Stability of Food Emulsions (2)

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1 Stability of Food Emulsions (2) David Julian McClements Biopolymers and Colloids Laboratory Department of Food Science

2 Droplet Coalescence Oiling Off Coalescence Aggregation due to fusing together of two or more individual droplets to form a bigger droplet

3 Droplet Coalescence Oil A few nms Water Oil Droplet coalescence depends on precise molecular details of droplet interfaces - difficult to predict!

4 Factors Influencing Droplet Coalescence Relative magnitude of forces between droplets Resistance of interface to disruption Duration of contact between droplets Shearing and tearing of interfaces

5 Evolution of Coalescence Homogeneous Coalescence Coalescence rate independent of droplet size Heterogeneous Coalescence Coalescence rate increases with droplet size

6 Factors Influencing Droplet Coalescence: Ingredient Interactions Without chitosan (1-month old emulsion) 0.01 wt. % chitosan (the same magnification)

7 Factors Influencing Droplet Coalescence: Freezing & Thawing 0 wt% sucrose 20 wt% sucrose Hydrogenated palm oil-in-water emulsions stabilized by WPI (-40 ºC/40ºC) sucrose modifies ice crystal formation

8 Factors Influencing Droplet Coalescence: Dehydration 0 wt% sucrose 20 wt% sucrose Oil-in-water emulsions stabilized subjected to freeze-drying

9 Droplet Coalescence: Influence of Interfacial Membranes 1º Highly Unstable 2º Stable to Coalescence Only 3º Stable to Coalescence, Flocculation & Creaming % Coalescence º -40º 1º 2º 3º Emulsion 3 Cycles: -10ºC/30ºC

10 Features of Coalescence φ (%) hours 24 hours Diameter (µm) Bimodal PSD Evolution Oiling off

11 Strategies to Reduce Coalescence Principle (1). Reduce Attraction (2). Increase Repulsion (3). Decrease droplet contact (4). Increase resistance of membrane to rupture Method Avoid depletion Avoid bridging Avoid hydrophobicity Alter ph or I (E/S) Increase thickness (S) Add thickening or gelling agent Use polymeric emulsifier

12 Measurement of Coalescence Techniques & Protocols Instrumental Techniques Microscopy Particle Sizing Creaming stability/oiling Off Experimental Protocols Storage Tests Accelerated Storage Tests Environmental Stress Tests

13 Characterization of Coalescence: Microscopy Methods Particle Size Distribution, Flocculation vs. Coalescence (Image Analysis Software)

Characterization of Coalescence: Particle Size Analysis 14 Volume% 12 10 8 6 4 37 0-20 37 ºC : All liquid -0 ºC: Fat

14 Characterization of Coalescence: Particle Size Analysis 14 Volume% ºC : All liquid -0 ºC: Fat crystallizes -20 ºC: Water crystallizes Particle Diameter (µm) Potential Problems: Sampling, Distinguishing from flocculation

15 Characterization of Coalescence: Distinguishing from Flocculation Volume% Particle Diameter (µm) Emulsion to Be Tested Volume% Particle Diameter (µm) Initially Flocculated Add Deflocculant (e.g., surfactant) Volume% Particle Diameter (µm) Initially Coalesced

16 Measurement of Oiling Off Stable Emulsion Coalescence Oiling Off Extensive droplet coalescence can lead to the formation of a thin layer of oil on top of a product (sometimes with little change in PSD of bulk emulsion)

17 Oiling Off : Solvent Extraction Method Petroleum ether shake Emulsion Measure amount of oil that can be extracted by an organic solvent

18 Oiling Off : Dye Dilution Method Add Dye Mix Centrifuge Absorbance Emulsion Cuvette Measure dilution of dye solution by free oil

Characterization of Coalescence: Coalescence/Oiling-off by DSC 0 Fat Crystallization -10 0 10 20 30 40-0.05 0 Water & Fat Crystallization -10 0 10 20 30 40-0.

19 Characterization of Coalescence: Coalescence/Oiling-off by DSC 0 Fat Crystallization Water & Fat Crystallization Heat Flow Heat Flow Temperature (ºC) Temperature (ºC) Fat crystallization behavior of oil-in-water emulsions

20 Characterization of Coalescence: Coalescence/Oiling-off by DSC 100 Oiling Off (%) Water Crystal n Fat Crystal n Tween 20 Casein Temperature (ºC)

21 Characterization of Coalescence: Centrifugation Methods Centrifuge Time Speed Oil Cream Serum H Released H C P CR OSM g = ρ ( ) V Total V Released A

22 Partial Coalescence Aggregation Fusion Clumping of partially crystalline droplets due to penetration of fat crystal from one droplet into another droplet

23 SEM Images of Partial Coalescence 40ºC (Liquid droplets) 0ºC (Partially Crystalline Droplets) O/W Emulsions viewed by SEM (John Coupland, Penn State)

24 Influence of Droplet SFC on Partial Coalescence E C (%) SFC (%)

25 Influence of Interfacial Membrane on Partial Coalescence Thin Membrane -Prone to PC - e.g., Tween 20 Thick Membrane -Resistant to PC - e.g., casein Oiling Off (%) Tween 20 Casein Temperature (ºC)

26 Case Study: Ice Cream Manufacture Add Surfactant & Age Fat globules covered with thick milk protein membrane Fat globules covered with thin surfactant membrane

27 Partial Coalescence in Ice Cream Partially coalesced droplets in continuous phase Air bubble Partially coalesced droplets around air bubble Ice cream viewed by cryo-sem (Douglas Goff. Guelph)

28 Methods of Controlling Partial Coalescence Aggregation Fusion Control droplet crystallization (SFC) Control thickness & viscoelasticity of membranes Control droplet-droplet interactions Control droplet collision frequency or contact time

29 Measurement of Partial Coalescence: Techniques & Protocols Instrumental Techniques Microscopy Particle Sizing Creaming stability/oiling Off Solid fat content versus temperature Experimental Protocols Storage Tests Accelerated Storage Tests Environmental Stress Tests

30 Ostwald Ripening Growth of large droplets at the expense of small droplets due to molecular diffusion of oil molecules through the aqueous phase driven by differences in Laplace pressure

31 Ostwald Ripening Time Growth of large droplets at the expense of small droplets due to molecular diffusion of oil molecules through the aqueous phase driven by differences in Laplace pressure

32 Features of Ostwald Ripening φ (%) hours 24 hours 48 hours Diameter (µm) Monomodal PSD Evolution d 3 proportional to time d 3 (µm 3 ) Time (hours)

33 Influence of Oil Type on Ostwald Ripening 4 d 3 (µm 3 ) Decane Hexadecane Time (hours)

34 Food Emulsions Susceptible to Ostwald Ripening High Susceptibility Emulsions containing oils with high water solubility, e.g., flavor oils, essential oils, SCFA Emulsions containing alcohol in the aqueous phase, e.g., cream liqueurs Low Susceptibility Emulsions containing oils with low water solubility, e.g., TAGS

35 Ostwald Ripening δ<r> 3 / δt = 8 γ V m S D / 9 R T Methods of Retarding Ostwald Ripening: Reduce oil solubility in water Reduce interfacial tension Incorporate low solubility oil into droplets Use membrane resistant to deformation

36 Measurement of Partial Coalescence: Techniques & Protocols Instrumental Techniques Microscopy Particle Sizing Experimental Protocols Storage Tests Accelerated Storage Tests Environmental Stress Tests

37 Conclusions Many different physicochemical processes contribute to the instability of food emulsions For a particular food product it is necessary to identify the dominant instability mechanism Emulsion science can then be used to improve food emulsion stability

Fat Crystals Influence Methylcellulose Stabilization of Lipid Emulsions

DOI 10.1007/s11746-016-2933-3 SHORT COMMUNICATION Fat Crystals Influence Methylcellulose Stabilization of Lipid Emulsions A. E. Thiel 1 R. W. Hartel 1 P. T. Spicer 2 Received: 18 August 2016 / Revised: