Development of Functional Inclusion Complexes Using Cycloamylose and Their Physicochemical Characteristics

Abstract

Inclusion complex formation with cycloamylose (CA) can exert a profound effect on the solubility and stability of highly insoluble and unstable guest molecules, since CA can take a hydrophobic cavity geometry as in the case of cyclodextrin (CD). Even though advantages of CA over CD have been reported such as high solubility and diverse cavity size, researches on CA in food and pharmaceutical fields are limited, probably because of its novelty. Therefore, in this study, the complex formation capability of CA with various guest molecules was investigated mainly in terms of its physicochemical characteristics to solubilize and stabilize those molecules. CA with a range of DP from 23 to 45 was produced by treating amylose with Thermus acuaticus 4-α-glucanotransferase (TAαGTase). The inclusion complex formation capability of CA was investigated using model guest materials, such as iodine, sodium dodecyl sulfate (SDS), and lysolecithin (LL). It was revealed that those model guests were inserted in the cavity of CA as measured using isothermal titration calorimetry (ITC) and nuclear magnetic resonance (NMR). Various functional guest molecules, such as quercetin, polyphenol oxidase substrates (PPOS) and fat-soluble vitamins (FSV), were reacted with CA and two other commercially available complexation agents, cyclodextrin (CD) and maltodextrin (MD), respectively, using a freeze-drying (FD) method. The characterization of functional inclusion complexes was measured using various physicochemical analysis techniques. These results revealed that CA formed stable inclusion complexes with quercetin, PPOS, and FSV. The water solubility of quercetin and FSV significantly increased in the presence of CA. Especially, at high concentration, CA improved the solubility more than CD or MD. The oxidative stability of PPOS was significantly improved by complexation, decreasing the oxidative rate and the activity of polyphenol oxidase (PPO) that caused enzymatic browning. Also, the photo-stability of FSV was significantly improved by forming a complex with CA, showing a decrease in degradation constant (Kd) and an increase in half-life (t1/2), compared to those of pure FSV. In order to investigate inclusion complexation performance of CA molecules depending on their size, twenty-three different degrees of polymerization (DPs) of CA from 23 to 45 were fractionated using a repeated prep-HPLC. The inclusion complex formation capability of each CA molecule with SDS was analyzed using ITC and NMR. The thermodynamic data obtained using ITC revealed that all the binding processes were enthalpy-driven and the binding stoichiometry (n) increased from about 2 to 3 as DP increased from 23 to 45. The strong binding of the SDS molecule to CA26 was observed, which might be attributed to structural stability of CA26 bound with SDS by forming stable double hydrophobic cavities. The ROESY spectrum of the CA26-SDS complexes confirmed that the alkyl chain of the SDS molecule was inserted into the cavity of CA26. The solubility of β-carotene (BC) was also enhanced in the presence of CA26. The characterization of inclusion complexes between CA26 and BC suggested that the stable inclusion complex was formed with the olefinic region of BC interacting with the hydrophobic cavity of CA26. The photo-stability and oxidative stability of BC were improved upon inclusion complexation with CA26, compared to that of pure BC. In conclusion, CA, as an efficient carrier molecule, formed stable inclusion complexes with various functional materials and greatly improved their solubility and stability, proposing a high potential of CA for various food and pharmaceutical industries.