Eating and textural qualities of Korean cooked rice are controlled by leachate and morphological changes during cooking = 밥의 품질은 생쌀의 물리적 특성보다 취상 중 나타나는 침출수와 형태적 변화에 의해 좌우된다

국문 초록 (Abstract)

취사방법과 아밀로스 함량에 따라 달라지는 침출물, 형태 및 식감 특성을 조사하여 밥의 품질을 평가하였다. 침출물은 밥을 90 ℃ 이상의 물을 이용하여 얻었다.
침출물 내 총 고형분과 아밀로펙틴 함량은 전기압력밥솥을 이용해 얻어진 밥(EPCR)에서 가장 높았다. 침출물의 단백질 함량은 조리방법에 따라 유의한 차이는 없었다. 침출물의 아밀로펙틴 사슬 길이 또한 샘플 간에 크게 다르지 않았다. 침출물 용액의 유변학적 특성은 조리방법에 따라 큰 차이를 보였고, 침출물 내 아밀로펙틴 함량이 가장 많았던 EPCR이 겉보기 점도가 가장 높았다. 쌀밥의 형태학적 특성은 압력조건과 관련있고, 이는 쌀의 미세구조 파괴를 유발하여 EPCR과 즉석밥 (ICR)에서 전분 구조의 심각한 파괴가 나타났다. 식감과 관능 특성 또한 조리 방법에 따라 유의한 차이를 보였다. EPCR과 ICR이 전기밥솥을 이용해 얻어진 밥 (ECR)에 비해 높은 부착성과 찰기를 나타냈다. 주성분분석(PCA) 스코어 플롯은 취사방법에 따라 밥의 침출물 및 식감 특성에 유의한 차이가 있음을 나타냈다.
찹쌀(동진찰, 백옥찰)이 아밀로펙틴 함량이 높아 생쌀의 수분흡수율이 가장 높았다. 침출물 내 총 고형분과 아밀로펙틴 함량은 도담이 가장 낮았고, 침출물 내 단백질 함량은 가장 높았다. 침출액의 겉보기 점도는 찹쌀에서 가장 높았고, 고아밀로스 쌀에서 가장 낮았는데 이는 침출된 아밀로펙틴 양에 의해 기인한 것이다. 밥의 식감 특성은 아밀로스 함량에 따라 유의한 차이를 보였다. 도담의 경도가 가장 높았고 찹쌀의 부착성이 가장 높았다. 부착성은 아밀로펙틴의 침출량과 총 고형분과 양의 상관관계를 보였다.

다국어 초록 (Multilingual Abstract)

The leachate, morphological and textural characteristics of cooked rice, which differ depending on the cooking methods and amylose content, were investigated to evaluate the quality of cooked rice. The leachate was obtained by rinsing cooked rice with hot distilled water (~90 ℃).
The amounts of total solids and amylopectin in the leachate were highest in electronic-pressure cooked rice (EPCR). The protein content in the leachate was not significantly different among the cooking methods. Amylopectin chain length of leachate was not substantially different among the samples. The rheological properties of leachate solution showed significant difference according to cooking methods, EPCR was the highest apparent viscosity, attributed to its highest amylopectin amount in the leachate solution. Morphological characteristics of cooked rice were related to pressure condition, inducing the disruption the microstructure of rice, thereby EPCR and instant cooked rice (ICR) were presented severe disruption in starch structure. Textural and sensory characteristics were also significantly different according to cooking methods. Principal component analysis (PCA) revealed that the cooking method affects the compositions of leachate and texture characteristics of cooked rice.
Water absorption ratio of raw rice was highest in waxy rice (Dongjinchal and Baekokchal) due to the higher amylopectin content. Dodam had the lowest amount of total solids and amylopectin in leachate, while the protein content in leachate was highest among the other samples. The apparent viscosity of leachate solution was highest in waxy rice, whereas lowest in high amylose rice, attributed to leached amylopectin amount. Textural characteristics of cooked rice were significantly different according to amylose content. Dodam had the highest hardness and waxy rice had the highest adhesiveness. The adhesiveness had positive correlations with leached amylopectin amount and total solids.
In short, this study indicates that leachate and morphological characteristics could be useful standards for evaluating the quality of cooked rice.

목차 (Table of Contents)

• Ⅰ. Chapter 1. The cooking method features controlling eating quality of cooked rice: An explanation from the view of leachate and morphological characteristics 1
• Abstract 2
• 1.1. Introduction 3
• 1.2. Materials and methods 6
• 1.2.1. Materials 6
• 1.2.2. Rice cooking 6
• 1.2.3. Extraction of leached materials 6
• 1.2.4. Water and lipid contents of cooked rice 7
• 1.2.5. Morphological characteristics of cooked rice 7
• 1.2.5.1. Scanning electron microscopy (SEM) 7
• 1.2.5.2. Confocal laser scanning microscopy (CLSM) 7
• 1.2.5.3. Light microscopy (LM) 8
• 1.2.6 Composition and structural analysis of the leachate 8
• 1.2.7. Rheological properties of leachate solution 9
• 1.2.8. Textural and sensory properties of cooked rice 10
• 1.2.9. Statistical analysis 10
• 1.3. Results and discussion 12
• 1.3.1. Water content of cooked rice 12
• 1.3.2. Lipid content of cooked rice 15
• 1.3.3. Morphological properties of cooked rice 17
• 1.3.3.1. Scanning electron microscopy (SEM) 17
• 1.3.3.2. Confocal laser scanning microscopy (CLSM) 21
• 1.3.3.3. Light microscopy (LM) 24
• 1.3.4. Compositional analysis of leachate 27
• 1.3.5. Amylopectin chain length distribution of leachate 30
• 1.3.6. Rheology properties of leachate solution 33
• 1.3.7. Texture properties of cooked rice 35
• 1.3.8. Sensory properties of cooked rice 38
• 1.3.9. Correlations between cooking methods and properties of cooked rice 41
• 1.4. Conclusions 43
• References 44
• Ⅱ. Chapter 2. Textural quality of Korean rice cultivars are controlled by leachate characteristics of cooked rice 51
• Abstract 52
• 2.1. Introduction 53
• 2.2. Materials and methods 56
• 2.2.1. Materials 56
• 2.2.2. Water absorption of raw rice 56
• 2.2.3. Rice cooking 56
• 2.2.4. Extraction of leached materials 56
• 2.2.5. Water and lipid contents of cooked rice 57
• 2.2.6. Compositions and structural analysis of the leachate 57
• 2.2.7. Rheological properties of leachate solution 58
• 2.2.8. Textural properties of cooked rice 58
• 2.2.9. Statistical analysis 59
• 2.3. Results and discussion 60
• 2.3.1. Water absorption and water content of rice 60
• 2.3.2. Lipid content of cooked rice 65
• 2.3.3. Compositional analysis of leachate 68
• 2.3.4. Amylopectin chain length distribution of leachate 73
• 2.3.5. Rheology properties of leachate solution 77
• 2.3.6. Textural properties of cooked rice 80
• 2.3.7. Correlations between amylose content and properties of cooked rice 84
• 2.3.8. Pearson correlations between leachate and textural parameters 87
• 2.4. Conclusions 94
• References 95
• Ⅲ. Conclusion 101
• Abstract in Korean 103