Browsing by Author "Neves, Filipa I. G."
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- 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.
- 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.