Pectin methylesterase activity determined by different methods and thermal inactivation of exogenous pme in mango juice

Abstract

Pectin methylesterase (PME) hydrolyzes methyl ester groups in pectin chains to form carboxylic groups, releasing methanol and H 3 O + . 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.Index terms: Pectin metilesterase, activity, thermal inactivation, mango juice. RESUMOA PME hidrolisa os grupos metil éster na cadeia da pectina, formando grupos carboxílicos, liberando metanol e H 3 O + . 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.Termos para indexação: Pectina metilesterase, atividade, inativação térmica, suco de manga.

Towards a test to verify that wood has been heattreated to the ISPM15 standard

“…Various enzymes and sugars have been detected in fresh wood samples (Sagisaka 1972;Haissig & Schipper 1978;Moeller et al 2006), but there have been few studies of either dry or ISPM15treated wood. In general, heating to 56°C is usually insufficient to completely inactivate enzymes, though it may reduce their activity (Anderson 2002;Gonzalez et al 2011;Iline et al 2013). Heating, however, should cause sap to move within xylem, thus metabolite concentrations in different parts of the wood profile may change with heat-treatment.…”