Effects Of Different Cooking Methods And Storage Conditions On The Rice Starch Digestibility

UNIVERSITI PUTRA MALAYSIA EFFECTS OF DIFFERENT COOKING METHODS AND STORAGE CONDITIONS ON THE RICE STARCH DIGESTIBILITY YOGESHINI A/P RAMAKRISHNAN FSTM 2009 27 EFFECTS OF DIFFERENT COOKING METHODS AND STORAGE CONDITIONS ON THE RICE STARCH DIGESTIBILITY By YOGESHINI A/P RAMAKRISHNAN Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of Science November 2009 i DEDICATION This work is dedicated to my husband Kalidasan and all family members who had given me constant encouragement and support. ii Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science EFFECTS OF DIFFERENT COOKING METHODS AND STORAGE CONDITIONS ON THE RICE STARCH DIGESTIBILITY By YOGESHINI A/P RAMAKRISHNAN November 2009 Chairperson: Sharifah Kharidah Syed Muhammad, PhD Faculty: Food Science and Technology Seven types of rice with different levels of amylose were selected to study the effect of different cooking methods, chilling and freezing on the digestibility of their starches. An in vitro enzymatic starch digestion method was applied in order to estimate the expected glycemic index (GI) in vivo based on the kinetics of starch hydrolysis in vitro. First, samples were cooked with different cooking methods to investigate the effect of cooking on the starch digestibility; second, samples were steamed and stored at temperatures of 4 and -20°C in order to simulate certain storage conditions of cooked rice. The results indicated significant differences in terms of starch digestibility or GI of the seven types of iii rice studied and the digestibility of their starches were further affected by different cooking methods. These differences can be attributed to the formation of resistant starch (RS). Steaming increased the RS formation in each type of rice. Cooking the rice with excess water, combi oven and rice cooker contributed only to small changes in the formation of RS. The proximate compositions of the rice before and after cooking were similar for all cooking methods. The amylose content of rice has an obvious impact on the rice starch digestibility due to its positive correlation with formation of RS. Starch hydrolysis was found to be rapid and complete for the waxy and low amylose rice rather than for the intermediate and high amylose rice. Chilling of steamed rice promoted the formation of RS more than freezing. The GI ranged between 68 and 98 for steamed rice and between 63 and 82 for chilled and frozen rice. Storing steamed rice at 4°C and -20°C gradually increased the formation of RS and reduced the estimated GI for all the seven types of rice. A high decrease in starch hydrolysis after chilling and freezing was found among the waxy rice. Thermal properties of rice that have undergone steaming, chilling and freezing showed a shift of the gelatinization temperature to a higher value. The pasting properties of steamed and chilled or frozen rice samples showed increased pasting temperatures and decreased peak viscosity compared to those of raw rice. The raw rice starches had the characteristic A-type crystalline pattern, with diffraction peaks at 15.2, 17.2, 17.9 and 23.2° (2θ). The steaming, chilling and freezing treatment on rice caused weak peak formation at 16° and 20° (2θ) representing crystalline B-type and V-amyloselipid complexes. Steaming, chilling and freezing of rice had reduced the relative crystallinity (RC) value. iv Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk Ijazah Sarjana Sains KESAN DARIPADA PELBAGAI KAEDAH MEMASAK DAN KEADAAN PENYIMPANAN TERHADAP KEBOLEHHADAMAN KANJI BERAS Oleh YOGESHINI A/P RAMAKRISHNAN November 2009 Pengerusi: Sharifah Kharidah Syed Muhammad, PhD Fakulti: Sains and Teknologi Makanan Tujuh jenis beras dengan tahap amilosa yang berbeza telah dipilih untuk dikaji terhadap kesan pelbagai kaedah memasak, penyejukan dan penyejukbekuan ke atas kebolehhadaman kanjinya. Kaedah penghadaman kanji secara enzim in vitro telah diaplikasi untuk menganggarkan indeks glisemik (GI) in vivo berdasarkan kinetik hidrolisis kanji in vitro. Pertama, sampel telah dimasak dengan pelbagai kaedah memasak yang berbeza untuk mengenalpasti kesan memasak ke atas kebolehhadaman kanji; kedua, sampel telah dikukus dan disimpan pada suhu 4°C dan -20°C untuk mensimulasi sesetengah kaedah penyimpanan nasi. Keputusan menunjukkan perbezaan yang ketara dari segi penghadaman kanji atau GI tujuh jenis beras yang dikaji dan kebolehhadaman v kanji tersebut, dipengaruhi oleh kaedah memasak. Perbezaan ini adalah disebabkan oleh pembentukan kanji rintang (RS). Pengukusan meningkatkan pembentukan RS pada setiap jenis beras. Memasak nasi dengan air yang berlebihan, ketuhar kombi dan periuk nasi menyumbang pada perubahan yang kecil dalam pembentukan kanji rintang. Komposisi proksimat nasi sebelum dan selepas memasak adalah hampir sama untuk semua kaedah memasak. Kandungan amilosa beras mempunyai impak yang ketara ke atas kebolehhadaman kanji beras disebabkan oleh korelasi positifnya dengan kanji rintang. Hidrolisis kanji didapati cepat dan lengkap untuk beras pulut dan beras rendah amilosa berbanding dengan beras pertengahan dan tinggi amilosa. Penyejukkan nasi menyebabkan pembentukkan kanji rintang yang lebih banyak berbanding dengan penyejukbekuan. Nilai GI adalah di antara 65 dan 98 untuk nasi yang dikukus dan di antara 63 dan 82 untuk nasi yang disejuk dan disejukbekukan. Penyimpanan nasi pada suhu 4°C dan -20°C meningkatkan pembentukkan RS secara berperingkat dan mengurangkan GI anggaran untuk kesemua tujuh jenis beras. Penurunan yang tinggi dalam penghadaman kanji selepas penyejukkan dan penyejukbekuan didapati berlaku pada beras pulut. Ciri terma beras yang telah dikukus, disejuk and disejukbeku menunjukkan pengubahan suhu pengelatinan ke nilai yang lebih tinggi. Sifat pempesan sampel nasi yang dikukus dan disejuk atau disejukbekukan menunjukkan peningkatan pada suhu pempesan dan penurunan puncak kelikatan berbanding dengan sampel beras. Kanji beras mempunyai ciri pembentukan penghabluran jenis A dengan puncak pembelauan pada 15.2, 17.2, 17.9 and 23.2° (2θ). Rawatan seperti pengukusan beras, penyejukkan dan penyejukbekuan nasi menyebabkan pembentukan puncak yang lemah pada 16° dan 20° (2θ) mewakili vi penghabluran jenis B and kompleks V-amilosa-lipid. Pengukusan, penyejukan dan penyejukbekuan telah menurunkan nilai penghabluran relatif (RC). vii ACKNOWLEDGEMENTS First of all, I would like to express my sincere gratitude and deepest appreciation to my supervisor, Assoc. Prof. Dr. Sharifah Kharidah Syed Muhammad for her invaluable advice and guidance, constructive criticisms and constant encouragement throughout the course of this study and the preparation of this thesis. She has been a great help, an inspiration, and both a teacher and a dear friend. My sincere appreciation also goes to all the members of the supervisory committee Professor Dr. Jamilah Bakar and Dr. Roselina Karim for their help in reviewing my thesis and offering suggestions for improvement. I would also like to extend my thanks to Hossien Amin, Nurrul Hasanah, Nura Hayati and Dwi Andiaz, postgraduate students for their generosity with advice regarding data analysis and interpretation. Last but not least, I am greatly indebted to my husband, all the family members and friends for their loving support and encouragement throughout the length of my study. viii ix This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Master of Science. The members of the Supervisory Committee were as follows: Sharifah Kharidah Syed Muhammad, PhD Associate Professor Faculty of Food Science and Technology Universiti Putra Malaysia (Chairperson) Jamilah Bakar, PhD Professor Faculty of Food Science and Technology Universiti Putra Malaysia (Member) Roselina Karim, PhD Faculty of Food Science and Technology Universiti Putra Malaysia (Member) ________________________________ HASANAH MOHD GHAZALI, PhD Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date: 11 February 2010 x DECLARATION I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously, and is not concurrently, submitted for any other degree at Universiti Putra Malaysia or at any other institution. _________________________________ YOGESHINI A/P RAMAKRISHNAN Date: 10 March 2010 xi TABLE OF CONTENTS DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENTS APPROVAL DECLARATION LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS Page ii iii v viii ix xi xv xvi xvii CHAPTER 1 INTRODUCTION 2 LITERATURE REVIEW 2.1 Rice 2.2 Structure and form of rice starch 2.2.1 Amylose 2.2.2 Amylopectin 2.2.3 Macrostructure of the starch granules 2.3 Functional properties of starch 2.3.1 Glass transition 2.3.2 Swelling power and solubility 2.3.3 Starch crystallinity 2.4 Effect of cooking on starch 2.4.1 The starch granule and its modification during cooking 2.4.2 Gelatinization of starch 2.4.3 Retrogradation of rice starch 2.4.4 Protein-starch and lipid-starch complexes 2.4.5 Food processing, digestibility of starch fraction and glycemic responses 2.5 Starch digestibility 2.5.1 Glycemic index 2.5.2 Resistant starch 2.6 Factors influence the formation of resistant starch 2.6.1 Crystallinity of starch 2.6.2 Granular structure 2.6.3 Amylose : amylopectin ratio 2.6.4 Retrogradation of amylose 2.6.5 Influence of amylose chain length 2.6.6 Heat and moisture 1 4 7 8 9 11 14 15 15 16 18 18 19 21 22 23 24 27 30 33 33 34 34 35 36 37 xii 2.6.7 2.6.8 3 4 Processing conditions Storage conditions 37 38 EFFECT OF DIFFERENT COOKING METHODS ON RICE STARCH DIGESTIBILITY 3.1 Introduction 3.2 Materials and Methods 3.2.1 Cooking in a steamer 3.2.2 Cooking in excess boiling water 3.2.3 Cooking in an electric rice cooker 3.2.4 Cooking in a combi oven 3.2.5 Sample powder preparation 3.2.6 Proximate composition determination 3.2.7 Amylose content determination 3.2.8 Total starch (TS) determination 3.2.9 Resistant starch (RS) determination 3.2.10 In vitro kinetics of starch digestion and GI determination 3.2.11 Statistical analysis 3.3 Results and Discussion 3.3.1 Hydration behavior of rice at ambient conditions 3.3.2 End point of cooking in excess water 3.3.3 Proximate composition 3.3.4 Amylose content 3.3.5 Total starch 3.3.6 Effect of cooking on the resistant starch content 3.3.7 Effect of cooking on the in vitro starch digestibility 3.4 Conclusions 39 EFFECT OF STORAGE CONDITIONS ON RICE STARCH DIGESTIBILITY 4.1 Introduction 4.2 Materials and Methods 4.2.1 Sample powder preparation 4.2.2 Proximate composition determination 4.2.3 Amylose content determination 4.2.4 Total starch (TS) determination 4.2.5 Resistant starch (RS) determination 4.2.6 In vitro kinetics of starch digestion and GI determination 4.2.7 Statistical analysis 4.3 Results and Discussion 4.3.1 Proximate composition 66 39 41 41 42 43 43 44 44 45 46 47 49 50 51 51 52 53 54 57 57 60 65 66 68 69 70 70 71 71 71 71 72 72 xiii 4.3.2 4.3.3 4.3.4 4.4 5 6 Amylose content Total starch Effect of chilling and freezing on the resistant starch content 4.3.5 Effect of chilling and freezing on the in vitro starch digestibility Conclusions CORRELATION OF RICE STARCH DIGESTIBILITY WITH RETROGRADATION AND CRYSTALINITY 5.1 Introduction 5.2 Materials and Methods 5.2.1 Sample powder preparation 5.2.2 Pasting properties 5.2.3 Thermal properties 5.2.4 X-ray diffraction 5.2.5 Statistical analysis 5.3 Results and Discussion 5.3.1 Correlation of rice starch digestibility with amylose contant 5.3.2 Correlation of rice starch digestibility with pasting properties 5.3.3 Correlation of rice starch digestibility with thermal properties 5.3.4 Correlation of rice starch digestibility with crystallinity 5.4 Conclusions SUMMARY, GENERAL CONCLUSION AND RECOMMENDATION FOR FUTURE RESEARCH REFERENCE APPENDICES BIODATA OF STUDENT 76 78 80 82 84 85 85 87 87 87 88 89 89 90 90 92 96 100 103 104 106 115 120 xiv LIST OF TABLES Table Page 1 Prevalence and mean frequency of the top 10 daily consumed food in Malaysia 5 2 Classification of types of resistant starch (RS), food sources, and factors affecting their resistance to digestion in the colon 32 3 End point of cooking in excess water 52 4 Proximate composition of rice 55 5 Amylose, total starch and resistant starch content of rice 56 6 Recommended daily intake of dietary fibre for adults 59 7 Hydrolysis index (HI) and estimated glycemic index (GI) of rice 61 8 Pearson’s correlation coefficients for the relationship between starch digestibility with pasting properties, thermal properties and crystallinity of steamed, chilled and frozen cooked rice 91 9 Pasting properties of the raw, steamed, chilled and frozen rice 95 10 Thermal properties and crystallinity of raw, steamed, chilled and frozen rice 98 11 Proximate compositions of raw, steamed, chilled and frozen rice 115 12 Total starch (TS) and resistant starch (RS) content of raw, steamed, chilled and frozen rice 116 13 Amylose content and GI of raw, steamed, chilled and frozen rice 117 xv LIST OF FIGURES Figure Page 1 Structure of rice grain 6 2 Amylose molecule 9 3 Amylopectin molecule 10 4 Schematic view of the structure of a starch granule, with alternating amorphous and semi-crystalline zones constituting the growth rings 12 5 Cluster structure showing linear chains of amylopectin. The C chain has the only free reducing group in the molecule 17 6 Influence of hydrothermic processing on physical starch characteristics 20 7 Schematic representation of a complex of amylose with two monopalmitin molecules. 27 8 Moisture uptake in rice grains during soaking 52 9 In vitro starch hydrolysis rate of rice cooked using (a) steaming method (b) excess water (c) rice cooker (d) combi oven 63 10 Effect of chilling on the (a) protein, (b) fat and (c) ash contents of steamed rice 73 11 Effect of freezing on the (a) protein, (b) fat and (c) ash contents of steamed rice 75 12 Effect of (a) chilling and (b) freezing on the amylose contents of steamed rice 77 13 Effect of (a) chilling and (b) freezing on the total starch contents of steamed rice 79 14 Effect of (a) chilling and (b) freezing on the resistant starch contents of steamed rice 81 15 Effect of (a) chilling and (b) freezing on the glycemic index of steamed rice 83 16 RVA pasting curves of the (a) raw, (b) steamed, (c) chilled and (d) frozen rice 93 17 DSC thermograms of (a) raw and (b) steamed rice 99 18 X-ray diffractograms of (a) raw and (b) steamed rice 102 19 Appearance of (a) raw rice, (b) steamed, (c) chilled or (d) frozen steamed rice 118 xvi LIST OF ABBREVIATIONS Tg Glass transition temperature RS Resistant starch TS Total starch DS Digestible starch GT Gelatinization temperature DSC Differential scanning calorimetry XRD X-ray diffractogram ΔT Temperature range over which gelatinisation occurs GL Glycemic load GI Glycemic index NSP Non-starch polysaccharides DPn Degree of polymerization µm Micrometer g Gram hr Hour L Liter °C Degree celsius ml Milliliter mg Milligram nm Nanometer M Molarity xvii min Minute HI Hydrolysis index ΔH The enthalpy of gelatinization Tc Conclusion temperatures To Onset of gelatinisation in excess water RC Relative crystallinity xviii CHAPTER 1 INTRODUCTION Differences in nutritional properties among starchy foods are intriguing. Elucidating the role of starch qualities in nutrition requires a greater understanding of how the physicochemical characteristics of food relate to their physiological properties. The rate and extent of starch digestion is influenced by many intrinsic food factors. Starch consists of two glucose polymers, amylose and amylopectin. The physical arrangement of amylose and amylopectin in food and their interrelation with other food components (proteins, fibres, lipids, etc.) determine the physicochemical and functional properties of starch and its susceptibility to amylolytic enzymes, and thus its bioavailability. Hydrothermic food processing (i.e.panification, pastification, extrusion cooking, etc.) has a major impact on starch availability (Bornet, 1993). The arrangement of starch components changes continuously under the influence of hydrothermic parameters during both food processing and storage conditions. Starch availability is influenced by its digestibility and is characterised by high glycemic index and low resistant starch formation. 1 The glycemic index (GI) is a measure of the effects of carbohydrates on blood sugar levels. Resistant starch (RS) is starch that escapes digestion in the small intestine of healthy individuals. Resistant starch is considered the third type of dietary fiber, as it can deliver some of the benefits of insoluble fiber and some of the benefits of soluble fiber. The food processes that lead to gelatinised, highly viscous and soluble starches result in high glycemic index food (Colonna et al., 1992). Food processes that limit the swelling of starch result in low glycemic index foods. The amount and quality of the resistant starch in food can also be modulated by hydrothermic processing and four different resistant starch fractions have been identified in cereal products (Bornet, 1993). Low glycemic index and high resistant starch diets have been known to have health benefits. Various studies have demonstrated the beneficial effect of high-carbohydratelow-glycemic index diets on insulin secretion in supporting ß-cell function. Meanwhile, resistant starch can act as a fermentation substrate in the colon, similar to non-starch carbohydrates, with positive implications for the prevention of colon cancer and hypolipidemia (Englyst et al., 2003). Rice is the staple food for more than half of the world’s population. An approximately 90% of the world’s rice is produced and consumed in Asia. As the primary dietary source of carbohydrate in these population, rice plays an important role in meeting 2 energy requirement and nutrient intake. Milled rice is composed of 90% starch. The rice starch digestibility and thus nutritional properties can, therefore, be modified by hydrothermic processing and storage conditions. The simplest form of hydrothermic processing of rice that can be performed in homes is by boiling. Rice can be cooked by boiling in excess water or in a rice cooker, and by steaming. The food service industry often cooks its rice using a combi oven. Since there is an increase in popularity of ready meal, storage conditions play an important role to develop products with chilled or frozen cooked rice. Storing the cooked rice at a low temperature contributes to starch retrogradation. Retrogradation of starch is a term used for the changes that occur in gelatinized starch from an initially amorphous state to a more ordered or crystalline state. The impacts of different cooking methods and storage conditions on rice starch digestibility, however, have not been evaluated. Therefore, the objective of the study reported here was to determine the cooking method and storage condition that will reduce glycemic index and increase resistant starch content of rice. The specific objectives of the study are; 1. To determine the effect of different cooking methods on formation of resistant starch and reduction of glycemic index in rice 2. To determine the effect of chilling and freezing on formation of resistant starch and reduction of glycemic index in rice 3. To evaluate the correlation of crystallization and retrogradation on rice starch digestibility 3 CHAPTER 2 LITERATURE REVIEW 2.1 Rice Rice is one of the most important cereals in the world. Most people in Asia, tropical and subtropical countries use rice as a major staple food. As much as 80% of the daily caloric intake of people in the Asian countries is derived from rice. A small amount of the rice crop is used to make ingredients for processed foods and as feed, but the bulk is consumed as cooked rice. Cooked rice is consumed by 97% of Malaysian twice daily and the average amount eaten was 2½ plates per day (Table 1). Rice grains (Figure 1) are naturally surrounded by a loose, inedible husk. To obtain white rice, the embryo and several layers of bran are removed by milling to improve palatability and keeping qualities. Milling, however, results in a disproportionate loss of lipid, protein, fibre, reducing sugars and total sugars, ash and minor components including vitamins, free amino acids and free fatty acids (Park et al., 2001). On the other hand, an available carbohydrate, mainly starch, is high in milled rice at about 90% of the dry matter. Protein and lipid content are also significant in the milled rice. 4 Table 1: Prevalence and mean frequency of the top 10 daily consumed food in Malaysia Type of food Prevalence who answered daily consumption (%) Mean frequency per day Total amount consumed daily Cooked rice 97.15 2.0 2½ plates (294.06g) Marine fish 40.78 1.61 1½ medium (100.27g) Green leafy vegetable 39.89 1.47 1 cup (93.26g) Sweetened condensed milk 35.55 1.57 3 teaspoons (50.93g) Powdered milk 17.13 1.41 3 teaspoons (20.61g) Bread 17.11 1.24 3 slices (96.48g) Biscuit 16.30 1.25 5 pieces (55.66g) Local “kuih” 16.30 1.25 2 pieces (62.27g) Chicken egg 12.06 1.15 1 whole medium (71.84g) “Ikan bilis” 11.94 1.24 2 teaspoons (15.45g) (Source: Malaysia’s Health 2006, Malaysian Ministry of Health) 5 Figure 1. Structure of rice grain (Source: Juliano, 1984) There are many methods to cook the rice but most methods are subtle variation of two basic techniques: (i) cooking in large amounts of water, and drained (and sometimes rinsed) – commonly referred to as the Excess or American method; or (ii) cooking rinsed rice in a measured amount (often twice the volume of rice) of water which is absorbed into the rice – commonly known as the Pilaf or Oriental method (Daniel et al., 2001). Besides these cooking methods, the rice is also commonly cooked or prepared at home by steaming using a steamer. The food service industry or catering professionals prefer to use a combi oven to cook the rice as they prepare cooked rice in a very large quantity. The cooking methods that are performed in homes or at catering industries are 6