Teresa R. S. Brandão

Technological Optimization of Manufacture of Probiotic Whey Cheese Matrices

In attempts to optimize their manufacture, whey cheese matrices obtained via thermal processing of whey (leading to protein precipitation) and inoculated with probiotic cultures were tested. A central composite, face-centered design was followed, so a total of 16 experiments were run using fractional addition of bovine milk to feedstock whey, homogenization time, and storage time of whey cheese as processing parameters. Probiotic whey cheese matrices were inoculated with Lactobacillus casei LAFTIL26 at 10% (v/v), whereas control whey cheese matrices were added with skim milk previously acidified with lactic acid to the same level. All whey cheeses were stored at 7 °C up to 14 d. Chemical and sensory analyses were carried out for all samples, as well as rheological characterization by oscillatory viscometry and textural profiling. As expected, differences were found between control and probiotic matrices: fractional addition of milk and storage time were the factors accounting for the most important effects. Estimation of the best operating parameters was via response surface analysis: milk addition at a rate of 10% to 15% (v/v), and homogenization for 5 min led to the best probiotic whey cheeses in terms of texture and organoleptic properties, whereas the best time for consumption was found to be by 9 d of storage following manufacture.

Modelling growth of, and removal of Zn and Hg by a wild microalgal consortium.

Microorganisms isolated from sites contaminated with heavy metals usually possess a higher removal capacity than strains from regular cultures. Heavy metal-containing soil samples from an industrial dumpsite in Northern Portugal were accordingly collected; following enrichment under metal stress, a consortium of wild microalgae was obtained. Their ability to grow in the presence of, and their capacity to recover heavy metals was comprehensively studied; the datasets thus generated were fitted to by a combined model of biomass growth and metal uptake, derived from first principles. After exposure to 15 and 25xa0mg/L Zn2+ for 6xa0days, the microalgal consortium reached similar, or higher cell density than the control; however, under 50 and 65xa0mg/L Zn2+, 71% to 84% inhibition was observed. Growth in the presence of Hg2+ was significantly inhibited, even at a concentration as low as 25xa0μg/L, and 90% inhibition was observed above 100xa0μg/L. The maximum amount of Zn2+ removed was 21.3xa0mg/L, upon exposure to 25xa0mg/L for 6xa0day, whereas the maximum removal of Hg2+ was 335xa0μg/L, upon 6xa0day in the presence of 350xa0μg/L. The aforementioned mechanistic model was built upon Monod assumptions (including heavy metal inhibition), coupled with Leudeking–Piret relationships between the rates of biomass growth and metal removal. The overall fits were good under all experimental conditions tested, thus conveying a useful tool for rational optimisation of microalga-mediated bioremediation.

Simulation of Food Solar Drying

This chapter discusses the simulation process of food solar drying, presenting the basic issues of mass and heat transfer under time-varying conditions. Food drying embraces several phenomena, and scientists do not completely understand its underlying mechanisms. However, mathematical simulation and modelling provide comprehensions to improve the knowledge on the drying mechanisms, allow the prediction of the drying behaviour as well as being essential tools in the design of solar drying equipment. The major difficulty in simulating food solar drying arises from variable meteorological conditions that change air temperature, moisture and velocity inside the solar equipment, during the drying process. Therefore, an integrated mass and heat transfer model under dynamic conditions is presented, and appropriate assumptions are discussed. A meteorological model and desorption isotherms are taken into consideration as well. The integrated model includes food’s shrinkage, changing boundary conditions and variable thermal properties and water diffusivity with time and space (non-isotropic characteristics).