Potato starch modification using the ozone technology
Graphical abstract
Introduction
Starch is an important energy source in human diet and a major component of many plants. Furthermore, it is an important component for many industrial applications, including different industries such as food (human and animal), pharmaceutical, cosmetic, chemical, petrochemical, textile, etc. Although being formed mainly by α-d-glucopyranosyl units, starch is a very complex material, being presented as a water insoluble granule with a double-helical, semi-crystalline and birefringent structure, formed by two main polysaccharides: amylose and amylopectin (Liu, 2005, Miles et al., 1985). Amylopectin is a highly branched molecule composed by short chains of (1 → 4)-linked α-d-glucopyranosyl units with (1 → 6)-linked branches, with a tree-like arrangement of double helices, being the main component of the crystalline domains in the starch granule. Amylose is essentially linear, composed by (1 → 4)-linked α-d-glucopyranosyl, presenting a small amount of branches, and it is believed to be randomly mixed with other materials in the amorphous domain of the starch granule (Hizukuri et al., 2006, Tester et al., 2004).
Starch has attracted much academic and industrial interest as it is an abundant, renewable, cheap and biodegradable resource, as well as generally regarded as safe and environmentally acceptable (Kochkar et al., 2001, Zhang et al., 2009). On the other hand, the naturally available starches have limited properties, being necessary the modification in order to provide further properties for the different industries requirements.
The modified starches present some characteristics that the native starches does not have, thus allowing further uses from a specific source. In fact, the modified starches can bring competitive advantages to some products, with many new functional and added value properties (Kaur, Ariffin, Bhat, & Karim, 2012). The starch modification can be carried out by chemical, physical and/or enzymatic processes, as well as by genetic improvement.
Oxidation is a chemical method of starch modification, being performed by a reaction with an oxidant agent under controlled conditions (Wang & Wang, 2003). The main reagents used for starch oxidation are sodium hypochlorite and hydrogen peroxide. However, by using these chemical agents, toxic wastes are generated (Chan et al., 2011).
In contrast, if compared to other chemical oxidants, the ozone is considered a “green” and “environmentally friendly” technology, since, by being quickly decomposed to oxygen, it does not leave any residues in food or in environment (Çatal & İbanoğlu, 2014). In fact, it meets the global demand for sustainability being safer for both consumer and environment. The ozone is a very powerful oxidizing agent, with a relatively high (E0 = +2.075 V) electrochemical potential (Mahapatra, Muthukumarappan, & Julson, 2005). It can be generated by the exposure of oxygen/air to a high-energy source, which convert molecules of oxygen (O2) to ozone (O3) (Khadre, Yousef, & Kim, 2001).
In fact, the ozone is already being used for starch modification in a wide range of starch sources, such as corn, sago, cassava, rice, wheat and potato, among others (Çatal and İbanoğlu, 2012a, Çatal and İbanoğlu, 2013, Çatal and İbanoğlu, 2014, An and King, 2009, Chan et al., 2009, Chan et al., 2011, Klein et al., 2014). However, it is a still fairly studied process. For example, Çatal and İbanoğlu, 2012a, Çatal and İbanoğlu, 2012b studied the effects of processing starches with ozone in aqueous solution for a determined time (1 h for both studies). In their first work (2012a), corn and potato starch suspensions were processed and the effects on the structural (only the granule morphology), thermal and pasting properties were evaluated. The second study (2012b) evaluated the effect of the ozonation on the structure (only the granule morphology), physic-chemical (pH and color) and microbiological (total bacteria and mold/yeast) properties of wheat, corn, potato and rice starches. Both works discuss the functional properties of the processed starches. However, they slightly discussed the mechanisms of ozone action and how it acts over the process. In addition, the structural changes are described only through the granule morphology, without further molecular information - chemical and structural modifications of starches, i.e. the possible changes in the crystallinity of the starch granules or carbonyl and carboxyl group contents, were not demonstrated. Finally, only one experimental condition was evaluated, which limits the understanding of the involved mechanisms. This present work, therefore, aims to deeply study the potato starch modification by ozone, providing more information about the molecular and granule modification and degradation by ozone and correlating it with the resulted changes on functional and technological properties. Therefore, it proposes a better understand about the process-structure-properties relationships.
Potato (Solanum tuberosum L.) is a worldwide known tuber, cropped under a wide range of climatic and soil conditions, and contains an unique starch, presenting a large granule size, long amylose and amylopectin chain lengths and the presence of phosphate ester groups (Vasanthan, Bergthaller, Driedger, Yeung, & Sporns, 1999). The phosphorus content in potato starch is relatively high when compared with other sources, and seems to be contained mostly in the branched (amylopectin) fraction in the form of covalently bonded phosphate groups (Posternak, 1950), which also affect the starch properties. The industrial application of starches is directly related to their characteristics. For example, when oxidized, the potato starch may present an even more clearer paste, a higher retrogradation tendency (and, therefore, stronger gels after cooling) and lower apparent viscosity at high solids concentration (Parovuori, Hamunen, Forssell, Autio, & Poutanen, 1995), if compared to the native starch. These characteristics are important to obtain starches with good binding capacity and film forming properties, among others (Chan et al., 2012).
In order to increase the possibilities of using potato starch, as well as meeting the growing industrial demand for specific functional characteristics, considering the environmental and food security claim, this work aimed to modify potato starch using the ozone technology. In addition, some structural and functional properties of the modified starch were evaluated and described aiming to better understand the degree of the oxidation in each processing time.
Section snippets
Potato starch oxidation: general hypotheses
To subsidize the evaluation and the discussion of the results in the present work, it is important to point out some assumptions and information that explain or at least elucidate the characteristics and the structure of starches and some hypothesis about its modification by oxidation. The most important information that should be enlightened is described in the topics listed below.
- 1.
Ozonation is an oxidation method, and it is considered a process of starch chemical modification (Kaur et al., 2012
Material and methods
The ozonation was carried out by dissolving the ozone into the starch suspension in water, by considering that the ozone in aqueous solution penetrates easier the starch than in gas form (Tiwari, Muthukumarappan, O’Donnell, Chenchaiah, & Cullen, 2008), as well as, it may react better in water due to different pathways (direct reaction with the sample or decomposition into radicals, and the radicals react with the sample, as described by Khadre et al. (2001)). Furthermore, it is the feasible way
Results and discussion
The goal of this work was not only to obtain starches with different characteristics, but also to understand how the oxidation occurred at the molecular level under the conditions studied, thus describing and correlating the process-structure-properties relationships. Therefore, after presenting and discussing the obtained results, a section with the proposed mechanisms of the ozone action is presented. The further discussion is subsidized by the information presented in Section 2 of the
Summarizing: proposed mechanisms
The data reported in the present work supports some statements about how the potato starch was affected by the ozonation in the evaluated conditions, as well as illustrate how these changes affected the starch properties. Firstly, it was observed through the carbonyl and carboxyl content that the hydroxyl groups of the starch molecules were highly affected. Also, as demonstrated by the GPC, the apparent amylose content, and the reducing sugar content evaluations, the glycosidic bonds of the
Conclusions
The results obtained with the starch functional and structural properties allows the statement that the potato starch was successfully oxidized by ozone in aqueous solution in this work conditions, being possible to understand and to correlate the process-structure-properties relationship. Thus, ozone can be stated as an alternative for oxidative processes of starch modification for food and non-food industrial applications, having as an advantage the fact of being safe for consumers and for
Acknowledgments
The authors are grateful to:
• the National Council for Scientific and Technological Development (CNPq, Brazil) for funding the project nº 401004/2014-7 and MD Matta Jr. post-doctoral fellowship (158545/2015-0);
• the Coordination for the Improvement of Higher Education Personnel (CAPES, Brazil) for the N Castanha M.Sc. scholarship;
• the “Núcleo de Apoio à Pesquisa em Microscopia Eletrônica Aplicada à Pesquisa Agropecuária” (NAP/MEPA-ESALQ/USP) for the support and facilities of Electronic
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