Gelation and Gel Properties of Gellan Gum and Xyloglucan Yoko Nitta 2005 Department of Food and Human Health Sciences Graduate School of Human Life Science Osaka City University ジェランガムとキシログルカンの ゲル化およびゲル特性 大阪市立大学大学院 生活科学研究科 食・健康科学講座 新田 陽子 2005 年 Contents ABBREVIATIONS AND SYMBOLS 1. INTRODUCTION Use of polysaccharides in foods 1 Objective and outline of this thesis 8 Overview of gellan gum 10 Overview of Tamarind seed xyloglucan 14 2. METHODS Rheology 19 Rheological properties of polysaccharide solutions 30 Determination of gel point by rheology 31 Thermal analysis: Differential scanning calorimetry (DSC) 32 Conformational transition of polysaccharides 35 Sol-gel transition of polysaccharide 35 Circular dichroism (CD) 36 Conformational transition of polysaccharides 41 3. GELATION AND GEL PROPERTIES OF GELLAN GUM The helix-coil transition of gellan in gels Introduction 43 Experimental 43 Results and discussion 45 Conclusion 49 The sol-gel transition of gellan affected by thermal history Introduction 50 Experimental 51 Results and discussion 52 Conclusion 59 4. THE EFFECT OF SURFACTANT, SALT, AND SUGAR ON GELATION AND GEL PROPERTIES OF GELLAN GUM The effect of SDS on the gelation of gellan Introduction 61 Experimental 62 Results and discussion 63 Conclusion 69 The effect of the immersion into salt solution on gel properties of gellan Introduction 70 Experimental 71 Results and discussion 71 Conclusion 76 The effect of sugars on gel properties of gellan Introduction 77 Experimental 77 Results and discussion 78 Conclusion 80 Appendix 80 5. GELATION OF XYLOGLUCAN BY ADDITION OF SMALL MOLECULES IN FOODS Gelation of tamarind seed xyloglucan by addition of epigallocatechin gallate Introduction 89 Experimental 91 Results and discussion 92 Conclusion 108 6. GELATION OF XYLOGLUCAN BY ADDITION OF MACROMOLECULES IN FOODS Gelation of tamarind seed xyloglucan by mixing with gellan Introduction 109 Experimental 110 Results and discussion 111 Conclusion 126 The effect of salts on the gelation of tamarind seed xyloglucan/gellan mixture Introduction 127 Experimental 127 Results and discussion 128 Conclusion 134 REFERENCES 135 SUMMARY 145 CONCLUDING REMARKS 149 ACKNOWLEDGEMENTS 151 LIST OF PUBLICATION 153 Abbreviations and symbols CD circular dichroism DSC differential scanning calorimetry EGCG epigallocatechin gallate KGM konjac glucomannan NMR nuclear magnetic resonance NOESY nuclear Overhauser effect spectroscopy Na-G sodium salt form of gellan SDS sodium dodecyl sulfate TSX tamarind seed xyloglucan, tamarind xyloglucan E Young’s modulus Ea activation energy E′ storage Young’s modulus E″ loss Young’s modulus G shear modulus G* complex shear modulus G′ storage shear modulus G″ loss shear modulus Mn number-average molecular weight Mw weight-average molecular weight Tc cloud point Tg gelation point Tm peak temperature, mid-point transition temperature t time tanδ mechanical loss tangent γ shear strain γ0 amplitude of shear strain γ shear strain rate ΔH enthalpy change Ψ specific ellipticity [Ψ]202 specific ellipticity at 202nm ε strain η viscosity θ ellipticity θ202 ellipticity at 202nm σ stress σ0 amplitude of stress ω angular frequency 1 Introduction USE OF POLYSACCHARIDES IN FOODS Polysaccharides are widely used in food industry. They are used as a texture modifier to enhance or standardize the eating quality of a product by thickening and gelling, by stabilizing emulsion or suspensions, and by reducing the undesired defect of water release (syneresis) in some processed foods. Besides texture modifier, some of polysaccharides except starch are used as food supplement of a dietary fiber, the functional component that provides a health benefit. Texture modifier So many food polysaccharides are used as a texture modifier. The commercially important polysaccharides used as a texture modifier and their origin are given in Table1.1. Texture is defined by International Organization for Standardization (ISO) as ‘all the rheological and structural (geometrical and surface) attributes of a food product perceptible by means of mechanical, tactile and, where appropriate, visual and auditory receptors’. Since addition of most polysaccharide changes rheological properties, for example, increases the viscosity of a liquid, polysaccharides are used as a thickener to control texture and organoleptic characteristics (like ‘mouth feel’ and - 1 - - 2 - Chapter 1 Introduction Table 1.1 Source of commercially important polysaccharides Botanical Trees cellulose Tree gum exudates gum arabic, gum karaya, gum ghatti, gum tragacanth Plants starch, pectin, cellulose Seeds guar gum, locust bean gum, tara gum, tamarind gum Tubers konjac mannnan Algal Red seaweeds agar, carrageenan Brown seaweeds Alginate Microbial xanthan gum, curdlan, dextran, gellan gum, cellulose Animal Chitosan (Williams and Phillips, 2000) ‘body’). Polysaccharides are also used to control texture as stabilizer and emulsifier (Lapasin and Pricl, 1995). Many food products are emulsions; a mixture of two immiscible liquids in which one phase is dispersed throughout the other as small, isolated droplets. Polysaccharides can assist in obtaining a fine dispersion and in maintaining the homogenous mixture. Foams are related to emulsions, being a dispersion of gas (or gases) in a liquid (or solid), and polysaccharides can be conventionally used to modify the interfacial tension and obtain a stable, firm foam. Suspending agents are those substances that are used to uniformly disperse solid particles through a liquid phase, and the polysaccharides help in preventing particle setting. The principal use of polysaccharides is as thickener and stabilizer in Japanese food industry, and thus there are so many polysaccharides approved and used as thickener and stabilizer in Japan as listed in Table 1.2. Use of polysaccharides in foods - 3 - Polysaccharides are also used to modify texture of foods by preventing syneresis (Innden and Yokawa, 1999). Syneresis is a phenomenon in which water containing dissolved components is released from a gel network. In most cases, occurrence of syneresis is undesirable for gel-like food products. It can be prevented by incorporating ingredients into the gel that have water binding properties. Polysaccharides are commonly used to help retain water within the gel network. Since some polysaccharides form thermoreversible or thermoirreversible gels at low concentrations (~1%), polysaccharides are added into foods as a gelling agent (Lapasin and Pricl, 1995; Innden and Yokawa, 1999). The gels resulting from different polysaccharides will present distinct structural forms and textures (from smooth to chewy) and thus polysaccharide gels are employed in a variety of food types. The principal gelling agents are listed in Table1.3. Japan is a typical country where various types of polysaccharide gels are eaten, such as ‘kuzukiri’ (kuzu starch gel), ‘mizuyokan’ (red bean-agar jelly dessert), ‘konnyaku’ (konjac glucomannan gel), ‘natadecoco’ (fermentation-derived cellulose gel), jams (pectin gel) and dessert jellies. Japanese tends to be perceptive of subtle difference of texture among similar foods. Product developers are required to create food products with new texture. Addition of polysaccharide to food products is one way to create new texture. In recent years, with increasing the interest about health, awareness of the link between health and texture is growing. Texture, in particular, plays an important role for many elder adults who are malnourished because of mental and/or oral problems. Texture modification of conventional foods is often appropriate for these problems and is necessary when dysphagia (chewing or swallowing problems) is present. Taking texture into consideration, the Ministry of Health and Welfare in Japan made a standard of functional foods for the elderly. For older adults diet, texture modification using polysaccharides is getting popular. - 4 - Chapter 1 Introduction Table 1.2 Thickening and stabilizing agent approved in Japan. Only thickeners consisting of polysaccharides were listed. Aeromonas gum Agrobacterium succinoglycan Alginic aid Almond gum, Cedo gum Aloe extract Aloe vera extract Arabino galactan Artemisia sphaerocephala seed gum, Artemisia seed gum Aureobasidium cultured solution Azotobacter vinelandii gum Carob bean gum, Locust bean gum Carrageenan, semirefined carrageenan, processed eucheuma algae, processed red algae, purified carrageenan, refined carrageenan, powdered red algae Cassia gum Chitin Chitosan Curdlan Demmar resin Dextran Elemi resin Enterobacter gum Enterobacter simanus gum Enzymatically hydrolyzed guar gum Erwinia mitsuensis gum Fermentation-derived cellulose Fukuronori extract Furcellaran Gellan gum Glucosamine Guar gum Gum Arabic, Arabic gum, Acacia gum Gum ghatti Karaya gum Kelp extract The Director-general of Environmental Health Bureau Notice, No. 56 (published by the Ministry of Health and Welfare on May 23, 1996) Use of polysaccharides in foods - 5 - Table 1.2 Continued Konjac extract Gum ghatti Karaya gum Kelp extract Konjac extract Linseed gum, Linseed extract Levan Macrophomopsis gum Mirofibrillated cellulose Oligoglucosamine Peach gum Pectin Psyllium seed gum Pullulan Rhamsan gum Sclero gum, Scleroglucan Seaweed cellulose Sesbania gum Soybean polysaccharides Sweetpotato cellulose Tamarind seed gum Tara gum Tororoaoi Tragacanth gum Triacanthos gum Welan gum Xanthan gum Yeast cell wall The Director-general of Environmental Health Bureau Notice, No. 56 (published by the Ministry of Health and Welfare on May 23, 1996) - 6 -