Optimizing the extraction parameters of epigallocatechin gallate using conventional hot water and ultrasound assisted methods from green tea

doi:10.1016/j.fbp.2018.06.003

Food and Bioproducts Processing

Volume 111, September 2018, Pages 37-44

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https://doi.org/10.1016/j.fbp.2018.06.003 Get rights and content

Highlights

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Extraction parameters were optimized to maximize the epigallocatechin gallate content.
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Epigallocatechin gallate content in hot water extraction was 3.86 g/100 g at optimum.
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Ultrasound extraction with ethanol increased epigallocatechin gallate content by 100%.
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Hot water extraction can easily be adapted to a pilot scale production.

Abstract

Epigallocatechin gallate (EGCG) is the main polyphenol present in green tea and is also known to possess various beneficial health effects. Extractions of EGCG, epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC) from green tea were investigated by both conventional hot water extraction and ultrasound assisted extraction (UAE) with water and ethanol. Response Surface Methodology was used in order to optimize the extraction conditions for obtaining maximum amount of EGCG in the extracts. Pilot scale conventional hot water extraction and UAE with water in continuous flow mode were also conducted for industrial use. UAE with ethanol was significantly (p < 0.05) efficient to extract more EGCG, EGC, ECG, and EC than conventional hot water extraction and UAE with water. At optimum conditions, almost 100 and 50% more EGCG content was obtained in UAE with ethanol than conventional hot water extraction and UAE with water, respectively. The optimal conditions for UAE of EGCG with ethanol were 66.53 °C, 43.75 min and, 67.81% ethanol. Conventional hot water extraction can easily be scaled up to a pilot scale and can be used for green tea beverage production. UAE should also be scaled up to a pilot scale by an efficient design either using an ultrasound probe in a larger volume continuously or ultrasound probes on each side of the extractor tank with an agitation system.

Graphical abstract

Introduction

The green tea catechins are among the strongest natural antioxidants. They are the most biological active groups of the tea components, which are thought to contribute to the health benefits of green tea. They can also account for 30–40% of the extractable solids of dried green tea leaves. Major catechins in green tea are: (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), and (−)-epigallocatechin gallate (EGCG), among which EGCG is the major catechin with most bioactive and cancer preventive properties (Singh et al., 2011, Ju et al., 2007). Epicatechins can change to their epimers that are non-epicatechins, which are known as: (−)-gallocatechin gallate (GCG), (−)-catechin gallate (CG), (−)-gallocatechin (GC), and (+)-catechin (C) (Banerjee and Chatterjee, 2015).

Extraction is the major step in obtaining catechins from green tea. Different techniques have been used to extract the bioactive compounds from green tea, including maceration, infusion, microwave assisted extraction (Li and Jiang, 2010), ultrasonic assisted extraction (UAE) (Lee et al., 2013), supercritical carbon dioxide (Chang et al., 2000), soxhlet extraction and ultrahigh pressure extraction (Jun et al., 2011), among others. UAE is preferred mode of tea catechins due to the increased efficacy of extraction process at lower temperature by retaining their antioxidant activity. Extraction parameters such as solvent, temperature, time, ratio of material to solvent and variety of tea influence efficiency of an extraction process. Emergence of novel techniques eases the extraction process, minimize extraction cost, time, and maximize the yield. Simultaneously, it is tried to retain maximum antioxidant potential and sensory attributes namely colour, flavour, sweetness reducing proteins and pectin contents (Banerjee and Chatterjee, 2015).

The catechins are polar compounds and solubilize in polar organic solvents such as ethanol, methanol, water, and acetone. During extraction using polar organic solvents, other components such as caffeine and chlorophyll also get extracted (Gadkari and Balaraman, 2015). Perva-Uzunalic et al. (2006) reported that the highest extraction efficiency of catechins was obtained by extraction with 50% aqueous acetone as 99.3%, with 50% acetonitrile as 99.8% and with 80% ethanol as 89.1%, respectively. There are numerous studies showing that hot water and ethanol are effective in extracting catechins from green tea. Vuong et al. (2011) studied the extraction of catechins from green tea using hot water, they showed that the best temperature and time combination for catechin extraction was at 80 °C for 30 min. Liang et al. (2007) also reported that the concentrations of EGCG increased with extraction temperature up to 80 °C and then decreased at 100 °C due to epimerisation reactions. They found that EGCG concentration was 55.8 mg/g tea at 80 °C extraction. They also studied the ethanol extraction and found that, the concentration of EGCG extracted by 50% ethanol, was 26.3% higher than those extracted in water at 80 °C. Moreover, Choung et al. (2014) determined 40% ethanol solution with UAE for optimal extraction of catechins and caffeine.

Due to the growing environmental problems and the adverse health effects of organic solvents, water is preferred as a cheap and safe solvent, and is widely used for producing green tea beverages. Ethanol is generally preferred to produce green tea extract powder. To obtain the maximum efficiency from conventional hot water extraction and UAE, extraction conditions of catechins need to be optimized and easily scaled-up. Therefore, the aim of this study was to optimize the parameters of conventional hot water and UAE with water and ethanol for green tea to maximize the EGCG concentration by using Response Surface Methodology (RSM) and to scale up a pilot scale extraction for industrial use.

Section snippets

Chemicals

Epigallocatechin gallate (95%), epigallocatechin (95%), epicatechin gallate (98%), epicatechin (98%), methanol (99.9%), ethanol (99.8%), acetonitrile Chromasolv^® for HPLC (≥99.9%), and ethylenediaminetetraaceticacid (EDTA) were obtained from Sigma Aldrich (Bo&Ga, Kaplan Metal, Prolab, and Interlab Co., Istanbul, Turkey.) Ascorbic acid and acetic acid were purchased from VWR Chemicals (Prolab, Istanbul, Turkey). Ethanol (96%) was obtained from TEKKIM Chemicals (Bursa, Turkey). Standard reference

Analysis of the model for conventional hot water extraction

The experimental data for catechin contents (EGCG, EGC, ECG, and EC) in conventional hot water extraction was analysed. The R² together with ANOVA and regression coefficients in terms of actual factors for the predicted models are shown in Table 1. According to the sequential model of the sum of squares, the models were selected based on the highest order polynomials where the additional terms were significant. Fitting of the data with various models and ANOVA showed that EGCG, EGC and EC were

Conclusions

This study was carried out to optimize the extraction parameters of conventional hot water extraction and UAE with water and ethanol in obtaining the maximum amount of EGCG. Maximum EGCG was extracted in UAE with aqueous ethanol. Temperature and time exhibited significant effects (p < 0.05) on EGCG content, while tea to water ratio had no effect (p > 0.05) during hot water extraction. Similarly, temperature, time, and ethanol concentration exhibited significant effects (p < 0.05) on EGCG

Acknowledgements

This research was supported by TÜBİTAK (The Scientific and Technological Research Council of Turkey) under the Project TARAL 1007 112G048 entitled “Development of New Value Added Products from Tea”. Any opinions, findings, and conclusions expressed in this material are those of the authors and do not necessarily reflect the views of TUBITAK. We are grateful to TÜBİTAK for financial support and ÇAYKUR Tea Enterprises (Rize, Turkey) for providing the green tea.

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Optimizing the extraction parameters of epigallocatechin gallate using conventional hot water and ultrasound assisted methods from green tea

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Analysis of the model for conventional hot water extraction

Conclusions

Acknowledgements

Ultrason. Sonochem.

Food Chem.

Ultrason. Sonochem.

Ultrason. Sonochem.

Food Chem.

Food Bioprod. Process.

Food Bioprod. Process.

Food Chem.

Semin. Cancer Biol.

Int. J. Pharm.

LWT—Food Sci. Technol.

Food Chem.