Efecto de la temperatura en la reacción de oxidación del almidón de plátano (Musa paradisiaca L. ). estimación de la energía de activación
Effect of temperature in the oxidation reaction of banana starch (Musa paradisiaca L.). activation energy determination
M. M. Sánchez–Rivera y L. A. Bello–Pérez
Centro de Desarrollo de Productos Bióticos del IPN. Km 8.5 Carr. Yautepec–Jojutla, Colonia San Isidro, Apartado Postal 24, 62731 Yautepec, Morelos, México. * Autor para la correspondencia. E–mail: labellop@ipn.mx
]]> Recibido 28 de Julio 2008
Resumen
El almidón nativo de plátano (Musa paradisiaca L.) fue sometido a cinéticas de oxidación con hipoclorito de sodio (NaClO) al 2 % de cloro activo (p/v) a diferentes temperaturas (30 °C, 40 °C y 50 °C) y dos pH (7.0 y 8.5). Las constantes de velocidad (k) y la energía de activación (Ea) se obtuvieron a partir de la concentración de hipoclorito ClO–, (expresado como cloro consumido) durante la oxidación del almidón. Se utilizaron ecuaciones de primer y segundo grado para determinar el orden de reacción, considerando las concentraciones iniciales de almidón [A]0 = 2.134 moles/L y agente oxidante [B]0= 140.84 mmoles/L. Al incrementarse la temperatura y a 40 minutos de reacción, prácticamente todo el cloro fue consumido y en mayor cantidad a pH 8.5, obteniendo valores cercanos a los 20 mg Cl2 / g de almidón. Más del 75 % de cloro reaccionó durante los 5 minutos presumiblemente con pigmentos del almidón. Los datos se ajustaron a una reacción de primer orden y la velocidad de reacción fue mayor a pH 7.0 que 8.5, incrementándose al aumentarse la temperatura. Los resultados permitieron calcular las Ea de 66.481 KJ/mol (pH 8.5) y 51.082 KJ/mol (pH 7.0).
Palabras clave: Musa paradisiaca, almidón, oxidación, velocidad de reacción, energía de activación.
Abstract
Native banana (Musa paradisiaca L.) starch was subjected to oxidation with sodium hypochlorite (NaClO) at 2 % of active chlorine (p/v) at different temperatures (30, 40 and 50 °C) and two pH (7.0 and 8.5). The rate constants (k) and the activation energy (Ea) were obtained from the concentration of hypochlorite ClO–, (expressed as chlorine consumption) during the starch oxidation. First and second order equations were used to determine the reaction order, considering the initial concentrations of the starch [A]0 = 2.134 moles/L and the oxidant agent [B]0= 140.84 mmoles/L. As the temperature increased and at 40 minutes of reaction, practically all chlorine was consumed and in major amount at pH 8.5, obtaining values near to 20 mg Cl2 / g of starch. More than 75 % of chlorine reacted during the five minutes, presumably with the starch pigments. The data were fit for a first order reaction and the reaction rate was higher at pH 7.0 than at 8.5, and it increased when temperature increased. The results allowed the calculation of the Ea of 66.481 KJ/mol (pH 8.5) and 51.082 KJ/mol (pH 7.0).
Keywords: Musa paradisiaca, starch, oxidation, reaction rate, activation energy.
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