Browsing by Author "Silva, C."
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- Critical evaluation of commonly used objective functions to optimize overall quality and nutrient retention of heat-preserved foodsPublication . Silva, C.; Hendrickx, M.; Oliveira, F.; Tobback, P.Two objective functions—volume average retention and volume average cook-value—commonly used to optimize the overall quality and nutrient retention of heat-preserved foods, were studied and optimal processing conditions based on the two approaches were compared. Case studies from the literature were run and tested for the two objective functions. The influence of the decimal reduction time (at the reference temperature, Dref value) of the quality factor on the optimal processing temperature was evaluated. For high Dref values, e.g. for vitamins, the two objective functions give the same results and the Dref value has a minor influence on the optimum processing conditions. For low Dref values, such as for texture and colour, the optimal sterilization temperature is affected by this parameter and the use of volume average cook-value, as objective function, does not take this effect into account, which may result in underestimation of the optimal processing temperature.
- Effect of pH upon viability of probiotic strains when in contact with fruit pulpsPublication . Rodrigues, C.; Sousa, S.; Pinto, A.; Brandão, T.; Silva, J.; Pintado, M.; Silva, C.; Morais, A.; Teixeira, P.; Gomes, A.; Almeida, D.In recent years many probiotic-containing products have been developed, being dairy and dried products the main vehicles for probiotic intake. Fruit juices have also been studied, with less good results, probably due to their low pH values, as well as to the presence of other components, adverse to the survival of the probiotic strains. In order to pinpoint possible reasons therefore, in this study we tried to evaluate the effect of the fruit pulp pH upon the survival of Lactobacillus acidophilus LA-5 and Bifidobacterium animalis BB-12. Two fruit pulps, with different pH values, were used, namely lemon (pH=2.5) and avocado (pH=6.5), and their pH was adjusted (to 2.5, 4.5 and 6.5), in order to access the effect upon probiotic survival over one week storage. Viability was evaluated at 0, 3 and 7 days. Results showed that, although the pH value is indeed important, it is not the only reason for low viability of probiotics when incorporated in fruit pulps. Viability was, as expected, the highest when the pulps had a pH value of 6.5. At 4.5, avocado still had considerable viable cell numbers after one week contact with the pulp, while for lemon, at the same pH, no probiotics were detected after 3 days. At 2.5, for both pulps, no viable cells were detected after only 3 days. These results indicate that, although pH is important, other constituents of the fruits are also responsible for the degree of survival of probiotics in fruit matrices.
- Effect of sulphate supplementation on polysaccharide production and composition in two Porphyridium cruentum strainsPublication . Sousa, A. M.; Silva, C.; Raposo, M. F. J.; Morais, R. M.
- Effect of sulphate supplementation on polysaccharide production and composition in two porphyridium cruentum strainsPublication . Sousa, A. M.; Silva, C.; Raposo, M. F. de J.; Morais, R. M.
- Generalized (semi)-empirical formulae for optimal sterilization temperatures of conduction-heated foods with infinite surface heat transfer coefficientsPublication . Hendrickx, M.; Silva, C.; Oliveira, F.; Tobback, P.A computer program was developed to model heat sterilization of one-dimensional conduction-heated foods with negligible surface resistance to heat transfer. The optimal sterilization temperature, defined as the processing temperature that results in a food product with minimum surface cook-value after achieving the desired degree of sterility, was calculated as a function of food properties (thermal diffusivity, Z-value of the quality factor), processing conditions (dimensions and geometry of the food or container, initial temperature of the product, heating medium come-up-time) and processing criteria (target F0-value). The initial temperature of the food and the heating medium come-up-time have a minor effect on the optimal temperature. Generalized (semi)-empirical formulae relating optimal sterilization temperatures and all relevant variables were developed.
- Influence of rotational speed on the statistical variability of heat penetration parameters and on the non uniformity of lethality in retort processingPublication . Smout, C.; Ávila, I.; Van Loey, A.M.L.; Hendrickx, M.E.G.; Silva, C.In a case study on white beans, the e ect of rotation on the statistical variability of heat penetration parameters and on the nonuniformity of lethality in industrial-scale retort processing was investigated. In addition, the in¯uence of process time on the nonuniformity of lethality was evaluated. No clear relation between the non-uniformity of the heating parameters and the rotational speed was observed. Rotation seemed to in¯uence process lethality variability throughout the retort by its e ect on non-uniformity in heating characteristics and in retort temperature. Absolute non-uniformity (i.e. standard deviation) increased with increasing holding time, whereas relative non-uniformity (i.e. coe cient of variation) decreased as holding time increases
- Optimal sterilization temperatures for conduction heating foods considering finite surface heat transfer coefficientsPublication . Silva, C.; Hendrickx, M.; Oliveira, F.; Tobback, P.Optimal sterilization temperatures are defined as the processing temperatures which result in a minimum surface cook-value after achieving the desired degree of sterility. They were calculated as a function of product heating rate, surface heat transfer coefficient, initial food temperature, heating medium come-up-time, z-value for the quality factor and target Fo-value. Different one-dimensional heat transfer shapes were considered. Compared to the other variables, initial temperature and heating medium come-up-time had little influence on optimal processing temperature. Regression equations were developed relating optimal temperatures with all relevant variables.
- Optimizing thermal processes of conduction heated foods: generalized equation for optimal processing temperaturesPublication . Hendrickx, M.; Silva, C.; Oliveira, F.; Tobback, P.Optimal sterilization temperatures, for maximum surface quality retention, were calculated as a function of : (I)product propertles (thermal diffusivity and z.value) (II) processlng conditions Igeometry and dlmensions of the food, surface heat transfer coefficient, initial product temperature and retort come up time) and z-value (III) processing criteria (target- Fo.value). From this theoretical study generalized empirical relations relating optimal temperatures and all relevant variables were formulated and presented. Applications in classical canning are lllustrated in detail.
- Storage stability of a safer ovos moles formulation: texture and microbiological assessmentPublication . Fundo, J.; Quintas, M.; Brandão, Teresa R. S.; Silva, C.
- Study of the influence of ethylene oxide sterilization variables on Bacillus subtilis inactivationPublication . Mendes, G.; Brandão, Teresa R. S.; Silva, C.