Sujin Shobsngob

A Study of Some Physicochemical Properties of High-Crystalline Tapioca Starch

Tapioca starch was partially hydrolyzed in hydrochloric acid solution at room temperature for various lengths of time to obtain high-crystalline starches. RVA viscoamylograms of acid-modified starches demonstrated a very low viscosity as compared to that of native tapioca starch. The relative crystallinity of native and acid-modified tapioca starches were measured by X-ray diffraction ranging from 39.53% to 57.75%. The native and acid-modified tapioca starches were compressed into tablets using various compression forces. The % relative crystallinity of starch increased with the increase in hydrolysis time and the crushing strength of the tablet was also increased in line with the crystallinity while the amylose content decreased when the crystallinity increased. These results suggested that the erosion of amylose might cause the rearrangement of starch structure into a new more tightly packed form, which provided the higher crushing strength for the tablets.

Morphological Properties of Acid-modified Tapioca Starch

Highly crystalline tapioca starch was prepared by partial hydrolysis of tapioca starch in hydrochloric acid at room temperature for various lengths of time. The crystallinity of the starch increased while its amylose content decreased with increasing reaction time. Scanning electron micrographs of these natural and highly crystalline starches were taken in order to study the morphological changes and mode of acid attack during hydrolysis. Exocorrosion all over the surface was observed after 96 h of hydrolysis. Further hydrolysis caused the outer layer of the starch grain surface to erode away. After complete erosion was accomplished, an inner layer or underlayer was revealed with a smooth surface similar to that of the native starch grain surface. Endocorrosion was not observed at any time in this study.

Studies of Flavor Encapsulation by Agents Produced from Modified Sago and Tapioca Starches

The efficiency of sago and tapioca starch stearates for encapsulating lemon oil were studied and compared to the efficiency of gum arabic. The stearates were prepared by esterification of stearic acid with starch. To accomplish esterification, the stearic acid was first coated on the surface of the starch granules. Then the coated granules were heated at 150 °C for 2 h to obtain sago or tapioca starch stearate (SSS or TSS). SSS or TSS can be prepared as ready-to-use products in the form of pregelatinized-hydrolyzed sago or tapioca starch stearate (PGHSSS or PGHTSS). The resulting modified starches were used for encapsulation of lemon oil. The lemon oil encapsulating efficiency for SSS with DS 0.009 and 0.014 were close to that of gum arabic, whereas the encapsulating efficiency for PGHSSS with DS 0.0052 and 0.016 were higher than that of the gum arabic. The TSS and PGHTSS provided encapsulating efficiencies lower than the gum arabic.

Covalent immobilization of a glucoamylase to bagasse dialdehyde cellulose

Cellulose fibres from bagasse were oxidized by sodium periodate in sulphuric acid media at positions 2 and 3 of the anhydroglucose unit to produce dialdehyde cellulose. The aldehyde groups of the dialdehyde cellulose were able to react with amino groups of a glucoamylase to form covalent bonds and result in a dialdehyde cellulose immobilized enzyme. The optimum pH of this immobilized enzyme and free enzyme were in the range of 3.0–5.0 and 3.5–5.0, respectively. The optimum temperature for both the free and immobilized enzymes was 60–65 °C. The relative remaining activity of the immobilized enzyme was 36% and its stability was very good, since it could be reused for over 30 cycles. Its activity decreased from the first to the seventh reuse cycles, due to the slow detachment of non-covalently bound enzyme. However, activity tended to stabilize after the seventh cycle of reuse, indicating very stable covalent binding between the enzyme and dialdehyde cellulose.

Freezing and thawing conditions affect the gel stability of different varieties of rice flour

The freeze-thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze-thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour Jasmine > amylose rice flour.

Influence of Freezing and Thawing Techniques on Stability of Sago and Tapioca Starch Pastes

The freeze-thaw stabilities of sago and tapioca starches have been studied by freezing starch gels (pastes) at -18 °C for 22 h and then thawing them at 30 °C, 60 °C and 90 °C in a water bath or at boiling temperature in a microwave oven. This freeze-thaw stability was determined for five cycles. It was found that starch paste thawed at high temperature had a lower syneresis value (percentage of water separation) than that thawed at low temperature. Sago starch gave higher syneresis values than tapioca starch. Moreover, when tapioca starch gel was frozen by the cryogenic quick freezing (CQF) method and thawed at 30 °C, 60 °C and 90 °C in a water bath or at boiling temperature in a microwave oven for five cycles, no separation of water was detected in any cycle, so that the percentage of syneresis was zero. It was also found that sago starch gel frozen by the CQF method had a lower percentage of syneresis than that frozen at -18 °C in every freeze-thaw cycle.

AMYLOSE/AMYLOPECTIN SIMPLE DETERMINATION IN ACID HYDROLYZED TAPIOCA STARCH

ABSTRACT Analysis of the shift of wavelength maximum using a rapid colorimetric method was used to determine the ratio of amylose:amylopectin (Am:Ap) in acid-hydrolyzed tapioca starch. The absorbance maximum of 600 nm (Am:Ap of tapioca starch ≈22:78) moved to shorter wavelengths (590, 585, 570, 560, and 534 nm) as the decrease of the Am:Ap ratio due to hydrolysis of shorter chains that are not be able to form a complex with iodine. The amount of amylopectin itself may be unaltered or slightly decreased but the decrease in amylose caused a decrease in Am:Ap ratio.Keywords: amylose, amylopectin, acid hydrolysis, colorimetricemail: scdar@mahidol.ac.th INTRODUCTION Starch is the major carbohydrate reserve of plant tubers and seed endosperm. 1 The largest source of starch is maize, wheat, potato, tapioca, and rice. Starch is widely used as thickener, water binder, emulsion stabilizer, and gelling agent. Each starch granule typically contains amylopectin, a linear chain of (1→4)-α-D-glucose residues connected through branched (1→6)-α-linkages, and a much larger number of the smaller amylose, α(1→4) linearly linked D-glucopyranosyl residues.Amylose is a hydrocolloid. Its extended conformation causes the high viscosity of water-soluble starch which varies relatively little with temperature. The extended loosely helical chains possess a relatively hydrophobic inner surface that is not able to hold water. Amylose forms useful gels and films. Its association and crystallization (retrogradation) on cooling and storage decrease storage stability, causing shrinkage and the release of water (syneresis). Increasing amylose concentration decreases gel stickiness, but increases gel firmness. Amylopectin interferes with the interaction between amylose chains (and retrogradation) and its solution can lead to an initial loss in viscosity and followed by a more slimy consistency.The simplest and most common starch modification is by acid hydrolysis, which is widely used in food, paper, textile, and pharmaceutical industries.