Abstract
The enzimatic activity of peroxidase (POD) and polyphenoloxidase (PPO) extracted from three grape cultivars (Vitis vinifera L.), cultivated in Marialva city, state of Paraná, was evaluated in this study. The enzymatic extracts were prepared starting from the Rubi, Borbon and Benitaka grape cultivars pulp and peel. The activity of the peroxidase was 53.00 units/100 g in the extract from the Rubi cultivar peel, and 327.00 units/100 g from the Benitaka cultivar, these values being superior to those observed in the same cultivars pulp extracts, which were 7.67 units/100 g and 44.00 units/100 g respectively. However, the result was opposite in the Borbon cultivar, with values of 141.11 units/100 g in the pulp and 11.50 units/100 g in the peel being found. The results of the polyphenoloxidase in the Borbon cultivar activity were 100.18 units/100 g in the pulp and 102.60 units/100 g in the peel, and in the Rubi and Benitaka cultivars were 60.40 units/100 g, 48.62 units/100 g in the pulp and 17.40 units/100 g, and 26.20 units/100 g in the peel, respectively. Protein determination was carried out in each extract, and the results found in the pulp and peel, respectively, were 0.56 and 0.64 mg/100 g for cultivar Benitaka, 1.38 and 6.45 mg/100 g for cultivar Rubi, and 21.38 and 5.68 mg/100 g for Borbon. The extracts were submitted to thermal treatments (60°C, 65°C, 70°C and 75°C for a 1 to 10 minutes period) to observe the behavior of the peroxidase and polyphenoloxidase enzymatic activity, being verified a continuous decrease of the peroxidase and polyphenoloxidase activities as a result of the thermal treatment. The extracts of the Rubi and Benitaka cultivars were more heat stable than the extract from the Borbon cultivar for both enzymes. However, the temperatures used were not enough for a total inactivation of the enzymes.
Highlights
In the present study the enzymatic activity of theThe largest Brazilian producer of Vitis venifera grapes is the State of Rio Grande do Sul, where the climatic conditions are favorable for the grape cultivaperoxidase and polyphenoloxidase extracted from the grape pulp and peel was evaluated, as well as the effect of thermal treatment on the activity of these enzymes.tion due to the occurrence of both rigorous winter, which makes the plant vegetative rest possible, and summer brightness, which promotes a full fructification (Amarante, 1986).The State of Paraná has recently been pointed as an economic support for having implanted new juice factories in the Northern area of the state
It is known that the grapes containing a high amount of those enzymes (PPO and POD) can suffer with oxidative reactions, causing a fast darkening when these grapes are squeezed for juices or wine production, and this decreases the quality of the final product (Oliveira et al, 1994)
The protein concentrations present in the peel and pulp of the three cultivars were shown to be different, the Borbon cultivar peel showing a higher protein concentration when compared with the other cultivars
Summary
In the present study the enzymatic activity of theThe largest Brazilian producer of Vitis venifera grapes is the State of Rio Grande do Sul, where the climatic conditions are favorable for the grape cultivaperoxidase and polyphenoloxidase extracted from the grape pulp and peel was evaluated, as well as the effect of thermal treatment on the activity of these enzymes.tion due to the occurrence of both rigorous winter, which makes the plant vegetative rest possible, and summer brightness, which promotes a full fructification (Amarante, 1986).The State of Paraná has recently been pointed as an economic support for having implanted new juice factories in the Northern area of the state. The results of POD, PPO and protein concentration activities in the assayed cultivars are shown in the Table 1. The POD and PPO enzymatic activities measurements before the thermal treatment revealed the presence of POD in the Rubi and Benitaka cultivar peels.
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