Structure―Digestibility Relationship of Recrystallized Starch by Using Amylosucrase-modified Starch as a Model System
아밀로수크레이스 처리 전분 모델을 활용한 재결정 전분의 구조―소화특성 간 관계 구명

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dc.description학위논문 (박사)-- 서울대학교 대학원 : 농업생명과학대학 농생명공학부, 2018. 8. 문태화.-
dc.description.abstractStarch can be classified into three fractions of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS), according to the time of digestion as suggested by Englyst et al. SDS and RS are generally classified as low-digestible starch, and their production and health beneficial effects have been widely studied. However, the classification of RDS and SDS has been argued because the in vitro digestion of starch can be described by a single rate constant k of a first order reaction. With increasing interests on carbohydrate-controlling diets because of health concerns, food industry requires a unified strategy for the production of health-functional starch. To achieve this goal, actual existence of each starch fraction should be verified primarily.

Waxy corn and waxy potato starches were modified by amylosucrase (AS) to obtain starch samples with different branch chain length distributions. Hydrolysis curves were obtained for native and AS-modified starches and then fitted to the logarithm of slope (LOS) plot, which can reflect the change of k during first order reaction. LOS plots for AS-modified starches revealed a discontinuity, demonstrating that digestion proceeded in two separate phases. It provided the evidence of a fraction that is digested more rapidly than the remainder, i.e., RDS and SDS, and their rate constants were defined as k_RDS and k_SDS, respectively. The values of the k_RDS and k_SDS, and the contents of RDS and SDS estimated by LOS plot method of AS-modified starches were affected by the amount of AS employed. The digestible properties related to RDS, SDS, and RS were investigated by both in vitro and in vivo study. This study could verify the existence of individual RDS and SDS fractions in a single starch source, and suggested the modified LOS plot approach as an alternative investigative tool for classification of starch fractions on the basis of its digestibility.

The structural characteristics of RDS, SDS, and RS were investigated by tracing the changes according to serial removal of each fraction. The changes in branch chain length distribution implied the branch chains with certain DP contribute to the organization of each fraction. Undigested RS was composed of rather short chains with DP 13-24. After the removal of RDS and SDS fractions, chains of DP ≥ 37 and DP ≥ 25 decreased, respectively. Certain structures found in common among RDS and SDS fractions, respectively, strongly supported the existence of individual RDS and SDS possessing specific structural characteristics of each. The AS-modified starches displayed B type X-ray pattern, and the relative crystallinity increased with the amount of AS, and also according to the degree of hydrolysis of RDS and SDS fractions. The branch chain length distributions of amylopectin determined the primarily generated crystallite organization of AS-modified starches, causing the diversity of digestion properties. Highly extended branch chains would favor the formation of more slowly digestible form of RDS and SDS. The different values of k_RDS and k_SDS among starch samples reflected the different structures of RDS and SDS.

The recrystallized starches prepared by using AS-modified waxy potato starch and amylose from potato starch by 3:1 ratio and the structures of their RDS, SDS, and RS were investigated. Co-crystallization of amylose and amylopectin occurred, where the branch chain length of amylopectin determined the length of amylose-amylopectin double helix and mobility of amylose. RDS was composed of singular amylose chains and amorphous double helices not long enough or not aligned ordered structure. Low digestible fractions, SDS and RS, were mainly composed of semi-crystalline or crystalline structure of double helices with DP 13-24. Unlike amylopectin-only environment, the amount of SDS did not show a linear increase according to the branch chain length. Certain length of amylopectin would prefer formation of SDS or RS by controlling the interaction with amylose.

In short, this study provided the knowledge on the formation of low digestible starch under various environments and detail structure of each fraction within starch. It would be utilized in the production of customized starch for specific digestive properties with health functionality.





Chapter 1. Introduction 1

1.1. Background 2

1.2. General aspects of starch 4

1.2.1. Structure of starch 4

1.2.2. Starch crystallinity 8

1.2.3. Gelatinization, pasting, and retrogradation of starch 12

1.2.4. Recrystallization of starch 15

1.3. Nutritional property of starch 17

1.3.1. Digestion of starch 17

1.3.2. Analysis methods of starch digestibility 22

1.3.3. Classification of starch fractions according to nutritional value 25

1.4. Low-digestible starch 26

1.4.1. Definition of low-digestible starch 26

1.4.2. Beneficial physiological effects of low digestible starch 30

1.4.3. Attempts to produce low digestible starch 32

1.4.4. Amylosucrase-modified starch and its applications 36

1.5. Research objectives 39

Chapter 2. Modified LOS plot method for in vitro digestibility analysis using amylosucrase-modified waxy starches with different branch chain length distributions 41

2.1. Introduction 42

2.2. Materials and methods 46

2.2.1. Materials 46

2.2.2. Enzyme assay of AS activity 47

2.2.3. Preparation of AS-modified starches 47

2.2.4. Determination of branch chain length distribution 48

2.2.5. Determination of in vitro digestibility 49

2.2.6. Determination of starch fractions using the Englyst method 50

2.2.7. Determination of starch fractions according to the modified log of slope (LOS) method 51

2.2.8. X-ray diffraction patterns and relative crystallinity 52

2.2.9. Postprandial blood glucose response in mice 53

2.2.10. Statistical analysis 54

2.3. Results and discussion 55

2.3.1. Preparation of starch samples with different branch chain length 55

2.3.2. Digestion pattern of AS-modified starches 61

2.3.3. Determination of starch fractions using the traditional Englysts method 66

2.3.4. LOS plotting of digestibility curve using modified method 68

2.3.5. Determination of starch fractions based on modified LOS plot method 83

2.3.6. Versatility of the modified LOS plot method on starches with various digestive property 86

2.3.7. Relationship between in vitro and in vivo digestibility 96

2.4. Conclusions 101

Chapter 3. Structure-digestibility relationship of amylosucrase-modified waxy corn starch: structure and formation mechanism of each starch fraction 103

3.1. Introduction 104

3.2. Materials and methods 107

3.2.1. Materials 107

3.2.2. Preparation of AS-modified starches 107

3.2.3. Determination and isolation of starch fractions 108

3.2.4. Determination of branch chain length distribution 109

3.2.5. X-ray diffraction patterns and relative crystallinity 110

3.2.6. Statistical analysis 111

3.3. Results and discussion 112

3.3.1. Structural characteristics of AS-modified starches 112

3.3.2. In vitro digestibility of AS-modified starches 118

3.3.3. Branch chain length distributions of each fraction 124

3.3.4. Changes in crystalline properties determined by X-ray diffraction 133

3.3.5. Structure-digestibility relationship of AS-modified starch 137

3.4. Conclusions 142

Chapter 4. The role of amylopectin chains length in the formation of low-digestible fraction in amylosucrase-modified waxy potato starches co-crystallized with amylose 144

4.1. Introduction 145

4.2. Materials and methods 148

4.2.1. Materials 148

4.2.2. Preparation of the starch mixture of AS-modified waxy potato starch and amylose 148

4.2.3. Determination of in vitro digestibility and isolation of low-digestible fractions 150

4.2.4. Determination of branch chain length distribution 151

4.2.5. X-ray diffraction and relative crystallinity 152

4.2.6. Thermal properties 152

4.2.7. Iodine binding property and apparent amylose content 153

4.2.8. Statistical analysis 153


4.3.1. Production of starches with different amylopectin chain length distribution 154

4.3.2. In vitro digestibility of starch samples 158

4.3.3. Iodine binding properties 165

4.3.4. Changes in chain length distribution after the removal of RDS and/or SDS fraction 171

4.3.5. X-ray diffraction and relative crystallinity of each fraction 184

4.3.6. Thermal properties of each fraction 190

4.3.7. Interaction between amylose and amylopectin molecules with different branch chain length distribution 196

4.4. Conclusions 203

References 205

국문초록 225
dc.publisher서울대학교 대학원-
dc.titleStructure―Digestibility Relationship of Recrystallized Starch by Using Amylosucrase-modified Starch as a Model System-
dc.title.alternative아밀로수크레이스 처리 전분 모델을 활용한 재결정 전분의 구조―소화특성 간 관계 구명-
dc.contributor.affiliation농업생명과학대학 농생명공학부-
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College of Agriculture and Life Sciences (농업생명과학대학)Dept. of Agricultural Biotechnology (농생명공학부)Theses (Ph.D. / Sc.D._농생명공학부)
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