Structural modification on potato tissue and starch using ethanol pre-treatment and drying process
Graphical abstract
Introduction
Starches are natural biopolymers with great importance as ingredients for different industries, such as food, feed, chemical, petrochemical, textile, paper and cellulose, adhesives, biodegradable plastics, among others.
Commercial starches are obtained from sources such as seeds (mainly maize, wheat, barley, and rice), roots and tubers (mainly cassava and potato). Potato starch is a valued source in different industries, due to some special properties (Grommers & Krogt, 2009). For instance, potato starch is used in the food industry due to its high clarity/transparency and neutral flavor, and in the textile industry due to its film properties, adhesive power, and paste penetration depth. In addition, potato starch is preferred as a pre-coating of filters due to its large granules, as well as it is also applied in water treatment due to its high phosphate content. In the paper and cellulose industry, potato starch is preferred due to its film-forming properties, less moisture retention, and excellent bonding power (Mitch, 1984).
However, roots and tubers have high moisture content, making them highly perishable after harvesting, which can result in economic losses if they are not quickly processed. In fact, although starches from potato and cassava present interesting industrial applications, they also present high variability and heterogenicity due to the vegetable senescence and partial degradation (for example due to fermentation) – which limits their production and application.
In this context, drying can be a simple, inexpensive, and efficient way to assure potato preservation focused on starch extraction. Particularly, convective drying uses hot air to remove the water from the product, being efficient and simple.
However, this process can take many hours, which is undesirable from a production perspective, as well as it can negatively impact the product quality. For instance, the presence of water in starchy raw materials, the long drying time, combined with the high temperatures, can promote changes in the starch characteristics, such as its gelatinization properties. Therefore, new approaches are necessary to enhance potato drying. Moreover, simple approaches are important for application by small producers.
In fact, ethanol pre-treatment promotes structural modifications and physical mechanisms that enhance the subsequent drying (Llavata et al., 2020). In fact, there is growing interest in using the ethanol pre-treatment to improve drying processes, such as the convective drying of pumpkin (Carvalho, Massarioli et al., 2020, Carvalho, Rojas et al., 2020; Rojas, Silveira, & Augusto, 2020), pineapple (Carvalho et al., 2020; Santos & Silva, 2009; Silva, Braga, & Santos, 2012), bananas (Corrêa et al., 2012; Silva et al., 2012), carrot (Santos et al., 2021), melon (Da Cunha et al., 2020), foam mat of pitayas (Araújo et al., 2020) and guaco (Silva, Celeghini, & Silva, 2018). Moreover, recently the ethanol pre-treatment started to be studied to improve other drying techniques, such as the convective drying assisted by ultrasound of apple (Rojas, Augusto, & Cárcel, 2020), infrared drying of potato (Rojas & Augusto, 2018b; Rojas, Silveira, & Augusto, 2019) and garlic (Feng et al., 2019), infrared with hot air in scallion (Wang et al., 2019) and scallion stalk (Zhou et al., 2020), and vacuum drying of apple (Amanor-Atiemoh et al., 2020).
However, although the high economic and industrial relevance, the effect of pre-treatment with ethanol and drying on a raw material whose final product is starch was still not evaluated.
Therefore, the objective of this study was to evaluate the pre-treatment with ethanol on the convective drying of potatoes, focused on the subsequent starch extraction. To achieve it, we evaluated the structural changes in both potato tissues and starch (both granules and molecules), correlating them with starch properties (pasting and gel), focusing on structural characteristics and properties of the starch as an industrial ingredient.
Section snippets
Material and methods
This work was divided in different steps. Firstly, potato slices were obtained and convectively dried, directly or after pre-treatments using ethanol. In this step, the drying kinetics was evaluated, and the dried slices were evaluated through their structure and rehydration kinetics. Next, the potato starch was extracted and purified from the rehydrated slices. Finally, both structure (granular and molecular) and properties of the obtained starches were evaluated.
Results and discussion
The purpose of this work was not only to study potato drying but also to understand more deeply the effect of ethanol on drying, rehydration, and microstructure of vegetables, as well as propose drying of starchy products as an approach before starch extraction. Consequently, the obtained results are divided in three sections: (1) effect of ethanol pre-treatment on potato structure and drying; (2) effect of ethanol on potato rehydration kinetics; and (3) structure and properties of the obtained
Conclusions
The use of pre-treatment with ethanol promoted structural changes in potato tissues and cells, improving the subsequent water flow during drying and rehydration. This pre-treatment reduced the drying time up to ∼56% and increased the initial rehydration rate up to ∼25%. Possible mechanisms were discussed, including the structural changes and physical mechanisms.
No changes were observed on the starch molecular profile, and low imperfections were observed in the granule surface of starches
CRediT authorship contribution statement
Jaqueline S. Guedes: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data curation, Writing - original draft, Visualization. Karoline C. Santos: Methodology, Formal analysis, Investigation, Data curation. Nanci Castanha: Methodology, Formal analysis, Data curation, Writing - review & editing, Visualization. Meliza L. Rojas: Methodology, Formal analysis, Data curation, Writing - review & editing, Visualization. Manoel D. Matta Junior: Methodology, Formal analysis,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors are grateful to the São Paulo Research Foundation (FAPESP, Brazil) for funding the project nº 2019/05043-6; this study was financed in part by the “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brazil (CAPES)” – for the JS Guedes (88882.378356/2019-01) and KC Santos (88882.378385/2019-01) M.Sc. scholarships; to the National Council for Scientific and Technological Development (CNPq, Brazil) for the JS Guedes M.Sc. scholarship (131235/2020-6) and the productivity
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