Percorrer por autor "Pereira, Pedro M."
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- Análise da mobilidade molecular em matrizes sólidas utilizando conceitos de ciências de biomateriais: aplicação na optimização da qualidade de produtos congeladosPublication . Oliveira, Jorge C.; Cruz, Isabel B.; Pereira, Pedro M.; Frias, Jesus M.O estudo de matrizes sólidas bioquímicas utilizando as noções de transição de estado vítreo desenvolvidos na ciência dos materiais (poliméricos) é um assunto que tem recebido crescente atenção na biotecnologia e ciência e engenharia de processos alimentares, sobretudo pela sua aplicação na melhoria de produtos desidratados, congelados preparações enzimáticas e culturas celulares. Esta comunicação apresenta uma revisão sucinta destes conceitos, aplicados em particular à optimização da qualidade de alimentos congelados. Esta teoria permite desenvolver linhas de investigação sobre alteração da formulação dos produtos no sentido de aumentar a sua capacidade de manter a qualidade obtida no processo de congelação durante o armazenamento e distribuição.
- Integrated approach on heat transfer and inactivation kinetics of microorganisms on the surface of foods during heat treatments: Software developmentPublication . Gil, Maria M.; Pereira, Pedro M.; Brandão, Teresa R. S.; Silva, Cristina L.M.; Kondjoyan, Alain; Valdramidis, Vassilis P.; Geeraerd, Annemie H.; Impe, Jan F.M. Van; James, SteveThe objective of this work was to create a software application (Bugdeath 1.0) for the simulation of inactivation kinetics of microorganisms on the surface of foods, during dry and wet pasteurisation treatments. The program was developed under the Real Basic 5.2 application, and it is a user-friendly tool. It integrates heat transfer phenomena and microbial inactivation under constant and time-varying temperature conditions. On the basis of the selection of a heating regime of the medium, the program predicts the food surface temperature and the change in microbial load during the process. Input data and simulated values can be visualised in graphics or data tables. Printing, exporting and saving file options are also available. Bugdeath 1.0 includes also a useful database of foods (beef and potato) and related thermal properties, microorganisms (Salmonella and Listeria monocytogenes) and corresponding inactivation kinetic parameters. This software can be coupled to an apparatus developed under the scope of the European Project BUGDEATH (QLRT-2001-01415), which was conceived to provide repeatable surface temperature-time treatments on food samples. The program has also a great potential for research and industrial applications.
- Measurement of glass transition in native wheat flour by dynamic mechanical thermal analysis (DMTA)Publication . Pereira, Pedro M.; Oliveira, Jorge C.This work describes a method to study glass transition on native starch powders, based on dynamical mechanical thermal analysis using compression tests, and was applied to wheat flour (13.5% water content). This method will allow the determination of Tg in native (unprocessed) starchy materials, with minimal disturbance of the natural structures. The influence of the test conditions (heating rate, frequency and strain) on the glass transition measurements was determined using factorial designs. The values of Tg determined as the maxima of the energy dissipation (peaks in E ) of native flour and of freezedried pre-gelatinized flour were not statistically different (around 64 C). The heating rate did not affect the measurements in the range tested (0.25 to 1 C min 1). An interactive effect of the strain amplitude and the frequency was detected. The significance of this interaction can be caused by differences in mechanical energy dissipation, which would indicate that not only temperature but also the total energy input may affect this transition. Slight effects of phase separation between gluten and starch were found on native flour.