Inclusion Complex of Resveratrol with γ-Cyclodextrin as a Functional Ingredient for Lemon Juices

Abstract

Microencapsulated resveratrol (RSV) is a pertinent ingredient in functional foods to be used in the prevention and management of cardiovascular diseases. Gamma-cyclodextrin (γ-CD) was evaluated for its RSV inclusion ability. Inclusion procedures comprised mixing equal concentration of an aqueous solution of γ-CD with an ethanol solution of RSV and freeze-drying to obtain a solid material. Solid-state characterization by vibrational spectroscopy, thermogravimetry, and powder X-ray diffraction (PXRD) confirmed the formation of the γ-CD·RSV complex in a ratio of 1:1. PXRD suggested that cyclodextrin molecules in the complex are stacked in infinite channels holding the RSV inside, with a wide inter-channel space where 14 water molecules are retained. Fresh lemon juices supplemented with 0.625 mg/mL of RSV in its free (RSV-juice) or complexed (γ-CD·RSV-juice) form were stored along 28 days under dark and room temperature or at 4 °C. Initially, the RSV level in γ-CD·RSV-juice was about nine times higher than in RSV-juice (43.1% and 4.8%, respectively), suggesting that the RSV complexation promoted its solubility in the lemon juice, a fact that was still noticed after 28 days of storage. Moreover, regardless the fact that the antioxidant capacity was similar among the juices, the loss of antiradical ABTS^•+ capacity in γ-CD·RSV-juice was reduced compared to that of the RSV-juice. Overall, this study allowed concluding that γ-CD can serve as a carrier of RSV, promoting its solubility and eventually protecting its antioxidant stability in lemon juices for at least 28 days.

Keywords: antioxidant; beverage; citric acid; cyclodextrin; inclusion; lemon juice; resveratrol; solubility; stability.

Figure 1

(a) FTIR spectra of gamma-cyclodextrin (γ-CD) (light blue), resveratrol (RSV) (orange), physical mixture (Mix, grey) and γ-CD·RSV hydrated complex (dark blue). The inset, (b), represents a selected spectral window where some guest bands are visible in γ-CD·RSV (dark blue), with highlight to those at 1592 and 1514 cm⁻¹ that are blueshifted in regard to the same bands of pure RSV (orange) and 1:1 mix (grey), occurring at 1587 and 1512 cm⁻¹; γ-CD (light blue).

Figure 2

Experimental powder X-ray diffractograms (PXRD) of RSV, γ-CD, and the γ-CD·RSV complex (rehydrated overnight to restore its microcrystalline structure); also shown for comparison is the trace of (γ-CD)₃·(RSV)₄·(H₂O)₆₂, calculated from its single-crystal atomic coordinates [17]. Structural data for this complex (refcode MUXBIT) was obtained from CCDC and the PXRD was calculated using the software Mercury 3.5.1 (Copyright CCDC 2001–2014). The inset depicts the top and side views of the complex, with γ-CD units aligned in the form of channels (disordered RSV not shown).

Figure 3

Thermogravimetric traces of RSV (dashed line), γ-CD·RSV (solid line), the 1:1 physical mixture of γ-CD with RSV (dash-dot line), and γ-CD (short-dash line).

Figure 4

Percentage of resveratrol dissolved in RSV-juice (dark green), RSV-CA (light green), γ-CD·RSV-juices (yellowish green) and γ-CD·RSV-CA (light yellow) along 28 storage days at room temperature (rt) (without pattern) and 4 °C (dotted pattern). Different letters in the same column indicate significant differences (p < 0.05).

Figure 5

Radical-scavenging ability of ABTS^•+ (a) and SO^•+ (b) of formulated juices in RSV-juice (dark green), RSV-CA (light green), γ-CD·RSV-juices (yellowness green) and γ-CD·RSV-CA (light yellow) along time of storage, protected from light, at room temperature (rt) (without pattern) and 4 °C (pattern dots). Plain lemon juice at room temperature (yellow without pattern) and citric acid solution at room temperature (0.18 M, white with striped pattern) are represented as reference. Different letters in the same column indicate significant differences (p < 0.05).