Saehun Mun

Development of reduced-fat mayonnaise using 4αGTase-modified rice starch and xanthan gum

In this study a disproportionating enzyme, 4-alpha-glucanotransferase (4alphaGTase), was used to modify the structural properties of rice starch to produce a suitable fat substitute in reduced-fat (RF) mayonnaise. The mayonnaise fat was partially substituted with the 4alphaGTase-treated starch paste at levels up to 50% in combination with xanthan gum and the physical and rheological properties of the modified RF mayonnaise samples were investigated. All mayonnaises prepared in this study exhibited shear thinning behavior and yield stress. Viscoelastic properties of mayonnaise were characterized using dynamic oscillatory shear test and it was observed that mayonnaises exhibited weak gel-like properties. The magnitude of elastic and loss moduli was also affected by 4alphaGTase-treated starch concentration and presence of xanthan gum. In relation to microstructure, RF mayonnaise prepared with 3.8 or 5.6 wt% of 4alphaGTase-treated starch and xanthan gum showed smaller droplets. The use of 5.6 wt% of 4alphaGTase-treated starch and 0.1 wt% of xanthan gum produced a RF mayonnaise with similar rheological properties and appearances as FF mayonnaise with gum. This study demonstrated a high feasibility for using 4alphaGTase-treated rice starch as a viable fat replacer in mayonnaise.

Photosensitizer-conjugated polymeric nanoparticles for redox-responsive fluorescence imaging and photodynamic therapy

Photosensitizers conjugated with hyaluronic acid via disulfide linkers were developed for biologically activatable near-infrared fluorescence imaging and photodynamic therapy. The nanoparticles prepared from the conjugate are nonfluorescent and nonphototoxic in their native state, but become highly fluorescent and phototoxic in response to reductive agents inside cancer cells.

Preparation and Characterization of Water/Oil/Water Emulsions Stabilized by Polyglycerol Polyricinoleate and Whey Protein Isolate

In this study we tried to prepare stable water-in-oil-in-water (W/O/W) emulsions using polyglycerol polyricinoleate (PGPR) as a hydrophobic emulsifier and whey protein isolate (WPI) as a hydrophilic emulsifier. At first, water-in-oil (W/O) emulsions was prepared, and then 40 wt% of this W/O emulsion was homogenized with 60 wt% aqueous solution of different WPI contents (2, 4, and 6 wt% WPI) using a high-pressure homogenizer (14 and 22 MPa) to produce W/O/W emulsions. The mean size of final W/O/W droplets ranged from 3.3 to 9.9 microm in diameter depending on the concentrations of PGPR and WPI. It was shown that most of the W/O/W droplets were small (<5 microm) in size but a small population of large oil droplets (d > 20 microm) was also occasionally observed. W/O/W emulsions prepared at the homogenization pressure of 22 MPa had a larger mean droplet size than that prepared at 14 MPa, and showed a microstructure consisting of mainly approximately 6 to 7-microm droplets. When a water-soluble dye PTSA as a model ingredient was loaded in the inner water phase, all W/O/W emulsions showed a high encapsulation efficiency of the dye (>90%) in the inner water phase. Even after 2 wk of storage, >90% of the encapsulated dye still remained in the inner water phase; however, severe droplet aggregation was observed at relatively high PGPR and WPI concentrations.

Indocyanine green-loaded perfluorocarbon nanoemulsions for bimodal (19)F-magnetic resonance/nearinfrared fluorescence imaging and subsequent phototherapy.

We have developed an indocyanine green-loaded perfluorocarbon (ICG/PFCE) nanoemulsion as a multifunctional theranostic nanomedicine which enables not only (19)F magnetic resonance (MR)/near-infrared fluorescence (NIRF) bimodal imaging but also subsequent photodynamic/photothermal dual therapy of cancer. The hydrodynamic size of ICG/PFCE nanoemulsions was 164.2 nm. The stability of indocyanine green (ICG) in aqueous solution was significantly improved when loaded on perfluorocarbon nanoemulsions. In addition, ICG/PFCE nanoemulsions showed good dispersion stability in aqueous media containing 10% fetal bovine serum, for at least 14 days. (19)F-MRI of ICG/PFCE nanoemulsions showed that the signal intensity increased with increasing nanoemulsion concentration with no signal observed from the surrounding background. Using NIRF imaging with perfluorocarbon nanoemulsion alone, without ICG, did not produce NIRF, while clear and bright fluorescent images were obtained with ICG/PFCE nanoemulsions at 10-µM ICG equivalent. The capacity of ICG-loaded nanoemulsions to generate heat following light irradiation by using an 810-nm laser was comparable to that of free ICG, while singlet oxygen generation of ICG-loaded nanoemulsions was significantly better than that of free ICG. In vitro cytotoxicity tests and fluorescence microscopy confirmed biocompatibility of the nanoemulsion. Upon light irradiation, U87MG glioblastoma cells incubated with ICG/PFCE nanoemulsions underwent necrotic cell death. The therapeutic mechanism during light illumination appears to be mainly due to the photodynamic effect at lower ICG concentrations, whilst the photothermal effect became more obvious at increased ICG concentrations, enabling combined photodynamic/photothermal therapy of cancer cells.

Influence of environmental stresses on the stability of W/O/W emulsions containing enzymatically modified starch

The present study was performed to investigate the stability of W/O/W emulsions containing 4-α-glucanotransferase (4αGTase)-treated starch against environmental stresses such as heating, shearing, and repeated freeze-thawing. W/O/W emulsions were subjected to thermal processing at different temperatures ranging from 30 to 90 °C for 30 min, constant shear for 0-7 min, and freeze-thaw cycling between -20 °C and 30 °C, respectively, and followed by encapsulation efficiency (EE) measurement. As for the case of thermal stress, it was clearly shown that addition of 4αGTase-treated starch in the internal aqueous phase of emulsions helped to maintain higher EE during thermal processing. However, at lower PGPR level (2%), the addition of 4αGTase-treated starch dramatically reduced EE at temperatures higher than 70 °C, which was probably related to the melting of 4αGTase-treated starch gel. The incorporation of 4αGTase-treated starch improved the stability of emulsions during shearing process, but could not prevent W/O/W emulsions from creaming and destabilizing during freeze-thaw cycling.

Effects of enzymatically modified starch on the encapsulation efficiency and stability of water-in-oil-in-water emulsions

The present study was performed to investigate the possibility of using 4-α-glucanotransferase (4αGTase)-treated starch in W/O/W emulsions to increase their encapsulation efficiency (EE) and stability. Emulsions were prepared using soybean oil, polyglycerol polyricinoleate (PGPR), 4αGTase-treated starch and Tween 20. The mean diameter of W/O/W droplets ranged from 4 to 10μm depending on the sonication time. When the dye was loaded in the internal water phase, the emulsion prepared by sonication for 1 and 2min showed a high EE of the dye (>90%). The W/O/W emulsion prepared by sonication for 3min showed an EE of<90%, but this EE was improved by adding 4αGTase-treated starch to the internal water phase. 4αGTase-treated starch was added to the internal water phase of W/O/W emulsions prepared with a low concentration of PGPR, and the PGPR concentration required to maintain an EE>90% was reduced. W/O/W emulsions containing 4αGTase-treated starch also showed better stability against heating and shearing stresses. These results indicated that 4αGTase-treated starch could be used in the preparation of W/O/W emulsions, which would allow the formulation of W/O/W emulsions with a reduced surfactant concentration.

Influence of methylcellulose on attributes of β-carotene fortified starch-based filled hydrogels: Optical, rheological, structural, digestibility, and bioaccessibility properties

There is considerable interest in controlling the gastrointestinal fate of nutraceuticals to improve their efficacy. In this study, the influence of methylcellulose (an indigestible polysaccharide) on lipid digestion and β-carotene bioaccessibility was determined. The carotenoids were encapsulated within lipid droplets that were then loaded into rice starch hydrogels containing different methylcellulose levels. Incorporation of 0 to 0.2% of methylcellulose had little impact on the dynamic shear rheology of the starch hydrogels, which may be important for formulating functional foods with desirable textural attributes. The microstructure, lipid digestion, and β-carotene bioaccessibility of the filled hydrogels were measured as the samples were passed through simulated oral, gastric, and small intestinal phases. The lipid digestion rate and carotenoid bioaccessibility decreased with increasing methylcellulose. This effect was attributed to the ability of the methylcellulose to inhibit molecular diffusion, promote droplet flocculation, or bind gastrointestinal components thereby inhibiting triacylglycerol hydrolysis at the lipid droplet surfaces. This information may be useful for rationally designing functional foods with improved nutritional benefits.

Release properties of gel-type W/O/W encapsulation system prepared using enzymatically-modified starch

A gel-based encapsulation system was developed by incorporating W/O/W emulsions and 4-α-glucanotransferase (4αGTase) treated starch capable of thermoreversible gel formation, and its physical and release characteristics were investigated as functions of preparation conditions and temperature. Release properties of the W/O/W gels were affected by stability and encapsulation efficiency (EE) of W/O/W emulsions embedded within. Lower EE caused by longer sonication time increased fast release dye portion, which resulted in higher dye release rate, even though emulsion stability improved at longer sonication time. Lower dye release rate of W/O/W gels prepared with relatively higher W/O volume fractions slightly increased as temperature increased from room temperature to 90 °C. However, samples prepared with relatively lower W/O volume fractions showed higher dye release rate and a larger increase at 90 °C. The 4αGTase-treated starch gel improved W/O/W emulsion stability and thus retarded dye release even at 90 °C.

Physicochemical functionality of 4-α-glucanotransferase-treated rice flour in food application.

The physicochemical properties of 4-α-glucanotransferase (4αGTase)-modified rice flours were examined by measuring the molecular weight distribution, moisture sorption isotherm, and melting enthalpy of ice crystals. The results obtained by measuring the moisture sorption isotherm and melting enthalpy of ice crystals revealed that 4αGTase-modified rice flours had high water binding capacity than that of control rice flour. When the textural properties of noodles containing 4αGTase-treated rice flours after freeze-thaw cycling were measured by texture profile analysis, the textural properties of control noodle deteriorated. However, those of noodle with 4αGTase-modified rice flours were retained. For the melting enthalpy of ice crystals formed within cooked noodles, 4αGTase-treated rice flour showed similar effect to sucrose for reducing the melting enthalpy of ice crystals, however, the texture and taste of noodle with sucrose was undesirable for consuming. 4αGTase-treated rice flour appeared to have good potential as a non-sweet cryoprotectant of frozen product.

Physicochemical interactions of cycloamylose with phenolic compounds

The complex formation capability of cycloamylose (CA), having a degree of polymerization of 23-45, with phenolic compounds (PCs) was investigated using various physicochemical techniques. The fluorescence intensity of PCs increased and then reached a plateau at 10-20mM cyclodextrin, while it continued to increase at up to 60mM CA. Thermodynamic data of CA complexes with PCs revealed that the binding process was primarily enthalpy-driven and spontaneous. CA favored to form the most stable complex with chlorogenic acid (CHA) among all PCs. Chemical shift changes for the protons in interior and exterior of CA, as well as in PCs suggested a possible formation of both inclusion and extramolecular interactions between CA and PCs. The ROESY spectrum confirmed that the aromatic moieties of CHA were partially interacted with CA molecules through relatively weak binding. XRD, DSC, and SEM results also supported the complex formation by intermolecular interaction between CA and CHA.