ABSTRACT
Aims: The objective of this work was to study the thermal inactivation of the polyphenol oxidase (PPO) and peroxidase (POD) activities of cassava (Manihot esculentaCrantz) root cv. Bocou 2 in order to preventenzymatic browning.Study Design: Crude PPO and POD from yellow-fleshed cassava root were subjected to heat treatment and their thermal inactivation characteristics were examined.Place and Duration of the Study: The study was conducted at Biocatalysisand Bioprocesses Laboratory, Food Science and Technology Unit, Nangui Abrogoua University Abidjan, Côte d’Ivoire, between January and December 2015.Methodology: The crude PPO and POD were extracted from three tissues (cortex, cambium and central pith) ofyellow-fleshed cassava root cv. Bocou 2. The thermal inactivation of these enzymatic activities was evaluated between 50 and 70 °C. The kinetic data of thermal inactivation and thermodynamics were analysed. Results: The t1/2-and D-values decreased with increasing temperature, indicating a faster inactivation of PPO and POD at higher temperatures. Z-values ranged from 16.10 to 27.70 °C and activation energy (Ea) from 73.37 to 129.66 kJ mol-1. Thermodynamic investigations indicated that the oxidation reactions involving these enzyme activities were: not spontaneous (?G > 0), slightly endothermic (?H > 0) and reversible (?S < 0).Conclusion: The PPO and POD activities from yellow-fleshed cassava root decreased due to heat denaturation with increasing temperature from 60 to 70 °C. These kinetic data can be used to prevent enzymatic browning in cassava roots.
ABSTRACT
O presente trabalho objetivou determinar parâmetros cinéticos da inativação térmica de Escherichia coli em lodo de esgoto. Os ensaios foram realizados em laboratório pelo método do frasco de três bocas nas temperaturas de 45, 50, 55, 60 e 65ºC. Os resultados indicaram que a cinética de inativação térmica deste microrganismo pode ser descrita por um modelo de primeira ordem. A resistência da bactéria é reduzida consideravelmente em temperaturas acima de 55ºC. A energia de inativação encontrada foi 2,48x10(5) J.mol-1. O tempo de redução decimal D55ºC foi de 3,61 minutos e o coeficiente térmico z foi 8,3ºC.
The present study aimed to determine the kinetic parameters of thermal inactivation of Escherichia coli in sewage sludge. The tests were performed in the laboratory using the three-neck flask method at temperatures of 45, 50, 55, 60 and 65ºC. The results indicated that the thermal inactivation kinetic of this microorganism can be described by a first order model. The resistance of bacteria is greatly reduced at temperatures above 55ºC. The inactivation energy was found 2.48x10(5) J.mol-1. The decimal reduction time D55ºC was 3.61 minutes and the thermal coefficient z was 8.3ºC.
ABSTRACT
Pectin methylesterase (PME) hydrolyzes methyl ester groups in pectin chains to form carboxylic groups, releasing methanol and H3O+. The aim of this study was to determine PME activity in samples of pectinases by UV-VIS spectroscopy, to measure the acid and methanol produced in the reaction of pectin with pectinase and to verify the thermal inactivation of exogenous PME in mango juice. The activity of PME in samples of pectinase was determined by potentiometry, UV-VIS spectroscopy, and by the action of alcohol oxidase. The reaction showed greater activity at pH 4.0 to 4.5 and at a temperature of 45° C. PME activity determined by UV-VIS spectroscopy with bromophenol blue indicator showed a good correlation with the activity determined by potentiometry and with alcohol oxidase. The results showed that bromophenol blue indicators can be used to determine PME activity in samples of pectinases where the optimum pH is located in the acidic range. The thermal inactivation of exogenous PME in mango juice occurred at 75° C for 20 min of exposure.
A PME hidrolisa os grupos metil éster na cadeia da pectina, formando grupos carboxílicos, liberando metanol e H3O+. Objetivou-se, com o presente estudo, determinar a atividade da PME em amostras de pectinases por espectroscopia Uv-vis para quantificar o ácido e o metanol produzido na reação da pectina com as pectinases e verificar a inativação térmica da PME exógena no suco de manga. A atividade da PME nas três amostras de pectinases foi determinada por potenciometria, espectroscopia Uv-Vis, e pela ação da álcool oxidase. A reação mostrou uma maior atividade em H de 4,0 a 4,5 e a temperatura de 45º C. A atividade da PME, determinada por UV-Vis com o indicador azul de bromofenol apresentou uma boa correlação com a atividade determinada por potenciometria e com a álcool oxidase. Os resultados mostraram que o indicador azul de bromofenol pode ser utilizado para determinar a atividade da PME em amostras de pectinases em que o pH ótimo situa-se na faixa ácida. A inativação térmica da PME no suco de manga ocorreu na temperatura de 75º C, por 20 min de exposição.