Published on January 9, 2008
GLASS TRANSITION RELATION TO STICKINESS DURING SPRAY DRYING: GLASS TRANSITION RELATION TO STICKINESS DURING SPRAY DRYING Bhesh Bhandari School of Land and Food Sciences University of Queensland St. Lucia Queensland 4072 AUSTRALIA Three states of matter: Three states of matter Gas Liquid Solid Molecular mobility Solid state: Solid state Amorphous Crystalline Amorphous solid: Amorphous solid Other terminologies Glass Vitrified solid Fourth state of matter Structure of a liquid but property of a solid Amorphous solid (Glass): Amorphous solid (Glass) Glass is a liquid molecular motion brought to halt due to cooling f(T) cooling Liquid m<107Pa.s Solid m>1012Pa.s Glass transition heating Thermal response- glass and crystal: Thermal response- glass and crystal Physical changes during transition: Physical changes during transition Solid Liquid Viscosity Thermal expansion Specific heat Dielectric constant Water mobility Glass transition region Changes during transition: Changes during transition m Pa.s T Tg Cp 1012 107 T Tg T Expansion coefficient Tg Slide9: Tg of some food materials Slide10: Tg as a function of water content Glass formation during food processing operations : Glass formation during food processing operations Crystalline solid Semi-crystalline solid Liquid Grinding, Extrusion cooking Thermal melting, Gelatinisation Rapid drying Rapid cooling below Tg Freezing Amorphous solid (GLASS) Physical states of various powders: Physical states of various powders Crystalline Refined sugars, organic acids, polyols, salts, … Amorphous Milk and some whey powders, instant coffee and tea protein powders coffee whitener cocoa powder Semi-crystalline (mixed) Whey powders (lactose crystals embedded in glassy matrix), starch powders (semi-crystalline regions) Icing sugar Amorphous powder production during spray drying: Amorphous powder production during spray drying Liquid product Atomisation Liquid surface Dehydration I - upper part of drier Plastic surface Plastic sticky surface Tsurface>>Tg m<107 Pa.s Dehydration II - middle part of drier Non-sticky surface Tsurface<Tg+20oC m>107 Pa.s Amorphous powder (Glassy state) Dehydration III - lower part of drier Stickiness profile of a drying droplet: Stickiness profile of a drying droplet Drying parameters Temperature Air dynamics Drier design Droplet surface property Product property (Tg) STICKY PROPERTY Slide15: Droplet surface property Development of an in-situ stickiness measuring device Slide16: Schematic diagram of stickiness in-situ testing device Initial drop radius: 3.41 mm Probe withdrawal speed: 30 mm/min Contact time: 2-5 seconds Slide17: FAILURE MODES (while withdrawing the probe from the drop surface) Cohesive failure weak cohesive strength- strong adhesive strength Cohesive-adhesive failure Cohesive or adhesive strength dominance Adhesive failure weak adhesive strength (strong cohesive strength) Slide18: Cohesive failure High H2O Mixed failure Intermediate H2O Adhesive failure Intermediate H2O Nonadhesion Low H2O Slide19: SURFACE STICKINESS OF DROPS OF FRUCTOSE-MALTODEXTRIN MIXTURES (63oC) 100%malto 20%Fruc 50%Fruc 80%Fruc 100%Fruc Slide20: Moisture Temperature >1012Pa.s <107Pa.s Stickiness and glass transition curves during spray drying Common approach to minimise stickiness during spray drying: Common approach to minimise stickiness during spray drying [Products exhibiting stickiness during spray drying Sugar- and acid-rich foods (fruit juices, honey etc..) High fat foods ] Addition of drying aids such as maltodextrin Starch hydrolysis product Widely used in food formulations Bland in taste Raise the glass transition temperature How much of maltodextrin is required?: How much of maltodextrin is required? Conventional method trial and error- expensive and time consuming Glass transition approach Composition dependent Major components of sticky products Sugars- fructose, glucose, sucrose Organic acids- citric acid, tartaric acid, malic acid Prediction models Food components+maltodextrin system Prediction models- Gordon and Taylor: Prediction models- Gordon and Taylor Tg = glass transition temperature of the mixture w1, w2 = mass fraction of solute and water respectively Tg1 and Tg2 = Tg (K) of solute and water (138K); k = constant applicable to binary systems Couchman and Karasz equation : Couchman and Karasz equation wi=fraction of component i Tgi=Glass transition temperature of component i DCpi=specific heat change of component i Works well with ideal system and anhydrous mixtures Poor prediction with aqueous and higher than ternary systems Or Simplified semi-empirical equationTruong et al. (2002) : Simplified semi-empirical equation Truong et al. (2002) XS, XG and XF = mass fractions of sucrose, glucose and fructose, respectively KSG, KSF and KGF=k values in Gordon-Taylor equation for binary mixtures of sucrose-glucose, sucrose-fructose and glucose-fructose, respectively. Conclusion: Conclusion Stickiness in spray drying is related to glass transition temperature Surface property of droplet drying parameters (temperature, humidity, air dynamics) Control of stickiness manipulation of the Tg by using an appropriate model
Molecular Motion in Glassy Systems Wageningen University and Research Centre . Molecular Motion in Glassy Systems . Marcus A.
drying and dehydration - PPT slides, PowerPoint presentations for download - Drying and Dehydration. Removes water. Occurs under natural conditions in the ...