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| Author(s): |
Valquíria Ros Polski
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia de Alimentos |
| Defense date: | 2011-05-05 |
| Examining board members: |
Gisele Anne Camargo;
Maria Isabel Berto;
Rosiane Lopes da Cunha;
Vijaya Grama Seetharamiengar Raghavan
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| Advisor: | Flávio Luis Schmidt |
| Abstract | |
The importance of using food thermal processing at high temperatures and short time (HTST) is that it guarantees the microbiological security of the product and leads to a higher preservation of quality characteristics, due to kinetic parameters that allow quality factors to have a lower destruction rate than that of microorganisms. There is a lack of data on rheological fluid behavior at high temperatures due to the difficulties brought by the experimental assembly and originated from the thermal degradation that the product can undergo during the long time required for reaching the equilibrium temperature. Product alterations can occur at high temperatures causing unexpected changes of viscosity, invalidating extrapolations obtained from equations that are true just for around 90°C (rheological measurements in non-pressurized equipment due to boiling of water). The increase or reduction of viscosity can modify the flow behavior of the fluid, thus causing an under or over-processing, depending on the case. For these reasons, it is important to know the rheological properties of the product, thermal treatment target microorganisms, pH, degradation kinetics of quality parameters at process temperatures, such as to make possible the design of optimized thermal treatments for specific products. The objective of this project was to study the rheological properties and degradation kinetics at high temperatures of products (food and model solutions) and to obtain quality degradation kinetic data such as browning, in order to optimize thermal treatments. In order to perform the experiments, the objective is to build a device (pressurized capillary rheometer and heat exchanger) capable of rapidly increasing the product temperature, thus minimizing changes due to heat. The capillary rheometer could be built, using microwave as the heating device. It was tested with sucrose solution and banana puree. It was observed a deviation from the Arrhenius curve for the rheological behavior of banana puree above 100°C, but not for sucrose solution. It was possible to model and study the dielectric properties at 915 MHz for different formulations of banana puree at thermal treatment temperatures. The methodology for obtaining the optimal region of thermal treatment was developed and improved. It was tested for banana puree in order to minimize browning (L value lower or equal to 56.2) and to guarantee safety based on Clostridium botulinum kinetics data. This region has 123°C as lower thermal processing temperature and 2 minutes as higher thermal treatment time (AU) | |
| FAPESP's process: | 07/00193-2 - Rheological measures and quality changes of products treated at high temperatures for microbiological safety and process optimization |
| Grantee: | Valquíria Ros Polski |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |