Hydroalcoholic extraction of bioactive compounds from expeller soybean meal under subcritical conditions
Graphical Abstract
Introduction
Current problems such as climate change and the threat of a future with a lack of resources due to a rapidly growing population have contributed to promoting changes in agro-industrial processes, with a trend to implementing green and sustainable processes, removing the focus from productivity. One of the key aspects of sustainable development is reducing or using waste or by-products, reusing them, and thus, making a more efficient use of energy and resources in each production stage [1].
Another global trend is the developing of functional foods or dietary supplements capable of proportionate physiological benefits, in addition to the nutritional and energetic ones. These functional foods are traditional foods enriched with bioactive compounds capable of providing and promoting benefits for human health, such as antioxidant, antihypertensive or anti-inflammatory effects [2]. These bioactive compounds are commonly extracted from natural sources, by-products of the food industry, or even compounds formed during the agroindustrial process [3]. Both trends could be integrated to develop a sustainable agro-industrial process that allows to obtain the product of interest and other co-products by using the waste generated from primary processes.
The soybean grain is one of the main products to consider when generating added value due to the produced volume and its excellent nutritional characteristics [4]. One of its destinations is the vegetable oil production industry by solvent extraction or pressing, which generates industrial by-products called flour or expeller soybean meal, according to the extraction method used [5]. The expeller soybean meal comes from a pressing method that is less efficient but more environmentally friendly, and in terms of protein content, its main application is animal feeding, although it represents an interesting source of bioactive compounds, which could be extracted from this matrix previously. Standing out is its isoflavones concentration (flavonoids), which act like powerful antioxidants that have been associated with the prevention of chronic cardiovascular disease, Alzheimer and cancer [6]. Expeller soybean meal extracts could be used as a natural food preservative, or incorporated as an ingredient in the formulation of functional foods, cosmetic and pharmaceutical products [7].
To obtain the bioactive compounds of interest within a sustainable process, it is necessary to develop a selective extraction method with acceptable yields from the matrix, avoiding loss of functional characteristics and ensuring its food quality. This requires using clean extraction technologies with green solvents, such as microwave accelerated extraction, ultrasound-assisted extraction, and extraction with sub and supercritical fluids [3].
The subcritical fluids extraction generally uses water or water + ethanol mixtures at high temperature and pressure enough to maintain the mixture in the liquid state. Subcritical process emerges as an alternative technology to replace traditional extraction methods. It is a green extraction technique that is environmentally friendly, safe, and fast, and high extraction yields of medium and high polarity compounds contained in a solid matrix could be achieved [8]. The composition of the obtained extract and the extraction yield could be changed by varying the operation variables (temperature, solvent mass flow rate and alcohol composition in the solvent mixture, among others). Different studies have demonstrated that it could be an adequate technology for the extraction of a variety of bioactive compounds from different matrices such as rice [9], pistachio [10], and peanut skin [11].
Some of the interesting bioactive compounds that could be obtained from plants are phenolic compounds, carotenoids, alpha acids, methylxanthines, and vitamins. Within the so-called phenolic compounds, flavonoids, phenolic acids, and tannins, among others, can be mentioned. All these natural compounds exhibit antioxidant activity and therefore have different applications in the food and pharmaceutical industries [12], [13].
Considering the nature of the antioxidants present in soybean, hydroalcoholic subcritical mixtures are shown as a possible alternative to extract flavonoids, organic acids, and, to a lesser extent, nonpolar flavanones. Along with the extraction process, the stages of purification, total quantification, and individual characterization of the extracted compounds must be developed. Furthermore, an analysis of the impact of the extraction process conditions on the chemical characteristics and biological activity of extracts must be carried out [14]. Nevertheless, literature is scarce on the extraction of bioactive compounds from soy by-products with hydroalcoholic mixtures at high temperatures. Therefore, the aim of this work is to evaluate the use of water + ethanol mixtures under subcritical conditions for the extraction of bioactive compounds (with antioxidant activity) from expeller soybean meal and the effect of modifying the operating conditions on the yield and characteristics of the extracts.
Section snippets
Plant material pretreatment and extraction solvent
The expeller soybean meal (ESM) used for the extractions was provided by a local company (DIEZ S.R.L., Pampayasta Sud, Córdoba, Argentina), which was obtained from a pressing method. The ESM was initially ground with a knife mill (Tecnodalvo TDMC, Santa Fe, Santa Fe, Argentina) and then classified using a vibrating sieve (Zonytest EJR 2000, C. A. de Buenos Aires, Buenos Aires, Argentina) according to mean particle size. Distilled water and absolute ethanol (99.5%, Cicarelli, San Lorenzo, Santa
Results and discussion
Despite new extraction methodologies have been studied in order to improve the soybean value chain, such as supercritical carbon dioxide extraction from ESM [28] and subcritical water extraction for the residue from the production of soy milk, referred to as okara [29], the authors of this work did not find information in the existent literature about the use of hydroalcoholic mixtures in subcritical conditions as an extraction method for the recovery of bioactive compounds from ESM.
Statistical
Conclusions
Based on the obtained results, it was possible to study the effect of different process variables on the yield and the type of antioxidant components extracted from ESM at subcritical conditions. It was found that lower mass flow rates increased the extracted amounts, since they allowed longer contact times between the solvent and the plant material. Similarly, the increase in the temperature not only favored the solubility of these compounds by modifying the solvent properties but also
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.
Acknowledgments
The authors express their gratitude to DIEZ S.R.L. and María Lucía Córdoba for their collaboration, and to National Council for Scientific and Technical Research (CONICET, Argentina) and the Secretariat of Science and Technology of the National University of Córdoba (SECyT, Córdoba, Argentina) for funding (grant ID: 33620180100044CB). To the National University of Córdoba (UNC), ICTA and IPQA for lending the working spaces and offering available equipment used in this work.
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