags and under moist conditions. Folacin was most stable when the vegetable was stored in plastic bags, followed by the moist condition, and least stable in open air at 21°C. The degradation of folacin in Swiss chard under all conditions followed firstorder kinetics. The temperature dependent folate degradation conformed to the Arrhenius equation and the activation energy was 24 kcal/mole.     

Degradation Kinetics of (−)-Epigallocatechin Gallate as a Function of pH and Dissolved Oxygen in a Liquid Model System

The degradation kinetics of (−)-epigallocatechin gallate (EGCG) as a function of pH (4 to 7) and dissolved oxygen concentration (0 to 7.59 mg/L) in citrate buffer solutions were determined. EGCG degradation followed a pseudofirst order kinetic model, regardless of the conditions when the fractional conversion technique was applied for data reductions. The rate constant increased log-linearly with respect to both pH and dissolved oxygen concentration. The temperature dependence of the rate constant was adequately modeled by the Arrhenius equation with an average activation energy of 18.7 ± 1 kcal/mol. A mathematical model that relates the rate constant to temperature, pH, and dissolved oxygen concentration was developed and validated. These results can help predict losses of EGCG during processing and/or storage.     

A kinetic study of the bisulphite reduction of methionine sulphoxide to methionine.

The rates of reduction of methionine sulphoxide to methionine by aqueous bisulphite solutions were measured by n.m.r. spectroscopy. The reaction was shown to follow overall second-order kinetics, being first-order with respect to methionine sulphoxide and first-order with respect to bisulphite anion. The reduction was shown to have a strong pH dependence, reaching a maximum rate at pH 2.9. The pH-rate profile has been related to the concentrations of bisulphite anion and protonated methionine sulphoxide and to the ionic state of methionine sulphoxide. A mechanism consistent with these results is proposed. An energy of activation of 14.1 kcal/mole was obtained for the reaction. These reductions are proposed to have important nutritional implications.     

Heat Inactivation of the Ethylene-Forming Enzyme System in Cucumbers

Heat inactivation of the ethylene-forming enzyme system (EFE) in cucumbers was biphasic and both phases followed first order kinetics. The activation energies for the thermal inactivation of the heat resistant (HR) and the heat susceptible (HS) EFE's were 77.67 and 68.92 kcal/ mole, respectively. The thermodynamic constants for the heat inactivation of both HS and HR are as follows: enthalauv. 68.27 (HS) and 77.03 (HR) kcal/mole; free energy; 21.2 (HS) and 22.9 (HR) kcal/mole; entropy, 146.1 (HS) and 168.2 (HR) cahdeg-mole. The heat resistant EFE appears to comprise 2535% of the total EFE activity     

Hydrolysis of Milk Fat with Lipase in Reversed Micelles

Enzymatic hydrolysis of milk fat was studied in a reversed-micelle system consisting of lecithin, water (1% total volume) and butteroil. Candida cylindracea lipase entrapped in the water pools of reversed micelles hydrolyzed surrounding triglycerides. The optimum temperature for enzyme activity was 55°C with an activation energy of 15.4 kcal/mole, while maximum enzyme activity was observed between pH 4 to 6. The molar ratio of water to surfactant (R value) in the system influenced enzyme activity with maximum activity at R = 10. Enzyme activity also increased with increasing surfactant or enzyme concentration.     

Thermal and pressure‐temperature denaturation kinetics of bacillus subtilis α‐amylase: A study based on gel electrophoresis

Abstract

The commercially available enzyme Bacillus subtilis α‐amylase was characterized by a molecular weight of about 55 kDa and contained isozymes with pI values ranging in a narrow zone (4.6–5.3). Furthermore, the sample was confirmed to contain no disulfide bonds. Upon thermal denaturation in the presence of sodium dodecyl sulfate, a band at half molecular weight was noticed, indicating that the native enzyme might be a dimeric form. Thermal as well as pressure‐temperature denaturation kinetics were investigated using gel electrophoresis and both could accurately be described by a first order kinetic model. For thermal denaturation an activation energy of 283 kJ/mole was calculated. As far as pressure‐temperature denaturation is concerned, activation energy and activation volume at a constant pressure of 5500 bar and a constant temperature of 40°C were calculated respectively as 77.6 kJ/mole and ‐23.2 cm³/mole. These values were compared with those for thermal and pressure‐temperature inactivation of Bacillus subtilis α‐amylase, as determined from residual enzyme activity measurements. No significant differences between the activation energy and volume characterizing denaturation and inactivation of Bacillus subtilis ct‐amylase were observed.     

光卤石分解制取KCl结晶过饱和度影响的研究

通过MSMPR结晶器系统对光卤石加水分解,采用不同的过饱和度进行氯化钾结晶动力学研究,建立了光卤石分解制取氯化钾结晶过程中氯化钾结晶动力学模型。探讨了氯化钾结晶过程中过饱和度对成核与生长速率的影响程度,为用光卤石生产氯化钾产品,提高其取得率及增大晶体粒度提供了理论依据。