Ingredient Functionality & Characterization David Julian McClements Biopolymers and Colloids Laboratory Department of Food Science • Emulsifiers • Texture Modifiers – Thickening Agents – Gelling Agents • Weighting Agents Emulsifiers: Major Functions in Food Emulsions Functional Properties • Emulsion Formation • Emulsion Stabilization • Modification of Interfacial Properties • Modification of Crystallization • Interaction with Biopolymers Displacement – Crystal modification – Polymer interaction – ice cream manufacture margarine manufacture Bread manufacture Emulsifiers: Formation Emulsifier Factors Affecting Formation: • Concentration and Surface Load Microfluidics – sufficient present to cover all surfaces formed • Adsorption Kinetics – adsorbs fast enough to form protective coating • Interfacial Tension – lower γ gives smaller droplets • Protective Coating – Emulsifier layer should protect against aggregation Movement Incorporation Film Formation − to surface − In surface − − − − − − − − − − Emulsifiers: Stability Emulsifier Factors Affecting Stability: • Colloidal Interactions - Interfacial Thickness, Charge & Hydrophobicity • Resistance of membrane to disruption - Interfacial rheology Hydrophobicity Charge + + + + Thickness Environmental Responsiveness: pH, I, T Common Food Emulsifiers Small Molecule Surfactants – Tweens, Spans, fatty acids, DATEM – Sucrose esters, polyglycerol esters, monoglycerides Phospholipids – Egg, soybean, milk − − Biopolymers − − − − − − − – whey, casein, egg, gelatin, soy – modified starch, gum arabic, modified cellulose Emulsifier Applications in Foods Salad Dressings – Tweens Soft Drinks – PGA – Gum Arabic – Proteins – Modified Starch Mayonnaise – Proteins Ice Cream – Phospholipids – Proteins – Yolk particles – Phospholipids Sauces & Dips – (Surfactants) – Mono/diglycerides Milk & Cream Nutritional Beverages – Proteins – Proteins – Phospholipids – Phospholipids Specifying Emulsifier Functionality Choosing the most appropriate emulsifier Physicochemical Factors • Emulsion type (O/W or W/O) • Minimum amount needed ( Cmin ) • Minimum droplet size achievable ( rmin ) • Ingredient compatibility • Sensitivity to environmental stresses (pH, I, T) Practical Factors • Ease of utilization • Reliability/Consistency of source • Long term stability • Sensory properties Currently no standard method of Economic & Marketing Factors specifying • Cost emulsifier • Label friendliness functionality Surfactants: Molecular Structure Head Group − + • Electrical charge (non-ionic/ionic) • Chemical groups • Length and cross-section Tail Group • Number of chains • Length of chains − − − • Saturation of chains Industrial Manufacture of Surfactants Tween 20 Structure: ChemBlink Commercial surfactants are actually a complex mixture of many different molecules Danisco Self Assembly of Surfactants Micelle Non-spherical Micelle Reverse Micelle Vesicle Surfactants can form a variety of structures, with different functional properties, depending on their molecular structure Classification of Surfactants • Bancroft rule – The phase in which the surfactant is most soluble (dispersible) forms the continuous phase of emulsion • HLB number – The ability of a surfactant to stabilize an emulsion depends on balance of hydrophilic to lipophilic groups HLB Classification Scheme Hydrophobic Group Hydrophilic Group Group Number Group Number − + -CH- 0.475 -SO 4 Na 38.7 -COO −H+ 21.2 -CH 2 - 0.475 Sorbitan ring 6.8 -CH 3 0.475 -COOH 2.1 O − + CH 3(CH 2)11 -O-S-O Na O HLB = 7 + Σ(hydrophilic groups) - Σ(lipophilic groups) HLB Numbers of Some Food Surfactants Surfactant Name HLB Number Sodium lauryl sulfate 40 Hydrophilic Potassium Oleate 20 Tween 20 15 Decaglycerol monooleate 14 Ethoxylated monoglyceride 13 Tween 20 DATEM 8 Soy lecithin 8 Calcium stearoyl lactylate 5.1 Lipophilic Glycerol monoleate 3.4 Sorbitan trioleate 1.8 Oleic acid 1.0 Oleic acid HLB Classification Scheme HLB Number Solubility Emulsion Type Very Low (<3) Oil Unstable Low (3-6) Oil W/O Medium (6-8) Oil&Water Unstable High (8-18) Water O/W Very High (>18) Water Unstable Benefits and Limitations of Classification Schemes Benefits • Provide information on emulsion type (O/W or W/O) • Enable rational selection of mixed surfactant systems Limitations • Not applicable to biopolymers • No insight into: • Minimum droplet size that can be created • Amount of emulsifier needed • Stability of emulsion to environmental stresses Testing Emulsifier Efficiency: Fundamental Measurements • Surface Load ( ΓΓΓ) – mg/m 2 – Maximum surface area that can be covered per gram • Binding Affinity (c 1/2 ) – Amount of emulsifier required to reach saturation www.dataphysics.de • Maximum Surface Pressure ( ΠΠΠSat ) 40 35 ) – mN/m 2 30 – Minimum droplet size achievable 25 c 20 1/2 π 15 ∞ (mJ/m • Adsorption Kinetics 10 Π Π Π Π − ∆c /δ t (measured under dynamic conditions) 5 i 0 – Minimum droplet size achievable 0.0001 0.01 1 [Emulsifier] Testing Emulsifier Efficiency: Practical Tests for Emulsion Formation 5 C min = minimum amount of m) 4 µ µ µ µ emulsifier to homogenize fixed 3 C quantity of oil min r 2 min = minimum achievable droplet size 1 Mean( Radius 0 rmin 0 2 4 6 8 10 Emulsifier Concentration (wt%) Depends on: • Solution Conditions • Mechanical Device Factors Affecting Emulsion Formation C r min & min Depend on: • Adsorption Rate • Interfacial Tension Reduction • Packing Efficiency • Membrane Protective Effect High Cmin Low Cmin Testing Emulsifier Efficiency Practical Tests for Emulsion Stability Emulsion Emulsion characterization preparation Test or Initial • Droplet Size Emulsion • Droplet charge • Rheology • Creaming Long term storage, accelerated or environmental stress tests Testing Emulsifier Efficiency Stability to Environmental Stress Minerals and pH • pH 2 to 8 • NaCl 0 – 1 M, CaCl 2 0 – 100 mM Thermal Processing • 30-90 ºC for 30 minutes Freeze Thaw Cycling -20ºC / +20ºC Dehydration • Spray drying or Freeze drying Mechanical Agitation • Shaking, Stirring Stable Unstable Stability to Environmental Stress Influence of Emulsifier Type - - - - - - - • Thickness - - - • Charge - - - - • Hydrophobicity - - - • Rigidity - - - - - Emulsifier Type Stabilizing Environmental Mechanism Sensitivity Proteins Electrostatic, Steric pH, I, T Polysaccharides Steric, Electrostatic - Surfactants • Non-ionic Steric, (Electrostatic) T • Ionic Electrostatic, Steric pH, I, T Stability to Environmental Stress Influence of Emulsifier Type 6 5 WPI 4 GA MS m) 3 µ µ µ µ ( 2 Mean Diameter 1 0 3 4 5 6 7 pH WPI stabilized emulsions are sensitive to pH, minerals, temperature Comparison of Physiochemical Properties of Emulsifiers Emulsifier Natural Adsorption Interfacial Amount Environmental Type Rate Tension Needed Sensitivity Surfactant No Rapid Low Low Freezing, Drying - Non-ionic Heating Surfactant No Rapid Low Low Freezing, Drying - Ionic (Yes) Heating, I Protein Yes Medium Medium Low / Freezing, Drying Medium Heating, I, pH Polysaccharide Yes Slow High High (Freezing, Drying) (No) The choice of an appropriate emulsifier depends on many factors Selecting an Emulsifier • Establish Operating Environment – pH, I, T, Mechanical stress, Water content • Establish Labeling Requirements – Natural? Kosher? Vegan? GMO? etc • Establish Maximum Cost-in-Use of Emulsifier • Identify Available Emulsifiers – Surfactants, Phospholipids, Biopolymers • Carry Out Product Tests – Particle Size, Amount Needed, Stability, Ease of Use Texture Modifiers Functional Properties: • Texture – Modify the overall textural properties and mouthfeel of the system • Stability – Retard movement of droplets and other particulate matter Mode of Operation: • Thickening Agents: – increase viscosity because of their large molecular dimensions • Gelling Agents – form gels because of their ability to form intermolecular cross-links −−−S−−−S−−− Thickening & Gelling Agents Typical Food Ingredients Polysaccharides – Agar, Alginic acid, Alginate, Carrageenan, Guar gum, Gellan gum, Curdlan, Modified Celluloses, Modified starches, Pectins, Xanthan Proteins – Gelatin, Whey, Casein, Soy, Egg Sugars & Polyols – Glycerol, Sorbitol, Lactitol, Mannitol – Trehalose Xanthan Gum: IFR, UK Thickening Agents Molecular Characteristics Conformation Random Coil Globular Rigid Rod Charge Sign Molecular Weight −−− + + + −−− −−− −−− + −−− + Low −−− + High Negative Positive Branching Charge Density + + + + + + + + Unbranched Branched Low High Biopolymer Solution Rheology Influence of Particle Concentration No Biopolymer Greater Energy Biopolymer Dissipation • Biopolymers Increase Fluid Viscosity η = η0 (1 + 2.5 φ) Thickening Agents Quantifying their Functionality Trapped Water Rotating Polymer η = η0 (1 + 2.5 Rvφ) Factors Influencing RV: Volume Ratio: • Molecular Weight • Degree of Branching Vsphere • Electrical Charge Density RV = • Conformation V polymer • Interactions Thickening Agents Influence on Solution Rheology Semi-Dilute 10 Dilute Concentrated Relative Viscosity c* 1 0.01 0.1 1 10 Concentration (kg m -3 ) -3 c* ≈ 530 / Rv (kg m ) Thickening Agents Influence of Structure on Rheology 10 Rv 1 100 1000 5000 Relative Viscosity 1 0.01 0.1 1 10 100 Concentration (kg m -3 ) Thickening Agents: Effective Volumes Proteins MW [η][η][η] RV (kDa) (g/mL) Lysozyme 14.1 2.7 1.7 Hemoglobin 68 3.6 2.3 Collagen 345 1270 810 Gelatin 383 69 44 -1 η Rv ≈ 0.64 × [η] (in g mL ) C * Adapted from Peter Wolf (2005) Thickening Agents: Effective Volumes Polysaccharides MW [η][η][η] RV (kDa) (g/mL) Alginate 100 270 173 300 550 350 Guar 100 62 40 200 120 77 LBG 100 71 45 300 170 109 Pectin 50 110