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.

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.

Standard-molded, one piece O-ring food processing plant gaskets (1.5 in or 36.1 mm diameter) made of seven different substances (Buna N, white Buna N, EPDM (ethylene propylene diene monomer), polyethylene, silicone rubber, PTFE (polytetrafluoroethylene or Teflon) and steam-resistant Viton) were treated with chlorine sanitizer or ozonated water. After treatment, only very slight differences were noted visually between control and treated gaskets. Measurements indicated that ozone treatment affected the tensile strength of EPDM and Viton, but not significantly more than chlorine treatment. The tensile strengths of other gasket materials were not significantly affected by ozone treatment. The elasticity of ozone-treated PTFE gaskets was significantly different from chlorine-treated PTFE gaskets. Other gasket materials were not significantly affected by ozone treatment.

Production of protein hydrolysate from shrimp precooking water using enzyme Nutrase 0.5 L was studied. Variations in the enzymatic hydrolysis were composed of the quantity of enzyme (0, 0.5, 1.0, 1.5 and 2.0 percent v/v), the pH (5.5, 6.5 and 7.5), the hydrolysing temperature (50, 55 and 60 deg C) and the hydrolysing time (15, 30, 45, 60, 75 and 90 min). The optimum condition for production of hydrolysate which gave the maximum amino acid nitrogen at 3.50 mgN/ml was 0.5 percent Nutrase, pH 6.5 50 deg C and 10 min. The chemical composition of the hydrolysate produced was 94.51 percent moisture, 2.52 percent protein, 0.33 percent fat, 1.77 percent ash and 0.88 percent carbohydrate. The hydrolysate was then freeze-dried. The dried product absorbed moisture quite easily and contained 3.80 percent moisture, 51.89 percent protein, 6.57 percent fat, 24.76 percent ash and 12.99 percent carbohydrate. To improve the quality of the dried product, the hydrolysate was mixed with 20 percent maltodextrin solution until the mixture had 10 percent total soluble solid before freeze-drying. It was found that the dried product absorbed moisture less rapidly and was ground easily. The composition of the improved product was 5.23 percent moisture, 36.98 percent protein, 3.71 percent fat, 16.61 percent ash and 41.98 percent carbohydrate. Sensory evaluation on the color and shrimp odor of these two dries products comparing to the freezed-dried unhydrolysed precooking water products showed that the freezed-dried hydrolysate without maltodextrin solution obtained the highest scores in color and odor. However, sensory evaluation the products after dissolving in water revealed that neither the hydrolysed nor unhydrolysed products had the significant differences in color, shrimp for, sweet taste, bitter taste and overall flavor.

The influence of water content and water activity (a sub(w)) on the concentration of volatile compounds in the head-space vapour over model and food samples was studied. Starch-water model systems and three different food systems (hard cheese, apple puree and raw ham) were prepared with a sub(w) values ranging from 0 to 1. For each sample gas chromatographic analyses of volatiles in the headspace vapour and water activity measurements were carried out. For solid foods at intermediate a sub(w) values the highest volatile concentration in the headspace strongly depended on the availability of water. The head-space volatile concentration decreased rapidly when the water became totally free and the water vapour pressure was close to that of pure water | E' stata studiata l'influenza del contenuto in umidita' e dell'attivita' dell'acqua (a inf(w)) sulla quantita' delle sostanze volatili presenti nel vapore dello spazio di testa di sistemi modello e di alimenti aventi una attivita' dell'acqua nell'intervallo di valori di a inf(w) tra 0 e 1. Sui campioni posti in recipienti chiusi ermeticamente sono state determinate per via gascromatografica le sostanze volatili nello spazio di testa e l'attivita' dell'acqua. La concentrazione delle sostanze volatili nello spazio di testa e' risultata fortemente influenzata dalle proprieta' di adsorbimento dell'acqua da parte delle diverse matrici alimentari. La presenza di sostanze volatili e' stata riscontrata al massimo livello, in tutti i casi esaminati, in corrispondenza dell'inizio del ramo ascendente della isoterma di adsorbimento dell'acqua, per discendere rapidamente ai valori piu' elevati di a inf(w), oltre i quali l'acqua presente nell'alimento diviene totalmente disponibile per agire come solvente

Study was preformed to assess the relationship between water consumption, feed intake, and respiratory disease in 2200 commercial finishing pigs in the U.K. The pigs were housed in 4 conventional finishing sheds in groups of 20-25 per pen and fed ad-lib. Water was supplied via bite drinkers. Meters were installed on the water supply line to each shed and daily readings were taken. Feed intake was assessed daily by the stockman. Coughing incidence was measured daily as an indicator of respiratory disease. On a clinicial evaluation Enzootic Pneumonia and/or Swine Influenza outbreaks occurred during the study. During the study 9 episode of decreased food intake occurred/ In 8 of these there was a concurrent decrease in water usage. During 4 episodes there was an increase in the coughing sours. In these 4 cases the water decrease preceeded the decline in food intake and the rise in coughing. A clear correlation between water consumption and food intake is demonstrated which suggests that daily water meter readings are an acceptable alternative to maintaining food intake as an indicator of health. It may be possible to use decreased water intakes as an indicator of impending respiratory disease. Overall a water intake of approx 1 litre per 10 kg body weight in the 30-60 kg range was observed.