A simple and efficient method for enrichment of cocoa polyphenols from cocoa bean husks with macroporous resins following a scale-up separation
Introduction
Cocoa beans (Theobroma cacao L.) have been cultivated for a long period of time as a major ingredient of cocoa and chocolate (Baba et al., 2000; Andres-Lacueva et al., 2008). Cocoa beans contain approximately 6–8% polyphenols by dry weight (Grassi et al., 2008). Polyphenols are secondary plant metabolites with high antioxidant properties and also have potentially beneficial effect on human health, such as treatment and prevention of cancer, cardiovascular disease and other pathologies (Ignat et al., 2011; Quideau et al., 2011). EU Commission approves health claim: Cocoa flavanols support a healthy blood circulation (2013).
The data obtained from the Food and Agriculture Organization of the United Nations Statistics Division have shown that 4.58 million ton of cocoa beans were produced in 2013. Whereas, cocoa husks about 5–10% weight of cocoa beans were generated as a waste by-product of the cocoa industries. Cocoa husks can be a rich source of polyphenols and its low cost as compared to cocoa beans make a better choice. Three main polyphenol groups can be distinguished in cocoa: catechins, anthocyanins and procyanidins, whose common skeletal structure is a flavanoid-type structure (Wollgast and Anklam, 2000). The molecular structure of EC is shown in Fig. 1. The crude polyphenol extracts of cocoa husks always contain alkaloids, proteins, polysaccharides and other impurities. Therefore, an efficient purification method is needed to enrich cocoa polyphenols.
The conventional method of decaffeination and enrichment of cocoa polyphenols were carried out by means of solid-liquid extraction (Chemat et al., 2011), precipitation or silica gel column chromatography. However, these separation methods are inefficient, time consuming, laborious and using high contents of toxic organic solvents.
Macroporous adsorption resins have been widely used for the separation and enrichment of biochemical products. Researches like madecassoside and asiaticoside from Centella asiatica (Jia and Lu, 2008), rutin and quercetin from Euonymus alatus (Thunb.) Siebold (Zhao et al., 2011), flavonoids from Glycyrrhiza glabra L. leaf (Dong et al., 2015) and rosavin from Rhodiola rosea (Ma et al., 2009) have been reported due to the large surface area and distinct pore structure on macroporous resin which increases the efficiency of purification process. In addition, the functional groups on the surface of the macroporous resin also enhance the separation selectivity. Therefore, compounds can be eluted based on polarity, molecular size and hydrogen-bond interactive forces. The mildness and low toxicity of these adsorption and desorption interactions make this process food-friendly.
Therefore, in this study the adsorption and desorption characteristics of EC and the optimal separation condition for polyphenols on macroporous resins were studied. Meanwhile, the adsorption kinetics and thermodynamics were also investigated. The decaffeination was achieved by gradient elution with different ratios of ethanol-water solutions. In the end, the experiments were scaled up to evaluate the feasibility of the industrial process.
Section snippets
Chemicals and materials
Distilled water was purchased from Hangzhou Wahaha Group Co., Ltd while HPLC grade methanol and acetonitrile were purchased from MERYER (Shanghai, China). Theobromine, caffeine and (−)-epicatechin standards of analytical grade were purchased from Sigma-Aldrich. Folin-Ciocalteu's phenol reagent, formic acid, n-hexane and ethanol were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). The standard solutions were prepared by weighing the appropriate amounts of standards and
Results and discussion
According to Langer's research (Langer et al., 2011), (−)-epicatechin (linear regression with total polyphenols, R2 = 0.96) was a reliable marker of total polyphenols. The molecular structure of (−)-epicatechin is similar to other polyphenols like catechin, epigallocatechin, procyanidin oligomers and procyanidin polymers. Furthermore, the adsorption and desorption characteristics of these polyphenols on the macroporous resins would also be similar. Therefore, the adsorption capacity and
Conclusion
The decaffeination and enrichment of cocoa polyphenols from low cost cocoa husks were achieved by gradient elution on the LX-17 macroporous resin. The optimal conditions for adsorption and desorption were achieved by static and dynamic adsorption experiments as: cocoa extracts 6.0 mg/mL, pH 2.0, column temperature 25 °C, flow rates of adsorption and desorption 1.6 BV/h and ethanol-water (20:80, 50:50, 95:5, v/v) solutions were used in the gradient elution. The results of scaling-up separation
Acknowledgements
This project was financially supported by Sky Herb Co., Ltd (Huzhou, China).
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