Browsing by Author "Reinas, Isabel"
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- Effect of whey protein purity and glycerol content upon physical properties of edible films manufactured therefromPublication . Ramos, Óscar L.; Reinas, Isabel; Silva, Sara I.; Fernandes, João C.; Cerqueira, Miguel A.; Pereira, Ricardo N.; Vicente, António A.; Poças, M. Fátima; Pintado, Manuela E.; Malcata, F. XavierThis manuscript describes the detailed characterization of edible films made from two different protein products e whey protein isolate (WPI) and whey protein concentrate (WPC), added with three levels of glycerol (Gly) e i.e. 40, 50 and 60%(w/w). The molecular structure, as well as barrier, tensile, thermal, surface and optical properties of said films were determined, in attempts to provide a better understanding of the effects of proteinaceous purity and Gly content of the feedstock. WPI films exhibited statistically lower (p < 0.05) moisture content (MC), film solubility (S), water activity, water vapor permeability (WVP), oxygen and carbon dioxide permeabilities (O2P and CO2P, respectively) and color change values, as well as statistically higher (p < 0.05) density, surface hydrophobicity, mechanical resistance, elasticity, extensibility and transparency values than their WPC counterparts, for the same content of Gly. These results are consistent with data from thermal and FTIR analyses. Furthermore, a significant increase (p < 0.05) was observed in MC, S, WVP, O2P, CO2P, weight loss and extensibility of both protein films when the Gly content increased; whereas a significant decrease (p < 0.05) was observed in thermal features, as well as in mechanical resistance and elasticity e thus leading to weaker films. Therefore, fundamental elucidation was provided on the features of WPI and WPC germane to food packaging e along with suggestions to improve the most critical ones, i.e. extensibility and WVP.
- A quantitative approach to assess the contribution of seals to the permeability of water vapour and oxygen in thermosealed packagesPublication . Reinas, Isabel; Oliveira, Jorge; Pereira, Joel; Mahajan, Pramod; Poças, Maria de FátimaShelf-life of many foods is largely dependent on the barrier to moisture and oxygen of the respective package. Barrier is often assessed by measuring the transmission rate of films. However, in thermosealed packages leaks and weak seals can give rise to increased total mass transfer entering the system and reaching the food. While leaks are random defects and are associated to early failure, lower integrity of regular seals tends to affect whole batch causing a decrease in the product shelf-life. In the present work the contribution of the seals to total permeability of packages was assessed by measuring transmission rate of the film and of thermosealed packages of different sizes, therefore with different seals length. Packages made of PA/PE and PVDC coated PET/PE and their respective films were tested for moisture and oxygen transmission rate at different temperature and relative humidity. Results indicate that industrial regular produced seals can account for ca. 25% of the total mass transfer through the system. This decrease of the package barrier as compared to the material barrier will have a significant impact on the product shelf-life and it should be considered in the packaging design process.