Protein resynthesis catalyzed by alpha-chymotrypsin was studied to modify the nutritive quality and physical properties of albumin. The increase in substrate concentration produced an increase in enzyme synthetic action. At low substrate concentration, several water activity depressing additives (salts or polyols) in the reaction media enhanced plastein synthesis. Polyols enhanced the synthetic reaction proportionally to an increase in their molecular size. The positive effect of alkali halides was related to an increase in cation size and decrease in anion size. All plastein products showed a clear increase in nutritional value with respect to the substrate.

Gift

La prediccion de actividad de agua (aw) mediante modelos matematicos, por lo general, esta limitada a disoluciones acuosas de electrolitos y no electrolitos. El efecto de componentes alimenticios tales como las grasas, las proteinas y la fibra no se considera cuando estos modelos se aplican a los alimentos. El valor estimado de aw en alimentos reales, generalmente, es mayor que el valor medido debido a que tanto las proteinas como las grasas ligan moleculas de agua. Por tal motivo, se desarrollo un programa para ordenadores que permite evaluar con buena precision el valor de actividad de agua, y que ademas es capaz de lo siguiente: (1) Predecir la aw a partir de modelos matematicos tales como Pitzer, Bromley, Norrish, Ross, Ferro-Chirife-Boquet y Ferro-Bermengui-Chirife. (2) Establecer un nivel de similitud entre alimentos de aw y composicion conocidos frente a alimentos a los que solo se conoce la composicion. (3) Definir un factor de desviacion en funcion del nivel de similitud anteriormente descrito en el que se considera la presencia de grasas, proteinas y fibra. El analisis de productos embutidos, para la primera iteraccion, dio un factor de desviacion de 1,07. En el caso de algunos productos azucarados, que incluyen gomas y pectinas, se encontro que el factor fue de 1,12. Una vez incrementado el numero de datos almacenados, los cuales dan apoyo al proceso iterativo de la prediccion de actividad de agua, el factor de desviacion converge rapidamente a uno.

This review examines recent published suggestions that "water dynamics" may be applied instead of water activity (aw) determination to predict microbial stability of concentrated and intermediate moisture food systems. Factors such as the relative effectiveness of additives for antimicrobial stabilization through aw-lowering (i.e. glucose vs fructose, glycerol vs propylene glycol) and the importance of glass transition temperature as an indicator of microbial stability were examined, based on available experimental data. Determination of the glass-rubber transition characteristics and/or the use of the "water-dynamics" map does not enable prediction of the microbial stability of foods (i.e. inhibition of growth) with confidence. These were no more effective alternatives than the concept of water activity as a basis for predicting microbial growth in foods.

En este trabajo se presenta una recopilacion de modelos matematicos apropiados para describir la actividad del agua en alimentos. Se incluyen, entre otros, la Ley de Raoult, modelos empiricos como Money-Born y Grover y modelos desarrollados a partir de aspectos termodinamicos como el modelo Norrish, Pitzer, Bromley. En el caso de mezclas multicomponentes se discuten los modelos de Ross, Ferro-Chirife-Boquet y Ferro-Benmergui-Chirife. Ademas, se presentan varios ejemplos que ilustran la aplicacion de los modelos.

Faecal pellets of Varanus salvator collected in Pulau Tulai in the South China Sea revealed that individuals there mainly feed on crabs and tourists' leftovers. The stomach contents of monitor lizards living in an oil palm estate in Peninsular Malaysia show that the main diet in that habitat consisted of various types of insects and occasionally small rodents. Hatchlings were strictly insectivorous. Both groups of lizards exhibited area-concentrated foraging behaviour and their preferred hunting technique was "open pursuit"

Solution thermodynamics was applied to the water sorption isotherms of foods. First, we corrected Le Maguer's theory. By this correction, it was found that the same thermodynamic equations were applicable to both water sorption data measured at constant total pressure (P) and to those measured under the particular vapor pressure, P Pw, for a food material. Second, the change in the water sorption behavior of rice flour by defatting and extrusion cooking was analyzed by solution thermodynamics. It was confirmed that the principle of solution thermodynamics is more appropriate than that of conventional adsorption thermodynamics for evaluating the affinity of food for water. The enhanced affinity of rice flour for water by defatting and extrusion was quantitatively evaluated by solution thermodynamics