Kinetic Parameters for Thermal Degradation of Green Asparagus Texture by Unsteady-state Method

An unsteady-state method was developed for estimating texture degradation during heating-cooling of green asparagus spears. The method used a mathematical model of heat transmission for time-temperature history estimation, and a nonlinear regression of texture measurements of asparagus spears to estimate kinetic parameters. The specific heat, conductivity and convective coefficient of green asparagus were determined experimentally and used in the mathematical model for temperature estimation. Values obtained were Ea = 76.19±0.13 kJ/mol and k_1158°C= 0.00528±0.00005 s^-1. Good agreement was found between predicted and observed texture values. The method was compared with the classical steady-state method. The mathematical model and kinetic parameters estimated could be used to design and evaluate thermal processes for green asparagus.     

Calculation of the variation of the heat of desorption with moisture content on the basis of the BET theory

Data of water desorption on different food products were analysed from the point of view of the BET theory. A plot of log C against 1/T as used for the independent evaluation of E₁-E_L and the pre-exponential a₁b₂/b₁a₂, in the expression for the constant C of the BET theory. It was found that a₁b₂/b₁a₂, may range from 10⁻³ to 10⁻⁶ and the E₁ - E_L values are correspondingly much higher than usual. An equation has been obtained within the framework of the BET theory for the dependence of the net heat of desorption on moisture content. In the present analysis the variation of the monolayer value with temperature is considered by means of a simple empirical equation. The results are compared with the heats of desorption calculated directly by the Clausius-Clapeyron equation.     

The effect of direct acidification on the microbiological,physicochemical and sensory properties of probiotic Minas Frescal cheese

Minas Frescal cheeses produced with the addition of the probiotic culture Bifidobacterium Bb‐12 and without (C1) or with (C2) lactic acid were evaluated in relation to the microbiological, physicochemical and sensory properties. After 28 days of storage, the cheeses without lactic acid showed lower moisture and pH, in addition to higher acidity and syneresis. This behaviour influenced the texture profile of the cheeses, making them harder and chewier. The colour attributes L* and b* diminished during the storage. The majority of the consumers classified the cheeses as having good acceptability and they would buy this type of functional food.     

Subsolidus Phase Equilibria and Ordering in the System ZrO2-Y2O3

The subsolidus phase relations in the entire system ZrO₂-Y₂O₃ were established using DTA, expansion measurements, and room- and high-temperature X-ray diffraction. Three eutectoid reactions were found in the system: ( a ) tetragonal zirconia solid solution→monoclinic zirconia solid solution+cubic zirconia solid solution at 4.5 mol% Y₂O₃ and ∼490°C, ( b ) cubic zirconia solid solutiow→δ-phase Y₄Zr₃O₁₂+hexagonalphase Y₆ZrO₁₁ at 45 mol% Y₂O₃ and ∼1325°±25°C, and ( c ) yttria C -type solid solution→wcubic zirconia solid solution+ hexagonal phase Y₆ZrO₁₁ at ∼72 mol% Y₂O₃ and 1650°±50°C. Two ordered phases were also found in the system, one at 40 mol% Y₂O₃ with ideal formula Y₄Zr₃O₁₂, and another, a new hexagonal phase, at 75 mol% Y₂O₃ with formula Y₆ZrO₁₁. They decompose at 1375° and >1750°C into cubic zirconia solid solution and yttria C -type solid solution, respectively. The extent of the cubic zirconia and yttria C -type solid solution fields was also redetermined. By incorporating the known tetragonal-cubic zirconia transition temperature and the liquidus temperatures in the system, a new tentative phase diagram is given for the system ZrO₂-Y₂O₃.     

A reduced polynomial chaos expansion method for the stochastic finite element analysis

The stochastic finite element analysis of elliptic type partial differential equations is considered. A reduced method of the spectral stochastic finite element method using polynomial chaos is proposed. The method is based on the spectral decomposition of the deterministic system matrix. The reduction is achieved by retaining only the dominant eigenvalues and eigenvectors. The response of the reduced system is expanded as a series of Hermite polynomials, and a Galerkin error minimization approach is applied to obtain the deterministic coefficients of the expansion. The moments and probability density function of the solution are obtained by a process similar to the classical spectral stochastic finite element method. The method is illustrated using three carefully selected numerical examples, namely, bending of a stochastic beam, flow through porous media with stochastic permeability and transverse bending of a plate with stochastic properties. The results obtained from the proposed method are compared with classical polynomial chaos and direct Monte Carlo simulation results.     

Effect of heat treatment on the antibacterial activity of bovine lactoferrin against three foodborne pathogens

The effect of different heat treatments on the antimicrobial activity of bovine lactoferrin against Escherichia coli O157:H7, Salmonella enteritidis and Listeria monocytogenes has been studied. We have observed that the heat treatments lower than 85°C for 10 min did not affect the antibacterial activity of the protein. Hydrolysates of bovine lactoferrin were found to be more active than the native protein against the three pathogens. Moreover, the antibacterial effect of bovine lactoferrin was also assayed in milk and whey, and although we found a reduction in the number of viable cells, this reduction was lower than in culture media.     

EFFECTS OF ORGANIC ACIDS, NISIN, LYZOZYME AND EDTA ON THE SURVIVAL OF YERSINIA ENTEROCOLITICA POPULATION IN INOCULATED ORANGE BEVERAGES

Inactivation of a Yersinia enterocolitica strain by 3.4% ascorbic acid (AA), 0.5% citric acid (CA), 0.2% lactic acid, 100 IU/mL nisin, 2,400 IU/mL lysozyme and 20 mM ethylenediaminetetraacetic acid disodium salt (EDTA ), alone and combined, was studied at different temperatures (4 and 25C) in commercial and laboratory-prepared orange beverages. In laboratory-prepared juice, highest reductions (between 3.06 and 4.07 log units) were obtained with acid mixtures at 25C after 20 min of incubation. At 24 h of incubation, EDTA was bactericidal and the mixtures with nisin or lysozyme resulted in count reductions of 6.03 and 5.98 log units, respectively. In commercial orange beverage, AA and CA gave reductions of 5.43 and 4.26 log units, respectively. The three acid mixtures were bactericidal within the first 10 min. EDTA alone or mixed completely inhibited Y. enterocolitica strain at 6 and 24 h of incubation. At 4C, all the results were significantly lower than at 25C.

PRACTICAL APPLICATIONS

Yersinia enterocolitica is a common cause of gastrointestinal disorders and may lead to sequelae. This pathogen can maintain its virulence in a wide temperature range and under adverse conditions such as pH lower than 4. There are reports describing the isolation of Y. enterocolitica from water and ice in Brazil and Latin America. The sale of unpasteurized drinks is a common practice in our region and their consumption has increased over the past years. In the present work, chemical compounds and biological inhibitors were studied. Some of these compounds showed to be efficient for reducing Y. enterocolitica populations. Furthermore, they did not modify the organoleptic characteristics of the beverages and they are not toxic for human beings.