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- Effect of cold chain temperature abuses on the quality of frozen watercress (Nasturtium officinale R. Br.)Publication . Cruz, Rui M.S.; Vieira, Margarida C.; Silva, Cristina L.M.The objective of this work was to study the effect of temperature abuses on the colour and vitamin C content of a new frozen vegetable, watercress (Nasturtium officinale R. Br.). The vitamin C content, expressed as ascorbic (AA) and dehydroascorbic (DHAA) acids, and colour, expressed in the Hunter Lab parameters, were evaluated along a plan of temperature abuses, based on a real situation for a four month frozen storage period. A comparison between the hue angle and AA experimental data and prediction models, using kinetic parameters determined under isothermal conditions, was also run. The colour showed some variation, namely on the parameters L, a, TCD (Total Colour Difference) and hue angle. Although, during the temperature abuses, some fluctuation was observed, no vitamin C degradation or major colour changes occurred. A zero-order and a first-order prediction models fitted well the experimental data for the hue angle and AA behaviour with temperature abuses, respectively. In general, the frozen watercress colour and vitamin C content were not impaired by the imposed temperature abuses. This work will help to predict and understand the sensory and nutritional quality changes of frozen watercress that might occur during frozen storage and distribution in the cold chain under the used conditions.
- Effect of conventional heat and thermosonication treatments on broccoli (brassica oleracea L.) total phenolic contentPublication . Gonçalves, Elsa M.; Alegria, C.; Abreu, Marta; Brandão, Teresa R. S.; Silva, Cristina L. M.
- Stability of sunflower and rapeseed oil-in-water emulsions supplemented with ethanol-treated rapeseed meal protein isolatePublication . Kalaydzhiev, Hristo; Gandova, Vanya D.; Ivanova, Petya; Brandão, Teresa R. S.; Dessev, Tzvetelin T.; Silva, Cristina L. M.; Chalova, Vesela I.A protein isolate (ERPI) was prepared from ethanol-treated rapeseed meal and used as a stabilizing agent in sunflower and rapeseed oil-in-water emulsions. The aim of the current study was to explore the influence of protein and oil concentrations on initial stability of sunflower and rapeseed oil-in-water emulsions by evaluating Gibbs free energy (ΔG) and particle size distribution. The 7-day dynamics of emulsion stability was investigated by turbidity measurement as well. A 32 factorial design was applied to assess the significance of oil (5%, 10% and 15% w/w) and ERPI protein (0.25%, 0.5% and 1.0% w/w) addition on stability of the emulsions. The results demonstrated that the increase of oil concentrations from 5 to 15% positively influenced the initial stability of sunflower and rapeseed oil-in-water emulsions. In both oil types, ERPI protein supplementation at all levels resulted in significant differences in the stability of 5% and 10% oil emulsions but did not alter the initial stability of the emulsions prepared with either 15% sunflower or rapeseed oil. With a few exceptions, there was a good agreement between Gibbs free energy data and microstructural profiles of the emulsions. Overall, emulsions with all sunflower oil concentrations and 1.0% ERPI protein exhibited better initial and a 7-day stability dynamics compared to all rapeseed oil-based emulsions. The study demonstrated the potential of ethanol-treated rapeseed meal protein isolate to serve as an emulsifying agent in sunflower and rapeseed oil containing emulsions.
- Modelling colour and chlorophyll losses of frozen green beans (Phaseolus vulgaris, L.)Publication . Martins, R.C.; Silva, C. L. M.Colour changes and chlorophyll degradation of frozen green beans (Phaseolus vulgaris, L., variety bencanta) were studied during 250 days of storage at 7, 15 and 30 C. Chlorophyll a and b losses and colour Hunter a and b coordinates and total colour difference (TCDH) changes were successfully described by first order and reversible first order models, respectively. The temperature effect was described by the Arrhenius law. Disagreement between the colour co-ordinates and chlorophyll content was obtained. Therefore, chlorophyll content is not a good colour index of frozen green beans. The results emphasise that colour is a more important parameter to assess frozen green beans visual quality. # 2002 Elsevier Science Ltd and IIR. All rights reserved.
- Modelling optimum processing conditions for the sterilization of prepackaged foodsPublication . Silva, C. L. M.; Oliveira, F. A. R.; Hendrickx, M.Mathematical methods available to optimize heat sterilization of prepackaged foods are critically reviewed. Heat transfer models, with special relevance to those considering external resistance to heat transfer, are discussed. Different optimization methods and constraints are analysed and their applicability is evaluated. Several objective functions suggested in the literature to minimize quality degradation, energy consumption or economic costs are presented along with their impact on optimum conditions. The use of variable heating medium time temperature profile in order to improve sterilization conditions, both interms of mass average and surface quality retention, is also extensively reviewed. The review suggests that sufficient experimental evidence is lacking. Most models do not provide experimental validation and it is thought that this impairs the potential applications that would arise.
- Novas tecnologias de processamentoPublication . Silva, Cristina L. M.; Alexandre, Elisabete M. C.; Santos, Dora M.; Vieira, Margarida C.; Gonçalves, Elsa M.; Oliveira, António J.
- Novas tecnologias de prétratamento de hortofrutícolasPublication . Gonçalves, E. M.; Abreu, M.; Oliveira, A. J.; Portela, M.; Vieira, M. M. C.; Brandão, Teresa R. S.; Silva, C. L. M.
- Influence of drying processes and pretreatments on nutritional and bioactive characteristics of dried vegetables: a reviewPublication . Oliveira, Sara M.; Brandão, Teresa R. S.; Silva, Cristina L. M.Drying has been applied to vegetables in order to preserve, store and transport these food products. However, drying implies not only physical changes, easily detectable by the consumer through visual assessment, but also chemical modifications. These are not always visible,but are responsible for alterations in colour, flavour and nutritional value, which compromise the overall quality of the final product. The main chemical changes associated with drying are related to the degradation of phytochemicals, such as vitamins, antioxidants, minerals, pigments and other bioactive compounds sensitive to heat, light and oxygen. Moreover, nutrient losses are inevitably associated with leaching as a result of the water removal from the vegetable during the drying process. In order to prevent or reduce nutrient losses and thus improve the quality of dried products, pretreatments are often applied. In this review, an overview of the procedures developed for dehydration of vegetables applying heat by convection, conduction or radiation is presented. The influence of pretreatments on nutritional and bioactive characteristics of dried vegetables is discussed. Blanching with steam, water or chemical solutions is the most commonly used, but power ultrasound, ohmic blanching, osmotic and edible coatings pretreatments have also been reported. The influence of the drying processes and conditions on nutritional contents and bioactive characteristics is also presented.
- Drivers of innovation in education and training in food science and technologyPublication . Pittia, Paola; Silva, Cristina L.; Costa, Rui; Scheleining, Gerhard; Saguy, I. Sam
- Thermal inactivation of Alicyclobacillus acidoterrestris spores in fruit product processingPublication . Brandão, Teresa R. S.; Silva, Cristina L. M.Alicyclobacillus acidoterrestris spores were recently proposed to be used as design criterion for thermal processes of acid fruit products. This microorganism has been found in commercial pasteurized acid fruit juices, such as orange and apple. Although being non-pathogenic and not easy to detect visually, it is responsible for off-flavours development. On the other hand, the first thermal inactivation kinetic studies confirmed that these spores are much more resistant than the usual spoilage microorganisms in acid foods. Therefore, in 2000 it was firstly proposed to be used in the design of hot-filling and continuous pasteurization conditions of a tropical fruit pulp and juice, respectively. This work presents a critical review on inactivation kinetics of Alicyclobacillus acidoterrestris spores. The available studies were obtained under thermal treatments, and studied the effects of temperature, pH and soluble solids. Those effects were quantified in terms of decimal reduction time (first order model) and z-values (Bigelow model). Furthermore, they were obtained under isothermal conditions. Future challenges in this field are to quantify the inactivation kinetics behaviour under dynamic conditions, using thermal and non-thermal treatments, such as ozonation, ultrasonication or high pressure. These alternative treatments have the advantage of minimizing quality attributes degradation and improving products. Moreover, predictive microbiology skills are suggested as a valuable tool for process design and optimization.