Microwave-assisted aqueous two-phase system based extraction of phenolics from pulses: Antioxidant properties, characterization and encapsulation

https://doi.org/10.1016/j.indcrop.2021.114144Get rights and content

Highlights

  • Microwave assisted-aqueous two-phase system was found effective.

  • Extracts obtained microwave system showed the highest antioxidant properties.

  • Microwave assisted-aqueous two-phase system affects releasing profile.

  • FTIR revealed aqueous two-phase system alters structure of the extracts.

Abstract

In the current study, a microwave-assisted aqueous two-phase system (MA-ATPS) was examined for the extraction of phenolic compounds from green lentils, chickpeas, and dry beans. The recovery of phenolic compounds by MA-ATPS was optimized by response surface methodology (RSM). A comparative study was performed by conventional ATPS (C-ATPS) and classical mono-phase extraction (C). The DPPH scavenging activity, ABTS antioxidant activity, and metal chelating activity of the extracts were determined. The highest extraction yield (6.68, 2.10, and 1.69 mg GAE/ g sample for green lentil, chickpea and dry bean, respectively) and antioxidant properties (70.98, 7.60, and 9.68 μmol TE/g for DPPH scavenging activity for green lentil, chickpea, and dry bean respectively) were observed from the extracts obtained by MA-ATPS. Furthermore, the phenolic extracts were encapsulated by freeze-drying and the structural characterization of microcapsules has been performed by Fourier Transform Infrared (FT-IR) spectrometry and Scanning Electron Microscopy (SEM). The releasing profiles of the encapsulated phenolic compounds were investigated. Additionally, the effects of extracts on oxidative stability on sunflower oil under accelerated storage conditions were assessed. The results of the present study proved that the MA-ATPS might be considered as an efficient environment-friendly method for extraction phenolic compounds from pulses as evidenced by the antioxidant activity of extracts. Moreover, the encapsulated phenolic extracts may serve as an alternative ingredient for the food industry to be used in various functional formulations potentially leading to an increase in the value of green lentil, chickpea, and dry bean and possibly their by-products.

Introduction

Pulses are important leguminous seeds consumed worldwide after drying (FAO, 1988). It has been known that the FAO declared 2016 as the International Year of Pulses (IYP) due to their nutritive properties and low negative effect of pulse production on the environment (FAO, 2016). Pulses are important protein sources for the human diet and they also provide phenolic compounds (Graham and Vance, 2003). Phenolic acids, flavonoids, and tannins are major bioactive compounds of pulses such as lentils, beans, chickpea, and soybean. The content of phenolic compounds of pulses was reported as between 38.6–542.7 mg GAE/100 g (Parikh and Patel, 2018). The pulses have high antioxidant activity due to their phenolic compounds and so they show cardioprotective, anticarcinogenic and anticholesterolemic properties (Singh et al., 2017). Generally, phenolic compounds are extracted by maceration technique using different solvents such as ethanol, acetone, dichloromethane, or the mixture of these solvents with water. Nevertheless, conventional extraction techniques require large amounts of organic solvents and a longer time besides they show low extraction yield (Guo et al., 2013). Recently, environmentally friendly extraction processes have an attraction in researches such as ultrasound-assisted extraction (Martínez-Ramos et al., 2020), supercritical fluid (Wenzel et al., 2020), pressurized liquid (Sumampouw et al., 2021), enzyme assisted (Lombardelli et al., 2020), and microwave-assisted extraction (MAE) (Sarfarazi et al., 2020) because of lower time and consumption of solvent and higher extraction yield. Therefore, the current study employed MAE for its excellent heating capacity, high performance, and moderate cost. MAE enhances the extraction of the bioactive phenolic compounds by increased penetration of solvent into materials (Chan et al., 2011).

Inorganic salts and short-chain alcohol are creating Aqueous Two-Phase System (ATPS) which has low viscosity, high efficiency, quite a good phase separation, and recovery of alcohol and salt. For these reasons, ATPS is not only a biocompatible technique but also a significant environmental-friendly alternative technique of conventional systems (Đorđević and Antov, 2017). ATPS is a single-step system that contains both extraction and purification (Zhao et al., 2021). Phenolic compounds of material and soluble sugar disperse in the top and bottom phases, respectively (Yin et al., 2017). Using ATPS and MAE together may provide better extraction efficiency and simpler purification steps than traditional methods (Zhao et al., 2021). Microwave energy could be easily absorbed by ATPS and thus produce a high thermal effect. As a result of the increased high temperature, the solvent penetrates the matrix of materials and enhance the extraction ratio (Zhang et al., 2016). As far as author knowledge, MA-ATPS has not been investigated for the extraction of phenolic compounds from green lentils, chickpeas, and dry beans.

Response surface methodology (RSM) which is a mathematical and statistical method is used in many engineering applications for the optimization of a process. RSM provides an analysis of the interaction between the response and the independent variable. Thus, it predicts an optimal system (Yin et al., 2017). RSM can be used as an effective method for any process which has many factors and interactions that may affect extraction yield. Central Composite and Box-Behnken Design (BBD) are the most used design of RSM (Box and Wilson, 1951). In previous works, optimization of MA-ATPS has been successfully conducted to the extraction of phenolic compounds from plants (Lin et al., 2019; Yin et al., 2017).

The microencapsulation processes are important for the food industry because of the protection of core material degradation from environmental parameters like light, oxygen, heat, and moisture. Transfer rate of core materials to the outside delay through encapsulation. Besides, encapsulation processes can provide a mask of unpleasant flavors of core material such as bitter taste and sourness of polyphenols. Polysaccharides especially maltodextrin, hydrophobically modified starches, chitosan, and gum Arabic at the same time mixture of them can be used as coating materials in food processing (Ray et al., 2016). Recently, encapsulation of phenolic compounds was studied by different materials and different drying methods (González et al., 2019; Navarro-Flores et al., 2020; Thakur and Thakur, 2020).

The present study aimed to evaluate a novel, rapid and effective MA-ATPS for extraction phenolic compounds from green lentil, chickpea, and dry bean as a biphasic extraction system Ethanol/ammonium sulfate system ((NH4)2SO4) was used to extract phenolic compounds from pulses by the MA-ATPS. It was also aimed to determine the optimal extraction parameters. For this end, the salt ratio of ATPS, microwave application time, and microwave power was selected as independent variables for BBD of RSM. The phenolic compounds of the top and bottom phases were analyzed for optimization procedure. It was seen that the top phase was considerably rich compared to the bottom phase. Therefore, the recovery of phenolic compounds from the top phase was used as the response factor. Moreover, a comparative study was performed by conventional ATPS (C-ATPS) and Classical mono-phase extraction (C). DPPH scavenging activity, antioxidant activity, and metal chelating activity of the extracts were evaluated. The extracts at the optimum point of RSM and extract of C-ATPS and C were encapsulated by dextrin through lyophilization. The structural characterization of microcapsules was analyzed by FTIR spectroscopy and SEM. The releasing profile of the encapsulated compounds was also evaluated in vitro assay simulating gastric and intestinal fluids systems.

Section snippets

Materials

Folin-Ciocalteu, 2,2′-azino-bis (3-ethylbenzothiazo- line-6-sulphonic acid) (ABTS) (A1888-1), ferrozine (160601) 2,2-diphenyl-1-picrylhydrazyl (DPPH) (D913-2), dextrin DE 8-15 (31410), and ammonium sulfate (A4915) were obtained from Sigma Aldrich Co. (St. Louis, MO, USA). Iron chloride (3260) was purchased from Carlo-Erba and sodium phosphate dibasic (Na2HPO4) (10028-24-7) were purchased from Merck. Analytical grade chemicals were used in this study. The pulses were purchased from a local

RSM optimization of MA-ATPS

The composition of ATPS is a significant parameter influencing the distribution of phenolic compounds between the top and bottom phases (Ran et al., 2019). When the previous optimization studies were examined, it was seen that ethanol concentration was effective at 26 % plant polysaccharide extraction (Lin et al., 2019), 28 % for genistein and apigenin extraction from pigeon pea roots (Zhang et al., 2013), 28 % for polyphenol and lutein extraction from the marigold flower (Fu et al., 2018).

Conclusion

In the present study, phenolic compounds extraction from pulses through MA-ATPS as an environmentally-friendly technique was optimized by RSM of BBD. The optimal condition was determined as 219 s, 300 W and 22.8 % (NH4)2SO4 (w/w) for green lentil, 98.76 s, 236 W and 17.2 % (NH4)2SO4 (w/w) for chickpea, and 60.93 s, 227.62 W and 17.01 % (NH4)2SO4 (w/w) for dry bean. MA-ATPS was compared with C and C- ATPS. The extraction efficiency of MA-ATPS was higher and an alteration in the chemical

CRediT authorship contribution statement

Elif Meltem İşçimen: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Validation, Visualization, Writing - original draft, Writing - review & editing. Mehmet Hayta: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Validation, Visualization, Writing - original draft, Writing - review & editing.

Declaration of Competing Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Prof. Dr. Mehmet HAYTA reports financial support was provided by Erciyes University.

Acknowledgments

The present study is a part of a research project (FDK-2020-10341) funded by Erciyes University Scientific Research Unit (ERU-BAP). The financial support provided by ERU-BAP and technical supports of the Nanotechnology Research Center of ERU (ERNAM) for SEM analysis is gratefully acknowledged.

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