Lipids and lipolysis in milk and milk products: A research journey

Foaming of milk
Hilton Deeth
Dairy Webinar 20 November 2013
Outline
Significance of foaming in the dairy
industry
Foams – general concepts
Causes of reduced foaming
 Lipolysis
 Other
Ways to improve foaming
Ways to reduce foaming
Some recent research on foaming
Significance
of foaming
Significance of foaming/frothing
to the dairy industry
Beneficial
Hot frothing for making cappuccino coffee
Cold frothing for making freddoccinos?

Poor frothing milk is a real problem
Detrimental
Cold frothing during pumping, filling vats, etc

too much froth causes product losses
Excess froth during reconstitution of powders, e.g.
infant formulae
Foams –
General concepts
Foams: General Concepts
A foam is a two phase system in which a distinct
gas bubble phase is surrounded by a continuous
liquid lamellar phase
Kamath et al., 2011
Foams: General Concepts 2
Foam formation involves the creation and
stabilisation of gas bubbles in a liquid.
Measured by foamability and foam stability
•
•
Foamability is the amount of foam formed
Foam stability is how long the foam lasts
Foams: General Concepts 3
Milk foams are stabilised by milk proteins
Surface active agents reduce foaming by
displacing the proteins
Foaming requires air incorporation through:
• Steam injection (as in cappuccino machines)
• Air injection
• Agitation (as in home frothers, e.g. Caffitaly,
Nespresso Aeroccino
• Other, e.g. pouring from one container to another
Causes of
reduced foaming
Common myths about
reduced foaming
Added water in the milk. Adding water
has little effect on frothing.
Too much or too little fat. The fat content
has some effect on frothing: skim milk generally
gives more froth
Due to additives in the milk. No
The milk is too fresh. Refrigerated storage
of pasteurised milk for up to three days has no
effect on foaming.
Causes of reduced foaming
Not completely known but…
Lipolysis is the major cause
Other reported causes include:
Cow factors – stage of lactation, breed, etc
The milk from some individual cows foams poorly
Free fat (ruptured milk fat globule)
Mastitis
Lipolysis – what is it?
 breakdown of fats (triglycerides, TG) to produce:
- free fatty acids (FFA) and
- diglycerides/monoglygerides (DG/MG) (or glycerol)
LIPASE
TG FFA + DG
DG  FFA + MG
[MG  FFA + glycerol]
Why is it a problem for
foaming?
FFAs and di- and monoglycerides
are surface active and reduce
foaming
Can replace proteins at the bubble surface
Lipolysis and steam foaming
Foamability %....
The amount of foam produced (foamability) as % of
original milk volume decreases with free fatty acid level
40
35
30
25
20
15
10
5
0
0
1
2
3
4
Free Fatty Acids (mequiv./L)
5
6
Milk foaming problems
LIPOLYSIS
 Two major causes :
Spontaneous lipolysis on farm:
Initiated by cooling to < 100C
Induced lipolysis: on farm from air
incorporation at teat cup cluster causing
foaming of warm raw milk (due to inadequate
maintenance of milking machines)
Can also occur in the factory
Spontaneous lipolysis
 After cooling and refrigeration for ~16 h:
 “normal” milk has a FFA content of ~0.5-1.0
(mmoles per litre)
 “spontaneous” milk has a FFA of > ~1.5 but
can be as high as 10.
 Major factors:
 cows in late lactation
 cows on poor feed
 certain cows/certain bulls’ progeny
 all of the above
Induced lipolysis – in raw milk
 Agitation - with air [causing foaming]
 Pumping – particularly with air intake
 Homogenisation – very effective
In practice, is always combined with
pasteurisation (~72°C/15 sec) which
destroys milk lipase
 Mixing homogenised (pasteurised) milk
and raw milk
Ways to
improve
foaming
Ways to improve foaming
Selection of good farm milk
Heating – pasteurisation, UHT
Homogenisation
 Foaming
increases with pressure of
homogenisation
Addition of milk solids, particularly
proteins
Addition of gums
Adding calcium
Selection of milk
 Lipolysis, the major cause of foaming
problems, occurs mostly at farm
A small amount can be induced during
transport
 Problem in bulk milk usually due to small
number of suppliers
 Can often be narrowed down to milk from
certain tanker runs, then to individual
suppliers
Steam frothing values (foamability)
of 12 tanker milks over 12 months
Month
Tanker
A
Tanker
B
Tanker
C
Tanker
D
Tanker
E
Tanker
F
Tanker
G
Tanker
H
1
2
3
4
5
6
7
8
9
10
11
12
106
120
104
102
103
95
90
92
83
72
54
57
19
22
33
36
55
130
86
66
70
39
64
57
78
78
100
85
94
90
98
93
88
96
170
32
27
41
42
48
90
92
92
59
44
42
61
58
43
47
49
56
63
77
78
71
56
55
90
90
61
52
82
10
10
20
10
20
Aver
age
90
56
97
56
59
84
17
Tanker
I
Tanker
J
Tanker
K
Tanker
L
120
70
107
11
17
19
23
28
56
47
69
72
113
43
70
108
90
107
104
89
85
83
71
115
78
80
83
71
76
66
37
70
79
93
100
102
70
72
78
84
54
110
98
95
53
72
71
83
73
108
90
107
80
110
98
95
53
72
71
79
84
76
83
87
FFA and steam frothing values of
individual farm supplies in tanker G
Farm
supplier
FFA
Steam frothing
value
G1
G2
G3
G4
G5
G6
G7
1.56
1.16
0.84
1.40
6.47
2.76
3.95
30
80
100
60
0
1
0
Effect of heating and
homogenisation on SFV
Milk
Raw
Pasteurised
Pasteurised and
homogenised
Steam frothing values
(average of 5 replications)
43
86
125
Homogenisation pressure
Steam frothing values
(MPa)
(average of 10 replications)
Deeth and Smith, 1983
6.9
92
13.8
112
20.6
124
Steam frothing values of bulk raw and
corresponding pasteurised milks
140
120
Pasteurised
100
80
SFV
Raw
60
40
20
0
1
2
3
4
5
6
7
MONTH
8
9
10
11
12
Effect of heating and
homogenisation on SFV
Milk
Raw
Pasteurised
Pasteurised and
homogenised
Steam frothing values
(average of 5 replications)
43
86
125
Homogenisation pressure
Steam frothing values
(MPa)
(average of 10 replications)
Deeth and Smith, 1983
6.9
92
13.8
112
20.6
124
Steam frothing values of bulk raw and
corresponding pasteurised milks
140
120
Pasteurised
100
80
SFV
Raw
60
40
20
0
1
2
3
4
5
6
7
MONTH
8
9
10
11
12
Proteins and foaming of
lipolysed milk
 Milk foams are stabilised by proteins at the
air-liquid interface
 Lipolysis produces surface-active lipids
 Suface-active lipids compete with proteins
and reduce foaming
 Addition of milk proteins improves foaming
Effect of adding SMP on
steam frothing value
160
140
120
100
SFV
80
milk a
milk b
60
40
20
0
0
1
2
3
% SMP added
Deeth and Smith, 1983
4
5
Effect of adding κ-carrageenan
on foam stability
600
Half life (mins)
500
400
300
200
100
0
0
10
20
30
40
50
60
70
80
90
Temperature (°C)
Control
0.0001
0.0003
Adding 0, 0.01% and 0.03% κ-carrageenan to
reconstituted low-heat skim milk powder
Kamath and Deeth, 2011
Effect of adding calcium chloride
on foam stability
800
700
Half-life (mins)
600
500
400
300
200
100
0
0
10
20
30
40
50
60
70
80
90
Temperature (°C)
Control
10 mM
15 mM
20 mM
Adding 0, 10, 15 and 20 mM calcium chloride to reconstituted
low-heat skim milk powder
20 mM addition not recommended – risk of coagulation
Kamath et al., 2011 (JDS)
Ways to
reduce
foaming
Possible ways to reduce
foaming of dry formulations
Avoid using milk powders forming
very stable foams at and below the
reconstitution temperature
Add milk fat?
Add calcium-binding agents, e.g.
citrate, polyphosphate
Foamability of reconstituted low, medium & high heat skim milk
powder
110
Initial foam volume (mL)
100
n=3
90
80
70
60
50
40
30
20
10
0
0
20
40
60
80
100
Temperature (oC)
low heat (Mfd: Dec 2003)
low heat (Mfd: Sep 2004)
medium heat (Mfd: Sep 2004)
high heat (Mfd: Jan 2005)
So low-, medium- and high heat SMP have same foamability
Foam stability of low, medium and high heat skim milk
powders
600
Half Life (mins)
500
Possible mixing temp
n=3
400
300
200
100
0
0
10
20
30
40
50
60
70
80
90
Temperature (oC)
low heat (Mfd: Dec 2003)
medium heat (Mfd: Sep 2004)
low heat (Mfd: Sep 2004)
high heat (Mfd: Jan 2005)
BUT low-, medium- and high-heat SMP have different foam stabibilities
Practical implication of foam
stability of reconstituted powders
 Different skim milk powders have similar
foamability but vary considerably in foam
stability
 Mixing often done at 40-50°C
corresponds to high foam stability of some powders
 Medium-heat powders should be avoided
but individual batches should be tested
Effect of adding 1.4% soft milk fat and oils to
reconstituted SMP- foam stability
Is result of one trial; may not be same for all batches of milk fat
Foam stability depressing effect
of calcium-binding agents
a
c
b
300
200
100
0
0
20
40
60
80
100
400
350
300
250
200
150
100
50
0
Half-life (mins)
Half-life (mins)
Half-life (mins)
400
5mM
200
100
0
0
20
40
60
80
100
0
10mM
Control
5mM
20
40
60
80
100
Temperature (°C)
Temperature (°C)
Temperature (°C)
Control
300
10mM
Control
5mM
10mM
20mM
a. Addition of EDTA
b. Addition of sodium citrate
c. Addition of sodium hexametaphosphate
[Note: Some UHT milks have added citrate or SHMP ]
Kamath, 2007
Some recent
foaming research
Recent UQ Research on foaming
 Done by Dr Sapna Kamath
 Set up foaming apparatus in lab which uses
compressed air
 Used for foaming at different temperatures
 Determined :
Foamability – amount of foam produced
measured immediately after foaming
Foam stability – time before amount of foam
remaining decreases to 50% of original volume
Apparatus for Measurement of
Foamability and Foam Stability
Room temperature: 22oC
Air pressure: 5-6 psi
Air flow rate: 2.4 mL/s
air inlet
glass tube
pressure
regulator
sintered glass disc
pressure gauge
milk (50 mL)
flow meter
Low form 250ml
measuring cylinder
Kamath, 2007
Initial foam volume (mL)
Foamability of commercial milk samples
100
80
60
40
20
0
0
10
20
40
50
60
70
80
Temperature (Deg C)
Full Cream milk
Kamath et al., 2008
30
Lite White
Skim milk
UHT full cream
UHT Skim
90
Foam stability of commercial milk samples
Half life (mins)
600
Cappuccino
temperature
500
400
300
200
100
0
0
10
20
30
40
50
60
70
80
Temperature (o C)
Full Cream milk
Lite White
Skim milk
UHT full cream
UHT Skim
90
Image analysis of foams
Whole
milk at
frothing
Skim
milk at
frothing
Whole
milk at
frothing
half -life
Skim
milk at
frothing
half-life
Effect of milk fat and vegetable oils
100
pasteurised homogenised
milk (3.4% fat)
Foamability (mL)
80
pasteurised homogenised
milk (1.4% fat)
60
1.4% olive oil
3.4% olive oil
40
1.4% canola oil
1.4% sunflower oil
20
0
0
20
40
60
Temperature (°C)
Kamath and Deeth, 2011
80
100
Effect of adding oil to reconstituted
SMP- foamability
140
Foamability (mL)
120
100
80
60
40
20
0
Kamath, 2007
Effect of adding oil to reconstituted
SMP- foam stability
350
300
Half-life (mins)
250
200
150
100
50
0
Bubble ghost analyses
 Bubble ghost material is the interfacial
material
 It remains after foam subsides
 Is mostly micellar casein
 Electron microscopy shows micelles
aggregated and spread over surface
Foam bubble surface –
electron micrograph (em)
INTERFACE
CASEIN
MICELLES
Kamath et al. 2011
Bubble ghost em analyses
Interfacial
Membrane
Spreading and
aggregation of
casein micelles
Bubble ghost em analyses
Spread
casein
micelles
Interfacial
material
Caseins are more effective
than whey proteins in
stabilising milk foams
Casein micelles have ability to aggregate
and spread over the bubble surface
Whey proteins are very mobile and move
quickly to the surface and create foam but
are unable to spread and aggregate and
stabilise the foam.
Caseins are responsible for
foam stability - more evidence
Half life (mins)
800
casein
600
ultracentrifugal
supernatant
400
defatted
ultracentrifugal
supernatant
200
milk
0
0
20
40
60
Temperature (oC)
80
100
Acknowlegements
 Sapna Kamath
 Bussarin Samarnphanchai
 Ross Smith
 Carolyn Fitz-Gerald
 Trent Seeto
 Erika Naranjo Martinez
 Dairy Australia
Thank you for your
attention