Advanced Materials Research Vol. 506 (2012) pp 35-38 © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.506.35
Effect of Physical Aging on Physical Properties of Pregelatinized Tapioca Starch S. Manchun1,2, S. Piriyaprasarth1,2, V. Patomchaiviwat1, S. Limmatvapirat1,2, P. Sriamornsak1,2,a,* 1
Department of Pharmaceutical Technology, and 2 Pharmaceutical Biopolymer Group (PBiG), Faculty of Pharmacy, Silpakorn University, Nakhon Pathom 73000 Thailand a [email protected]
Keywords: Tapioca Starch, Aging, Pregelatinization, Ultrasonic Treatment, Modified Starch
Abstract. The effect of physical aging on the properties of starch is important to understand structural relaxation and to control the physicochemical changes after pregelatinization which induced by aging. In this study, the effect of physical aging on the physicochemical properties of pregelatinized tapioca starch was investigated. The tapioca starch was pregelatinized by either heating at 80°C or using high power (400 W) ultrasonic treatment. After pregelatinization, dextrose equivalent (DE), viscosity, turbidity, swelling power and solubility were determined and compared with native tapioca starch. Compared to fresh tapioca starch, the aged starch exhibited an increase in DE, turbidity and solubility. The viscosity and swelling power were decreased after storage. Similar results were found for both tapioca starches pregelatinized by heat and ultrasonic treatments. The results of the physicochemical properties of pregelatinized starches obtained from ultrasonic treatment related to the formation of low molecular weight components that aging starch are easily changed by disruption of molecular structure within the starch granule. Introduction Starch, main storage carbohydrate of plants, is an important polysaccharide of plant origin and is of considerable interest for various industries, e.g., food, phamaceutical, paper, etc. The basic chemical structure of starch is a polymeric carbohydrate consisting of anhydroglucose units linked together by glycosidic bonds. Starch granules consist of two types of molecule, amylose and amylopectin, which arrange themselves in semi-crystalline granules. Amylose molecules are linear, resulting from D-glucopyranosyl units connected by α-1,4 linkage. Amylopectins include a large number of short chains linked together at their reducing end side by α-1,6 linkage, which give rise to branching (1). The composition of both molecules varies depending on plant origin. Starch has been widely used as ﬁller, binder and disintegrant in pharmaceutical tablets. However, native starches have some limitation such as poor ﬂowability, poor water solubility, etc. Gelatinization, a physical modification, has been used to improve these undesirable properties. The process of gelatinization causes substantial changes in both chemical and physical nature of granular starch due to the rearrangement of intra- and intermolecular hydrogen bonding between the water and starch molecules, resulting in the collapse or disruption of molecular orders within the starch granule (2). This results in irreversible changes in the starch properties (3). Starch can be stored for long periods of time, however, physical properties changes may occur during aging. The effect of physical aging on thermal transitions and physicochemical properties is of importance to the processing and properties of starch-based products, and can play major roles in the quality and storage stability of tapioca starch-containing products. The term ‘physical aging’ is a structural transformation (relaxation) toward equilibrium as a function of storage time (4). Physical All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 126.96.36.199-24/04/12,15:05:43)
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aging is a phenomenon that has been regarded with great importance considering the storage behavior of starch (5) and thus physical aging characteristics of starch should be understood to control the physicochemical changes after pregelatinization. Therefore, this study was aimed to investigate the effect of physical aging on the physicochemical properties of pregelatinized tapioca starch. Different gelatinization methods were used, i.e., heat and ultrasonic treatment. The aged (6 years) tapioca starch was characterized and compared with fresh tapioca starch. Experimentals Ultrasonically treated sample was prepared by high intensity probe (model UP400S, Hielscher, Germany). Aqueous starch slurry (3% w/w) was treated for 30 min with ultrasound power of 400 W and 24 KHz. For heat-treated starch, the aqueous starch slurry was heated at 80°C in an oil bath with stirring for 30 min to completely solubilize. The transmittance (%) at 650 nm of pregelatinized starches, after cooling the samples to room temperature for 30 min, was measured to determine its turbidity. The viscosity was investigated with a Brookfield digital viscometer (model RVTD, Brookfield Engineering Laboratories, Inc., USA) The reducing sugar value of the pregelatinized starches was measured using the dinitrosalicylic acid method and represented as dextrose equivalent (DE). Briefly, a 0.5-mL aliquot of 3% (w/w) pregelatinized starch was pipetted into a test tube, and 0.5 mL dinitrosalicylic acid solution was added. The solution was boiled for 5 min and cooled immediately under running tap water. The absorbance at a wavelength of 575 nm was measured. Glucose was used as a standard and the analysis was performed in triplicate. DE was calculated as follows (6): DE
mg of reducing sugar × 100 mg of dry solid weight
The solubility and swelling power of dry powder of the pregelatinized starches were assessed using established methods (7). Starch was weighed (W0) into a centrifuge tube with coated screw cap to which 10 mL of distilled water were added. The tube was heated at 80°C in an oil bath for 30 min. The tube was cooled to room temperature and centrifuged for 15 min at 2,200 rpm. The supernatant was decanted and dried to constant weight (W1) in an hot-air oven at 100°C. The wet starch sediment was weighed (W2) to obtain the swelling of the starch. The solubility and swelling power were calculated as follows: So lub ility (%)
W1 × 100 W0
Swelling power (g g)
W2 × 100 W0 (100 − so lub ility )
Results and Discussion Physical properties. According to Atwell et al. (8), gelatinization is the collapse (disruption) of molecular order within the starch granule manifested in irreversible changes in properties such as granular swelling, native crystallite melting, loss of birefringence and starch solubilization. A decrease in turbidity and viscosity and an increase in DE value of pregelatinized starch is related to the formation of low molecular weight components that are easily dispersed (9). Therefore, the influence of physical aging on physical properties of pregelatinized starch was investigated by determining turbidity, viscosity and DE. The turbidity of gelatinized starches was determined by measuring the transmittance. The transmittance of aged tapioca starch was similar to that of fresh starch, in both treatments (Fig. 1a). The viscosity of aged and fresh starches after gelatinization is presented in Fig. 1b. It is observed that the viscosity of aged tapioca starch was significantly lower trend than that fresh starch, for both heat and ultrasonic treatments. The DE, which also represented
Advanced Materials Research Vol. 506
the degree of hydrolysis, of fresh and aged tapioca starches after pregelatinization by heating and ultrasonic treatment is shown in Fig. 1c. The aged tapioca starch has higher DE than fresh starch for both heat and ultrasonic treatments. This is probably because starch is converted into sugars during storage (10). Thus, an increase in the DE of aged starch was observed. The results suggested that the granule of aged starch was destroyed easier than that of fresh starch. It is possible that aged starch has weaker granular structure and could be easily influenced by storage time and condition, i.e., temperature, moisture, microbial activity. However, the ultrasonically treated starch has lower turbidity and viscosity than heat-treated starch. During ultrasonication, the cavitation forces could break starch granules (especially the aged starch) into smaller fragments, resulting in a reduced viscosity and turbidity. (a)
Figure 1. (a) Transmittance, (b) viscosity, and (c) dextrose equivalent of aged and fresh tapioca starches.
Swelling power and solubility. The swelling power and solubility of fresh and aged tapioca starches after pregelatinization by heat and ultrasonic treatments are shown in Fig. 2. It is observed that, after pregelatinization, the solubility of aged starch is slightly higher than fresh starch. It is possible that the granule of aged starch was disrupted and low molecular weight components that are easily dispersed and solubilized were formed. Moreover, the ultrasonically treated starch has higher solubility than heat-treated starches. The higher solubility may associate with a higher water uptake of the broken granules resulted from ultrasound treatment. The starch granule disintegration is mainly caused by the cavitation forces, which can break the crystalline molecular structure and chains of tapioca starch by disrupting covalent bonds. Therefore, the water molecules could bind more to free hydroxyl groups of amylose and amylopectin by hydrogen bonding, which cause an increase in solubility (11). However, the swelling power was not significantly different in both starches and treatments.
Biomaterials and Applications
Figure 2. (a) Solubility and (b) swelling power of aged and fresh tapioca starches.
Conclusions The storage time affected to the chemical and physiochemical characteristics of starch during aging process. The physicochemical properties of pregelatinized starches obtained from ultrasonic treatment related to mechanical damages of the starch granules. The aged starch is easily changed by rupturing of molecular structure within the starch granule. Acknowledgements The authors wish to acknowledge the Thailand Research Fund for financial support through Royal Golden Jubilee Ph.D. Program (PHD/0361/2551). References  C.G. Biliaderis: Polysaccharide association structures in food, Marcel-Dekker, New York, 1998, p.57.  R.A. Freitas, R.C. Paula, J.P.A. Feitosa, S. Rocha, M.R. Sierakowski: Carbohydr Polym, Vol.55(2004), p.3.  R. Kizil, J. Irudayaraj: J Agric Food Chem, Vol.54(2006), p.13.  H.J. Chung, S.T. Lim: Food Hydrocolloid, Vol.17(2003), p.855.  L. Niba: Food Chem, Vol.83(2003), p.493.  U. Uthumporna, I.S.M. Zaidul, A.A. Karima: Food Bioprod Process, Vol.88(2010), p.47.  T.J. Schoch: Method in Carbohydrate Chemistry, Academic Press, New York, 1964, p.106.  W.A. Atwell, L.F. Hood, D.R. Lineback, E. Varriano-Marston, H.F. Zobel: Cereal Foods World, Vol.33(1988), p.306.  T.O. Martinez, D.B. Ancona: Starch/Starke, Vol.56(2004), p.241.  O. Smith: Potato processing. AVI-Van Nostrand Reinhold, New York, 1987, p.203.  A.R. Jambrak, Z. Herceg, D. Šubarić, J. Babić, M. Brnčić, S.R. Brnčić, T. Bosiljkov, D. Čvek, B. Tripalo, J. Gelo: Carbohydr Polym, Vol.79(2010), p.91.