Loading...
3 results
Search Results
Now showing 1 - 3 of 3
- Characterisation of ‘Starking’ apple polyphenoloxidasePublication . Rocha, Ada M. C. N.; Cano, M. Pilar; Galeazzi, Maria A. M.Experiments were performed to optimise the extraction conditions of “StarkingÏ apple fruit polyphenoloxidase (PPO), to evaluate the affinity and speciÐcity towards several substrates and to study the stability of enzyme extracts from apple samples stored under di†erent conditions. Sodium phosphate bu†er (0É2 M, pH 6É5) plus 0É25% Triton X and 1% or 2% PVPP was found to be the most efficient extraction mediu10m0. Chlorogenic acid, dopamine and 4- methylcatechol showed similar speciÐcity towards PPO, and chlorogenic acid was found to be the best substrate for the enzyme. Enzyme extracts from frozen cut apple stored at [4¡C, and extracts from lyophilised apple samples stored at 4¡C were more stable than extracts obtained from fresh-cut or acetone powder samples
- a* values to follow lycopene concentration during ripening and storage of tomato (cv. Caruso)Publication . Schauwers, Axelle; Rocha, Ada M. C. N.; Morais, Alcina M. M. B.The ripening of tomato fruit is a highly regulated process during which colour, flavour, aroma and texture change in a coordinated manner. This research work aims to correlate the colour changes measured objectively with the lycopene concentration in tomatoes during ripening at room temperature (21 and 26°C). These results were compared with colour and lycopene content of pink and light red tomatoes stored at 14°C, temperature used to prevent ripening and therefore extend the shelf life of the fruits. The duration of heat treatment at 100ºC was previously optimized in order to release the maximum lycopene from chromoplasts during extraction. An a* value of 20 for the peel corresponds to an increase of lycopene content of Caruso tomato from 9 to 43 mg/100 g TSS, at room temperature. The shelf life of pink and light red tomatoes can be extended to two weeks at 14ºC without loss of lycopene content, presenting the same content as green tomatoes ripened at room temperature for one week.
- Polyphenoloxidase activity and total phenolic content as related to browning of minimally processed ‘Jonagored’ applePublication . Rocha, Ada MCN; Morais, Alcina M. M. B.Phenolic content, polyphenoloxidase (PPO) activity and browning have been reported by different authors to vary in different ways, depending on cultivar, picking maturity, storage conditions, etc. Numerous authors have attempted to correlate browning results with the phenolic content and/or enzymatic activity of apples, but data published in the literature are divergent as to which of the two factors, ie the enzyme or the substrate, plays the decisive role in the overall phenomenon of enzymatic browning. The aim of this work was to follow the PPO activity and phenolic content of minimally processed apple (cv ‘Jonagored’) during cold storage and to establish a potential relationship with enzymatic browning. Increasing storage time of minimally processed apple seemed to result in an increase in PPO activity. No changes (P > 0.05) in total phenolic content were observed during storage. Colour degradation of apple cubes, as indicated by changes in colour parameters, was found to be highly correlated with PPO activity. Browning of ‘Jonagored’ apple cubes during storage was found to be moderately correlated with PPO activity. No correlation was found between the browning index and the total phenolic content.