Dynamic mathematical model of the crystallization kinetics of fats

A new model able to describe the kinetics of isothermal crystallization is presented: it is a model written in the form of a differential equation allowing use under dynamic temperature variations. It describes the crystallization process as if it is a reversible reaction with a first order forward reaction and a reverse reaction of order n. The model has the advantage of having an analytical solution under isothermal conditions that facilitates parameter estimation. The quality of this model was compared with the more traditional Avrami (with and without induction time) and Gompertz models using different model selection criteria. To show the universality of the model, different fat samples, different crystallization temperatures and different measuring techniques were used for model evaluation. The new model was selected as the best for the majority of the samples and this independent of the model selection criterion used.     

An activated-state model for the prediction of solid-phase crystallization growth kinetics in dried lactose particles

Molecular-level understanding of solid-phase crystallization growth kinetics has the potential to improve the fundamental basis for understanding this process. This understanding has been developed here as part of an activated-state model, which accounts for the effects of the moisture content and the temperature on the crystallization rate. Water-induced crystallization (WIC) at different temperatures (15 °C, 25 °C, 40 °C) and a constant relative humidity (75%) environment has been used to analyze the changes in enthalpy, entropy and Gibbs free energy of activation for the solid-phase crystallization of lactose. WIC showed that, at higher temperatures, crystallization commences at lower moisture contents. The enthalpy and Gibbs free energy of activation increased during the crystallization process, which suggested that the binding energy needed for the formation of an activated complex increased as the moisture content decreased, making the formation of the activated complex more difficult. The entropy of activation, on the other hand, decreased with the decrease in the moisture content. From the activated rate equation, the energy of activation has been estimated to be 39 ± 2 kJ mol⁻¹, which is similar to the literature value (40 kJ mol⁻¹) for the solid-phase crystallization of lactose. The reaction rate constant at 25 °C is 1.4 × 10⁻⁴ s⁻¹, which is similar to the literature value of 1.3 × 10⁻⁴ s⁻¹. The WLF equation is inconsistent and hence unreliable in predicting the rates of crystallization at the glass-transition temperature from the analysis of experimental data at different temperatures.     

Calorimetric study of the glass transition occurring in aqueous glucose: Fructose solutions

Glass transition temperatures (T_g) for dilute and concentrated glucose: fructose: water solutions have been determined by differential scanning calorimetry. The supplemented phase diagrams (glucose: fructose 1:4, 1:2, 1:1, 2:1, 4:1 (w/w)) are presented and from these the temperature (T_g') and concentration (C'_g) of the maximally freeze-concentrated glass have been determined. Theoretical predictions of T_g for binary (glucose: fructose) and tertiary (glucose: fructose: water) systems according to the Couchman–Karasz and Gordon-Taylor equations are given and discussed. Annealing vitrified glucose: fructose glasses above their T_g allows the glass concentration to approach C'_g as a result of ice formation. Viscosity measurements of fructose and fructose: glucose mixtures allow for a calculation of T_g of the non-aqueous solutions.     

Computational fluid dynamics modeling of mass transfer for aroma compounds recovery from aqueous solutions by hydrophobic pervaporation

In this work, a mass transfer study on aroma compound recovery by pervaporation process was performed using a model based on solution–diffusion theory. CFD method was employed to solve the governing mass transfer equations by considering the flux coupling. Concentration profiles of penetrants inside the membrane as well as permeation flux and aroma permeate concentration through the membrane were determined. The modeling results were validated by the experimental data obtained for pervaporative recovery of isopentyl acetate and n-hexanol from their binary aqueous solutions with composite PDMS membrane. The influence of key operating parameters such as feed aroma concentration and temperature on the flux and permeate concentration was also investigated theoretically and experimentally. The results showed that the aroma permeate concentration as well as the total and partial fluxes increased with an increase in the feed aroma content and feed temperature. The predicted results were in good agreement with experimental data.     

On the production of glucose and fructose syrups from cashew apple juice derivatives

The cashew crop is an important agro-economic activity in many equatorial areas, although less than 10% of the cashew apple production is exploited industrially. This work focuses on two aspects: obtaining food-grade syrups from cashew apple juice and studying fixed bed adsorption dynamics to separate fructose from glucose. Syrups obtained by concentrating clarified cashew apple juice under vacuum showed similar characteristics to a reference food-grade syrup, with a higher content in fructose, which may contribute to a higher sweetening power with less caloric intake. Adsorption equilibrium studies were performed with synthetic solutions of fructose and glucose by frontal analysis under the concentration range found in the syrups (10-120 g/L) at 30, 40 and 60 °C, using the cation exchange resin Dowex MTO 99Ca. Fructose was more strongly adsorbed than glucose, with measured selectivities ranging from 1.50 to 2.25. Resistance to mass transfer was significant and thought to be due to resin crosslinkage. Glucose and fructose breakthrough curves using cashew apple syrup as feed were practically identical to those measured with synthetic solutions, which leads us to believe that high-fructose syrups may be readily obtained by using current continuous chromatographic units, such as SMB.     

Preliminary study of the influence of dextran on the precipitation of legumin from aqueous salt solutions

Ultrasound has been used to study the behaviour of dextran, legumin (11s globulin of the broad bean Vicia faba ) and their mixtures in aqueous salt solutions under different physico-chemical and thermodynamic conditions. The attenuation coefficient of the solutions was measured as a function of pH (3–10) and ionic strength (0, 0.025, 0.05 M NaCl). The attenuation in the dextran solutions was independent of pH and ionic strength, whereas that in the solutions containing legumin had a maximum value near to the isoelectric point of the legumin (∼φ 5). The magnitude of this maximum depended on the ionic strength of the solution. The cause of the observed attenuation was scattering of ultrasound by precipitated protein. The addition of dextran to solutions where the biopolymers are thermodynamically compatible decreases the attenuation, whereas its addition to solutions where the biopolymers are incompatible increases it. This is because protein precipitation is greater in incompatible systems.     

Investigation of the factors influencing the survival of Bifidobacterium longum in model acidic solutions and fruit juices

The survival of Bifidobacterium longum NCIMB 8809 was studied during refrigerated storage for 6 weeks in model solutions, based on which a mathematical model was constructed describing cell survival as a function of pH, citric acid, protein and dietary fibre. A Central Composite Design (CCD) was developed studying the influence of four factors at three levels, i.e., pH (3.2–4), citric acid (2–15 g/l), protein (0–10 g/l), and dietary fibre (0–8 g/l). In total, 31 experimental runs were carried out. Analysis of variance (ANOVA) of the regression model demonstrated that the model fitted well the data. From the regression coefficients it was deduced that all four factors had a statistically significant (P < 0.05) negative effect on the log decrease [log₁₀N_{0 week}−log₁₀N_{6 week}], with the pH and citric acid being the most influential ones. Cell survival during storage was also investigated in various types of juices, including orange, grapefruit, blackcurrant, pineapple, pomegranate and strawberry. The highest cell survival (less than 0.4 log decrease) after 6 weeks of storage was observed in orange and pineapple, both of which had a pH of about 3.8. Although the pH of grapefruit and blackcurrant was similar (pH ∼3.2), the log decrease of the former was ∼0.5 log, whereas of the latter was ∼0.7 log. One reason for this could be the fact that grapefruit contained a high amount of citric acid (15.3 g/l). The log decrease in pomegranate and strawberry juices was extremely high (∼8 logs). The mathematical model was able to predict adequately the cell survival in orange, grapefruit, blackcurrant, and pineapple juices. However, the model failed to predict the cell survival in pomegranate and strawberry, most likely due to the very high levels of phenolic compounds in these two juices.     

Effect of salt and sucrose addition on the formation of the Amadori compound from methionine and glucose at 40 °C

Four model solutions with the Maillard precursors methionine and glucose were reacted at 40 °C for up to 15 days. The solutions had a high or low precursor concentration leading to either high or medium water activity (0.96; 0.86). The water activity of the two other solutions was reduced by adding either salt or sucrose. Glucose, methionine and the Amadori compound (Fru–Met) were quantified after 1, 2, 6, 10 and 15 days. The results show that high salt and sucrose levels had a much more pronounced influence on glucose consumption and Fru–Met formation than differences in water activity. Glucose degradation and Fru–Met formation was favoured by high sucrose levels and inhibited by high NaCl levels.     

Antioxidant activity of Maillard reaction products derived from aqueous glucose/glycine,diglycine, and triglycine model systems as a function of heating time

The purpose of this study was to evaluate the antioxidant activity of Maillard reaction products (MRPs) derived from aqueous glucose/glycine, diglycine, and triglycine model systems as a function of heating time. The pH of MRPs derived from the Glu-G model system decreased markedly as the heating time increased, while MRPs derived from the Glu-Di model system showed the highest increase in absorbance at 420 nm. MRPs derived from the Glu-G model system showed the highest cupric ion chelating ability, while MRPs derived from the Glu-Di model system had the highest ferrous ion chelating activity. MRPs derived from the Glu-Di model system were found to be effective antioxidants in different in vitro assays with regard to the 2,2′-azinobis(3-ethylbenothiazoline-6-sulphonic acid) diammonium salt (ABTS) and 1,1-diphenyl-2-picryl-hydrazil (DPPH) radical scavenging activities and ferric reducing/antioxidant power (FRAP).     

A new model for the reconstruction of biomass history from carbon dioxide emission during batch cultivation of Geotrichum candidum

A non-structured model has been developed to describe the CO2 emission during growth of Geotrichum candidum on a lactate + peptone-based liquid medium. From the nitrogen and carbon mass balances, it was shown that about 50% of the total CO2 released was from the metabolism of the energy supply for biosynthesis, and the remaining from that for maintenance; thus, CO2 production was considered to be partially associated with growth. The model fitted the experimental data as long as a net growth was observed (0-50 h). The coefficients for growth- and non-growth-associated CO2 production were A = 0.646 (dimensionless) and B = 0.017 h(-1), respectively. From the coefficients of the model and the CO2 history data, the biomass kinetics has been reconstructed, and the calculated biomass concentrations agree fairly well with the experimental data. From this, measurement of the CO2 evolved may be used as an indirect and non-intrusive method of monitoring fungal growth during the first 50 h of cultivation.     

Minerals,polysaccharides and antioxidant properties of aqueous solutions obtained from macroalgal beach-casts in the Noto Peninsula,Ishikawa, Japan

To clarify the useful properties of the macroalgal beach-casts for food, we determined mineral, water-soluble polysaccharide and total phenolic compound contents and antioxidant properties of aqueous solutions obtained from frond of eight brown and four green algae. These algae were washed ashore from the East Sea (the Sea of Japan) to the northeast beaches of the Noto Peninsula in autumn. There were fresh and large amounts of Ecklonia stolonifera (Es), Ecklonia kurome (Ek), Sargassum ringgoldianum subsp. coreanum (Sr) and Sargassum macrocarpum on the beaches. Potassium, magnesium and calcium ions were high in Sr-solution. High molecular weight water-soluble polysaccharide, mainly alginates, and relative viscosity were also high in Sr-solution. Both Es and Ek solutions showed high contents of total phenolic compounds and high antioxidant activities, including DPPH radical- and hydroxyl radical-scavenging and ferrous reducing power. On the other hand, the highest superoxide anion radical-scavenging activity was in the Sr solution. In the case of Sr, the same antioxidant properties were also found in the aqueous solution obtained from stem. These results suggest that some macroalgal beach-casts, especially Sr, can be utilised as new natural resources for functional foods, cosmetics, medical applications and fertilizer instead of being processed to landfill or incineration.     

Sugarcane bagasse treated with hydrous ferric oxide as a potential adsorbent for the removal of As(V) from aqueous solutions

The mechanism of As(V) removal from aqueous solutions by means of hydrated ferric oxide (HFO)-treated sugarcane bagasse (SCB-HFO) (Saccharum officinarum L.) was investigated. Effects of different parameters, such as pH value, initial arsenic concentration, adsorbent dosage, contact time and ionic strength, on the As(V) adsorption were studied. The adsorption capacity of SCB-HFO for As(V) was found to be 22.1 mg/g under optimum conditions of pH 4, contact time 3 h and temperature 22 °C. Initial As(V) concentration influenced the removal efficiency of SCB-HFO. The desorption of As(V) from the adsorbent was 17% when using 30% HCl and 85% with 1 M NaOH solution. FTIR analyses evidenced two potential binding sites associated with carboxyl and hydroxyl groups which are responsible for As(V) removal. Adsorption, surface precipitation, ion exchange and complexation can be suggested as mechanisms for the As(V) removal from the solution phase onto the surface of SCB-HFO.