CBQF - Documentos de Conferências / Conference Objects
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- Optimization of heat transfer in thermal processing of conduction heated foodsPublication . Hendrickx, M.; Silva, Cristina L. M.; Oliveira, F.; Tobback, P.Optimal sterilization temperature was defined as the temperature resulting in a minimum surface cook-value product together with the desired degree of sterility. Sterilization of conduction heated foods, with simple shapes as infinite slab, infinite cylinder and sphere, was modelled. The model assumed first order inactivation kinetics for microorganisms and quality. The temperature distribution was solved by an explicit finite difference numerical method with a non-capacitance surface node. Optimal temperatures were calculated as a function of : i) Food Properties - thermal diffusivity, Z-value for the quality factor, Processing Conditions - dimensions and geometry of the food or container, surface heat transfer coefficient, initial product temperature, heating medium come-up-time and Processing Criteria - target Fovalue.Initial food temperature and heating medium come-up-time have a minor influence on the optimal conditions. Generalized (semi)-empirical formulas relating quantitatively optimal temperatures and all relevant variables were developed. The generalized equations are a valuable tool to calculate or estimate processing sterilization conditions for regularly and irregularly shaped products. They were successfully applied to predict the optimal sterilization temperatures for conduction heated foods, packaged in typical cylindrical cans and retortable pouches, with different surface resistances to hea, transfer.
- Obtaining a well balanced product quality in thermally processed conduction heating foods by analyzing surface and volume average quality optimum processing conditionsPublication . Silva, Cristina L.M.; Oliveira, Fernanda A. R.; Hendrickx, MarkSterilization temperatures that maximize each of the two objective functions - surface or volume average quality - were calculated as a function of the relevant influential variables using computer modeling. The resulting volume average and surface quality retentions were both determined for each case study. The effect of using sterilization conditions defined, for optimal surface quality on volume average quality and the effect of using sterilization temperatures defined for optimum volume average quality on surface quality were qualitatively and systematically investigated using the statistical 21.1 factorial design method. If the degradation kinetics for the quality factors considered at the surface and in volume average terms are similar, the use of sterilization temperatures for maximizing surface quality is suggested, when the aim is to obtain a product with a well balanced maximum final quality. On the other hand, if the quality factors have different degradation kinetics, the use of optimum sterilization conditions maximizing the quality at the surface or in volume average terms has to be analyzed on a case by case basis.
- Potencial biotecnológico das microalgasPublication . Carvalho, A. P.; Meireles, L. A.; Malcata, F. X.; Oliveira, G.; Raposo, M. F.; Morais, R.
- Determinação de nitratos em culturas de microalgasPublication . Carvalho, Ana P.; Meireles, Luís A.; Malcata, F. Xavier
- A new methodology for optimizing solar drying of fruitsPublication . Ramos, Inês N.; Silva, Cristina L. M.
- Impact of microfiltration on the manufacture of goat’s milk cheese - microbiological studiesPublication . Pintado, M. Manuela E.; Gomes, Ana M. P.; Eloy, Susana; Pereira, C. Dias; Malcata, F. Xavier
- Effects of mercury and zinc on growth of isolated consortiaPublication . Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. Xavier
- Simultaneous determination of tartaric acid and potassium in wines using a dialysis multicommuted flow systemPublication . Oliveira, Sara M.; Lopes, Teresa I. M. S.; Tóth, Ildikó V.; Rangel, António O. S. S.
- Survival of different Listeria monocytogenes strains to combined stressesPublication . Ramalheira, R.; Brandão, T.; Silva, J.; Hogg, T.; Teixeira, P.
- Improvement of whey cheese matrices via incorporation of Lactobacillus acidophilus — proteolytic and glycolytic activities and their impact upon sensory analysisPublication . Pintado, A. I. E.; Araújo, J. C. C.; Pintado, M. M. E.; Gomes, A. M. P.; Malcata, F. X.Requeijão is a highly nutritious soft Portuguese whey cheese, yet with such organoleptic limitations as poor flavour and grainy texture. Furthermore, it offers excellent conditions for survival and growth of lactic acid bacteria, owing to its high water activity, pH above 5.0 and low salt content. The objective of this research effort was thus to study the contribution of Lactobacillus acidophilus LAC 1 to the improvement of the organoleptic quality of Requeijão, via its proteolytic and glycolytic activities. Experimental whey cheese matrices were produced, and subsequently inoculated with L. acidophilus; these matrices, as well as a control curd, were stored at 7 °C, and samples were taken at 0, 2, 7, 14 and 21 d. Cell viability, pH, and fat, protein and moisture contents were assessed. The contents of water-soluble nitrogen (WSN), nitrogen soluble in 12 %(w/v) trichloroacetic acid (TCA) and nitrogen soluble in 5 %(w/v) phosphotungstic acid (PTA), as well as of lactose and organic acids were also determined. Sensory analysis was finally performed, using a five-point scale for the various attributes. L. acidophilus viable cells number remained constant up to 21 d, while pH decreased by ca. 0,6; this was consistent with an increase in lactic acid content up to 28 mg/g of whey cheese. Values of TCA and PTA in L. acidophilus matrices indicated relevant proteolytic breakdown of whey proteins. These matrices received the highest overall preference scores in sensory evaluation.