Catarina Sri Budiyati

H2O2/UV Photo-Oxidation of Gadung (Dioscorea Hispida Dennst.) Starch and its Product Physicochemical Characterization

This work aimed to study the preparation and physicochemical properties characterization of oxidized gadung starch obtained from oxidation process implementing combined H 2 O 2 -UV irradiation. The photo-oxidation process was carried out in a well-mixed slurry reaction system at ambient temperature. The extent of oxidation was determined based on the carboxyl and the carbonyl contents of the oxidized gadung starch. The results show that oxidation process altered the carbonyl and carboxyl contents of the starch. Except the morphology of the starch, the swelling power, solubility and gelatinization temperature of the starch were severely affected by H 2 O 2 /UV oxidation process.

Implementation of steady state approximation for modelling of reaction kinetic of UV catalysed hydrogen peroxide oxidation of starch

With regard to its low viscosity, high stability, clarity, film forming and binding properties, oxidised starch has been widely used in various applications specifically in the food, paper, textile, laundry finishing and binding materials industries. A number of methods have been used to produce oxidised starch through reactions with various oxidizing agents, such as hydrogen peroxide, air oxygen, ozone, bromine, chromic acid, permanganate, nitrogen dioxide and hypochlorite. Unfortunately, most of previous works reported in the literatures were focused on the study of reaction mechanism and physicochemical properties characterization of the oxidised starches produced without investigation of the reaction kinetics of the oxidation process. This work aimed to develop a simple kinetic model for UV catalysed hydrogen peroxide oxidation of starch through implementation of steady state approximation for the radical reaction rates. The model was then verified using experimental data available in the literature. The model verification revealed that the proposed model shows its good agreement with the experimental data as indicated by an average absolute relative error of only 2.45%. The model also confirmed that carboxyl groups are oxidised further by hydroxyl radical. The carbonyl production rate was found to follow first order reaction with respect to carbonyl concentration. Similarly, carboxyl production rate also followed first order reaction with respect to carbonyl concentration. The apparent reaction rate constant for carbonyl formation and oxidation were 6.24 × 104 s−1 and 1.01 × 104 M−1.s−1, respectively. While apparent reaction rate constant for carboxyl oxidation was 4.86 × 104 M−1.s−1.