Percorrer por autor "Brecht, Jeffrey K."
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- Influence of low oxygen and high carbon dioxide on shredded Galega kale quality for development of modified atmosphere packagesPublication . Fonseca, Susana C.; Oliveira, Fernanda A. R.; Brecht, Jeffrey K.; Chau, Khe V.Respiration rate, sensory attributes, colour alterations, and water, chlorophyll and ascorbic acid contents were monitored during storage of shredded Galega kale (Brassica oleracea var. acephala DC.) at 20 ◦C to define an adequate range of O2 and CO2 partial pressures for product preservation. Different low O2 and high CO2 atmospheres were tested. First, tolerance to low O2 partial pressures (1, 2, 3 or 21 kPa O2 with balance N2) was tested. Quality retention was improved as O2 partial pressure was reduced and there was no induction of anaerobic respiration. Then, tolerance to high CO2 partial pressures (0, 10, 15 or 20 kPa CO2 plus 21 kPa O2 and balance N2) was tested. The high CO2 partial pressures extended the shelf life of the shredded kale and no symptoms of CO2 injury were detected. Finally, combinations of low O2 and high CO2 (1 or 2 kPa O2 plus 15 or 20 kPa CO2, with balance N2, and an air control) were analysed. No differences were observed among the different gas combinations. An atmosphere of 1–2 kPa O2 plus 15–20 kPa CO2 and balance N2 extends the shelf life of shredded Galega kale to 4–5 days at 20◦C, compared with 2–3 days in air storage. Predictive models of chlorophyll a and b degradation as a function of time and gas composition were developed.
- Modelling O2 and CO2 exchange for development of perforation mediated modifed atmosphere packagingPublication . Fonseca, Susana C.; Oliveira, Fernanda A.R.; Lino, Isabel B.M.; Brecht, Jeffrey K.; Chau, Khe V.Perforation-mediated modi®ed atmosphere packaging relies on the use of macro perforations or tubes to control the O2 and CO2 exchange and create the desired atmosphere inside an otherwise gas-tight package. In this work, the O2 and CO2 exchange through a single tube was studied. Di erent temperatures (5±20°C) and tube dimensions (length from 9 to 17 mm and diameter from 6 to 30 mm) were tested. O2 and CO2 mass transfer coe cients were determined according to a lumped mass transfer capacitance model that yielded a good description of the gas transfer. Temperature in the range tested did not show a signi®cant e ect on the mass transfer coe cients. A multiplicative non-linear equation was found to yield a good prediction of the dependence of the O2 mass transfer coe cient on tube diameter and length. The ratio between the CO2 and O2 mass transfer coe cients, an important parameter in the design of MAP, was 0.81 and none of the factors tested in¯uenced its value.
- Modelling respiration rate of fresh fruits and vegetables for modified atmosphere packages: a reviewPublication . Fonseca, Susana C.; Oliveira, Fernanda A.R.; Brecht, Jeffrey K.Respiration rate and gas exchange through the package material are the processes involved in creating a modified atmosphere inside a package that will extend shelf life of fresh fruits and vegetables. Thus, modelling respiration rate of the selected produce is crucial to the design of a successful modified atmosphere packaging (MAP) system. In this paper, general aspects of the respiration process are presented. The major methods for measuring respiration rates, along with their advantages and limitations are discussed. Factors affecting the respiration rate and respiratory quotient are outlined, stressing the importance of temperature, O2 and CO2 concentrations, and storage time. Respiration rate models in the literature are also reviewed. 2002 Elsevier Science Ltd. All rights reserved.
- Modelling respiration rate of shredded Galega kale for development of modified atmosphere packagingPublication . Fonseca, Susana C.; Oliveira, Fernanda A.R.; Frias, Jesus M.; Brecht, Jeffrey K.The design of modified atmosphere packaging (MAP) for fresh-cut produce requires an adequate model for prediction of respiration rate as a function of both temperature and gas composition. In this work, the O2 consumption and CO2 production rates of shredded Galega kale were studied. The storage temperatures used were 1, 5, 10, 15 and 20 C. The atmospheres tested were all combinations of 1, 5 and 10% v/v O2 plus 0, 10 and 20% v/v CO2 with the balance being N2, as well as ambient air. Temperature was the variable with the greatest influence on respiration rate and the effect of gas composition increased with temperature. The dependence of respiration rate on gas composition was well described by a Michaelis–Menten type equation with uncompetitive CO2 inhibition. The respiratory quotient (RQ) was found to be constant for the range of temperatures and gas compositions tested and was equal to 0:93 0:01. The constants of the Michaelis–Menten equation increased exponentially with temperature. The change over time of respiration rate of leaves exposed to air at 20 C was also analysed. It was observed that respiration rate decreased with time and that the ratio between the respiration rate of shredded and intact leaves was approximately constant in the period tested and equal to 2.8. 2002 Elsevier Science Ltd. All rights reserved.
- Possible influences of water loss and polyphenol oxidase activity on anthocyanin content and discoloration in fresh ripe strawberry (cv. Oso Grande) during storage at 1 degrees CPublication . Nunes, M. Cecília N.; Brecht, Jeffrey K.; Morais, Alcina M. M. B.; Sargent, Steve A.Fresh‘Oso Grande’strawberries wrapped in polyvinyl chloride stretch film lost 0.7% of their initial weight during storage for 8 d at 1 °C, whereas unwrapped fruit lost 11%. Greater water loss was associated with darker and less red fruit, lower concentrations of anthocyanins and other soluble phenolics, and higher polyphenol oxidase (PPO) activity. Anthocyanin degradation and oxidation of soluble phenolic compounds, caused possibly by increased PPO activity as a result of water loss, contributed to the development of strawberry surface browning during storage. Proper handling to reduce water loss during postharvest operations should be used to maintain acceptable color of strawberries during shipping and retailing.