Some results on system equivalence

Simple, necessary and sufficient conditions for system equivalence at infinity and strong system equivalence of systems in the form (T(s), B, C, D) are established. A necessary condition for system equivalence at infinity of systems in the general form (T(s), U(S), V(S), W(S)) is also established.     

Starch/Solute Interaction in Water Sorption as Affected by Pretreatment

The effect of the freeze-drying process on the structure of starch and starch-sucrose mixtures was studied. The technique of inverse gas chromatography was used to study the interaction between organic compounds (probes) and starch (hylon 7) as well as starch-sucrose mixtures. The structural and morphological characteristics of the starch-solute mixtures from the thermodynamic parameters of these interactions was also examined. The porous freeze-dried samples interacted more with certain organic probes compared with untreated starch as indicated by higher values of specific retention volumes (Vg_o). Untreated starch apparently interacted only on the surface with organic probes. Freeze-dried starch reacted only with polar organic probes, particularly those with hydrogen bonding propensity. Cluster analysis of the water sorption isotherms correlated with data obtained from the injected probes.     

MULTIVARIATE STATISTICAL ANALYSIS OF VOLATILE COMPOUNDS AS A CRITERION FOR SELECTING TECHNOLOGICAL PARAMETERS IN THE OSMOTIC DEHYDRATION OF PINEAPPLE

Principal component analysis and cluster analysis of volatile compounds were used for selecting technological parameters in the osmotic dehydration of pineapple. Assessment of volatile losses permitted differentiation between samples obtained by different osmotic treatments. Treatments at 30C for 1 h at atmospheric pressure or under vacuum and at 30C or 40C for 1 to 3 h with pulsed vacuum (1 cycle) produce the lowest losses of volatile compounds. Apparently, pulsed vacuum allows higher aromatic volatiles retention than two other pressure modes. It also allows increases in both process temperature and time without an important increase in losses.     

Starch/Sucrose Interactions by Organic Probe Analysis: An Inverse Gas Chromatography Study

The effect of freeze drying of high amylopectin starch was determined with samples of starch dispersed in water with or without solubilized sucrose. The X-ray diffraction data showed that this treatment disrupted crystalline structures of amylopectin and sucrose exposing additional sites for water sorption. This was shown also by sorption isotherms of the starch alone. The Hylon 7-sucrose freeze-dried samples produced a greater effect on sorption than did the corresponding Amioca freeze-dried mixtures. Organic probe analysis of the starch and starch-sucrose mixtures indicated that high amylose starches were more reactive with polar organic probes than high amylopectin starches when freeze-dried. Untreated high amylopectin starches were more reactive with probes in agreement with the water sorption data for a more branched polymer.     

Viscosity and Density of Boron Trioxide

Extensive and accurate viscosity values for molten B₂O₃ are reported over the continuous range from 20 poises (at 1400°C) to 10¹⁰ poises (at 318°C). The measurements were made with a wide-range rotating-cylinder viscometer. The melts were pretreated by bubbling superdry nitrogen through them to ensure a minimum water content. Above 800°C the temperature dependence of the viscosity curve obeyed the Arrhenius equation; below 800°C the curvature was smooth showing no breaks. At the low temperatures, although its curvature decreased, the viscosity curve did not obey the Arrhenius equation. Densities were determined between 411° and 1400°C. Over this range the volume expansion coefficient changed by 1 order of magnitude from 3.35 × 10⁻⁴/°C to 3.34 × 10⁻⁵/°C. The liquid volume expansion coefficient above 1200°C was smaller than that of the glass below the glass transition temperature, indicating some type of structural rearrangement in B₂O₃.     

INFLUENCE OF OSMOTIC DEHYDRATION ON THE VOLATILE PROFILE OF GUAVA FRUITS

ABSTRACT

The effect of osmotic dehydration (OD) on the volatile compounds of guava fruits was studied. Osmotic treatments were carried out at atmospheric pressure, at continuous vacuum and by applying a vacuum pulse (5 min under vacuum and the remaining time at atmospheric pressure) at different temperatures (30, 40 and 50C) and times (1, 2 and 3 h). The volatile compounds of fresh and dehydrated samples were obtained by simultaneous distillation–extraction, and were analyzed by gas chromatography/mass spectrometry. In general, OD caused changes in the concentration of volatiles, depending on the process conditions. The use of lower temperatures and shorter treatment times can diminish the loss of volatiles with respect to the fresh samples. The greatest damage to volatiles loss is produced at 50C for up to 2 h under both pulsed and continuous vacuum. The lowest total volatiles loss occurred at 30 and 40C for up to 3 h under pulsed vacuum or atmospheric pressure.

PRACTICAL APPLICATIONS

Consumer demand for high‐quality products with freshlike characteristics has promoted the development of a new category, minimally processed fruits and vegetables. Although these products present, as distinguishing features, simplicity in use and convenience, they generally perish more quickly than the original raw material because of tissue damage caused by mechanical operations. The use of osmotic dehydration process has been presented as a tool for the development of minimally processed fruits. The slight water activity reduction promoted by the process may provide stable products with good nutritional and sensorial quality and with characteristics similar to those of the fresh products. The application of minimal processing to tropical fruits can represent an interesting world market. Fruit flavor is an important quality factor that influences consumer acceptability, and for this reason, its study is relevant in the minimally processed food product.

     

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.     

POTENTIAL FOR BACTERIAL GROWTH ON THE FRESH CUT TROPICAL SQUASH, CALABAZA (CURCUBITA MOSCHATA), DURING STORAGE

Calabaza (Curcubita moschata) is a tropical squash which is gaining popularity as a specialty crop for agricultural producers in the Northeast United States. It is commonly marketed by being cut in half, wrapped in plastic and may be held unrefrigerated until sold. This method of display is essential for consumer acceptance, yet unrefrigerated storage means that some potential for food safety problems exists. Experiments were conducted to determine the potential for bacterial growth during storage of cut calabaza. Freshly cut calabaza contained between 1.3 and 4.7 log₁₀CFU/g aerobic mesophiles. By 10 h, duplicate counts from some samples exceeded 4 log₁₀ CFU/g. After 24 h of room temperature storage, total aerobic plate counts ranged from 5.2 to 7.7 log₁₀ CFU/g. Rapid bacterial growth on cut calabaza stored at room temperature indicates that these products are highly perishable, and may be able to support the growth of pathogenic bacteria, should they be introduced during the slicing process.