Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2024 Jan 24;9(5):5319–5329. doi: 10.1021/acsomega.3c06311

Enhancing the Stability of Strawberry Anthocyanins Complexed to β-Cyclodextrin and Starch toward Heat, Oxidation, and Irradiation

Hussein M Ali 1,*, Mohamed H Attia 1, Eman N Rashed 1
PMCID: PMC10851268  PMID: 38343986

Abstract

graphic file with name ao3c06311_0007.jpg

The instability of anthocyanins limits their application in food supplementation and in the food industry. Stabilities of strawberry anthocyanins (AN) were improved by complexation with both β-CD and starch against heat, H2O2, light, and UV irradiation. The stability of AN against H2O2 (2.21 mM) dropped (<20%) in 6 h but was enhanced in β-CD (49.32%) and starch (96.84%) complexes. Under light conditions, AN in the solid and solution (3.88 g/100 mL) forms degraded to 36.49 and 11.11%, while β-CD and starch complexes displayed stabilities of 98.20 and 91.76%, respectively, after 60 days. Under UV irradiation, AN showed similar instability where both AN forms expressed stabilities of 36.75 and 66.18%, respectively, after 168 h, while β-CD and starch complexes exhibited 51.13 and 40.10%, respectively. LC-MS-ESI showed that photoirradiation of both destroyed the full conjugation of the flavylium ring of the major components, pelargonidin and cyanidin hexoses; the mechanism was proposed. Docking binding models of major AN components in β-CD were obtained.

1. Introduction

Despite the crucial role of antioxidants in the protection against oxidative stress1,2 and the presence of a large number of known natural antioxidants,3,4 their applications in food, pharmaceutics, and cosmetics industries suffer from being easily oxidized.5 Particularly, anthocyanins have a significant role in foods and food industry because of their characteristic colors as natural pigments, in addition to their potent antioxidant6 and diverse protective activities against many diseases including hepatoprotective, cardioprotective, hypocholesterolemic, nephroprotective, neuroprotective, antiobesity, and antidiabetic activities.7 Anthocyanins are known to have low stability and are affected by many environmental factors such as heat, light, pH, enzymes, sugar, sulfur dioxide, oxygen, phenolic acids, ascorbic acid, and metal ions in addition to undergoing degradation reactions during food processing and storage periods. Thereby, these obstacles limit their applications in many industries,5,7−10 especially in modern food processing technologies that require high temperatures.11,12

Hydrogen peroxide is well-known to oxidize anthocyanins5,13,14 and phenolic compounds.15 Hydrogen peroxide, as a hydroxyl radical and superoxide anion, is a reactive oxygen species (ROS) produced naturally in biological systems but with less reactivity.16 It is produced mainly either from a superoxide anion, which in turn is formed during the electron transport chain in mitochondria, or from NAD(P) reactions.16 It can also be produced during some physiological processes, e.g., xanthine oxidase reactions.17

Strawberry is a popular fruit with considerable economic and nutritional value. It is used fresh or processed as juices, jams, purees, smoothies, and dried.18 Strawberries are a rich source of monomeric anthocyanins, ranging from 200 to 600 mg/kg;19 the major anthocyanins in strawberries are cyanidin-3-glucoside (3–32%), pelargonidin-3-glucoside (52–90%), and pelargonidin-3-rutinoside (6–17%).20 However, strawberry is susceptible to environmental factors with a short shelf life (3–4 days); in addition, it is affected by processing methods, e.g., temperature, pressure, and drying methods.18

One solution for protecting sensitive antioxidants from chemical oxidation and enhancing their hydrophilicity is encapsulation in nontoxic polymeric or oligomeric biomolecules.5,11,21−23 β-Cyclodextrins are cyclic oligosaccharides that are nontoxic, eco-friendly, and biodegradable. Among them, β-CD with seven glucose units is the most frequently used in the food and pharmaceutical industry because of its availability as well as its suitable inner cavity size and hydrophobic characteristics for many hosts, which enhances hydrophilicity and protects many bioactive compounds.24,25

There are a few reports on the anthocyanin stabilization by β-CD against heat21,23,26 or during storage;27 however, stability against oxidation by the harmful biologically present reactive oxygen species, hydrogen peroxide, or photodegradation by either normal light or UV irradiation, as well as identification of the degradation products and postulating the degradation mechanism, has not been previously examined. In addition, inclusion starch-anthocyanin complexes and their characterization and stabilities were not described although there has been growing interest in starch as a host of inclusion complexes because of its slow enzymatic degradation in the gastrointestinal system, which provides sustainable control release of nutrients or pharmaceutics in starch complexes.22,28−32 The type of interaction and the properties of formed complexes depend on the phenolic compound structure, starch source, and preparation method.28 Nevertheless, starch inclusion complexes with anthocyanins were not previously described. Moreover, the identification of the photodegradation products as well as postulating the degradation mechanism considering the photosensitization and excitation mechanism of anthocyanins5,33 is first described.

Inclusion complexes can exhibit various advantages for the applications of bioactive compounds. The main objective of the encapsulation is protecting the guest molecules against environmental factors, e.g., heat, light, and oxidants, as well as during the food industry, in addition to tailoring the drug release over a specific period of time.34 Antioxidant activity could also be improved as a result of enhancing solubility and availability in biological systems.35 In addition, guest molecules in complexes are protected in the gastrointestinal tract against enzymes, pH, and gastric juice components.34

Both β-CD and starch are characterized by having a nonpolar inner surface and a polar outer surface. In solutions, β-CD cavities are occupied by water molecules, and thus, the formation of β-CD inclusion complexes is favored by the replacement of water molecules by the guest molecule, which increases the host–guest hydrophobic interaction, and the increased number of H-bonds among water molecules outside the cavity.25 The starch complexes are generally formed through unwinding the amylose helix either by heat, DMSO, or alkali to form random coils; then, the guest compound is mixed; afterward, the mixture was allowed to cool, diluted or neutralized, and then precipitated.30 The complexation is also driven by the hydrophobic interaction between the guest and the inner amylose surface.31 The complexation process is largely affected by the structure of both the host (cavity size and substituent groups) and the guest (molecular dimensions and substituents) molecules; in addition, the preparation method has a great impact on complexation stability, e.g., the physical state of reactants, solvents, pH, and temperature.24

Therefore, β-CD and starch inclusion complexes with strawberry anthocyanins were prepared and characterized. Their stability was examined against oxidation by hydrogen peroxide as well as their photodegradation by light and UV irradiation. Products of the photodegradation were identified, and degradation mechanisms were postulated. Docking of the identified major strawberry anthocyanins in β-CD and their interactions were discussed.

2. Materials and Methods

2.1. Chemicals and Instrumentations

All chemicals and solvents were of reagent grade except for those used in LC-ESI-MS analysis, where HPLC grade was used. β-Cyclodextrin (β-CD) was purchased from Sigma-Aldrich (C42H70O35, MW of 1134.98, 97%). Methanol (99%) was obtained from Koch-Light Laboratories Ltd., Colebrook Bucks, UK. Trifluoroacetic acid (TFA, 98%) was purchased from Loba Chemie Pvt. Ltd., India. Corn starch was obtained from Naser Chemical Co., Egypt. Strawberry was obtained from the local market and identified based on the morphological characteristics as Fragaria vesca. For solvent evaporation, a freeze-dryer (lyophilizer) Christ model (Alpha 1–4 LSC plus) was operated for 24 h at −60 °C and a vacuum of 10–3 mbar.

UV–vis spectra were recorded with a Thermo Fisher instrument model Evolution 300; the scan range was 200–600 nm. An FT-ATR-IR model Bruker vertex 80/80 V was used to record the IR spectra in the range of 4000–400 cm–1.

Thermographs were conducted using a TA SDT Q600 instrument under nitrogen gas. The operation conditions were as follows: an initial temperature of 50 °C, a final temperature of 550 °C, and a heating rate of 10 °C min–l. Samples (10 mg) were placed in open crucibles for thermogravimetry (TG) and differential thermogravimetry (DTG) measurements. In differential scanning calorimetry (DSC), sealed pans with lids containing a hole pierced with a thick pin were used. The degradation peaks were observed in the DTG thermograph, and the onset temperatures were measured at the intersection of the extrapolated baseline before the transition with a tangent to the deflected peak. Fragments were assigned based on the fragment percentage of the molecular weight (MW) in the TG analysis.

2.2. Strawberry Anthocyanin (AN) Extraction

Anthocyanins were extracted from strawberry fruits and purified by the method described by da Silva et al.19 with some modifications. Strawberry fruits (1 kg) were homogenized in 1 L of aqueous methanol (80%) containing 0.1% HCl with shaking. The flask was stoppered, covered with aluminum foil, and kept in a refrigerator at 4 °C overnight. The mixture was filtered in a cloth sheet, centrifuged at 4 °C, and concentrated in a rotary evaporator. The extract was defatted by washing with n-hexane and then passed through a Sep-Pak C18 cartridge (Waters Corp., Milford, MA). The column was first activated with methanol and washed with HCl (0.01%). The extract was then loaded and eluted first with distilled water to get rid of polar materials, e.g., sugars and amino acids, and then with 1% trifluoroacetic acid (TFA) in methanol to elute the anthocyanins, which can easily be monitored by their red color. The solvents were evaporated by a rotary evaporator, and the resulting extract was freeze-dried. The product was kept at −4 °C for further use.

2.3. Preparation of the β-Cyclodextrin-AN Complex

The β-cyclodextrin complex was prepared following the Pradhan et al.procedure21 with some modifications. β-Cyclodextrin (0.3405 g, 3.0 × 10–4 mol, MW of 1134.98) was dissolved in 20 mL of distilled water with a vortex to obtain a 15 mM β-CD solution. Strawberry anthocyanin extract, AN (1.0 g), was added to 20 mL of β-CD solution and sonicated then magnetically stirred for 24 h; a clear solution was obtained, which was freeze-dried and washed with cold methanol.

2.4. Preparation of Starch-AN Complexes

The starch complex was prepared following the Kim and Huber procedure29 with a few amendments. Starch (5.0 g) was suspended in 50 mL of distilled water, and then, AN (1.0 g) dissolved in 25 mL of methanol (80%) was added. The mixture was shaken in tubes with screw caps or closed flasks and covered by aluminum foil and then heated in oven at 150 °C for 75 min. Tubes were cooled and refrigerated overnight. The precipitates were centrifuged (2000 rpm) then filtered, washed with methanol, and dried in an incubator at 50 °C for 3 h (Figure S1).

2.5. Oxidative Stability of AN, β-CD-AN, and Starch-AN

AN (0.19 g) was dissolved in 5.0 mL of HCl solution containing 1.25, 12.5, 22.5, and 60 μL of H2O2 in screw-capped tubes to give pH 1 and an initial absorbance (A) of ∼0.8. The final H2O2 concentrations were 2.21, 22.06, 39.71, and 105.89 mM, respectively. Tubes were covered with aluminum foil at room temperature for different intervals up to 48 h in the dark, and then, absorbance was recorded at 520 nm. The UV–vis spectra of AN oxidation, at a H2O2 concentration of 105.89 mM, were recorded at 0, 24, and 48 h.

The β-CD-AN complex (0.02 g) was dissolved in 5 mL of HCl and treated as pure AN extract. Stability was determined as the decreased percentage of the absorbance at 520 nm.

For the starch-AN complex, 5.0 mL of methanol containing one of the specified concentrations mentioned above of H2O2 was added to 0.5 g of the complex in screw-capped tubes covered with aluminum foil. Tubes were kept in the dark for different intervals; then, the solvent was decanted, and the complex was washed with 1.0 mL of cold MeOH. AN was extracted by suspending the starch-AN complex in 3.0 mL of methanol (70%) and 1.0 mL of HCl (6.0 N) in screw-capped tubes covered by aluminum foil and then placed in a water bath at 75 °C for 10 min. The mixture was centrifuged (2000 rpm) for 5 min at 4 °C; then, the supernatant was decanted, and fresh methanol and HCl solution were added to the complex. The process was repeated at least three times until complete extraction was achieved (no decrease in absorbance, Figure S2); then, the methanolic extracts were combined and completed to 25.0 mL, and the absorbance was measured at 520 nm. The concentration was calculated as pelargonidin (Pg)-3-glucoside using its molar absorptivity (31,620 mol–1Lcm–1).36

2.6. AN Stability under Visible-Light Conditions

All stability experiments of the examined compounds (AN, β-CD-AN, and starch-AN) were performed under normal conditions, i.e., 25 °C, visible daylight, exposure to air, and room temperature.

After exposing solid AN extract to light, in open Petri dishes, a constant weight (0.116 g), at different intervals, was dissolved in 3.0 mL of HCl solution (pH 2), and absorbance was recorded at 520 nm.

For AN solution in HCl (3.88 g/100 mL, pH 2), tubes were capped to give an initial absorbance of ∼0.780 and then exposed to light. At various intervals, the solution was shaken and centrifuged to remove any turbidity; finally, the absorbance was measured.

For the β-CD-AN complex, at each interval, 0.02 g of the complex was dissolved in 5.0 mL of HCl solution (pH 2), and then, absorbance was recorded.

The starch-AN complex was exposed to light; at each interval, 0.5 g was suspended in acidic methanol, and then, AN was extracted and determined as described before.

2.7. AN Stability under UV Radiation

The same experimental procedures of visible-light experiments for AN, β-CD-AN, and starch-AN were applied, except for putting the samples in dark containers and solutions in closed quartz cuvettes exposed to UV radiation at 254 nm (Figure S3). The lamp used was a Spectroline lamp model ENF-260 C/F, Spectronics Corporation, NY, USA.

2.8. LC-ESI-MS Analysis

Samples were extracted with 80% methanol and then filtered through a 0.45 μm micropore membrane before injection (10 uL). Samples were analyzed at a flow rate of 0.7 mL/min using an Agilent 1200 LC-MS-ESI instrument (positive mode) with a diode array detector set at 254, 280, 320, and 520 nm. An Agilent Zorbax Eclipse Plus C18 column using nitrogen as the nebulizing gas was used. The mass was scanned in the range m/e 100–1000 at fragmentation energies of 70 and 20 eV and a potential of 4.0 kV. Drying gas (N2) flow (12 L/min), nebulizing pressure (35 psi), and dry gas temperature (350 °C) were applied. For AN extract separation, the mobile phase used was 0.5% formic acid (A) and acetonitrile (B); the gradient was 0 min 5% B, 1 min 20% B, 6 min 20% B, 8 min 80% B, 18 min 80% B, and 19 min 5% B.

2.9. Molecular Docking of Pg-3G and Cn-3G with β-CD

Structural files (3D) of pelargonidin-3-glucoside (Pg-3G) and cyanidin-3-glucoside (Cn-3G) were downloaded from PubChem (CID 3080714 and 12303220, respectively), while the structural file of β-CD was downloaded from the ChemSpider database (10469496) and energy-minimized through MM2 calculation using Chem 3D ChemOffice 2018. Docking was performed using AutoDock Vina implemented in PyRx 0.8 software. PDB files of ligands molecular files were uploaded and converted to the pdbqt format then energy-minimized using the force field UFF. Grid box dimensions (16.2048, y 13.8125 and z 16.8918 Å) included the whole β-CD molecule. Docked ligand files were saved (pdb) and visualized along with β-CD in Discovery Studio-19 software, where molecular interactions were examined.

3. Results and Discussion

3.1. Preparation and Identification of Encapsulated AN Extract in Starch

Starch complexes were prepared by suspending the starch in water (5%), and then, the AN extract was added and dissolved. The mixture was then heated to unwind the amylose helix to allow encapsulation of the guest molecule. The mixture was cooled to rewind the amylose helix. Tubes were refrigerated to allow for complex precipitation.

IR spectra of starch, AN, and their complex are shown in Figure 1A. It can be noticed that the main difference among the spectra of starch, AN, and the starch-AN complex is the position of the O–Hstr band (3297, 3288, and 3304 cm–1, respectively), which is known to be sensitive toward involvement in H-bonding where it is expected to have different strengths between starch and guest molecules from those among each of the parent molecules separately. In addition, the aliphatic C–Hstr in the complex appeared relatively strong as a doublet at 2987 and 2900 cm–1 close to that of AN and differed from that of starch, which appears as a weak peak at 2921 cm–1 indicating complex formation.

Figure 1.

Figure 1

Open in a new tab

IR spectra of starch, AN, and the starch-AN complex (A). TG, DTG, and DSC (in descending order) of the starch-AN complex (B).

Thermographs of starch (Figure S4A) indicated three degradation steps; during the first step, a little weight loss (11.09%) at a low temperature (65.85 °C) was observed as shown in the TG and DTG thermographs, while the DSC indicated that the step is endothermic, which suggests water evaporation. In the second step, the main weight loss (69.39%) appeared at 322.27 °C in the DTG with an endothermic peak at 329.72 °C as shown by the DSC thermograph. The third step showed a steady slow degradation over the range of 400–700 °C, which represents 6.51% of the sample; similar results were observed by De Oliveira et al.37

Thermal analysis of strawberry anthocyanins (AN) depicted in Figure S4C (TG and DTG) shows complete degradation (99.50%) at a low temperature (106.27 °C) with the onset temperature at 40.02 °C. A preliminary thermal analysis of strawberry AN and complexes was previously reported.38 Thermographs (TG and DTG) of the starch-AN complex presented in Figure 1B showed more stability with minor degradation steps at 75.57 (onset temperature of 63.25 °C) and 184.19 °C with a total degradation of 11.21%. The main degradation step appeared at 289.90 °C (67.60%). DSC showed also an additional endothermic peak at a lower temperature preceding the main degradation at 144.34 °C suggesting amylose helix rewinding and release of AN. The complex total degradation (78.81%) is less than each of starch (86.99%) and AN (99.50%) endorsing also the complex formation.

3.2. Preparation and Identification of Encapsulated AN Extract in β-CD

UV–vis spectra of the β-CD-AN complex and its host and guest are presented in Figure 2A. AN gave three absorbance bands at 222, 274, and 517 nm, while the complex showed a similar first band (223 nm), but the other two bands were shifted (277 and 512 nm, respectively) with different relative intensities compared to those of the AN extract spectrum. The shifts in band positions indicate the involvement of the AN aromatic resonance electrons in the interaction with the host molecule.

Figure 2.

Figure 2

Open in a new tab

β-CD-AN complex identification. UV–vis spectra of β-CD, AN, and the β-CD-AN complex (A). IR spectra of β-CD, AN, and the β-CD-AN complex (B). TG and DTG (in descending order) of the β-CD-AN complex (C). Docking models of Pg-3G (D) and Cn-3G (E). Colors are gray for β-CD, green for guest molecules, and green lines for H-bonds.

The IR spectra of β-CD and AN extract along with their complex are presented in Figure 2B. The AN spectrum gave characteristic peaks of O–Hstr at 3288 cm–1, C–Hstr at 2929 and 2885 cm–1, C=Ostr at 1716 cm–1, aromatic C=Cstr at 1627 cm–1, and C–Ostr at 1025 cm–1. The results suggest the presence of conjugated esters (C=Ostr at 1716 cm–1) in the extract; a similar spectrum was obtained for anthocyanins from plant extract.39 The resulting complex also gave characteristic AN peaks, especially those of the carbonyl (1716 cm–1) and aromatic (1627 cm–1) peaks, indicating the formation of the inclusion complex. The complex O–Hstr appeared at a lower frequency (3288 cm–1) compared with that of the free β-CD (3304 cm–1) indicating the formation of H-bonding.40

TG and DTG results of β-CD (MW of 1135.0) are presented in Figure S4B; a similar analysis was previously reported.41 The thermodegradation takes place in two steps; the first degradation (14.47% weight loss) appeared at a low temperature (92.70 °C), which could be explained by losing one glucose unit (calculated loss of 14.27%). The second degradation (14.47% weight loss) occurred at a high temperature (334.34 °C) to give a total weight loss of 92.16%; the remaining weight (7.84%) accounts for three (CHOH) units (calculated 7.93%).

Thermographs of strawberry AN (Figure S4C) showed one-step degradation (99.50%) with an early onset temperature (40.02 °C) and a maximum peak (106.27 °C). On the other hand, the complex β-CD-AN thermographs (Figure 2C) showed two-step degradation. The first peak starts at 70.10 °C, higher than that of pure AN (40.02 °C) with a maximum peak at 79.46 °C; the second step appeared at 321.30 °C. The total weight loss (84.43%) was less than those of both β-CD (92.16) and AN (99.50%) indicating the complex formation and better thermal stability.

Complexation of anthocyanins with β-CD increased their thermal stability and half-life periods.21 After 4 weeks and at pH 3.6, β-CD could enhance the stability of chokeberry anthocyanins 49% more than that of the control samples at 4 °C, while at 25 °C, the complex stability reached 178% compared to the control treatment.11 Thermal stability was also observed for blackberry anthocyanins by β-CD complexation where the half-life period of the major component (cyanidin-3-glucoside) was increased from 14.0 and 3.6 h for the pure compound to 41.0 and 4.4 h for the complex at 60 and 90 °C, respectively.26

The appearances of the prepared complexes, β-CD-AN and starch-AN, along with their precursors are presented in Figure S5, which shows that the AN red color was preserved in the formed complexes. It should be noted that in all AN complex preparations, the AN was re-extracted, and UV–vis spectra were measured to ensure that no structural alteration has occurred.

3.3. Molecular Docking of Pg-3G and Cn-3G with β-CD

Molecular docking was performed to examine the binding sites and molecular interactions between Pg-3G or Cn-3G and β-CD. The resulting models along with the possible hydrogen bonds between the host and guest molecules are presented in Figure 2D,E; the assignment of H-bonds and the calculated free energies are listed in Table S1. To assign the interaction between β-CD and the guest molecules, the glucose rings of β-CD were arbitrarily numbered (R1–R7). Results revealed that both guest molecules fit in the β-CD cavity where all A, B, and C and glucose rings are located inside the cavity, as previously indicated.42 The AN ring B is directed toward the wide β-CD end while the sugar unit is located near the narrow β-CD end with binding energies of −4.2 and −4.4 kcal/mol, respectively, indicating that binding both molecules with β-CD is a thermodynamically favored process. In both complexes, the three AN rings and glucose moiety interacted with all seven β-CD glucose units. For Pg-3G, 16 hydrogen bonds are assigned. The flavylium ring forms H-bonds with β-CD rings 1, 2, and 3, while the AN ring B binds to β-CD ring 4; the AN glucose moiety interacted with β-CD rings 4, 6, and 7. Cn-3G could also form a large number of hydrogen bonds with β-CD (17 bonds). The flavylium ring binds to β-CD rings 1, 6, and 7, whereas the two hydroxyl groups of ring B bind to the β-CD ring 4; the AN glucose unit binds to rings 2, 3, 5, and 6. The importance of the H-bonding in stabilizing the β-CD-AN complexes and the involvement of the glycosidic oxygen and β-CD hydroxy groups in bonding were recently reported.24 This number of H-bonds can account for the lower frequency of O-Hstr (3294) in complex compared to that of the free β-CD (3304 cm–1) and the observed thermal and oxidative stability of strawberry anthocyanins.

3.4. Oxidation of AN, β-CD-AN, and Starch-AN by H2O2

It was reported that the stability of anthocyanins against heat, light, and oxidation by H2O2 increases with lowering the pH, while absorbance at 520 nm was used to monitor the degradation.43 Therefore, all anthocyanin experiments executed in solutions were performed at pH 2 to preserve the most possible stability.

Oxidative stability of AN, β-CD-AN, and starch-AN against different concentrations of hydrogen peroxide (2.21, 22.06, 39.71, and 105.89 mM) is presented in Tables S2–S4, respectively, and in Figure 3B. Results showed that unencapsulated anthocyanins were the most sensitive toward oxidation in all concentrations where their stability dropped sharply in the first 6 h to less than 20% then slowly up to 48 h to less than 14.0% in all hydrogen peroxide concentrations, while in a concentration of 105.89 mM, the stability deteriorated to 2.77% after 6 h.

Figure 3.

Figure 3

Open in a new tab

Oxidation reaction of AN by H2O2 (A). Effects of various H2O2 concentrations on AN, β-CD-AN, and starch-AN (B). UV–vis spectra of AN oxidation by 105.89 mM H2O2 at various intervals (C).

The red color disappearance of AN solutions by H2O2 oxidation during different periods in the reaction vessels is shown in Figure S6. The red color disappearance is also manifested in the UV–vis spectrum of AN at a H2O2 concentration of 2.21 mM after 24 h by complete vanishing of the 517 nm absorbance (Figure 3C) indicating the destruction of the flavylium ring aromaticity. A possible mechanism of anthocyanidin oxidation in the presence of hydrogen peroxide is previously reported, which involves a nucleophilic attack of hydrogen peroxide at the C2 carbon as a crucial step to form hydroperoxide,13 while nucleophilic attack of water at the same carbon gives a colorless hemiketal44 as depicted in Figure 3A. Spectra in Figure 3C indicate the sensitivity of the UV–vis measurement in detecting AN decomposition and structural alteration in the AN chromophore, especially the 520 nm peak; accordingly, in all complex treatments, the AN decomposition was monitored by re-extracting AN and recording the spectra and absorbance at 520 nm.

On the other hand, the β-CD-AN complex in H2O2 (2.21 mM) was more stable in the first 6 h (49.32%) but degraded after 48 h to 13.31%, similar to that of unencapsulated anthocyanins. At higher H2O2 concentrations, β-CD-AN showed stability much similar to that of the unencapsulated sample. However, the starch-AN complex was the most stable in all concentrations where stability reached 96.84, 81.82, 53.36, and 16.01% after 6 h and 49.61, 48.82, 47.59, and 8.7% after 48 h in the examined H2O2 concentrations, respectively.

The lower stability βCD/AN than that of starch/AN could be explained since, in the former complex, the H2O2 molecule can still contact the AN through the two β-CD mouths. In addition, the β-CD-guest complexes are not permanent but rather in dynamic equilibrium (Del Valle25) allowing release of the guest molecule into the solution and interacting with H2O2. On the other hand, in the starch complex, the amylose rewinds around the whole AN molecule to provide high protection; in addition, the release of the guest molecules in starch-guest complexes requires either heating to rewind the helix or enzymatic hydrolysis of starch as in the gastrointestinal system, which accounts for the slow release of these complexes.32

3.5. Stability of AN, β-CD-AN, and Starch-AN under Visible-Light Conditions

Because of the lack of studies, the stability of β-CD-AN and starch-AN complexes, in comparison with strawberry anthocyanins, under visible-light conditions (visible light, exposed to air and room temperature) and UV irradiation in addition to possible transformations that may occur under these conditions, was examined. The stability of AN was measured in the solid state and in solution at pH 2 under visible-light conditions, and results are presented in Table S5 and Figure 4A. Both solid and solution (3.88 g/100 mL) showed sharp degradation up to 39.37 and 36.50%, respectively, after 9 days; then, the solid showed stability (36.49%) up to 60 days, while AN in solution continued degradation up to 11.11% after 17 days. Alternatively, AN in the β-CD or starch complex displayed stability (98.20 and 91.76%, respectively) up to 60 days but deteriorated afterward to 40.72 and 37.14%, respectively, after 139 days.

Figure 4.

Figure 4

Open in a new tab

Stability of AN and complexes β-CD-AN and starch-AN under visible-light and UV irradiation conditions.

3.6. Stability of AN, β-CD-AN, and Starch-AN under UV Radiation

The harmful effects of UV radiation on biological systems and biomolecules are well-documented.45 A decrease in total phenols, flavonoids, and antioxidant activity with prolonged exposure to UV radiation was also observed.46 Therefore, it is important to examine the stability of natural anthocyanins under UV radiation.

AN in the solid and solution (3.88 g/100 mL) forms showed high sensitivity toward UV radiation where the remaining percentage decreased in the first 24 h to 43.34 and 75.24%, respectively, then reached 36.75 and 66.18%, respectively, after 168 h (7 days) as presented in Table S6 and Figure 4B. Although the β-CD and starch complexes showed better stability where they reached 51.13 and 40.10%, respectively, after 168 h, the complexes were less stable under UV radiation than under visible-light conditions (98.20 and 91.76%, respectively, up to 60 days) indicating more sensitivity of anthocyanins toward UV radiation than in visible light. Identification of photoexposure of AN toward light and UV irradiation in addition to possible mechanisms is discussed in the following section.

The observed similar photosensitivity of β-CD and starch complexes, compared to that against H2O2, could be attributed to the ability of photoradiation to penetrate both complexes almost equally. In addition, complexes are examined in these experiments as solids without any solvents, which does not allow guest release as in the H2O2 experiments.

3.7. Identification of Products and the Mechanism of AN Photoexposure to Light and UV by LC-ESI-MS

To examine the photoexposure effects on the chemical constituents of anthocyanins in strawberry extract, the extract was analyzed by LC-ESI-MS before and after light and UV exposure. The chromatograms of the original extract (Figure 5A at 280 nm and B at 520 nm) showed that before light exposure, the main anthocyanins (Figure 5B) appeared at tR of 11.67 and 10.95 min. After light exposure (Figure 5C at 280 nm and D at 520 nm), these peaks disappeared, while new similar peaks appeared at tR of 10.85 and 10.39 min, respectively (Figure 5C), representing the products. The mentioned resulting peaks did not appear in the chromatogram of λ 520 (Figure 5D) indicating the destruction of the anthocyanidin conjugation in products.

Figure 5.

Figure 5

Open in a new tab

Chromatograms of the AN extract at 280 nm before light exposure (A), at 520 nm before light exposure (B), at 280 nm after light exposure (C), and at 520 nm after light exposure (D). Mass spectra of major anthocyanins in strawberry extract: Pg-Hex (E) and Cn-Hex (F).

Before light exposure, the peak at 11.67 min gave the mass spectrum in Figure 5E with a peak at m/z 126 for the general flavonoid 0,4A+2H fragment, and a molecular ion peak appeared as a base peak at m/z 433 suggesting pelargonidin-hexose (Pg-Hex). The mass spectrum of the peak at a tR of 10.95 min (Figure 5F) showed a molecular ion peak at m/z 449, and the fragments shown in the figure indicate the presence of cyanidin-hexose (Cn-Hex). It is repeatedly reported that the major strawberry anthocyanins are pelargonidin and cyanidin glucosides.19,47 Both cyanidin and pelargonidin express high antioxidant activity with the former displaying higher activity because of the two o-hydroxyl groups on the B ring.48

After light exposure, the product of Pg-Hex (tR of 10.85 min) gave a spectrum expressing a peak at 405 for [M-CO] + [H] and a base peak at m/z 144 for rings A and B with extrusion of oxygen atoms as illustrated in Figure 6A for the suggested quinone product. The mass spectrum of the Cn-Hex product (Figure 6B) at a tR of 10.39 min suggested also the quinone formation with a molecular ion peak (M+2H) at m/z 450 and the fragmentations illustrated in the figure.

Figure 6.

Figure 6

Open in a new tab

Mass spectra of light products of Pg-Hex (A) and Cn-Hex (B). The chromatogram (C) and mass spectrum of a new product (D) are extracted after UV exposure. Plausible degradation mechanism (E) and color change (F), before light exposure (F1), after light exposure (F2), and after acid addition (F3).

After UV exposure, the extract gave the chromatogram (at 280 nm) presented in Figure 6C, which indicates clearly the absence of the anthocyanin peaks of both Pg-Hex (tR of 11.67 min) and Cn-Hex (tR of 10.95 min) and formation of at least a new compound that appeared at 4.60 min. The new peak is not found in the chromatogram of λ 520 indicating the destruction of the anthocyanin structure. The mass spectrum of the formed compound (Figure 6D) suggested also the quinone structure with the indicated fragmentations.

According to previous results, it could be proposed that anthocyanins, upon exposure to visible light or UV irradiation, undergo losing a proton and retroenolization with the resonance of the double bonds to neutralize the oxonium charge as postulated in the Figure 6E equation.

The identified products and the proposed mechanism are also consistent and complementary to the photosensitization and excitation mechanism of anthocyanins recently reviewed.5,35 The anthocyanin ground state (AH+) undergoes photoexcitation to the excited singlet state (AH+*), which is subjected to rapid deprotonation in equilibrium with the excited base form (A*); the latter then quenches to the colorless quinone base product (A), which can undertake a protonation step. The mechanism is termed the excited-state proton transfer (ESPT) process. This process found significant applications in photodynamic therapy for the destruction of malignant tissues.41 The importance of this mechanism is that it also explains that under photoexposure conditions, anthocyanins can undergo deprotonation and consequent discoloration processes even in strong acidic conditions (pH < 2). As additional confirmation that the colorless quinone base (A) is in equilibrium with the colored AN (AH+) in the ground state, after the red color of anthocyanins disappeared upon light or UV exposure, the addition of ascorbic or citric acids resumed the color in tubes as shown in Figure 6F. It should also be mentioned that acylation and glycosylation stabilize anthocyanin against photoexcitation.5

4. Conclusions

The stability of strawberry anthocyanins (AN) could be enhanced by complexation with β-cyclodextrin and starch. The stability of AN was improved against H2O2 (2.21 mM) from less than 20 to 49.32 and 96.84% for β-CD and starch complexes, respectively, in 6 h. Under light conditions, AN stability increased from 36.49 in the solid form and 11.11% in the solution (3.88 g/100 mL) form to 98.20 and 91.76% for β-CD and starch complexes, respectively, after 60 days. Under UV irradiation, both AN forms (solid and solution) exhibited stabilities of 36.75 and 66.18%, respectively, while complexes showed stabilities of 51.13 and 40.10%, respectively, after 168 h. Major AN components were identified as pelargonidin and cyanidin hexoses, while their products upon exposure to light and UV were identified by LC-MS-ESI; the destruction of the flavylium ion chromophore mechanism is postulated. In addition, docking revealed that all AN rings (A, B, and C) and the glucoside unit fit in the β-CD cavity and are bound by H-bonds with the seven β-CD rings, which explain the observed complex stability.

Despite the well-known nutritive, antioxidant, and biological activities of anthocyanins, the present work showed that they undergo structural alteration and color disappearance under various environmental factors, which limits their applications in food and pharmaceutics industries. However, the present work also indicated that the complexation of anthocyanins with cheap, safe, and biodegradable materials, i.e., β-CD and starch, can effectively enhance stability against the main degrading factors affecting food and pharmaceutical shelf life, i.e., oxidation, light, and UV irradiation. Further work should include a drug release examination, which differs in complexes of the same guest depending on the nature of the host materials and the guest–host interaction; therefore, complexation with various suitable guest materials is required to attain a suitable formulation for each application.

Glossary

List of abbreviations

β-CD

β-cyclodextrin

AN

anthocyanins

DSC

differential scanning calorimetry

TG

thermogravimetry

DTG

differential thermogravimetry

LC-ESI-MS

liquid chromatography-electrospray ionization-mass spectrometry

ESPT

excited-state proton transfer mechanism

AH+

anthocyanin ground state

AH+*

excited singlet state of anthocyanins

A

quinone base form of anthocyanins

Pg-Hex

pelargonidin-hexose

Cn-Hex

cyanidin-hexose

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.3c06311.

  • (Table S1) Binding energy and H-bonds of β-CD docking with Pg-3G and Cn-3G; (Table S2) stability of the unencapsulated AN complex against H2O2; (Table S3) stability of the β-CD-AN complex against H2O2; (Table S4) stability of the starch-AN complex against H2O2; (Table S5) stability of AN and complexes β-CD-AN and starch-AN under visible-light conditions; (Table S6) stability of AN and complexes β-CD-AN and starch-AN under UV radiation; (Figure S1) preparation of the starch-AN complex; (Figure S2) extraction of AN from the starch-AN complex; (Figure S3) experiment of AN complex stability under UV radiation; (Figure S4) TG and DTG of starch, β-CD, and strawberry anthocyanins; (Figure S5) prepared β-CD-AN and starch-AN complexes and their precursors; (Figure S6) color disappearance of acidic methanolic AN solution with H2O2 concentrations in duplicates at 105.89, 39.71, 22.06, and 2.21 mM at various intervals (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao3c06311_si_001.pdf (691.9KB, pdf)

References

  1. Ali H. M.; Ali I. H. QSAR and mechanisms of radical scavenging activity of phenolic and anilinic compounds using structural, electronic, kinetic, and thermodynamic parameters. Med. Chem. Res. 2015, 24, 987–998. 10.1007/s00044-014-1174-y. [DOI] [Google Scholar]
  2. García-Caparrós P.; De Filippis L.; Gul A.; Hasanuzzaman M.; Ozturk M.; Altay V.; Lao M. T. Oxidative stress and antioxidant metabolism under adverse environmental conditions: a Review. Bot. Rev. 2021, 87, 421–466. 10.1007/s12229-020-09231-1. [DOI] [Google Scholar]
  3. Mendonça J. d. S.; Guimaräes R. d. C. A.; Zorgetto-Pinheiro V. A.; Fernandes C. D. P.; Marcelino G.; Bogo D.; Freitas K. d. C.; Hiane P. A.; de Pàdua Melo E. S.; Vilela M. L. B.; Nascimento V. A. d. Natural antioxidant evaluation: a review of detection methods. Molecules 2022, 27, 3563. 10.3390/molecules27113563. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Valgimigli L.; Baschieri A.; Amorati R. Antioxidant activity of nanomaterials. J. Mater. Chem. B 2018, 6, 2036–2051. 10.1039/C8TB00107C. [DOI] [PubMed] [Google Scholar]
  5. Cai D.; Li X.; Chen J.; Jiang X.; Ma X.; Sun J.; Tian L.; Vidyarthi S. K.; Xu J.; Pan Z.; Bai W. A comprehensive review on innovative and advanced stabilization approaches of anthocyanin by modifying structure and controlling environmental factors. Food Chem. 2022, 366, 130611 10.1016/j.foodchem.2021.130611. [DOI] [PubMed] [Google Scholar]
  6. Ali H. M.; Ali I. H. Energetic and electronic computation of the two-hydrogen atom donation process in catecholic and non-catecholic anthocyanidins. Food Chem. 2018, 243, 145–150. 10.1016/j.foodchem.2017.09.120. [DOI] [PubMed] [Google Scholar]
  7. Ghareaghajlou N.; Hallaj-Nezhadi S.; Ghasempour Z. Red cabbage anthocyanins: Stability, extraction, biological activities and applications in food systems. Food Chem. 2021, 365, 130482 10.1016/j.foodchem.2021.130482. [DOI] [PubMed] [Google Scholar]
  8. Jiménez N.; Bohuon P.; Lima J.; Dornier M.; Vaillant F.; Pérez A. M. Kinetics of anthocyanin degradation and browning in reconstituted blackberry juice treated at high temperatures (100–180 °C). J. Agric. Food Chem. 2010, 58, 2314–2322. 10.1021/jf902381e. [DOI] [PubMed] [Google Scholar]
  9. Jing P.; Zhao S. J.; Ruan S. Y.; Xie Z. H.; Dong Y.; Yu L. L. Anthocyanin and glucosinolate occurrences in the roots of Chinese red radish (Raphanus sativus L), and their stability to heat and pH. Food Chem. 2012, 133, 1569–1576. 10.1016/j.foodchem.2012.02.051. [DOI] [Google Scholar]
  10. Sui X.; Bary S.; Zhou W. Changes in the color, chemical stability and antioxidant capacity of thermally treated anthocyanin aqueous solution over storage. Food Chem. 2016, 192, 516–524. 10.1016/j.foodchem.2015.07.021. [DOI] [PubMed] [Google Scholar]
  11. Cortez R.; Luna-Vital D. A.; Margulis D.; Gonzalez de Mejia E. Natural pigments: Stabilization methods of anthocyanins for food applications. Compr. Rev. Food Sci. Food Saf. 2017, 16, 180–198. 10.1111/1541-4337.12244. [DOI] [PubMed] [Google Scholar]
  12. Xie Y.; Ma M.; Zhang C.; Yang Y.; Shumin S.; Ma W.; Li Q. Experimental and theoretical research on the effect of coupling heat and pH on the structure and antioxidant activity of cyanidin-3- O -glucoside from black soybean coat. J. Sci. Food Agric. 2022, 102, 1842–1850. 10.1002/jsfa.11519. [DOI] [PubMed] [Google Scholar]
  13. Dangles O.; Fenger J.-A. The chemical reactivity of anthocyanins and its consequences in food science and nutrition. Mol. 2018, 23, 1970. 10.3390/molecules23081970. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Ichiyanagi T.; Hatano Y.; Matsugo S.; Konishi T. Kinetic comparisons of anthocyanin reactivities towards 2,2′-azobis(2-amidinopropane) (AAPH) radicals, hydrogen peroxide and tert-buthylhydroperoxide by capillary zone electrophoresis. Chem. Pharm. Bull. 2004, 52, 434–438. 10.1248/cpb.52.434. [DOI] [PubMed] [Google Scholar]
  15. Yi Z.; Jia-Qing X.; Ci L.; Jun L.; Hong-li S. Mechanism of oxidation of aqueous phenol by H2O2 catalysed by a macrocyclic iron (II) complex. Prog. React. Kinet. Mech. 2008, 33, 241–252. 10.3184/146867808X339304. [DOI] [Google Scholar]
  16. Lennicke C.; Rahn J.; Lichtenfels R.; Wessjohann L. A.; Seliger B. Hydrogen peroxide—Production, fate and role in redox signaling of tumor cells. Cell Commun. Signal. 2015, 13, 1–19. 10.1186/s12964-015-0118-6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Pacher P.; Nivorozhkin A.; Szabó C. Therapeutic effects of xanthine oxidase inhibitors: Renaissance half a century after the discovery of allopurinol. Pharmacol. Rev. 2006, 58, 87–114. 10.1124/pr.58.1.6. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Salazar-Orbea G. L.; García-Villalba R.; Tomás Barberán F. A.; Sánchez-Siles L. M. High–pressure processing vs. Thermal treatment: Effect on the stability of polyphenols in strawberry and apple products. Foods. 2021, 10, 2919. 10.3390/foods10122919. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. da Silva F. L.; Escribano-Bailón M. T.; Pérez Alonso J. J.; Rivas-Gonzalo J. C.; Santos-Buelga C. Anthocyanin pigments in strawberry. LWT - Food Sci. Technol. 2007, 40, 374–382. 10.1016/j.lwt.2005.09.018. [DOI] [Google Scholar]
  20. Kelebek H.; Selli S. Characterization of phenolic compounds in strawberry fruits by RP-HPLC-DAD and investigation of their antioxidant capacity. J. Liq. Chromatogr. Relat. Technol. 2011, 34, 2495–2504. 10.1080/10826076.2011.591029. [DOI] [Google Scholar]
  21. Pradhan P. C.; Mandal A.; Dutta A.; Sarkar R.; Kundu A.; Saha S. Delineating the behavior of Berberis anthocyanin/β-cyclodextrin inclusion complex in vitro: A molecular dynamics approach. LWT. 2022, 157, 113090 10.1016/j.lwt.2022.113090. [DOI] [Google Scholar]
  22. Mehran M.; Masoum S.; Memarzadeh M. Improvement of thermal stability and antioxidant activity of anthocyanins of Echium amoenum petal using maltodextrin/modified starch combination as wall material. Int. J. Biol. Macromol. 2020, 148, 768–776. 10.1016/j.ijbiomac.2020.01.197. [DOI] [PubMed] [Google Scholar]
  23. Ahmad M.; Ashraf B.; Gani A.; Gani A. Microencapsulation of saffron anthocyanins using β glucan and β cyclodextrin: Microcapsule characterization, release behaviour & antioxidant potential during in-vitro digestion. Int. J. Biol. Macromol. 2018, 109, 435–442. 10.1016/j.ijbiomac.2017.11.122. [DOI] [PubMed] [Google Scholar]
  24. Hu Y.; Qiu C.; Qin Y.; Xu X.; Fan L.; Wang J.; Jin Z. Cyclodextrin–phytochemical inclusion complexes: Promising food materials with targeted nutrition and functionality. Trends Food Sci. Technol. 2021, 109, 398–412. 10.1016/j.tifs.2020.12.023. [DOI] [Google Scholar]
  25. Del Valle E. M. M. Cyclodextrins and their uses: a review. Process Biochem. 2004, 39, 1033–1046. 10.1016/S0032-9592(03)00258-9. [DOI] [Google Scholar]
  26. Fernandes A.; Rocha M. A. A.; Santos L. M. N. B. F.; Brás J.; Oliveira J.; Mateus N.; de Freitas V. Blackberry anthocyanins: β-Cyclodextrin fortification for thermal and gastrointestinal stabilization. Food Chem. 2018, 245, 426–431. 10.1016/j.foodchem.2017.10.109. [DOI] [PubMed] [Google Scholar]
  27. Aguilera Y.; Mojica L.; Rebollo-Hernanz M.; Berhow M.; De Mejía E. G.; Martín-Cabrejas M. A. Black bean coats: New source of anthocyanins stabilized by β-cyclodextrin copigmentation in a sport beverage. Food Chem. 2016, 212, 561–570. 10.1016/j.foodchem.2016.06.022. [DOI] [PubMed] [Google Scholar]
  28. Zhu F. Interactions between starch and phenolic compound. Trends Food Sci. Technol. 2015, 43, 129–143. 10.1016/j.tifs.2015.02.003. [DOI] [Google Scholar]
  29. Kim J.-Y.; Huber K. C. Preparation and characterization of corn starch-β-carotene composites. Carbohydr. Polym. 2016, 136, 394–401. 10.1016/j.carbpol.2015.08.069. [DOI] [PubMed] [Google Scholar]
  30. Tan L.; Kong L. Starch-guest inclusion complexes: Formation, structure, and enzymatic digestion. Crit. Rev. Food Sci. Nutr. 2020, 60, 780–790. 10.1080/10408398.2018.1550739. [DOI] [PubMed] [Google Scholar]
  31. Shi L.; Zhou J.; Guo J.; Gladden I.; Kong L. Starch inclusion complex for the encapsulation and controlled release of bioactive guest compounds. Carbohydr. Polym. 2021, 274, 118596 10.1016/j.carbpol.2021.118596. [DOI] [PubMed] [Google Scholar]
  32. Putseys J. A.; Lamberts L.; Delcour A. J. Amylose-inclusion complexes: Formation, identity and physico-chemical properties. J. Cereal Sci. 2010, 51, 238–247. 10.1016/j.jcs.2010.01.011. [DOI] [Google Scholar]
  33. Oliveira H.; Correia P.; Pereira A. R.; Araújo P.; Mateus N.; de Freitas V.; Oliveira J.; Fernandes I. Exploring the applications of the photoprotective properties of anthocyanins in biological systems. Int. J. Mol. Sci. 2020, 21, 7464. 10.3390/ijms21207464. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Fang Z.; Bhandari B. Encapsulation of polyphenols–a review. Trends Food Sci. Technol. 2010, 21, 510–523. 10.1016/j.tifs.2010.08.003. [DOI] [Google Scholar]
  35. Calabrò M. L.; Tommasini S.; Donato P.; Stancanelli R.; Raneri D.; Catania S.; Costa C.; Villari V.; Ficarra P.; Ficarra R. The rutin/β-cyclodextrin interactions in fully aqueous solution: spectroscopic studies and biological assays. J. Pharm. Biomed. Anal. 2005, 36, 1019–1027. 10.1016/j.jpba.2004.09.018. [DOI] [PubMed] [Google Scholar]
  36. Giusti M. M.; Wrolstad R. E. Characterization and measurement of anthocyanins by UV-Visible spectroscopy. Curr. protoc. food anal. chem. 2001, F1.2.1–F1.2.13. 10.1002/0471142913.faf0102s00. [DOI] [Google Scholar]
  37. De Oliveira C. S.; Andrade M. M. P.; Colman T. A. D.; Da Costa F. J. O. G.; Schnitzler E. Thermal, structural and rheological behaviour of native and modified waxy corn starch with hydrochloric acid at different temperatures. J. Therm. Anal. Calorim. 2014, 115, 13–18. 10.1007/s10973-013-3307-9. [DOI] [Google Scholar]
  38. Rashed E. N.; Ali H. M.; Attia M. H.; Bendary E. S.; Ramadan K. M. A. Preparation and thermal stability of α-tocopheryl acetate and strawberry anthocyanins complexed with starch and β-cyclodextrin. Arab Univ J. Agric Sci. 2021, 29, 833–837. 10.21608/ajs.2021.91732.1408. [DOI] [Google Scholar]
  39. Favaro L. I. L.; Balcão V. M.; Rocha L. K. H.; Silva E. C.; Oliveira J. M. Jr; Vila M. M. D. C.; Tubino M. Physicochemical characterization of a crude anthocyanin extract from the fruits of jussara (Euterpe edulis Martius): Potential for food and pharmaceutical applications. J. Braz. Chem. Soc. 2018, 29, 2072–2088. 10.21577/0103-5053.20180082. [DOI] [Google Scholar]
  40. Silverstein R. M.; Webster F. X.; Kiemle D. J. (2005) Spectroscopic Identification of Organic Compounds. Seventh ed., John Wiely & Sons, Inc. p 88. [Google Scholar]
  41. Ai L.; Hu J.; Ji X.; Zhao H. Structure confirmation and thermal kinetics of the inclusion of cis-jasmone in β-cyclodextrin. RSC Adv. 2019, 9, 26224–26229. 10.1039/C9RA03343B. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Xie J.; Xu Y.; Shishir M. R. I.; Zheng X.; Chen W. Green extraction of mulberry anthocyanin with improved stability using β-cyclodextrin. J. Sci. Food Agric. 2019, 99, 2494–2503. 10.1002/jsfa.9459. [DOI] [PubMed] [Google Scholar]
  43. Matsufuji H.; Kido H.; Misawa H.; Yaguchi J.; Otsuki T.; Chino M.; Takeda M.; Yamagata K. Stability to light, heat, and hydrogen peroxide at different pH values and DPPH radical scavenging activity of acylated anthocyanins from red radish extract. J. Agric. Food Chem. 2007, 55, 3692–3701. 10.1021/jf063598o. [DOI] [PubMed] [Google Scholar]
  44. Fernandes A.; Sousa A.; Azevedo J.; Mateus N.; de Freitas V. Effect of cyclodextrins on the thermodynamic and kinetic properties of cyanidin-3-O-glucoside. Food Res. Int. 2013, 51, 748–755. 10.1016/j.foodres.2013.01.037. [DOI] [Google Scholar]
  45. Pérez-Sánchez A.; Barrajón-Catalán E.; Herranz-López M.; Micol V. Nutraceuticals for skin care: A comprehensive review of human clinical studies. Nutrients. 2018, 10, 403. 10.3390/nu10040403. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Topcu Y.; Dogan A.; Kasimoglu Z.; Sahin-Nadeem H.; Polat E.; Erkan M. The effects of UV radiation during the vegetative period on antioxidant compounds and postharvest quality of broccoli (Brassica oleracea L.). Plant Physiol. Biochem. 2015, 93, 56–65. 10.1016/j.plaphy.2015.02.016. [DOI] [PubMed] [Google Scholar]
  47. Kamiloglu S. Effect of different freezing methods on the bioaccessibility of strawberry polyphenols. Int. J. Food Sci. Technol. 2019, 54, 2652–2660. 10.1111/ijfs.14249. [DOI] [Google Scholar]
  48. Ali H. M.; Almagribi W.; Al-Rashidi M. N. Antiradical and reductant activities of anthocyanidins and anthocyanins, structure–activity relationship and synthesis. Food Chem. 2016, 194, 1275–1282. 10.1016/j.foodchem.2015.09.003. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao3c06311_si_001.pdf (691.9KB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES