Characterization of glucan-coated porous wheat starch prepared by high pressure and enzyme treatments for microencapsulation

다국어 초록 (Multilingual Abstract)

This study aimed to develop a porous wheat starch-based delivery system for the encapsulation and intestinal release of lipophilic bioactive compounds by modulating the internal structure of wheat starch through ultra-high pressure （UHP） pretreatment. The porous starch granules （PSGs） were prepared using enzymatic hydrolysis, which was following a UHP pretreatment at different pressure levels. Their structural characteristics, physicochemical properties, loading performance, and release behavior during digestion were also comprehensively evaluated. The FE-SEM observations showed that the UHP pretreatment altered the internal structure of the wheat starch granules as well as also largely preserved their overall morphology and promoted the formation of more distinct porous structures after the subsequent enzymatic hydrolysis. The XRD and DSC analyses demonstrated that the UHP pretreatment significantly modified the crystalline order and the thermal properties of starch in a pressure-dependent manner. The BET analysis further revealed that the UHP pretreatment prior to the enzymatic hydrolysis improved the pore-related properties, which included the specific surface area, pore volume, and pore accessibility, under the appropriate pressure conditions. In addition, the UHP-pretreated PSGs exhibited reduced particle sizes in conjunction with increased water-holding and oil-holding capacities, which indicated the development of a more accessible internal structure that was favorable for interactions with both aqueous and lipid phases. The functional behavior of the starch system varied according to the treatment history. The UHP pretreatment in native wheat starch increased viscosity-related RVA parameters and induced more pronounced changes in amylopectin branch-chain length distribution, whereas PSGs maintained a very low pasting behavior and showed relatively moderate molecular changes. These findings indicate that the structural response of wheat starch to UHP strongly depended on whether the starch remained in its native form or if it was subsequently converted into a porous matrix. The oil-based loading experiments that used β-carotene and curcumin as model lipophilic bioactive compounds showed that PSGs had higher loading capacities than native wheat starch did and that the UHP pretreatment further enhanced the loading performance, which the highest values were observed in the 200 MPa-treated PSGs. THUNDER imaging confirmed that the loaded compounds were distributed on the granule surface as well as also within the internal porous regions of the starch matrix. The porous starch system during in vitro digestion effectively limited the loss of the loaded compounds during the oral and gastric phases and enabled their release during the intestinal phase. The highest loading capacity was observed at 200 MPa, but the greatest release of both compounds was obtained at 100 MPa, which indicated that the structural conditions that are favorable for retention were not identical to the conditions that are required for efficient release. Furthermore, the α- glucan coating improved the physical stability of oil-loaded PSGs and enabled their conversion into a stable powder form with enhanced handling properties. These findings overall suggest that UHP-pretreated porous wheat starch, such as in particular when it is combined with an α-glucan coating is a promising food-grade carrier for the encapsulation, protection, and intestinal delivery of lipophilic bioactive compounds. This study therefore provides a useful basis for the design of delivery systems that are intended to improve the stability, handling, and bioaccessibility of poorly water-soluble functional ingredients.

목차 (Table of Contents)

• Ⅰ. Introduction 14
• 1. Ultra-high pressure 14
• 2. Porous wheat starch 17
• 3. Bioactive compounds 19
• 3.1. β-carotene 19
• 3.2. Curcumin 20
• 4. Microencapsulation 22
• 4.1. Microencapsulation 22
• 4.2. α-Glucan layer coating 24
• Ⅱ. Materials and methods 26
• 1. Materials 26
• 2. Methods 27
• 2.1. Preparation of starch by ultra-high pressure 27
• 2.2. Enzyme assay 28
• 2.3. Preparation of PSGs by amylolytic enzyme treatment 28
• 2.4. Morphological and structural Analysis 29
• 2.4.1. Morphological analysis by FE-SEM 29
• 2.4.2. Crystalline structure analysis by XRD 29
• 2.4.3. Thermal properties by DSC 30
• 2.5. Physicochemical properties 31
• 2.5.1. Specific surface area and porosity evaluation by BET 31
• 2.5.2. Particle size distribution analysis 31
• 2.5.3. Water and Oil absorption capacity 32
• 2.5.4. Pasting properties by RVA 33
• 2.6. Carbohydrate profile analysis by HPAEC-PAD 34
• 2.7. Encapsulation of bioactive compounds 35
• 2.8. NpAS expression, purification, and application 36
• 2.8.1. Expression and purification of NpAS 36
• 2.8.2. Coating PSGs encapsulating bioactive compounds using NpAS 37
• 2.9. Characterization of coated PSGs 38
• 2.9.1. In vitro gastrointestinal digestion stability 38
• 2.9.2. Visual appearance of uncoated and coated PSGs 39
• 2.9.3. Microscopic observation using THUNDER 40
• 2.10. Preparation and release analysis of bioactive compounds 41
• 2.10.1. Preparation of β-carotene or curcumin loaded MCT oil phase 41
• 2.10.2. Measurement of bioactive compounds release 42
• 2.11. Statistical analysis 43
• III. Results and discussion 44
• 1. Morphological characterization by FE-SEM 44
• 2. Crystalline structure analysis by XRD 47
• 3. Thermal properties by DSC 51
• 4. Surface area and pore characteristics by BET 55
• 5. Particle size distribution by laser diffraction 58
• 6. Water and oil absorption capacity 60
• 7. Pasting properties by RVA 64
• 8. Degree of polymerization analysis by HPAEC-PAD 67
• 9. In vitro digestion properties 70
• 10. Effect of coating on the physical appearance and powder of PSGs 74
• 11. Microstructural observation by THUNDER microscopy 78
• 12. Encapsulation of bioactive compounds in oil 82
• 13. Release behavior of bioactive compounds 86
• IV. Conclusions 89
• Ⅴ. References 92