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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.
- Novas tecnologias de processamentoPublication . Silva, Cristina L. M.; Alexandre, Elisabete M. C.; Santos, Dora M.; Vieira, Margarida C.; Gonçalves, Elsa M.; Oliveira, António J.
- Effect of heat and thermosonication treatments on watercress (Nasturtium officinale) vitamin C degradation kineticsPublication . Cruz, Rui M. S.; Vieira, Margarida C.; Silva, Cristina L.M.The use of ultrasound in food processing creates novel and interesting methodologies, which are often complementary to classical techniques. In this work, the effect of heat and the combined treatment heat/ultrasound (thermosonication) on the thermal degradation kinetics of vitamin C in watercress (Nasturtium officinale) was studied in the temperature range of 82.5 to 92.5 °C. First order reaction kinetics adequately described the vitamin C losses during both blanching processes. The activation energies and the reaction rates at 87.5 °C for heat (H) and thermosonication (Ts) treatmentswere, respectively, EavitCH =150.47± 42.81 kJ mol⁻¹ and EavitCTs =136.20±60.97 kJ mol⁻¹, and K₈₇.₅ °CvitCH=0.75±0.10 min−1 and K₈₇.₅°CvitCTs=0.58±0.11 min−1. No significant differences (P>0.05) were detected between both treatments. The thermosonication treatment was found to be a better blanching process, since it inactivates watercress peroxidase at less severe blanching conditions and consequently retains vitamin C content at higher levels. The present findings will help to optimise the blanching conditions for the production of a new and healthy frozen product, watercress, with heat and a new blanching process methodology.
- Kinetic parameters estimation for ascorbic acid degradation in fruit nectar using the partial equivalent isothermal exposures (PEIE) method under non-isothermal continuous heating conditionsPublication . Vieira, Margarida C.; Teixeira, Arthur A.; Silva, Cristina L. M.With the purpose of testing the Paired Equivalent Isothermal Exposures (PEIE) method to determine reaction kinetic parameters under non-isothermal conditions, continuous pasteurizations were carried out with a tropical fruit nectar [25% cupuacüu (Theobroma grandiflorum) pulp and 15% sugar] to estimate the ascorbic acid thermal degradation kinetic parameters. Fifteen continuous thermal exposures were studied, with seven being cycled. The experimental ascorbic acid thermal degradation kinetic parameters were estimated by the PEIE method (Ea ) 73 ( 9 kJ/mol, k80°C ) 0.017 ( 0.001 min-1). These values compared very well to the previously determined values for the same product under isothermal conditions (Ea ) 73 ( 7 kJ/mol, k80°C ) 0.020 ( 0.001 min-1). The predicted extents of reaction presented a good fit to the experimental data, although the cycled thermal treatments presented some deviation. In addition to being easier and faster than the Isothermal method, the PEIE method can be a more reliable method to estimate first-order reaction kinetic parameters when continuous heating is considered.
- Enterococcus faecalis and pseudomonas aeruginosa behaviour in frozen watercress (Nasturtium Officinale) submitted to temperature abusesPublication . Oliveira, Sílvia R.; Cruz, Rui M.S.; Vieira, Margarida C.; Silva, Cristina L.M.; Gaspar, Maria N.Watercress is an herb traditionally consumed fresh. If frozen, would be readily available to consumers. However, pathogenics resistant to frozen storage are a safety concern in this new product. In this study watercress was artificially contaminated with Pseudomonas aeruginosa ATCC 27853 and Enterococcus faecalis ATCC 29212. Their survival was evaluated after blanching, frozen storage and temperature fluctuations of the frozen product. The blanching caused a reduction of about 2 log cfu per gram of product of total viable count (TVC) and about 1.7 and 1.3 log cfu per gram of product of P. aeruginosa and E. faecalis, respectively. P. aeruginosa seemed to be more sensitive to temperature abuses than E. faecalis. After 3 months, TVC was still observed with a reduction of about 3 log cfu per gram of product. At the end of the study, exposure to freeze–thaw cycles resulted in death or injury of the microorganisms. These findings on the behaviour of two microorganisms of concern in frozen watercress will help improving the safety and cold chain settings for this product.
- Effects of UV pre-treatments on frozen vegetables qualityPublication . Neves, Filipa I. G.; Vieira, Margarida C.; Silva, Cristina L. M.Vegetables play a particularly important role in human diet and their stabilization after harvesting and during sub-sequent storage is critical. Among several long-term preservation processes, freezing is widely recognized as a proven and efficient method for vegetables. Most vegetables require a short heat treatment (blanching) prior to freezing to reduce microbiota and inactivate enzymes responsible for deteriorative reactions. However, detrimental effects occur during this process, such as alterations of plant tissues and consequent texture changes, solubilisation of nutrients in the blanching medium, thermal degradation of nutrients, weight loss and color changes, resulting in quality losses. Therefore, a rigorous balance between enzyme inactivation (correlated to degradation) and minimization of quality losses must be achieved in order to produce the highest final quality of frozen product. The increasing consumers demand for high-quality food standards, have stimulated research on alternative and/or mild processing technologies that extend shelf-life without the detrimental effects caused by severe heating. From an industrial perspective, thermal processes are extremely energy consuming and have high environmental impact. Nonthermal processes, or their combination with less severe heat treatments applied before low-temperature storage, are emergent challenges with potential applications in the food industry. The application of ultraviolet irradiation is an example of such processes.Ultraviolet radiation (UV) occupies a wide band in the non-ionizing region of the electromagnetic spectrum, with a wavelength between 100 and 400 nm. Application of UV-C radiation in the germicidal range (240-260 nm) as a non-thermal food processing technology, by pulses or continuously to food right after thermal processing of frozen vegetables, may improve the process‘ quality by reducing heat. It is generally claimed that the main parameters influencing sensory and quality changes on food are the dose of UV radiation applied (measured in intensity of flux in J/m2), treatment time, and the distance between the UV source and product. UV-C pre-treatments present a high potential to retain the vegetable quality after freezing process and storage.
- Processing zucchini (Cucurbita pepo L.) with low UV-C radiationPublication . Portela, Mauro; Silva, Cristina L. M.; Brandão, Teresa R. S.; Gonçalves, Elsa M.; Abreu, M.; Oliveira, António J.; Gaspar, Nelma P.; Vieira, Margarida C.
- Stability of cupuaçu (Theobroma grandi orum) nectar during storagePublication . Vieira, Margarida C.; Silva, Cristina L.M.A shelf-life study on cupua cu nectar (Theobroma grandi orum) was carried out in two parts. Part I studied the microbial stability of the regular nectar (batch R) and the same nectar forti ed with synthetic ascorbic acid (AA) (batch F), pasteurized at 90 C for 3 min and hot lled in glass bottles. Total Plate Count (TPC), yeast and molds as well as pH, total soluble solids (TSS), titratable acidity and hidroxymethylfurfural (HMF) were followed along 43 storage days at 4, 25 and 35 C. At the end of the storage period neither TPC nor molds or yeast had recovered the initial loads observed before pasteurization, for both R and F batches. Right after pasteurization, acidity increased slightly, pH decreased from 3.52 to 3.3, and TSS increased from 18.7 to 19.0 Brix, with all stabilizing afterwards. Part II evaluated ascorbic (AA) and dehydroascorbic (DHAA) acids' stabilization in the two batches, R and F, and dissolved oxygen (DO) was monitored. Both batches were stored at the same temperatures as in Part I for two months. For batch R, the AA degradation results followed a reversible rst order reaction (EaAA(R) =-34 6 kJ/mol, kAA(R)25 C=0.006 0.003 days 1, C0AA(R)=0.92 0.01 and C1AA(R)= 0.43 0.19). For the (F) nectar, the experimental data tted a rst order model well (EaAA(F)=30 17 kJ/mol, kAA(F)25 C=0.0016 0.0004 days 1). DO was modeled as a fractional conversion model (EaDO= 67 17 kJ/mol, kDO25 C= 1.94 0.94 days 1, C0DO=0.97 0.03 and C1DO= 0.55 0.01). For both nectars, storage at environmental temperatures was preferred (AA retention above 80%) to refrigeration, due to the slower rate of di usion of DO at lower temperatures.
- Mathematical modeling of the thermal degradation kinetics of vitamin C in cupuaçu (Theobroma grandiflorum) nectarPublication . Vieira, Margarida C.; Teixeira, A. A.; Silva, C. L. M.The thermal degradation kinetics of both components of vitamin C, ascorbic acid (AA) and dehydroascorbic acid (DHAA), were determined in a nectar of Cupuacßu (Theobroma grandi¯orum) with 25% of pulp and 15% of sugar in water. AA was assayed by HPLC and the results showed that AA degraded into DHAA. A reversible ®rst order model described well the AA degradation data, with an activation energy of 74 5 kJ/mol and k80 C 0:032 0:003min ÿ1. DHAA kinetic behavior suggested a consecutive ®rst order reaction where DHAA was the intermediate product of AA degradation. A mechanistic model was derived to predict DHAA concentration. Rate constants were replaced by the Arrhenius equation in the model to evaluate the temperature dependence and the kinetic parameters for AA degradation, previously determined, were used. An activation energy of 65 9 kJ/mol and a k80 C of 0:013 0:003 min ÿ1 were estimated. The present ®ndings will help to predict the best Cupuacßu nectar processing conditions that minimize degradation of an important quality factor such as vitamin C.
- Efeito dos abusos de temperatura no teor de ácido ascórbico em agrião congelado ao longo da cadeia de distribuiçãoPublication . Cruz, Rui M. S.; Vieira, Margarida C.; Silva, Cristina L. M.Este trabalho consistiu no estudo do efeito dos abusos de temperatura no teor de ácido ascórbico (AA) em agrião congelado ao longo da cadeia de distribuição. Para tal, simulou-se um conjunto de condições a que os produtos congelados são sujeitos desde a saída da fábrica até ao consumidor. O agrião, antes do processo de congelação, foi branqueado a uma temperatura de 95 ºC durante 20 s, para uma redução de 90% na actividade específica da enzima peroxidase. O teor de ácido ascórbico do agrião congelado foi determinado ao longo do plano de abusos de temperatura, baseado numa situação real e comparado com um modelo de previsão, usando os parâmetros cinéticos determinados em condições isotérmicas. Verificou-se que durante os abusos de temperatura o teor de AA sofreu oscilações, mas não apresentou grandes alterações no final do plano a que foi submetido. Alguns pontos experimentais e o valor final do teor de ácido ascórbico do agrião congelado abusado foram semelhantes aos valores previstos, apesar de na maior parte dos casos os valores experimentais terem sido superiores aos previstos. O processo de branqueamento, apesar de ter sido responsável por degradar o ácido ascórbico, contribuiu para a estabilidade do agrião ao longo do armazenamento. Este tipo de estudos são uma ferramenta importante, pois permitem a previsão de resultados de diferentes cenários de armazenamento e condições de distribuição, e assim poderão contribuir para a melhoria da qualidade dos produtos congelados e para o estabelecimento de melhores condições da cadeia de frio.
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