13 research outputs found
Modelling colour and firmness changes of stored tomatoes (Lycopersicum esculentum L.) at different conditions
The effect of temperature and storage time
on tomatoes (Lycopersicum esculentum L.) colour (a* and ºh) and firmness (maximum force) were analysed at 2º, 5º, 10º, 15º and 20 ºC. The development of these quality attributes followed a fractional kinetic model. The regression coefficient (R2) for the generated models were high, 0.94 for both colour parameters (a* and ºh) and 0.84 for firmness. A significant (p<0.05)
increase and decrease for a* and maximum force, respectively, were observed during storage. This study can contribute for the understanding of the real effect of temperature and storage time on two important
quality attributes of tomatoes, such as colour and firmness
Avaliação e otimização da termossonicação como tratamento alternativo de pós-colheita de tomate fresco (Lycopersicum esculentum, cv. Zinac)
info:eu-repo/semantics/publishedVersio
Evaluation of alternative preservation treatments (water heat treatment, ultrasounds, thermosonication and UV-C radiation) to improve safety and quality of whole tomato
Previously optimised postharvest treatments were compared to conventional chlorinated water treatment in
terms of their effects on the overall quality of tomato (‘Zinac’) during storage at 10 °C. The treatments in question were water heat treatment (WHT = 40 °C, 30 min), ultrasounds (US = 45 kHz, 80 %, 30 min), thermosonication (TS =40 °C, 30 min, 45 kHz, 80 %) and ultraviolet irradiation (UV-C: 0.97 kJ m−2). The quality factors evaluated were colour, texture, sensorial analysis, mass loss, antioxidant capacity,
total phenolic content, peroxidase and pectin methylesterase enzymatic activities, and microbial load reduction.
The results demonstrate that all treatments tested preserve tomato quality to some extent during storage at 10 °C. WHT, TS and UV-C proved to be more efficient on minimising colour and texture changes with the additional advantage of microbial load reduction, leading to a shelf life extension when compared to control trials. However, at the end of storage, with exception of WHT samples, the antioxidant activity and phenolic content of treated samples was lower than for control samples. Moreover, sensorial results were
well correlated with instrumental colour experimental data. This study presents alternative postharvest technologies that improve tomato (Zinac) quality during shelf life period and minimise the negative impact of conventional chlorinated water on human safety, health and environment.info:eu-repo/semantics/publishedVersio
Optimization, Heat Stability and Kinetic Characterization of Pectin- Methylesterase Enzyme from Tomato (Solanum lycopersicum ‘Zinac’) Fruits
Textural changes during fruit ripening have been attributed to pectin
degradation due to pectic enzymes such as pectinmethylesterase (PME, EC 3.1.1.11).
PME catalyzes the de-esterification of pectin, a complex mixture of polysaccharides,
namely methyl esterified polygalacturonic acid, with the release of hydrogen and
methanol, producing shorter chains causing drastic losses in firmness. Thus, control of
PME activity in fruits aiming at texture maintenance and/or improvement is
extremely important to the food industry. However, PME activity and properties are
dependent on product, environmental and physico-chemical conditions, such as pH
and temperature. Therefore, the aim of the present work was to optimize the pectinmethylesterase
(PME) enzyme assay from tomato (Solanum lycopersicum ‘Zinac’)
fruits, and determine its kinetics behavior and thermal stability. The highest PME
activity was found with a 1.0 M of NaCl extraction solution, with 0.5% citrus pectin,
and revealed optima of temperature at 60°C and pH of 8.8. The low kM value (0.011%)
for tomato PME describes the high affinity between enzyme and substrate (citrus
pectin), whereas the obtained Vmax value (0.712 U mg-1) relates to the enzyme quantity
present in the reaction. The study of PME thermal stability showed two distinct
behaviors: an increase of activity from 40 to 50°C and a decrease from 55 to 80°C. At
50°C/10 min an increase in activity up to 17% of activity was observed. At 60°C, about
50% of the activity still remained after heating for 25 min, and PME was completely
inactivated at 80°C after 10 min. Data obtained in the temperature range of 55 to
80°C were also satisfactorily described by an Arrhenius first-order kinetic model.
These results provide useful information about the different factors that affect tomato
PME activity and may be used as a tool for firmness control during postharvest
handling and fruit processing
Heat treatment evaluation on quality and safety of whole tomato (lycopersicum esculentum l.) fruits
Proceedings of the International Conference “Environmentally friendly and safe
technologies for quality of fruit and vegetables”, held in Universidade do Algarve, Faro,
Portugal, on January 14-16, 2009. This Conference was a join activity with COST Action 924.Quality and safety attributes, like colour (CIELab parameters), texture (Maximum force – MF), total
phenolics content (TPC), peroxidase activity (POD), microbial count and moulds & yeasts (Log10 cfu g-1)
were determined on heat treated mature-green tomatoes at temperature ranging of 40 to 50 ºC and
different times. Heat treatments (HT) did not affect significantly (p>0.05) the tomatoes colour. In terms
of texture, a reduction of 10% MF was observed at 50 ºC_15min..