Food Hydrocolloids 26 (2012) 339e343
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Effect of deproteinization on degree of oxidation of ozonated starch Hui-Tin Chan a, Arifﬁn Fazilah a, Rajeev Bhat a, Chiu-Peng Leh b, Alias A. Karim a, * a b
Food Biopolymer Research Group, Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia Bioresource, Paper & Coatings Division, School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 September 2010 Accepted 9 March 2011
Effects of deproteinization on the degree of oxidation of ozonated starch (corn, sago, and tapioca) were investigated. Starch in dry powder form was exposed to ozone for 10 min at different ozone generation times (OGTs: 1, 3, 5, 10 min), and then native starches (NS) and deproteinized starches (DPS) were analyzed for protein content. Deproteinization caused a signiﬁcant reduction in protein content for corn (w21%) and sago (w16%) starches relative to NS. Carbonyl and carboxyl contents increased signiﬁcantly in all ozonated deproteinized starches (ODPS) with increasing OGT. Carbonyl and carboxyl contents of ODPS ranged from 0.03 to 0.13% and 0.14 to 0.28%, respectively. The carboxyl content for all ODPS was signiﬁcantly higher than that of ozonated native starches (ONS). A Rapid Visco Analyser was used to analyze pasting properties of all starches. Deproteinization increased the pasting viscosities of corn and sago starches compared to their native forms. Generally, pasting viscosity of all ODPS decreased drastically as OGT increased. At the highest oxidation level (10 min OGT), all ODPS exhibited the lowest pasting viscosities compared to their ozonated native form, except for peak viscosity, breakdown viscosity, and setback viscosity for ozonated deproteinized corn starch. In conclusion, deproteinization as a pretreatment prior to starch ozonation successfully increased the degree of oxidation in the three types of starch studied. However, the extent of starch oxidation varied among the different starches, possibly due to differences in rates of degradation on amorphous and crystalline lamellae and in rates of oxidation of carbonyl and carboxyl groups. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: Starch Ozone oxidation Modiﬁed starch Oxidized starch Deproteinized starch
1. Introduction Starch is a mixture of two polysaccharides: the linear molecule of amylose and a highly branched molecule of amylopectin. Starch is widely used in the food, paper, and textile industries. However, the uses of native starches are limited by some undesirable properties. Therefore, starches must be modiﬁed chemically, physically, genetically, or enzymatically to enhance their positive attributes or to minimize their defects. In the paper, textile, and building material industries, oxidized starch is widely used to provide surface sizing and coating properties (Chang, Park, Shin, Suh, & Kim, 2008). In the food industry, the use of oxidized starch has become increasing important because it has low viscosity and good binding and ﬁlm forming properties (Kuakpetoon & Wang, 2006). Oxidized starch is produced by reacting starch with a speciﬁed amount of oxidizing reagent under controlled temperature and pH (Wurzburg, 1986). Sodium hypochlorite is the most common chemical oxidizing agent used to study starch oxidation. However,
* Corresponding author. Tel.: þ60 4 653 2268; fax: þ60 4 657 3678. E-mail address: [email protected]
(A.A. Karim). 0268-005X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2011.03.006
in the hypochlorite oxidation process, the oxidized starch yield is low because small molecules are lost due to starch breakdown (Wing & Willett, 1997). In addition, a large amount of waste water is produced during the process of oxidation (Kesselmans & Bleeker, 1997a). Ozone is a more powerful oxidant than oxygen, it reacts with most substances at ambient temperatures, and it creates no waste water disposal problem. Furthermore, a dry process using ozone can reduce the puriﬁcation cost and produce a product with high recovery. Several patents have been ﬁled for a method of oxidizing dry starch (Kesselmans & Bleeker, 1997a) and polysaccharides (Kesselmans & Bleeker, 1997b) using ozone as an oxidizing agent. In addition, some recent scientiﬁc publications have reported the use of ozone in starch modiﬁcation. An and King (2009) reported that ozonated rice starch exhibited similar pasting properties to those from oxidized starches treated with low concentrations of chemical oxidizing agents. On the other hand, Lii, Liao, Stobinski, and Tomasik (2003) reported that the corona discharge method used discharges decomposed starches to low molecular fragments together with oxidation of the polysaccharides. Our previous study (Chan, Bhat, & Karim, 2009) demonstrated that ozone gas successfully oxidized starches from a variety of different starches. However, the degree of oxidation in
H.-T. Chan et al. / Food Hydrocolloids 26 (2012) 339e343
terms of total carboxyl content was lower than that reported in the literature. Therefore, we postulated that if the ozone gas has more access to the interior or subsurface of the starch granule, a higher degree of oxidation would occur. In addition to amylose and amylopectin, starch granules contain minimal quantities of components like protein, lipids, and minerals (Morrison, 1995). Starch granule associated proteins (SGAPs) are deﬁned as the proteins naturally positioned in and on starch granules (Baldwin, 2001).The presence of protein in/on starch granules might inﬂuence the starch’s physicochemical properties, such as swelling, solubility, and gelatinization temperature (Shull, Chandrashekar, Kirleis, & Ejeta, 1990; Tester & Morrison, 1990). The presence of surface material on the granule acts as the ﬁrst barrier to processes such as granule hydration, enzyme attack, and chemical reaction with modifying agents. Therefore, we postulated that removal of these surface materials might increase the extent of chemical reactions with the modifying agent. Eerlingen, Cillen, and Delcour (1994) reported that sodium dodecyl sulfate (SDS) treatment can efﬁciently remove the surface protein from starch granules. We previously reported a signiﬁcant reduction in protein content for all starches studied after treatment with 0.2% SDS solvent compared with the starches in their native form (Chan, Bhat, & Karim, 2010). This study was designed to explore the effect of deproteinization on starches in greater detail. The objectives of this study were to investigate the effect of deproteinization on the degree of oxidation of ozonated starch and to determine the effect of these treatments on the pasting properties of the treated starch. 2. Materials and methods 2.1. Materials Corn, potato, and sago starch were purchased from the Sims Company Sdn. Bhd (Penang, Malaysia). All other reagents used in this work were of analytical grade. All native starches and chemicals were used directly without further puriﬁcation. 2.2. Sodium dodecyl sulfate (SDS) treatment
2.4. Protein content analysis Protein content of native starch (NS) and deproteinized starches (DPS) was determined using the macro-Kjeldahl method (AOAC, 1990). The crude protein content on a wet basis was calculated by multiplying nitrogen content by a factor of 6.25. Each starch was analyzed in duplicate and the protein content was reported as the percent of protein. 2.5. Carbonyl content (%) The carbonyl group content for ONS and ODPS was determined following the titrimetric method of Smith (1967). The carbonyl group content was calculated as follows:
Percentage of carbonyl content ¼ ½ðblank sampleÞ mL acid normality 0:028 100=sample weight ðdry basisÞ in g
2.6. Carboxyl content (%) The carboxyl content of ONS and ODPS was determined according to the modiﬁed procedure of Chattopadhyay, Singhal, and Kulkarni (1997). A starch sample (2 g) was mixed with 25 mL of 0.1 M HCl, and the slurry was stirred continuously for 30 min with a magnetic stirrer. The slurry then was vacuum ﬁltered through a 150 mL medium porosity fritted glass funnel and washed with 400 mL of distilled water. The starch cake was carefully transferred into a 500 mL beaker, and the volume was adjusted to 300 mL with distilled water. The starch slurry was heated in a boiling water bath with continuous stirring for 15 min to ensure complete gelatinization. The hot starch dispersion was then adjusted to 450 mL with distilled water and titrated to pH 8.3 with standardized 0.01 M NaOH. A blank test was performed with unmodiﬁed starch. The carboxyl content was calculated as follows:
Milliequivalents of acidity=100 g starch ¼ ½ðsample blankÞ mL normality of NaOH
Starch (40% w/v) was suspended in SDS solvent (2% w/v) at room temperature. The starch suspension was stirred for 30 min using a magnetic stirrer and then centrifuged (Kubota 5100, Kubota Corp., Tokyo, Japan) at 3500 rpm for 15 min. The supernatant was carefully removed. The pellet was washed three times, re-suspended with distilled water, centrifuged, and dried in an oven at 40 C for 12 h. Duplicate samples from each type of starch were prepared and used for ozone oxidation. 2.3. Preparation of ozone-oxidized starches Oxidized-native and SDS-treated corn, sago, and tapioca starches were prepared by a method originally described in Chan et al. (2009). Brieﬂy, a starch sample in powder form (“as is” moisture content) was placed in a reaction vessel that was connected to an ozone (O3) generator. O3 was generated for 1 min, 3 min, 5 min, and 10 min (i.e., oxygen generation times, OGTs) and the reaction vessel was rotated at 150 rpm to ensure homogeneous contact between starch and O3 during the reaction. Following the speciﬁed OGT, 10 min of contact time elapsed with both the gas inlet and outlet closed to allow the oxidation reaction to take place. Finally, O2 was ﬂushed through the vessel for 20 min to ﬂush out the O3 that did not react with the starch. When this process was completed, the oxidized starch was collected and analyzed. Duplicate samples for each OGT were prepared for each starch type.
100=sample weight ðdry basisÞ in g
Percentage of carboxyl content ¼ ½milliequivalents of acidity=100 g starch 0:045
2.7. Pasting properties of starch The pasting proﬁle of the starches (12% w/w) was determined using a Rapid ViscoÔ Analyser (Model RVA-4, Newport Scientiﬁc Pvt. Ltd., Warriewood, Australia). The samples were equilibrated at 50 C for 1 min and then increased to 95 C in 3.75 min, held for 2.5 min, cooled to 50 C in 3.75 min, and held for 5 min. The paddle speed was set at 960 rpm for the ﬁrst 10 s to consistently disperse the starch slurry and then it was reduced to 160 rpm throughout the remainder of the experiment. The units of viscosity were expressed as Rapid Visco Units (RVUs). 2.8. Statistical analysis The starch type (ONS or ODPS) and OGTs were two factors that were analyzed by analysis of variance (ANOVA) using SPSS 15.0 software (SPSS, Inc., Chicago, IL, USA). Duncan’s least signiﬁcant test was used to compare means at the 5% signiﬁcance level. Type of
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starch (ONS or ODPS) was the independent variables, whereas OGTs were the dependent variables in this study. 3. Results and discussion In the following discussion, NS refers to the starch that has not undergone any form of modiﬁcation. ONS (corn, sago, or tapioca) refers to NS samples that were oxidized with ozone gas for 1, 3, 5, or 10 min OGTs. DPS refers to the starch that has undergone deproteinization treatment. ODPS (corn, sago, or tapioca) refers to DPS samples that were oxidized with ozone gas for 1, 3, 5, or 10 min OGTs. 3.1. Protein content Fig. 1 shows the protein content of corn, sago, and tapioca starch before and after deproteinization. The protein content of corn, sago, and tapioca starch was 0.28%, 0.22%, and 0.19%, respectively. SDS treatment caused a signiﬁcant reduction in protein content for corn and sago starches compared to their native forms (approximately 21% and 16%, respectively). This result suggests that SDS was able to partially remove the protein content of corn and sago starch. The higher reduction in protein content for corn starch may be due to the existence of pores and channels on the corn starch granules; these would provide the SDS with access to the granule interior (Chan et al., 2010). The lesser decrease in protein content after SDS treatment seen in tapioca starch might be due to the absence of pores and channels on tapioca starch granules.
Fig. 2. Carbonyl content of oxidized-native and oxidized-deproteinized corn, sago, and tapioca starches at different OGTs. Bars bearing the same letter within a category in a particular starch are not signiﬁcantly different (p > 0.05).
Figs. 2 and 3 show the results for carbonyl and carboxyl content of ONS and ODPS at different OGTs. Generally, both carbonyl and carboxyl content of the oxidized starches increased as OGT increased. This is in accordance with the ﬁndings of Kuakpetoon and Wang (2001), who reported that both carbonyl and carboxyl contents of oxidized starch increased as the concentration of oxidizing agent increased. SDS treatment decreased the carbonyl content of all ODPS compared to their ONS, except ODP corn starch (Fig. 2). On the other hand, SDS treatment increased the carboxyl content of all ODPS starches compared to their ONS (Fig. 3). This result was caused by the removal of surface protein from starch
granules, which increased the granules’ susceptibility to ozone gas, thereby facilitating the entrance of the gas into the granule interior and allowing the interior part of the granules to be oxidized. The higher rate of depolymerization of starch chain to carbonyl group and oxidation of carbonyl group to carboxyl group in deproteinized corn starch was probably due to the presence of natural pores and channels on the corn starch granules compared to sago and tapioca starches. The carboxyl content for OPDS ranged from 0.14% to 0.28%. This value is higher than that reported by Kuakpetoon and Wang (2001), who reported that at 2% NaOCl, the carboxyl content of corn starch was 0.14%. Wang and Wang (2003) reported that a carboxyl content of 0.27% was obtained after oxidizing corn starch with 3% NaOCl. However, according to Wurzburg (1986), carboxyl content of most commercial hypochlorite oxidized starches can reach about 1.1%. In our study, the highest carboxyl content was found in deproteinized corn starch after oxidation at 10 min OGT, and we attribute this result to the speciﬁc structural and morphological characteristics of the starch granules in corn (i.e., pores and channels that allow more ozone gas to diffuse into the starch granules). The inconsistent trend for carboxyl content seen among the oxidized starches at different OGTs might be due to different rates of depolymerization of starch chains and oxidation
Fig. 1. Protein content of native and deproteinized corn, sago, and tapioca starches. Bars bearing the same letter within a particular starch are not signiﬁcantly different (p > 0.05).
Fig. 3. Carboxyl content of oxidized-native and oxidized-deproteinized corn, sago, and tapioca starches at different OGTs. Bars bearing the same letter within a category in a particular starch are not signiﬁcantly different (p > 0.05).
3.2. Carbonyl and carboxyl content
H.-T. Chan et al. / Food Hydrocolloids 26 (2012) 339e343
Fig. 4. Peak viscosity of oxidized-native and oxidized-deproteinized corn, sago, and tapioca starches at different OGTs. Bars bearing the same letter within a category in a particular starch are not signiﬁcantly different (p > 0.05).
of carbonyl groups to carboxyl groups that occur during the oxidation process.
3.3. Pasting properties The pasting properties of ONS and ODPS are shown in Figs. 4e6. Generally, pasting viscosity of all ODPS decreased drastically as OGT increased. At 0 min OGT, corn and sago starches exhibited the highest peak viscosity after SDS treatment (Fig. 4). This result might be due to the effective removal of protein layers, which would help to increase the swelling power of corn and sago starch. These results agree with those reported by Debet and Gidley (2006) and Chan et al. (2010). They reported an increment in peak viscosity after SDS treatment. In contrast, tapioca starch showed a decrease in peak viscosity after SDS treatment. This might have been caused by solubilization of amylose from tapioca starch granules during water washing after the centrifugation process, which would result in a lower peak viscosity. All ODPS exhibited a noticeable decrease in peak viscosity as OGT increased due to the effective removal of surface protein from the starch granules (Fig. 1). The reduction of peak viscosity after oxidation results from structural weakening and disintegration during oxidation (Lawal, 2004). Sandhu, Kaur,
Fig. 6. Setback viscosity of oxidized-native and oxidized-deproteinized corn, sago, and tapioca starches at different OGTs. Bars bearing the same letter within a category in a particular starch are not signiﬁcantly different (p > 0.05).
Singh, and Lim (2008) found a signiﬁcant reduction in peak viscosity for normal corn starches after oxidation. Adebowale and Lawal (2003) also reported a decrease in peak viscosity for mucuna bean starch after oxidation. The decrease in peak viscosity for ODPS could be attributed to partial cleavage of the glycosidic linkages after treatment with gaseous ozone, which would produce starch molecules with a lower molecular weight. An incompletely degraded network would not be resistant to shear and ultimately could not maintain the integrity of the starch granules, thus producing a lower viscosity. Fig. 5 shows breakdown viscosity for all of the starches. The breakdown viscosity of SDS-treated corn and sago starches was higher than that of their native starches. This could be due to the weakened structure of the granules caused by SDS treatment. These results show that SDS treatment was able to reduce the thermal stability of corn and sago starch during processing. Doublier, Llamas, and Le Meur (1987) reported that a relationship exists between swelling capacity and rheodestruction: the more swollen the starch granules (high peak viscosity), the more shear-sensitive the paste becomes (high breakdown viscosity). Breakdown viscosity for all ODPS decreased signiﬁcantly as OGT increased. This was the result of the introduction of new substituent groups into the oxidized starches (Adebowale & Lawal, 2003). All starches showed an increase in setback viscosity after SDS treatment (Fig. 6). Setback viscosity was associated with the reassociation of the solubilized starch during the cooling portion of the RVA proﬁle. Thus, the higher setback viscosity for SDS-treated starches is attributed to the higher breakdown viscosity of the starch paste. The setback viscosity for ODPS decreased signiﬁcantly as OGT increased because the introduction of carboxyl groups to replace hydroxyl groups during oxidation limited the reassociation of the starch chain during cooling. Sandhu et al. (2008) also reported a marked decrease in setback viscosity for oxidized normal corn starch. 4. Conclusions
Fig. 5. Breakdown viscosity of oxidized-native and oxidized-deproteinized corn, sago, and tapioca starches at different OGTs. Bars bearing the same letter within a category in a particular starch are not signiﬁcantly different (p > 0.05).
Deproteinization as a pretreatment prior to ozonation successfully increased the degree of oxidation in the three types of starches studied. Furthermore, all ODPS showed a signiﬁcant reduction in pasting viscosity as OGT increased. However, under identical conditions, the degree of oxidation varied among the starches studied. Carboxyl content for oxidized-deproteinized corn starch at highest OGT (10 min) in this study was comparable to that of
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oxidized corn starch treated with 3% NaOCl. This result reveals that deproteinization prior to ozonation can serve as an alternative to common hypochlorite oxidation process to produce oxidized starch at a more environmental friendly way. Acknowledgement This work was funded by a Science Fund Grant from the Ministry of Science, Technology, and Innovation (Project No. 05-01-05SF0347). H.T. Chan acknowledges a fellowship and postgraduate research grant awarded by the Universiti Sains Malaysia. References Adebowale, K. O., & Lawal, O. S. (2003). Functional properties and retrogradation behaviour of native and chemically modiﬁed starch of mucuna bean (Mucuna pruriens). Journal of the Science of Food and Agriculture, 83(15), 1541e1546. An, H. J., & King, J. M. (2009). Using ozonation and amino acids to change pasting properties of rice starch. Journal of Food Science, 74(3), C278eC283. AOAC. (1990). Ofﬁcial methods of analysis (15th ed.). Washington: Association of Ofﬁcial Analysis Chemists. Baldwin, P. M. (2001). Starch granule-associated proteins and polypeptides: a review. Starch e Stärke, 53, 475e503. Chan, H. T., Bhat, R., & Karim, A. A. (2009). Physicochemical and functional properties of ozone-oxidized starch. Journal of Agricultural and Food Chemistry, 57(13), 5965e5970. Chan, H.-T., Bhat, R., & Karim, A. A. (2010). Effects of sodium dodecyl sulfate and sonication treatment on physicochemical properties of starch. Food Chemistry, 120, 703e709. Chang, P. S., Park, K. O., Shin, H. K., Suh, D. S., & Kim, K. O. (2008). Physicochemical properties of partially oxidized corn starch from bromide-free TEMPO-mediated reaction. Journal of Food Science, 73(3), C173eC178. Chattopadhyay, S., Singhal, R. S., & Kulkarni, P. R. (1997). Optimisation of conditions of synthesis of oxidised starch from corn and amaranth for use in ﬁlm-forming applications. Carbohydrate Polymers, 34(4), 203e212. Debet, M. R., & Gidley, M. J. (2006). Three classes of starch granule swelling: inﬂuence of surface proteins and lipids. Carbohydrate Polymers, 64, 452e465.
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