Cream

1
Cream
2

• Fat globules
• Size distribution
• Number of particles with a certain diameter
• dvs Volume of dispersed fat/surface area 3.4 ?m
• Shape of size distribution constant
• Surface layer
• Protein glycoproteins, enzymes
• Phospholipids
• Cerebrosides
• Cholesterol
• Monoglycerides, free fatty acids
• Cu, Fe, carotenoids
• Water
• 10-20 nm thickness, negative charge (-12 mV)
• 1-1.5 mN/m interfacial tension

3

• Coalesence decreases surface area, release of
  membrane material
• Air contact, loss of part of membrane
• Cooling, migration of membrane material to
  plasma, 20 of phospholipids, some protein,
  xanthine oxidase, Cu
• Adsorption of cryoglobulins (immunoglobulin M,
  lipoproteins)
• If lose membrane material, proteins adsorb onto
  surface

4

• Crystallization in a globule
• Network formation
• Variation with respect to composition
• Summer vs winter
• triglycerides
• Size differences

5

• Emulsion stability
• Creaming
• Flocculation and coalescence
• Aggregates
• Floccules spontaneous
• but electrostatic and steric repulsions on the
  membrane
• Agglutination
• Clusters two globules share part of the membrane
  (micellar casein), homogenization clusters,
  heat-coagulated clusters
• Granules interaction of fat, network of fat
  crystals, rigidity

6
Coalescence

• Interaction between two droplets
• True coalescence Film between the globules is
  ruptured and globules can coalesce into one
  droplet
• Large globules formed from small globules
• Unhomogenized milk at sterilization temperature
• Partial coalescence If globules contain fat
  crystals, film can be pierced by crystals
  sticking out of the globule
• Large, irregularly shaped granules
• Easily occur if solid fat present

7
Factors affecting partial coalescence

• Stirring
• Beating in of air
• Fat content
• Solid fat content
• Too much, liquid fat is entrapped in crystals and
  no adhesion between the globules
• Size
• The smaller the more stable globules
• Larger crystals can pierce easily
• Surface layer
• Protein more stable, homogenization
• Surfactants less stable

8

• Disruption of fat globules
• Beating in of air
• Intense turbulence by homogenization
• Shearing stress exerted on the globule of
  diameter d should exceed the resistance to
  deformation as caused by Laplace pressure (4?/d)

9
Interaction with air bubbles

• When a milk fat globule contact with air-water
  interface, membrane material and part of its
  contents spread over the interface
• If no other surface-active substance especially
  proteins are not adsorbed onto the interface
• Globules can attach to the interface and to an
  air bubble
• Globule can be in contact with an air bubble or
  between the bubbles
• Electrostatic and steric repulsions prevent
  rupture of the interface
• If solid fat crystals present, they can pierce
  the interface and globule can contact air, spread
  its membrane material over the interface, rupture
  of foam lamella

10

• Beating in of air
• Churning
• Continuously formed new air-water interface
• Fat spread over the interface
• If fat is liquid, breaking up of air bubbles
  covered with fat causes disruption of fat
• If globules also contain solid fat, they become
  attached to air bubbles,
• Air bubbles tend to coalesce, air surface area
  diminishes, attached fat globules come closer,
  liquid fat spreads over the air bubble causing
  the globules to form granules
• Further aggregation of granules yields butter
  grains
• Phase inversion
• Concentrating and working the grains remove
  excess moisture, reduce moisture droplet size,
  butter

11

• Whipping
• High fat content
• Very little liquid fat
• Fat clumps
• Network formation entrapping air bubbles

12
Creaming

• Density difference between plasma and fat
  globules according to Stokess equation
• Globule size and temperature determine extent of
  creaming in high-pasteurized milk
• Homogenization
• Temperature reduces density and viscosity
• Clusters speeds up creaming
• Homogenization, sterilization

13

• Temperature
• Concentration of agglutinin
• Lactation, individual cow
• Fat globule size
• Fat content
• Agitation at low T, agglutinins aggregate so
  less available for aggregation
• Warming restores flocculation ability,
  dissociates agglutinin from the aggregates
• Heat treatment inactivate agglutinin, 78C
  complete
• Homogenization inactivates agglutinin

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Homogenization

• Prevent creaming
• Reduce globule size
• Prevent partial coalescence
• Reduce globule size
• Acquired surface layer, casein and serum proteins
• Creating desirable rheological properties
• Formation of homogenization clusters
• Increase in viscosity

15
Homogenization

• Liquid stream has a high potential energy
• On entering the valve, the energy is converted
  into kinetic energy, high velocity in the narrow
  gap causes intense turbulence
• Kinetic energy of the liquid is converted mostly
  to heat, ?1 of the energy is used for disruption
  of the globules (interfacial energy)
• Intense turbulence, small eddies in which high
  liquid velocity gradients occur, pressure
  fluctuations can disrupt particles
• Cavitation sudden formation and collapse of
  vapor bubbles caused by pressure fluctuations
• 40-75C, upto 40 MPa

16

• Homogenization clusters
• Homogenization of cream
• Large agglomerates of fat globules, 105
• Interconnected by casein micelles
• Protein is not too high to cover up all the
  surface
• Clusters contain interstitial liquid, effective
  volume fraction of particles increases
• Viscosity increases
• High fat content (gt9 fat), low protein content,
  high pressure, high surface excess of protein
  (low T, intense preheating, high P)
• Two-stage homogenization
• At low P (0.1 MPa), can disrupt clusters but not
  disrupt the fat globules

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Cream products

• 10-48 fat
• No off-flavor
• Stable to oxidation and lipolysis
• Sterilization
• Homogenization
• Coffee cream
• Dessert cream
• White color, no oil droplets

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• In-bottle sterilization
• 115C / 20 min
• UHT sterilization
• Homogenization after sterilization
• Coagulation of proteins and fat globules cause
  coalescence of fat globules
• For high viscosity, homogenization at lower T at
  one stage, formation of homogenization clusters

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• Heat stability
• As the surface area of fat globules covered by
  caseins increases, less heat stability
• Higher homogenization pressure lower heat
  stability (more casein on the surface)
• Lower P, creaming and partial coalescence
• Compromise between high and low P
• Feathering in coffee, coagulation of fat globules
• Age thickening, T, pH, Ca activity
• Can increase solid-non-fat content

20

• Clustering
• Desirable in dessert cream
• High viscosity
• Homogenization clusters, thickening agents
  (carrageenan, alginate)
• Larger volume fraction of fat globules
• Entrapped plasma between the globules
• Irregularly shaped clusters
• High fat content
• Can prevent clustering by a second stage
  homogenization

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Whipping cream

• 35-40 fat
• Beaten into a foam with or without sugar
• Pasteurized not to change flavor
• Keeping quality
• No Bacillus cereus
• No heat-resistant lipases
• Recontamination avoided
• In-can or in-bottle pasteurization
• Cu contamination avoided
• Whippability fast, homogeneous, firm texture,
  50 v/v air (100 overrun)
• Retain its shape, remain stable, not exhibit
  coarsening of the air cells, show negligible
  leakage of the liquid
• Thickener carrageenan
• Overrun Relative increase in volume by air
  beaten in

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• Pasteurization
• High enough to inactivate milk lipase, improve
  keeping quality
• 85C/30 min, 103C/20 min in-can heating
• No pumping unless fat is completely liquid or
  solid
• Homogenization applied before in-bottle or in-can
  pasteurization, but whippability decreases
• UHT heating preferred (also for flavor),
  homogenization at low P after heating
• T fluctuations avoided as it causes rebodying and
  increase in viscosity, impairs whippability

23
Whipping

• Refrigeration for a day to obtain some fat
  crystals
• To prevent creaming during storage thickener
  added (0.01 ?-carrageenan)
• Beating
• Air incorporation into the structure
• Fat globules penetrate into the air-water
  interface attaching themselves on the surface
• Spread some liquid fat onto the bubble surface
• Since concentration of fat globules is high, they
  cover the surface of the bubbles and prevent
  their coalescence but they partially coalesce
  themselves
• Clumped fat globules enclosing air bubbles and
  giving a rigid and stable foam
• Size of air cells and fat clumps should be
  similar in size
• The foam increases in firmness during whipping
  but it also becomes coarser
• On prolonged beating, clumps become large and
  few, butter grains formed

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• Balance between foaming and churning
• Depends on speed of beating
• Too slow churn prematurely
• Vigorous beating high overrun, finely structured
  smooth foam
• The smaller the air cells less clumping needed to
  enclose bubbles, a firm foam is obtained
• Fat globules diminish overrun, should not
  destabilize the bubbles
• Reducing globule size
• Proteins and surfactants may increase foam
  stability but they do not encapsulate the
  bubbles, but have a high overrun, unstable to
  manipulation

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Factors

• Fat content
• The more intense beating, the lower the fat
  content, the higher the overrun
• Crystallization of the fat is essential for
  clumping
• If too much liquid fat, clumping is too rapid,
  foam becomes unstable
• Deep cooling and sufficient time for
  crystallization
• Composition of cream
• Protein is needed to form foam cells at the
  beginning
• Addition of thickening agents, reduce leakage of
  liquid
• Homogenization impairs whippability
• Too small globules cannot clump
• Homogenization clusters better
• Two stage homogenization at low P
• Addition of surface-active substances decreases
  formation of clusters and increases the tendency
  to clumping, monoglyceride or Tween