Diah Susetyo Retnowati

Physical, thermal and functional properties of flour derived from Ubi Gembili (Dioscorea esculenta L.) tubers grown in Indonesia

Gembili ( Dioscorea esculenta L.) tuber is one of the important food sources in term of cultural, nutritional and economic perspectives for the people in the Africa, Caribbean islands, Asia, and Oceania regions. The tubers can be eaten after being boiled, roasted, fried or cooked. However, there is lack of information on the advanced utilizations of the tubers as raw material in the manufacture of modern foods. This study aims to characterize the physical, functional and thermal properties of Gembili flour, so that this information can be used as the basis in the development of novel foods. The microstructure, crystallinity, gelatinization temperature, swelling power and solubility of the flour were determined. The electron microscope observation revealed that Gembili flour consisted of smooth surface oval granules, which were light brown in color and having 23 µm average diameter. They are comprised of polygonals or some clusters of irregular fragments. Similar to most of tuber flours, Gembili flour also exhibited B-type crystallinity with approximately 31 ±3.7% crystallinity. The gelatinization temperature of Gembili flour was high and being comparable to that of cereal flour. The enthalpy of gelatinization of Gembili flour (9.52 ±0.80 J.g -1 ) was comparable to that of Dioscorea alata . Unfortunately, Gembili flour exhibited low swelling power (3.90 ±0.01 g.g -1 ). The Gembili flour granules were highly soluble in water (11.07 ±0.05%). Based on those reported properties, Gembili flour can be a suitable raw material for the manufacture of bakery, cookies, noodle and infant foods.

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.

Effect of catalyst concentration and reaction time on the extraction of glucomannan from porang (Amorphophallus oncophyllus) flour via acid hydrolysis

High demand of glucomannan for various applications has attracted the attention of researchers to look for efficient extraction method from its botanical sources. The aim of this study is to investigate the effect of catalyst concentration and reaction time on the yield and purity of glucomannan, and profile of reducing sugar during glucomannan extraction from crude porang flour via acid hydrolysis. The effect of catalyst concentration was found to be more pronounced over the effect of reaction time. When catalyst concentration was varied from 0.03125 to 1 M, extraction of glucomannan from porang flour for 1 hour at 60°C yielded 40.5 to 70% glucomannan with purity of 47.35 to 90.18% (w/w). The yield and purity of glucomannan obtained from extraction using catalyst concentration of 1 M for 0.25 to 3 hour ranged between 49 to 66.67% and 58.32 to 90.18% (w/w), respectively. Reduction in glucomannan yield and purity observed at high catalyst concentration and prolong reaction time was likely to be due to over-decomposition. Glucomannan with highest purity (90.18% w/w) was obtained at 66.67% yield from acid hydrolysis of porang flour using 0.5 M hydrochloric acid solution with flour:water ratio of 1:50 at 60°C for 1 hour.

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.