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Animal food sience - milk > Lecture 3/4 - milk fat > Flashcards

Lecture 3/4 - milk fat Flashcards

1
Q

Vad står MFG för?

A

Milk fat globules

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2
Q

Vilka eg har milk fat?

A

– Creaming and homogenisation
– True and partial coalescence
– Oxidation and lipolysis

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3
Q

Vad används milk fatt mest till, var är de viktigast?

A

Vid smör och grädde

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4
Q

Vad contributes mjölkfettet med till i produkten?

A

Contributes to unique texture and flavour of milk

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5
Q

Vilka biologiska funktioner har mjölkfettet?

det är en källa till…

A

– Energy
• Fat gives double amount of energy in comparison with carbohydrate

– Essential fatty acids (EFA)
• PUFAs that cannot be made by man or animals, must be derived from dietary sources. Linoleic acid and α-linolenic acid are parent compounds of the n-6 and n-3 families of essential fatty acids

– Fat-soluble vitamins
• Vitamin A (retinol), vitamin D (calciferols), vitamin E
(tocopherols)
• Vitamin A fortification of low fat consumption milk in Sweden

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6
Q

Vad består mjölkfett av?

A 
• Neutral lipids 98.7 %
– triglycerides 98.3 %
– diglycerides 0.3 %
– monoglycerides 0.03 %
– free fatty acids 0.1 %
• Polar lipids
– phospholipids (total) 0.8 %
– sterols 0.3 %
• Vit A,D,E,K + carotenoids 0.02 %
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7
Q

Hur påverkar cic/trans fettet?

A

Smältpunkten varierar

trans härlägre smältpunkt - kan ej packas lika lätt

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8
Q

vad är rekomenderat att man ax får i sig av transfetter

A

WHO recommendation < 1% of energy intake

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9
Q

Hur fås conjugated linoleic acid i mjölken?

obs, kolla upp denna syra. Pratas mycket om

A

Mammals convert vaccenic acid into rumenic
acid, a conjuaged linoleic acid (CLA)
– anticarcinogenic

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10
Q

Hur hålls fettet flytande?

A
  • Biohydrogenation to stearic acid (C18:0); MP 70oC
  • Physiological limit for secretion; MP 39oC
  • Desaturation of stearic acid to oleic acid (MP 13oC)
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11
Q

Varifrån kommer fettet?

A 
1. Circulation
– Stemming from feed
– Mobilised body fat ≥C16
– Stemming from rumen microbial synthesis
     • odd-numbered FA, e.g. C15, C17
    • branched FA, e.g. 4-ethyl C8:0
2. Endogenous synthesis in the mammary gland C4
- C16
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12
Q

Hur påverkar dieten fettet?

vet ej riktigt vad jag menar

A

• Diet/feeding – pronounced effects
- forages vs. concentrate
- protection of unsaturated oils to reduce their
hydrogenation in rumen
- risk for milk fat depression if too much unsaturated
feed sources

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13
Q

Hur är mjölkfettete organiserat i mjölken?

Vad är mjölk för typ av emolsion?

A

• Milk fat located in separate globules
- Only 0.025% of lipid material in milk serum
• Milk thus an oil-in-water emulsion
- Milk fat globules dispersed in a continuous milk serum phase

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14
Q

Hur stora är mjölk fett globulärerna?

hur många finns per ml?

A

• 0.1-10 μm in size
– bacteria cell 0.5-5 μm

• Number 10^10 per ml

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15
Q

Vad är mjölkfett globulärens membran uppbyggt av

vet inte vad jag menar

A 
• Milk fat globule membrane (MFGB)- a trilayer!
– Neutral and polar lipids
– Carbohydrates
– Proteins, including enzymes
     • xanthine oxidase
     • alkaline phosphatase
     • many others

• Phospholipids are amphilic
• MFGM makes the milk fat globule dispersible in water
environment
• Negatively charged due to polysaccharides
• Glycosylated proteins
• Electrical and steric repulsion
• Prevent fat globules from coalescence
• Dynamic surface
• e.g. in homogenization, adsorption of milk proteins

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16
Q

Var finns de neutrala fettet - vilka är dessa?

A

• Neutral fat in the core of milk fat globuler
– triglycerides
– vit A,D, E, K, carotenoids

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17
Q

Hur kategoriseras mjölkfettsglobulärerna?

A

– Small fat globules (< 0.1 μm)
• comprise 80% of number of MFG but only 2 % of TG
– Medium sized fat globules ( 0.5-5.0 μm)
• comprise 20% of number of MFG but 96 % of TG
– Large fat globules (> 5.0 μm)
• comprise <0.5% of number MFG and only 2 % of TG

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18
Q

Vilka är de mest känsliga globulärerna?

A

The largest milk fat globules are the most

sensitive ones, associated with quality problems

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19
Q

Hur kan man separera mjölkfettet?

vilka metoder finns och hur går de till?

A

• Independent on underlying mechanism:
- The larger the globules, the faster the separation
• Creaming
- Due to differences in densities between fat and milk serum (Stokes law)
• Cold-agglutination
- Occurs at low temperatures
- IgM in milk forms complex with lipoproteins in serum
- Complex precipitates onto fat globules and
cause clusters of fat globules
• Flocculation
- Reversible clustering of fat globules
- Identity of globules remain
- Held together by weak forces

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20
Q

varför homogeniseras mjölk?

hur går det till, vad sker?

A

Process to counteract creaming

Högt tryk genom ett “munstycke”

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21
Q

Hur går det med fettmembranen då det blir ökat total yta på fett globulärerna?

A

– Ten times larger surface area of MFG. The
requirement for extra membrane material is
supplied by caseins micelles, ß-caseins and/or
whey proteins

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22
Q

Vad blir effekten av att honomengisera?

A

• Makes milk more white
– number of particles increase
– light scattering effect

• Marked increase in emulsion stability
– small dispersed particles far more stable than large

• Improves stability toward partial coalescence

• Creates desirable rheological properties
– Formation of homogenization clusters
– In fermented milk casein particles, now covering the fat globules, will participate in aggregation

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23
Q

När sker sammansmältning av MFG?

Hur går det till?

A

In (true) coalescence MFG fuse into one droplet
– If two droplets are close together, the MFGM is thin or disrupted
– Can only occur if the fat is liquid
– The surface area will decrease
– Phospholipids (MFGM) are released into milk plasma

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24
Q

När sker kristallisering av fettet?

vad händer med globulärerna?

A

• Upon cooling of milk fat, network of lipid crystals
builds up in the MFG core
• Crystals protruding from the MFG may induce
coalescence – usually partial coalescence (punkterar)

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25
Q

Vad är partial coalescence? - hur går det till?

Under vilken produktion är detta fenomen viktigt?

A

• Different from true coalescence

• crystals protruding from MFG may pierce the membrane between
two adjacent globules
- liquid fat acts as sticking agent and holds globules together men går ej ihop helt pga kristallen är ivägen

• Partical coalescence is important when
whipping cream
- stability of foam

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26
Q

Vilka globulärer är mest känsliga för partial coalescence?

Vilka är mer resistanta

A

• Smaller globules are more stable to coalescence
- Larger globules, larger crystals
• Surface layers containing protein, as formed by
homogenisation, are far more stable

27
Q

Oxidized flavour och komponenter

A

cardboard, metallic, oily, fishy

Off-flavour caused by reaction end products
aldehydes and ketones
- low taste/ smell threshold
- detection typically by sensory analysis

28
Q

Vilka reaktioner är orsaken till mest smakfel i mjölk?

A

Oxidation och lipolys

29
Q

Vad är det i mjölken som oxiderar i mjölken?

A

Reaction between oxygen and PUFAs of MFGM

30
Q

Vad är det som gör att oxidation sker?

A

Reaction may occur
- spontaneously
− induced by external (environmental) factors

31
Q

Factors affecting oxidized milk flavour

A
  • Animal factors
    • stress, age, stage of lactation, milk yield
  • Diet
    • changes, composition, quality of stored forages
  • Excessive changes in body conditioning
  • Milking procedures
  • Equipment design
  • Water quality
32
Q

Varför sker spontanoxidation?

A

• Primary cause seems to be related to cows nutrition
• Imbalance in the milk
– pro-oxidants (Cu, Mn, Fe)
– anti-oxidants (vit E, Se)
• Non-nutritional factors
– Stress
• Elevated levels of free radicals in circulation
– High milk production
• Lower in fat content (higher levels of pro-ox vs fat)
• MFGM more fragile
– Stage of lactation
• Milk is higher in Cu in early and late lactation (higher levels of pro-ox vs fat)

33
Q

Antioxidant vitamins in milk - vilka finns?

A

• Vitamin A (b-carotenoids)
- associated with the core lipid in MFG
• Vitamin E (a-tocopherol)
- associated with the membrane
- low transfer efficiency to milk ~ 0.3%
• Ascorbic acid (vitamin C)
- water soluble antioxidant

34
Q

Hur påverkar feeding oxidationen? (fettet)

vet ej vad jag menar

A

• Dietary supplementation with unsaturated lipids
changes the composition of neutral (core) and
polar (membrane) lipids
• Antioxidant vitamins are found in green forages;
by feeding fat you may
- reduce the levels of lipid soluble antioxidants in milk
(a-tocopherol, b-carotene)
- decrease feed intake, depress fat and
protein content of milk

35
Q

Vad är LPL?

A

• Lipoprotein lipase (LPL)

  • Endogenous enzyme found in blood, mammary and adipose tissue
  • Is only active at the oil-water interface
36
Q

Hur påverkar höga nivåer av LPL the rate of lypolysis?

A

High levels LPL in milk – yet low rate of lipolysis during
normal conditions:
- MFGM protects the milk fat droplet against attack
- optimum pH 8.5 for LPL
- LPL largely bound to casein micelles
- Adsorption of lipase to MFG requires presence of blood serum

37
Q

Hur inaktiveras LPL?

A

Note: LPL inactivated by heat

  • D-value 70°C is 20 s
  • Low pasteurisation is 15 s at 72°C
  • Lipolysis in heat-treated milk due to microbial lipases
38
Q

Vilka componenter bildas vid lipolys?
Hur smakar lipolyslys?
“flavour threshold”

A

Lipolytic off-flavours: rancid, butyric, goaty, blue cheese

39
Q

Vilka två typer av lipolys finns?

A 
• Spontaneous lipolysis
- milking frequency (AMS?)
- udder health (apolipoprotein)
- stage of lactation (increased risk - early and late)
• Induced lipolysis (60-70%)
- Machine milking
- Pumping; air bubbles collide with MFG and disrupt the membrane
- Temperature fluctuations in the milk
40
Q

Desirable properties Whipping cream

A 
• Flavor
• Keeping quality, negatively affected by:
– B cereus
– Heat-resistant lipases
– Auto-oxidation (pro-oxidants e.g. Cu)
– Coalescence
• Whippability
• Stability after whipping
41
Q

Manufacture of whipping cream

- hur görs detta?

A

• Fat standardisation and pasteurization
– Heat treatment varies, e.g. 30 min at 85°C
• Gentle handling of cream to avoid damage of fat globules, esp. (partial) coalescence (vill endast ha då vispar)
• Thickening agent often added, e.g.
carrageenan
– By interaction with casein, prevents creaming of
fat globules due to increase in yield stress

42
Q

The whipping process - vad händer, hur går det till

A
  • Large air bubbles are beaten into the cream, breaking up in smaller ones
  • Air bubbles collide and coalesce
  • Protein adsorbs to the air-water interphase, rate of coalescence decreases
  • Fat globules collide with air bubbles and get attached to them
  • Liquid fat from globules spread over air-water interphase
  • Partial coalescence of fat globules occur
43
Q

Vad består strukturen av vispad grädde av?

A

• Structure/ network consisting of:
– Air comprises 50-60% of the volume
– Air bubbles 10-100 μm, fully covered by fat globules and fat clumps
– Clumped fat globules make up a space-filling network through the plasma phase, also making contact with the bubbles

44
Q

vilka stadier går grädde igenom när det vispas?

A

emulsion till foam

45
Q

Vad är Overrun?

A

= (Density of unwhipped cream – density of whipped cream) / Density of whipped cream
- hur mycket volymen ökar i %

46
Q

Hur påverkar visspnigstiden the overrun?

vilken overrun är mest önskvärt?

A
  • The percentage increase in volume due to gas inclusion

* High overrun desirable (fluffy, voluminous)

47
Q

Vad händer om man fortsätter vispa?

A

• If whipping continues > maximal overrun:
– Fat clumps too large, air bubbles will break and coalesce
– Foam will collapse and cream
start to churn

48
Q

Vilka faktorer påverkar the whipping process?

A

• Beating rate and bowl size/ shape
• Fat content (amount of fat globules)
– Too low, too high
• Solid fat content
– Balance between liquid and solid phase, solid phase not <40%
– Morphology of fat crystals
– Location of fat crystals within the fat globules
• Partial coalescence of paramount importance for the result

49
Q

Vad påverkar stabiliteten av vispad grädde?

- vad och hur

A

• Leakage of plasma from the product
– Can be addressed by adding a thickening agent
• Ostwald ripening
– Can be appreciable if low fat content and high overrun
• Collapse of the foam
– If Ostwald ripening is substantial and coalescence of air bubbles also occurs
• Sagging
– The foam sags under its own weight if product is not sufficiently firm

50
Q

Whippability of homogenized cream?

A

• Partial coalescence too slow
– Small size of MFG
– Proteinaceous surface layer provides good stability
• Whippability of homogenized cream can be improved
– Low-pressure homogenization resulting in formation of homogenization clusters (15μm)
– Addition of an emulsifier that replaces (part of) the protein on the MFG surface

51
Q

Hur kan man ersätta grädde?

Hur fungerar de jämnfört med grädde?

A

• Based on vegetable fat
– Functional and economical aspects

  • Water, emulsifier, stabilizer, sugar, flavor and protein (sodium-caseinate, skimmed milk, soya protein)
  • Often possess better whipping properties than dairy creams
52
Q

Butter by definition

A

• >80% milk fat
– Existing regulations related to water content;
<16%

53
Q

Butter kvalitetparametrar?

A 
• Flavor
– Off-flavors
    • Lipolysis and oxidation
    • Volatile contaminants
    • Shelf life
– Microbiological spoilage
– Off-flavors
  • Texture
  • Color
54
Q

Vad påverkr texturen av smör?

- vilken textur vill man ha

A 
• Texture important for acceptability of butter
– Spreadability
– Taste
– Mouthfeel
– Appearance
– Suitability for various uses
55
Q

Vad beror the texture av smör på

A

• Ratio between solid and liquid fat essential

– Solid fat inside and outside fat globules
• Network of crystals outside globule
• Crystals inside globules do not participate in network

– Without solid fat butter would be fully liquid

– Without liquid fat butter would be hard and brittle

56
Q

Vilka varianter på smör finns?

A

• Sweet cream butter
- less sensitive to oxidation defects

• Cultured or sour butter
- historically unavoidable due to duration of
gravity creaming
- rich in aroma (diacetyl)
- more sensitive to oxidation defects
- Cu migration to fat globules at lower pH

• Unsalted, salted & extra salted
- Historically for preservation purposes

57
Q

Process of cultured butter making - hantering av mjölken

A
  1. Cream (35% fat)
  2. Heat treatment (3-5 s, 85-90°C)
    – Kills bacteria, inactivate enzymes (lipase)
    – Too severe heat treatment increases risk for oxidation (Cu migration)
    – Souring of cream also increases risk for oxidation (Cu migration)
  3. Aroma forming lactic acid bacteria added
    - Alternatively sweet-cream butter grains worked together with a concentrated lactic acid starter permeate
  4. Ripening (20 h, 14°C)
    - Souring of cream (optional)
    - ”Physical ripening (Alnarp method, 1937)
    • Temperature treatment (e.g. 8/ 20/ 14°C) adapted to the physical properties of the milk fat
    • Crystallisation of fat
58
Q

Hur fås olika hårdhet på smöret?
Hur påverkar orginal fett compositionen detta?
(extra koll)

A

Hard fat: Rapid cooling to 8°C
for 2 hrs, gentle heating to
21°C and kept for 2 hrs, cooling
to 16°C and churning

Soft fat: Rapid cooling to 6°C
for 2 hrs, gentle heating to
15°C and kept for 2 hrs, cooling
to 10°C and churning

Very soft fat: Cooling to 20°C
and soured for 5 hrs, cooled to
8°C and kept for 2 hrs, gentle
heating to 11°C and churning

Variation in milk fat composition- necessity
to regulate proportion of solid fat - smält punkt

59
Q

Ripening (ageing) of cream

jag förstår ej vad jag menar

A

• Program of cooling designed to control the size and number of fat crystals formed
- During cooling after pasteurization a proportion of the fat will crystallize
• If rapid cooling – many and small crystals, i.e. more of the fat will form the solid phase and less liquid fat
• If gradual cooling – fewer but larger crystals

• Fat crystals will adsorb the liquid fat to their surface
- If many and small crystals, total crystal surface area will
be larger and more liquid fat will be adsorbed
• i.e. the continuous fat phase will be smaller and the butter
will be firmer

60
Q

Hur går churning till?

Varför görs detta?

A

Churning (steg 5 i process)

  • Beating in of air
  • Rapidly and completely (high yield, i.e. low fat content in buttermilk)
  • Shape (size, firmness) of butter grains important for firmness and for efficient working.

After churning butter milk drawn off
– Control of water content extra important if addition of culture permeate

61
Q

varför tvättas smör kornen?

A

Washing (optional) (steg 6)
- Reduces non-fat dry-matter content of butter moisture
- If needed, washing can be used to control
temperature (to control grain firmness)

62
Q

Varför knådas smörkornen?

Finns det några alternativ till den här behandlingen+

A 
Working (kneading) (steg 7)
- Transform butter grains into continuous mass
- Disperse moisture in the butter
- Regulate water content
- Incorporate salt (optional)
Optional vacuum treatment
– smoother texture
– smoother appearance
63
Q

Hur förvaras smör?

A
  1. Cold storage
    - Stored for 1-3 days before selling
    - Shelf life typically 12 weeks in cold storage
    - Longer storage time stored frozen (-20°C)
64
Q

Hur produceras low fat brebara smör?

A

Cannot be achieved by churning

– Dispersion of water, a great number of fat globules, fat crystals and even air in oil phase
– Aqueous droplets from <1 μm-50 μm of protein solutions
– Large water droplets favour microbial attacks and coalescence
• Rancidity
• Continuous aqueous layer
– Use of preservatives, emulsifiers and gelling agents

Animal food sience - milk (14 decks)

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