Diffusional analysis of air drying of grain sorghum

Pick's law of diffusion (moisture flux proportional to the moisture gradient) for diffusion out of spheres was successfully applied to describe the drying of grain sorghum. It was found that the diffusion coefficient of water was independent of moisture content in the approximate range of 21–6% (dry basis) moisture content. An Arrhenius type temperature dependency of moisture diffusivity was found, the energy of activation being 7.5 kcal/g mol.     

Kinetics of Deteriorative Reactions in Model Food Systems of High Water Activity: Glucose Loss, 5-Hydroxymethylfurfural Accumulation and Fluorescence Development Due to Nonenzymatic Browning

The kinetics of nonenzymatic browning reactions in the water activity range 0.900 - 0.950 was studied to minimize the deteriorative changes of foods preserved by a combination of a mild water activity reduction and other microbial stress factors. Glucose loss, 5-hydroxymethylfurfural accumulation, and development of fluorescence were measured during storage of aqueous model systems. The results obtained showed a strong dependence on temperature and pH and a negligible influence of water activity on the rate of nonenzymatic browning reactions.     

铸铁熔炼热分析技术发展九十年

自从1931年Esser和Lautenbusch第一次在铸铁文献中谈及热分析以来,铸铁的热分析技术已经走过了漫长的道路.目前,热分析已被广泛应用于各种铸铁的过程控制.文中综述了热分析在设备和分析方法方面的最新进展,正是这些技术进步使得热分析得以成功应用于评估化学成分、石墨化潜能、石墨形状和数量等.详细分析了热分析技术在...     

Statistical Evaluation of Water Activity Measurements Obtained with the Vaisala Humicap Humidity Meter

The objective of this study was to determine the suitability, precision and accuracy of the Vaisala Humicap electric hygrometer for a_w measurements in the range 0.752-0.974 (at 25°C). Results of the statistical evaluation indicated that this hygrometer, when calibrated and operated as described here, provides a convenient and fast means of a_w measurement having adequate accuracy and precision for most food applications.     

QUALITY CHANGES IN AUSTRALIAN RED CLAW CRAYFISH (CHERAX QUADRICARINATUS) SUBJECTED TO MULTIPLE FREEZING‐THAWING CYCLES1

Abstract The influence of repeated freezing‐thawing (F/T, six cycles) treatment on Australian red claw crayfish (Cherax quadricarinatus) muscle quality was investigated. For each F/T cycle, five raw tails were analyzed for lipid oxidation, proteolysis, and thermal stability, and another five tails were cooked to determine cooking yield and tenderness (shear). Lipid oxidation occurred during repeated F/T treatment, as evidenced by a marked TBARS increase, i.e., from 0.070 mg/kg (fresh) to 1.201 mg/kg (cycle 6). While F/T induced small proteolytic and thermal stability changes, it caused a major loss in cooking yield as well as in tenderness of meat. The results showed an overall susceptibility of the main quality traits of red claw muscle to F/T abuses. Thus, to retain good eating qualities, red claw tails should not be subjected to more than three F/T cycles.     

Moisture desorption isotherms of rough rice

Desorptions isotherms of rough rice have been determined at 40, SO, 60 and 70°C and water activities (a,) from 0.036 to 0.823. An attempt is made to describe the experimental equilibrium moisture content data using mathematical relationships available in the literature. A statistical analysis was performed to evaluate the goodness of fit of the different equations. From this analysis it was concluded that Henderson's equation permits to correlate satisfactorily the experimental data for the whole range of water activity investigated. Finally, a simple empirical equation was postulated to take into account the effect of temperature on water sorption isotherms of rough rice grain.     

On the Temperature Dependence of Isosteric Heats of Water Sorption in Dehydrated Foods

The usual procedures for calculating isosteric heats of sorption by the application of the Clausius-Clapeyron equation (e.g. sorption isosteres or the intregated form) to isotherms at different temperatures, was examined. For almost all foods studied the magnitude of the heat curves seemed to be dependent on the temperature interval used for its calculation. However for some foods the relative differences in the isosteric heat curves were much more marked than in others. The observed behavior may be tentatively attributed to changes occurring in foods subjected to increased temperatures in the “Semi-dry” or “dry” state. These changes may be identified with among others cross-linking and denaturation of proteins, nonenzymatic browning reactions and the like.