Pilar Buera

Non-enzymatic browning kinetics analysed through water-solids interactions and water mobility in dehydrated potato.

Non-enzymatic browning (NEB) development was studied in dehydrated potato at 70°C. It was related to the macroscopic and molecular properties and to water-solid interactions over a wide range of water activities. Time resolved (1)H NMR, thermal transitions and water sorption isotherms were evaluated. Although non-enzymatic browning could be detected in the glassy state; colour development was higher in the supercooled state. The reaction rate increased up to a water content of 26g/100g of solids (aw=0.84) and then decreased at higher water contents, concomitantly with the increase of water proton mobility. The joint analyses of NEB kinetics, water sorption isotherm and proton relaxation behaviour made it evident that the point at which the reaction rate decreased, after a maximum value, could be related to the appearance of highly mobile water. The results obtained in this work indicate that the prediction of chemical reaction kinetics can be performed through the integrated analysis of water sorption, water and solids mobility and the physical state of the matrix.

Influence of water activity and temperature on the accumulation of zearalenone in corn

The influence of water activity (aw) and temperature on the zearalenone biosynthesis in corn has been examined. Viable corn kernels were conditioned at different values of water activity (0.90, 0.95 and 0.97), inoculated with Fusarium graminearum and incubated at different temperatures. Zearalenone was determined at selected times. For the strain used, a constant temperature of 25 degrees C resulted more favorable than 15 degrees C, 20 degrees C and the combination of two weeks at 25 degrees C followed by incubation at 15 degrees C shown by other authors to increase the zearalenone accumulation. Both F. graminearum growth and zearalenone production at 25 degrees C were inhibited at water activity 0.90. At short incubation times, toxin accumulation was greater at water activity 0.97 than at water activity 0.95 (25 degrees C). This relation was inverted at longer periods of incubation. A combined effect of water activity and temperature on the zearalenone accumulation was observed.

Water activity influence on aflatoxin accumulation in corn

The influence of water activity on the production of B1, B2, G1 and G2 aflatoxins in corn has been examined. Viable corn kernels were conditioned at three water activity levels (0.87, 0.90 and 0.97) and inoculated with Aspergillus parasiticus at 30 degrees C. Aflatoxin accumulation was determined at selected times by thin-layer chromatography. For the strain used total aflatoxin accumulation was greater at water activity 0.90 than at 0.87 and 0.97 for the incubation times studied.

Temperature influence on Penicillium citrinum thom growth and citrinin accumulation kinetics.

To study the temperature influence on both Penicillium citrinum growth and citrinin accumulation, a 20, 25 and 30 degrees C. Radial and 30 degrees C. Radial growth rate and lag phase were determined from the increase in colony diameter with time. The optimal temperature for P. citrinum growth was 30 degrees C. Citrinin extracted from the agar medium was determined by thin layer chromatography. Citrinin accumulation kinetics were analyzed by fitting the data to curves generated by using a logistic function. The parameters obtained from this equation demonstrated, for all temperatures studied, that the maximum citrinin accumulation by P. citrinum on Czapek agar with maize extract was at about 30 degrees C. At 37 degrees C a rapid decrease in the citrinin concentration was observed after a maximal value was reached.