Estudo sobre a ação de pectinesterase em suco de laranja
Leonardo Cesar Amstalden
DATA DE PUBLICAÇÃO
An investigation was undertaken to determine and compare various parameters related to the action of Pectinesterase (PE) in orange juice, and its effect on cloud stability. The juice was made from four varieties of orange used by brazilian citrus processors: Pera Rio, Pera Coroa, Natal and Valencia. The following items were studied: 1) Enzyme activity and effect of heat treatment, on enzyme inactivation at various temperatures. The results show that the optimum temperature for enzyme activity was approximately 60°C for all the juice samples but the maximum activities differed widely among the varieties. They were 169.5 x 109 PEu/g ss (of soluble solids) for the Valencia juice, 75.1 x 109 PEu/g ss for the Pera Rio juice, 65.2 x 109 PEu/g ss for the Pera Coroa juice and 164.6 x 109 PEu/g ss for the Natal juice. There was no residual enzyme activity found after two minutes of heat treatment at 90°C. with the exception of the Valencia juice. At 80°C only the juice made from Pera Coroa oranges was completely inactivated after a short holding time (4 minutes). All of the others showed residual activity after seven minutes. 2) Effect of pH on enzyme activity. The optimum pH values were between 7.5 and 8.0 for the varieties Pera Rio, Pera Coroa and Valencia, and 7.0 for the variety Natal. At pH values ranging from 3.0 to 4.0 (normal pH of the fruit) the measured activity was 0 to 6.1% of the maximum values. 3) Effect of fruit ripening on enzyme activity. The enzyme activity in the juice was higher at a very low Brix/acid ratio (green fruit), decreasing as the fruit ripens. 4.) Search for residual activity in industrial orange juice concentrate and determination of the levels of Ca2+ and Mg2+ ions in different juice samples. No residual activity was found on industrial. Also no abnormal levels of Ca2+ and Mg2+ were found concentrates, in the samples. 5) Cloud loss on single strength, PE active orange juice. Cloud loss as a function of time showed to be a particular caracteristic of each variety. The most stable one was Pera Coroa and the least stable was Valencia. 6) Cloud loss on PE active and inactive concentrates. The concentrates, PE active and inactive, had a very sable cloud, even after standing 120 hours at 30°C. 7) Effect of Ca2+ ion on cloud loss. The addition of 10mg/100g and 20mg/100g of Ca2+ ions to the juice accelerated the loss of cloud. When 30mg/100g and 40mg/100g were added the pattern was the same as the control sample.