Mathematical modelling of the osmotic dehydration of cherry tomato (Lycopersicon esculentum var. cerasiforme)

Osmotic dehydration of cherry tomato as influenced by osmotic agent (sodium chloride and a mixed sodium chloride and sucrose solutions) and solution concentration (10 and 25% w/w) at room temperature (25°C) was studied. Kinetics of water loss and solids uptake were determined by a two parameter model, based on Fick's second law and applied to spherical geometry. The water apparent diffusivity coefficients obtained ranged from 2.17x10-10 to 11.69x10-10 m²/s.

Determination of pectin methylesterase activity in commercial pectinases and study of the inactivation kinetics through two potentiometric procedures

Pectinases are enzymes that degrade pectic substances and are widely used in juice and fruit beverages to improve the quality of the process. The objective of this study was to determine the optimum pH and temperature of two samples of commercial pectinases and propose an alternative procedure to determine the residual activity comparing the data with those of the traditional procedure. The pectin methylesterase (PME) activity in Pectinex 100 L Plus and Panzyn Clears was determined by potentiometry. The reaction consisted of 5.00 mg.mL-1 apple pectin, 0.100 mol.L-1 NaCl, and 50 µL enzyme to a total volume of 30 mL. The pectin reaction in the presence of PME in all experiments revealed a first order kinetics. The PME in the two enzyme preparations showed higher activity at pH 4.0 to 4.5 and temperature of 45 ºC. From the results of both procedures ΔV NaOH/Δt and ΔpH/Δt, it was concluded that the inactivation of PME occurred at 75 ºC. The results obtained from the ratio ΔpH/Δt showed good correlation with those obtained from the ratio ΔV NaOH/Δt. In the reaction accompanied by the ratio ΔpH/Δt, the release of H3O+ occurred in the real time reaction.

Modeling the water uptake by chicken carcasses during cooling by immersion

In this study, water uptake by poultry carcasses during cooling by water immersion was modeled using artificial neural networks. Data from twenty-five independent variables and the final mass of the carcass were collected in an industrial plant to train and validate the model. Different network structures with one hidden layer were tested, and the Downhill Simplex method was used to optimize the synaptic weights. In order to accelerate the optimization calculus, Principal Component Analysis (PCA) was used to preprocess the input data. The obtained results were: i) PCA reduced the number of input variables from twenty-five to ten; ii) the neural network structure 4-6-1 was the one with the best result; iii) PCA gave the following order of importance: parameters of mass transfer, heat transfer, and initial characteristics of the carcass. The main contributions of this work were to provide an accurate model for predicting the final content of water in the carcasses and a better understanding of the variables involved.

Color degradation kinetics in low-calorie strawberry and guava jellies

The purpose of this study was to follow-up color changes in low-calorie strawberry and guava jellies during storage. To this end, one formulation of each flavor was prepared varying the application of hydrocolloids (pectin and modified starch). The jellies were studied regarding pH, soluble solids, water activity and syneresis. In order to follow-up color changes, the samples remained stored for 180 days in chambers with controlled temperatures of 10 °C (control) and 25 °C (commercial), and color instrumental analyses (L*, a*, and b*) were performed every 30 days. Arrhenius model was applied to reaction speeds (k) at different temperatures, where light strawberry and guava jellies showed greater color changes when stored at 25 °C compared to the samples stored at 10 °C. Activation energy values between 13 and 15 kcal.mol-1 and Q10 values between 2.1 and 2.3 were obtained for light strawberry jelly and light guava jelly, respectively. Therefore, it was concluded that, with respect to color changes, every 10 °C temperature increase reduces light jellies shelf-life by half.

Acid and salt uptake during the marinatig process of Engraulis anchoita fillets influence of the solution: fish ratio and agitation

The aims of this research were to determine the effect of different conditions of the marination stage on the salt and acid uptake, immersion time, and sensorial characteristics during the marinating process of anchovy (Engraulis anchoita). Different solution:fish ratios and the agitation effect during this stage were analyzed. The ratios used were: 0.77:1, 3:1 and 10:1 (with and without agitation). An increase of marinating solution:fish ratio causes a higher speed of acid and salt penetration The product obtained with the 10:1 ratio had a dry and fibrous texture and a slightly salty taste. Salt concentration was statistically significantly lower (p < 0.01) in the samples with agitation. Agitation did not influence the acid uptake, and the salt penetration speed decreased, but rancidity was detected in this product. The ratio 3:1 decreases the marinating time without damaging sensory attributes and can be used in the fish marinating process.

The kinetics of lipase activity and hydrolytic rancidity of raw, parboiled, and extruded rice bran during storage

The main problem related to rice bran use is that it goes rancid right after its production. The objective of the present study was to apply a mathematical model to evaluate the kinetics of the lipase activity and hydrolytic rancidity of the raw rice bran (RRB), extruded rice bran (ERB), and parboiled rice bran (PRB) stored in low density polyethylene bags at room temperature for 180 days. Extrusion and parboiling were efficient in preventing free fatty acid formationin ERB and PRB.Extrusion reduced the velocity constant of lipase activity as compared to that of RRB while parboiling increased it, and both decreased the lipase activity after equilibrium from 150 days. The extrusion and parboiling treatments increased the velocity constants for the liberation of free fatty acids although the equilibrium was reached with reduced production of free fatty acids in relation to the production of raw rice bran after 150 days ofstorage. Extrusion proved the best treatment under the storage temperature conditions of rice bran from cultivar BRS Primavera.

Dehydration of "dedo de moça" pepper: kinetics and phytochemical concentration

Red pepper is rich in vitamin C and other phytochemicals and can be consumed as a dehydrated product. The evaluation of the best drying conditions can ensure a better quality product. This study aimed to investigate the effect of air temperature (55, 65, and 75 ºC) on drying kinetics of red peppers and on vitamin C, total phenolic content, and color of dried pepper as compared to the fresh product. Dehydration was carried out in a forced convection oven. Drying kinetics was determined by periodic weighting until constant weight. The moisture content of the fresh pepper was approximately 86%. The drying curves were fitted to three different models available in the literature. The Page model showed the best fit for this process. Analysis of variance revealed that the air drying temperature significantly influenced (p < 0.05) the quality parameters (vitamin C content, total phenolic content, and color) of the dried pepper as compared to the fresh pepper. After drying, the vitamin C retention increased with reduced air-drying temperature. In general, products dried at lower temperatures exhibited better quality due to reduced losses of bioactive compounds.

Hydration kinetics, physicochemical composition, and textural changes of transgenic corn kernels of flint, semi-flint, and dent varieties

The hydration kinetics of transgenic corn types flint DKB 245PRO, semi-flint DKB 390PRO, and dent DKB 240PRO was studied at temperatures of 30, 40, 50, and 67 °C. The concentrated parameters model was used, and it fits the experimental data well for all three cultivars. The chemical composition of the corn kernels was also evaluated. The corn cultivar influenced the initial rate of absorption and the water equilibrium concentration, and the dent corn absorbed more water than the other cultivars at the four temperatures analyzed. The effect of hydration on the kernel texture was also studied, and it was observed that there was no significant difference in the deformation force required for all three corn types analyzed with longer hydration period.

Drying kinetics of potato pulp waste

Potato pulp waste (PPW) drying was investigated under different experimental conditions (temperatures from 50 to 70 °C and air flow from 0.06 to 0.092 m³ m- 2 s- 1) as a possible way to recover the waste generated by potato chip industries and to select the best-fit model to the experimental results of PPW drying. As a criterion to evaluate the fitting of mathematical models, a method based on the sum of the scores assigned to the four evaluated statistical parameters was used: regression coefficient (R²), relative mean error P (%), root mean square error (RMSE), and reduced chi-square (χ²). The results revealed that temperature and air velocity are important parameters to reduce PPW drying time. The models Midilli and Diffusion had the lowest sum values, i.e., with the best fit to the drying data, satisfactorily representing the drying kinetics of PPW.

Convective, vacuum and microwave drying kinetics of mallow leaves and comparison of color and ascorbic acid values of three drying methods

Mallow leaves (Malva sylvestris L.) with initial moisture of 5.02±0.003 on dry basis (82.5% on wet basis) were dried using three different drying methods, microwave, convective and vacuum. The leaves that weigh 75 g each were dried until their moisture fell down to 0.10±0.005 on dry basis (approximately 9% on wet basis). The following drying levels were used in each of the drying processes: 6.67, 8.67, 10, 11.33 W g-1 microwave power density; 50, 75, 100 and 125 °C for convective drying; and 3, 7 kPa at 50 and 75 °C for vacuum drying. Drying periods ranged from 6-10, 26-150 and 38-130 min. for microwave, convective and vacuum drying, respectively. Effective moisture diffisuvities ranged from 2.04403 10-10-3.63996 10-12 m2 s-1, 1.70182 10-11-1.10084 10-10 m2 s-1 and 1.85599 10-11-5.94559 10-10 m2 s-1 for microwave, convective and vacuum drying, respectively. According to ascorbic acid content and color parameters, the best microwave power density was found 10 W g-1 with a drying period of 6.5 min.

Screening and kinetics of glutaminase and glutamate decarboxylase producing lactic acid bacteria from fermented Thai foods

L-glutaminase and glutamic acid decarboxylase (GAD) catalyzes the hydrolysis of L-glutamine and glutamate, respectively. L-glutaminase widely used in cancer therapy along with a combination of other enzymes and most importantly these enzymes were used in food industries, as a major catalyst of bioconversion. The current investigation was aimed to screen and select L-glutaminase, and GAD producing lactic acid bacteria (LAB). A total of 338 LAB were isolated from fermented meat, fermented fish, fermented soya bean, fermented vegetables and fruits. Among 338 isolates, 22 and 237 LAB has been found to be positive for L-glutaminase and GAD, respectively. We found that 30 days of incubation at 35 ºC and pH 6.0 was the optimum condition for glutaminase activity by G507/1. G254/2 was found to be the best for GAD activity with the optimum condition of pH 6.5, temperature 40 ºC and ten days of incubation. These LAB strains, G507/1 and G254/2, were identified as close relative of Lactobacillus brevis ATCC 14869 and Lactobacillus fermentum NBRC 3956, respectively by 16S rRNA sequencing. Further, improvements in up-stream of the fermentation process with these LAB strains are currently under development.

A reaction engineering approach to homogeneously catalyzed glycerol hydrochlorination

The production of biodiesel through transesterification has created a surplus of glycerol on the international market. In few years, glycerol has become an inexpensive and abundant raw material, subject to numerous plausible valorisation strategies. Glycerol hydrochlorination stands out as an economically attractive alternative to the production of biobased epichlorohydrin, an important raw material for the manufacturing of epoxy resins and plasticizers. Glycerol hydrochlorination using gaseous hydrogen chloride (HCl) was studied from a reaction engineering viewpoint. Firstly, a more general and rigorous kinetic model was derived based on a consistent reaction mechanism proposed in the literature. The model was validated with experimental data reported in the literature as well as with new data of our own. Semi-batch experiments were conducted in which the influence of the stirring speed, HCl partial pressure, catalyst concentration and temperature were thoroughly analysed and discussed. Acetic acid was used as a homogeneous catalyst for the experiments. For the first time, it was demonstrated that the liquid-phase volume undergoes a significant increase due to the accumulation of HCl in the liquid phase. Novel and relevant features concerning hydrochlorination kinetics, HCl solubility and mass transfer were investigated. An extended reaction mechanism was proposed and a new kinetic model was derived. The model was tested with the experimental data by means of regression analysis, in which kinetic and mass transfer parameters were successfully estimated. A dimensionless number, called Catalyst Modulus, was proposed as a tool for corroborating the kinetic model. Reactive flash distillation experiments were conducted to check the commonly accepted hypothesis that removal of water should enhance the glycerol hydrochlorination kinetics. The performance of the reactive flash distillation experiments were compared to the semi-batch data previously obtained. An unforeseen effect was observed once the water was let to be stripped out from the liquid phase, exposing a strong correlation between the HCl liquid uptake and the presence of water in the system. Water has revealed to play an important role also in the HCl dissociation: as water was removed, the dissociation of HCl was diminished, which had a retarding effect on the reaction kinetics. In order to obtain a further insight on the influence of water on the hydrochlorination reaction, extra semi-batch experiments were conducted in which initial amounts of water and the desired product were added. This study revealed the possibility to use the desired product as an ideal “solvent” for the glycerol hydrochlorination process. A co-current bubble column was used to investigate the glycerol hydrochlorination process under continuous operation. The influence of liquid flow rate, gas flow rate, temperature and catalyst concentration on the glycerol conversion and product distribution was studied. The fluid dynamics of the system showed a remarkable behaviour, which was carefully investigated and described. Highspeed camera images and residence time distribution experiments were conducted to collect relevant information about the flow conditions inside the tube. A model based on the axial dispersion concept was proposed and confronted with the experimental data. The kinetic and solubility parameters estimated from the semi-batch experiments were successfully used in the description of mass transfer and fluid dynamics of the bubble column reactor. In light of the results brought by the present work, the glycerol hydrochlorination reaction mechanism has been finally clarified. It has been demonstrated that the reactive distillation technology may cause drawbacks to the glycerol hydrochlorination reaction rate under certain conditions. Furthermore, continuous reactor technology showed a high selectivity towards monochlorohydrins, whilst semibatch technology was demonstrated to be more efficient towards the production of dichlorohydrins. Based on the novel and revealing discoveries brought by the present work, many insightful suggestions are made towards the improvement of the production of αγ-dichlorohydrin on an industrial scale.

Mass transfer and reaction kinetics in single droplet systems

As reactive extraction grown more and more popular in a variety of technological applications, optimizing its performance becomes more and more important. The process of complex formation is affected by a great number of both physical and chemical properties of all the components involved, and sometimes their interference with one another makes improving the effectiveness of such processes very difficult. In this Master’s Theses, the processes of complex formation between the aqueous phase - represented by copper sulfate water solution, and organic phase – represented by Acorga M5640 solvent extractor, were studied in order to establish the effect these components have on reactive extraction performance and to determine which step is bottlenecking the process the most.

Hydration, conformational states and kinetics of yeast hexokinase PII /

The kinetic study of the coupled enzymatic reaction involving monomeric yeast hexokinase PII (HK) and yeast glucose-6-phosphate dehydrogenase (G-6-PDH) yields a Michaelis constant of 0.15 ± 0.01 mM for D-glucose. At pH 8.7 HK is present in monomeric form. The addition of polyethylene glycol (PEG), to the reaction mixture increased the affinity of HK for glucose, independent ofMW of the PEG from 2000 to 10000. The osmotic stress exerted by PEG can be used to measure the change in number of water molecules that accompany enzyme conformational changes (Rand, et al., 1993). Results indicate that the G-6-PDH is not osmotically sensitive and thus, the change in the number of PEG-inaccessible water molecules (ANw) measured in the coupled reaction is only the difference between the glucose-bound and glucosefree conformations of HK. ANw ~ 450 with PEGs of MW > 2000 under conditions for both binding (Reid and Rand, 1997) and kinetic assays. The contribution water may play in the binding of ATP (Km = 0.24 + 0.02 mM) has also been examined. It was found that in this case ANw = (for osmotic pressures < 2.8x10* dynes/cm^), suggesting no additional numbers of waters are displaced when ATP binds to HK. Osmotic pressure experiments were also performed with dimeric HK. It was determined that both the monomeric and dimeric forms of HK give the same ANw under low pressures. If this large ANw is due to conformational flexibility, it would appear that the flexibility is not reduced upon dimerization ofthe enzyme.

The influence of skeletal muscle cell volume on the regulation of carbohydrate uptake and muscle metabolism

This study investigated the regulation of carbohydrate metabolism and glucose uptake through changes in skeletal muscle cell volume. Using an established invitro isolated whole muscle model, soleus (SOL) and extensor digitorum longus (EDL) muscles were dissected from male rats and incubated in an organ bath containing Sigma medium-199 with 8 mM D-glucose altered to target osmolality (hypo-osmotic: HYPO, iso-osmotic: ISO, hyper-osmotic: HYPER; 190, 290, 400 mmol/kg). Muscles were divided into two groups; metabolite (MM) and uptake (MU). MM (N=48) were incubated for 60 minutes and were then immediately flash frozen. MU (N=24) were incubated for 30 minutes and then the extracellular fluid was exchanged for media containing ^H-glucose and ^'*C-mannitol and incubated for another 30 minutes. After the incubation, the muscles were freeze clamped. Results demonstrated a relative water decrease and increase in HYPER and HYPO, respectively. EDL and SOL glucose uptakes were found to be significantly greater in HYPER conditions. The HYPER condition resulted in significant alterations in muscle metabolite concentrations (lower glycogen, elevated lactate, and G-6-P) suggesting a catabolic cell state, and an increase in glycogen synthase transformation when compared to the HYPO group. In conclusion, skeletal muscle cell volume alters rates of glucose uptake with further alterations in muscle metabolites and glycogen synthase transformation.