Browsing by Author "Vieira, Margarida C."
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- Alicyclobacillus acidoterrestris spores as a target for Cupuaçu Theobroma grandiflorum) nectar thermal processing: Kinetic parameters and experimental methodsPublication . Vieira, Margarida C.; Teixeira, Arthur A.; Silva, Filipa M.; Gaspar, Nelma; Silva, Cristina L.M.The kinetic parameters of thermal inactivation of a spore former, Alicyclobacillus acidoterrestris, in a tropical fruit nectar [25% of Cupuac u (Theobroma grandiflorum) pulp and 15% sugar] were determined by the isothermal method (IM), under batch heating, and by the paired equivalent isothermal exposures (PEIE) method, under non-isothermal continuous conditions. The isothermal experiments were repeated three times, every 4 months, with the same spore suspension kept frozen between experiments. The aging of spores, under frozen storage, seemed to produce a notorious increase in the z-value from experiment to experiment: Experiment 1 (z = 7.8F2.6 jC, D95 jC = 5.29F0.96 min), Experiment 2 (z=22F5 jC, D95 jC = 5.99F0.63 min), and Experiment 3 (z=29F10 jC, D95 jC = 3.82F0.48 min). The evaluation of the kinetic parameters by the PEIE method was carried out in parallel with Experiment 3, with the same aged spores, and the results (z=31F6 jC, D95 jC = 5.5F1.2 min) were close to the ones obtained in this experiment. From this work, it seems that the PEIE method can also be applied to evaluate the reduction parameters of a spore-forming microorganism, and in a more realistic way, since the continuous system eliminates the errors caused by come-up and cool-down times (CUT and CDT) that are unavoidable in isothermal experiments. Therefore, when designing a thermal process for a continuous system, the PEIE method should be used, or the chances are that the process would be underdesigned, risking that the desired level of spore inactivation would not be achieved. An optimization of the thermal processing conditions was next performed for Cupuac u nectar, considering a 5D reduction in A. acidoterrestris spores. If a pasteurization process is considered, the conditions that ensure safety (9 min at 98 jC) only allow a 55% retention of ascorbic acid (AA). If sterilization is considered, 8 s at 115 jC will ensure a safe product and retain 98.5% of the original ascorbic acid. Therefore, if A. acidoterrestris is considered as the target microorganism, the nectar should undergo an aseptic high temperature short time principle (HTST) process to achieve a 5D reduction in this acidophilus spore former. However, if the hot-fill-and-hold pasteurization process is preferred, the product should be fortified with ascorbic acid.
- Combined pre-treatments effects on zucchini (Cucurbita pepo L.) squash microbial load reductionPublication . Neves, Filipa I. G.; Silva, Cristina L. M.; Vieira, Margarida C.Freezing vegetables requires pre-treatments to reduce microbial load and destroy enzymes that impair the frozen product quality. So far blanching has been the most effective pre-treatment, preferred by the food industry, despite its severity: heating up to temperatures close to 100 °C for 1–3 min causes sensory and texture changes in most horticultural products. Alternative blanching treatments, using UV-C radiation combined with milder thermal treatments or with thermosonication, may improve the quality of the final frozen vegetables. Zucchini (Cucurbita pepo L.), the vegetable under study, has an availability in fresh restricted to a season, needing therefore to be often frozen to be used throughout the year. In this study, its surface was first inoculated with two vegetable contaminants, Enterococcus faecalis and Deinococcus radiodurans cells, which are resistant, respectively, to high temperatures and to radiation and then submitted to several blanching treatments, single or combined, and the effect on these microorganisms reduction was evaluated. As single treatments, water blanching (the control treatment, as it is the blanching treatment traditionally used) was applied up to 180 s at temperatures ranging from 65 to 90 °C, and UV-irradiation applied in continuous. As combined pre-treatments, water blanching combined with UV-C (continuous or in pulses), and thermosonication (20 kHz at 50% of power) combined with UV-C pulses were also studied. The continuous UV-C radiation incident irradiance was 11 W/m2 up to 180 s, and the pulses at incident radiance of 67 W/m2, lasting 3.5 s each (35 pulses). Mathematical modeling of bacterial reduction data was carried out using the Bigelow, the Weibull and Weibull modified models, and estimation of their respective kinetic parameters proved that the latter models presented a better fit below 75 °C. The best results proved to be the combination of water blanching at temperatures as low as 85 °C during <2 min with 25 pulses of UV-C (incident irradiance of 67 W/m2) or thermosonication at 90 °C also combined with UV-C pulses, both resulting in 3 log reductions of both microorganisms under study. These results proved to overcome what industry is requiring so far (a 2 log microbial reduction in 3 min), hence minimizing quality changes of frozen zucchini.
- 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.
- 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 heat and thermosonication treatments on peroxidise inactivation kinetics in watercress (nasturtium officinale)Publication . Cruz, Rui M. S.; Vieira, Margarida C.; Silva, Cristina L. M.The effect of heat and the combined heat/ultrasound (thermosonication) treatment on the inactivation kinetics of peroxidase in watercress (Nasturtium officinale) was studied in the temperature range of 40-92.5 degrees C. In the heat blanching processes, the enzyme kinetics showed a first-order biphasic inactivation model. The activation energies and the rates of the reaction at a reference temperature for both the heat-labile and heat-resistant fractions were, respectively, E-a1 = 421 +/- 115 kJmol(-1) and E-a2 = 352 +/- 81 kJmol(-1), k(184.6 degrees C) = 18 +/- 14min(-1) and k(284.6 degrees C) = 0.24 +/- 0.14min(-1). The initial relative specific activity for both isoenzyme fractions were also estimated, being C-01 = 0.5 +/- 0.08 mu mol min(-1)mg protein(-1) and C-02 = 0.5 +/- 0.06 mu mol min(-1)mg protein(-1), respectively. The application of thermosonication was studied to enable less severe thermal treatments and, therefore, improving the quality of the blanched product. In this treatment the enzyme kinetics showed a first-order model. The activation energy, the rate of reaction at a reference temperature and the initial relative specific activity were, respectively, E-a3 = 496 +/- 65 kJmol(-1), k(387.5 degrees C) = 10 +/- 2min(-1) and C-03 = 1 +/- 0.05 mu mol min(-1)mg protein(-1), proving that the enzyme became more heat labile. The present findings will help to design the blanching conditions for the production of a new and healthy frozen product, watercress (Nasturtium officinale), with minimized colour or flavour changes along its shelf life.
- 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.
- 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. Non- thermal 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.
- Enhancing carob flour (Ceratonia siliqua L.) for by-product utilization in food industries: carob syrup production, functional profiling and applicationPublication . Vilas-Boas, Ana Martins; Brassesco, María Emília; Quintino, Andreia C.; Medronho, Bruno; Vieira, Margarida C.; Brandão, Teresa R. S.; Silva, Cristina L. M.; Silva, Beatriz; Azevedo, Miguel; Pintado, ManuelaThe focus on by-product valorization in the food industry, particularly from the carob pod, underscores a commitment to sustainability and resource efficiency. This fruit, sourced from the leguminous evergreen carob tree (Ceratonia siliqua L.), is renowned for its adaptable flavour and nutritional value, in Mediterranean regions such as Portugal. Its production yields significant by-products, presenting environmental challenges when not managed efficiently. Innovative approaches, including integral carob flour production, aim to optimize utilization while minimizing waste and energy consumption. This study repurposed carob waste to produce novel, value-added ingredients like carob syrup, by thermal hydrolysis of integral carob flour using water at 1:3 solid-to-liquid ratio - obtaining up to 50 % solubility yield. The resulting syrup exhibited 72 % °Brix, a melting temperature (Tm) of approximately 130 °C and predominantly viscous behavior with minimal elastic (solid-like) response. Lastly, the syrup was incorporated into a carob-based brigadeiro, replacing conventional glucose-fructose syrup. Simulated gastrointestinal digestion revealed enhanced bioaccessibility of sugars and phenolics, and increased antioxidant activity during the intestinal phase. Despite sugar availability, the prebiotic activity of the syrup decreased when embedded in the brigadeiro matrix, potentially due to interactions with polyphenols or organic acids. Cytotoxicity and permeability assays confirmed safety at ?0.5 % (w/v) and supported intestinal barrier integrity. These findings support the use of integral carob flour for producing multifunctional ingredients, contributing to circular economy models while meeting consumer demands for healthier, sustainable food products.
- 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.
- Impact of thermal blanching and thermosonication treatments on watercress (Nasturtium officinale) quality: thermosonication process optimisation and microstructure evaluationPublication . Cruz, Rui M. S.; Vieira, Margarida C.; Fonseca, Susana C.; Silva, Cristina L. M.The objectives of the present work were to optimise watercress heat and thermosonication blanching conditions, in order to obtain a product with better quality for further freezing, and to evaluate the effects of thermosonication on the microstructure of watercress leaves. In a chart of optimal time-temperature conditions for a 90% peroxidase inactivation (imposed constraint), vitamin C (objective function) and a-value (improvement toward green) were mathematically predicted for both heat and thermosonication blanching treatments. Two optimal thermosonication combinations were selected: 92 A degrees C and 2 s, retaining 95% of vitamin C content and 5% a-value improvement, and a better condition in terms of practical feasibility, 86 A degrees C and 30 s, allowing a 75% vitamin C retention and 8% a-value improvement. The experimental values, for each thermosonication optimal time-temperature zone, were in good agreement with the models' predicted responses. In terms of microstructure, thermosonicated watercress at 86 and 92 A degrees C showed similar loss of turgor and release of chloroplasts. The proposed optimal thermosonication blanching conditions allow the improvement of the blanched watercress quality and consequently contribute for the development of a high-quality new frozen product. However, a suitable scale-up is mandatory for industrial implementation.
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