Complexing of chlorogenic acid with β-cyclodextrins: Inclusion effects, antioxidative properties and potential application in grape juice
Graphical abstract
Introduction
Chlorogenic acid (CGA) is a polyphenol derivative existed widely in fruits, vegetables, black teas, soy beans, and wheat (Wang, Wang, & Yang, 2007). Our previous work also demonstrated that the major phenolic compound in Eucommia ulmoides Oliver (Du-Zhong in Chinese, a traditional Chinese medicine) leaf is CGA (Shao, Hong, Liu, He, & Sun, 2011). CGA possesses well documented bioactivities such as antioxidant activity (Sato et al., 2011), antimicrobial properties (Puupponen-Pimia et al., 2001, Zhu et al., 2004), and anxiolytic activity (Bouayed, Rammal, Dicko, Younos, & Soulimani, 2007). However, CGA is easily to be oxidized and sensitive to heat and light (Chao, Wang, Zhao, Zhang, & Zhang, 2012), which restricts its application in industries.
Encapsulation of polyphenols has been proposed as an alternative to improve their stability, bioactivity and extend its application (Fang & Bhandari, 2010). Inclusion complexation with cyclodextrins (CDs) has been evidenced to be a good encapsulation technology (Davis and Brewster, 2004, Loftsson and Duchene, 2007). CDs are a series of water-soluble cyclic oligomers consisting of six to eight d-glucose monomers linked by α (1→4) glycosidic bonds, which form hydrophobic central cavities with hydrophilic external walls (Del Valle, 2004, Hamilton et al., 2000, Szejtli, 2004). Hence, CDs are able to interact with a variety of hydrophobic compounds to form inclusion complexes (Ambrus et al., 2011, Karathanos et al., 2007, Zielenkiewicz et al., 2010). When CDs form inclusion complex with guest molecules, the physicochemical properties of the guest molecules could be positively modified, such as enhancing the solubility and stability of the guest molecules (Caliceti et al., 2003, Yang et al., 2010), reducing the drug bitterness and decreasing tissue irritation (Carrier et al., 2007, Misiuk and Zalewska, 2009, Roik and Belyakova, 2011).
Among the natural CDs, β-cyclodextrin (β-CD) is particularly useful in the pharmaceutical industry because of its high encapsulation efficiency, suitable cavity dimensions, and low cost (Sancho, Gasull, Blanco, & Castro, 2011). In addition, its modified derivative of hydroxypropyl-β-cyclodextrin (HP-β-CD) is well studied in drug encapsulation because of its good inclusion capacity as well as high water solubility, non-toxicity and biocompatibility (Eid et al., 2011, Stella and He, 2008).
The addition of phenolic compounds to prevent anthocyanin degradation due to copigmentation effect has been widely recognized (Chen and Hrazdina, 1981, Mazza and Brouillard, 1987, Mazza and Miniati, 1993). Earlier studies also demonstrated that CGA could be applied as a copigment to enhance the color stability and intensity of cyanidin-3-glucoside (Bakowska, Kucharska, & Oszmianski, 2003). However, to our knowledge, no literature is available on utilization of inclusion complexed polyphenols as copigments of anthocyanins. Therefore, the aim of this study was to prepare inclusion complexes between CGA and two different CDs, namely β-CD and 2-HP-β-CD, to investigate their effects on preservation of anthocyanins and color quality of grape juice. The obtained complexes were characterized by FT-IR, XRD, SEM, and 1H NMR spectroscopy and their physical, chemical and biological properties were compared. This study may expand the industrial applications of CGA inclusion complexes as enhanced antioxidants and provide a new method to improve the color stability of anthocyanin rich products through copigmentation with encapsulated polyphenols.
Section snippets
Materials and chemicals
CGA (molecular weight = 354.31), β-CD (molecular weight = 1134.98) and 2-HP-β-CD (molecular weight = 1541.54) were purchased from Aladdin (Shanghai, China). DPPH (2, 2-di (4-tert-octylphenyl)-1-picrylhydrazyl) free radical, ferrous sulphate (FeSO4), potassium ferricyanide (K3Fe(CN)6), and ferric chloride (FeCl3) were purchased from Sigma–Aldrich (St. Louis, MO, USA). Other reagents and chemicals were of analytical reagent grade. The water used was double distilled and deionized.
Grapes were
XRD analysis
X-ray diffractometry (XRD) is a useful method for assessment of CD complexation in powder or microcrystalline states (Yang et al., 2012). Fig. 1 is the XRD spectra of CGA, β-CD, HP-β-CD and their inclusion complexes. The results indicated that β-CD, HP-β-CD and CGA showed intense and sharp peaks that demonstrated all of them are in a crystalline form. In contrast, the XRD of the CGA/β-CD and CGA/HP-β-CD inclusion complexes were amorphous and showed halo patterns, which were evidently different
Conclusions
The formation of complexes of CGA with β-CD and HP-β-CD was identified by FT-IR, XRD SEM and 1H NMR techniques where CGA/CDs have different physicochemical characteristics from CGA. The aromatic ring and the ethylene side chain of CGA were revealed to be deeply included inside the CDs cavity. In addition, the results of FT-IR and 1H NMR spectroscopy both showed that the inclusion effect of HP-β-CD was better than that of β-CD. The antioxidant activity of CGA on complexation with CDs was
Acknowledgments
This work was financially supported by National Natural Science Foundation of China (No. 31301560), Young Talent Program of Zhejiang University of Technology and the Key Projects for Science and Technology Foundation of Zhejiang Province (No. 2011C12040).
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