Lecture 3/4 - milk fat Flashcards
Vad står MFG för?
Milk fat globules
Vilka eg har milk fat?
– Creaming and homogenisation
– True and partial coalescence
– Oxidation and lipolysis
Vad används milk fatt mest till, var är de viktigast?
Vid smör och grädde
Vad contributes mjölkfettet med till i produkten?
Contributes to unique texture and flavour of milk
Vilka biologiska funktioner har mjölkfettet?
det är en källa till…
– 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
Vad består mjölkfett av?
• 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 %
Hur påverkar cic/trans fettet?
Smältpunkten varierar
trans härlägre smältpunkt - kan ej packas lika lätt
vad är rekomenderat att man ax får i sig av transfetter
WHO recommendation < 1% of energy intake
Hur fås conjugated linoleic acid i mjölken?
obs, kolla upp denna syra. Pratas mycket om
Mammals convert vaccenic acid into rumenic
acid, a conjuaged linoleic acid (CLA)
– anticarcinogenic
Hur hålls fettet flytande?
- Biohydrogenation to stearic acid (C18:0); MP 70oC
- Physiological limit for secretion; MP 39oC
- Desaturation of stearic acid to oleic acid (MP 13oC)
Varifrån kommer fettet?
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
- C16Hur påverkar dieten fettet?
vet ej riktigt vad jag menar
• 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
Hur är mjölkfettete organiserat i mjölken?
Vad är mjölk för typ av emolsion?
• 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
Hur stora är mjölk fett globulärerna?
hur många finns per ml?
• 0.1-10 μm in size
– bacteria cell 0.5-5 μm
• Number 10^10 per ml
Vad är mjölkfett globulärens membran uppbyggt av
vet inte vad jag menar
• 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
Var finns de neutrala fettet - vilka är dessa?
• Neutral fat in the core of milk fat globuler
– triglycerides
– vit A,D, E, K, carotenoids
Hur kategoriseras mjölkfettsglobulärerna?
– 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
Vilka är de mest känsliga globulärerna?
The largest milk fat globules are the most
sensitive ones, associated with quality problems
Hur kan man separera mjölkfettet?
vilka metoder finns och hur går de till?
• 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
varför homogeniseras mjölk?
hur går det till, vad sker?
Process to counteract creaming
Högt tryk genom ett “munstycke”
Hur går det med fettmembranen då det blir ökat total yta på fett globulärerna?
– Ten times larger surface area of MFG. The
requirement for extra membrane material is
supplied by caseins micelles, ß-caseins and/or
whey proteins
Vad blir effekten av att honomengisera?
• 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
När sker sammansmältning av MFG?
Hur går det till?
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
När sker kristallisering av fettet?
vad händer med globulärerna?
• 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)
Vad är partial coalescence? - hur går det till?
Under vilken produktion är detta fenomen viktigt?
• 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
Vilka globulärer är mest känsliga för partial coalescence?
Vilka är mer resistanta
• Smaller globules are more stable to coalescence
- Larger globules, larger crystals
• Surface layers containing protein, as formed by
homogenisation, are far more stable
Oxidized flavour och komponenter
cardboard, metallic, oily, fishy
Off-flavour caused by reaction end products
aldehydes and ketones
- low taste/ smell threshold
- detection typically by sensory analysis
Vilka reaktioner är orsaken till mest smakfel i mjölk?
Oxidation och lipolys
Vad är det i mjölken som oxiderar i mjölken?
Reaction between oxygen and PUFAs of MFGM
Vad är det som gör att oxidation sker?
Reaction may occur
- spontaneously
− induced by external (environmental) factors
Factors affecting oxidized milk flavour
- 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
Varför sker spontanoxidation?
• 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)
Antioxidant vitamins in milk - vilka finns?
• 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
Hur påverkar feeding oxidationen? (fettet)
vet ej vad jag menar
• 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
Vad är LPL?
• Lipoprotein lipase (LPL)
- Endogenous enzyme found in blood, mammary and adipose tissue
- Is only active at the oil-water interface
Hur påverkar höga nivåer av LPL the rate of lypolysis?
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
Hur inaktiveras LPL?
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
Vilka componenter bildas vid lipolys?
Hur smakar lipolyslys?
“flavour threshold”
Lipolytic off-flavours: rancid, butyric, goaty, blue cheese
Vilka två typer av lipolys finns?
• 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
Desirable properties Whipping cream
• Flavor • Keeping quality, negatively affected by: – B cereus – Heat-resistant lipases – Auto-oxidation (pro-oxidants e.g. Cu) – Coalescence • Whippability • Stability after whipping
Manufacture of whipping cream
- hur görs detta?
• 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
The whipping process - vad händer, hur går det till
- 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
Vad består strukturen av vispad grädde av?
• 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
vilka stadier går grädde igenom när det vispas?
emulsion till foam
Vad är Overrun?
= (Density of unwhipped cream – density of whipped cream) / Density of whipped cream
- hur mycket volymen ökar i %
Hur påverkar visspnigstiden the overrun?
vilken overrun är mest önskvärt?
- The percentage increase in volume due to gas inclusion
* High overrun desirable (fluffy, voluminous)
Vad händer om man fortsätter vispa?
• If whipping continues > maximal overrun:
– Fat clumps too large, air bubbles will break and coalesce
– Foam will collapse and cream
start to churn
Vilka faktorer påverkar the whipping process?
• 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
Vad påverkar stabiliteten av vispad grädde?
- vad och hur
• 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
Whippability of homogenized cream?
• 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
Hur kan man ersätta grädde?
Hur fungerar de jämnfört med grädde?
• 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
Butter by definition
• >80% milk fat
– Existing regulations related to water content;
<16%
Butter kvalitetparametrar?
• Flavor
– Off-flavors
• Lipolysis and oxidation
• Volatile contaminants
• Shelf life
– Microbiological spoilage
– Off-flavors
- Texture
- Color
Vad påverkr texturen av smör?
- vilken textur vill man ha
• Texture important for acceptability of butter – Spreadability – Taste – Mouthfeel – Appearance – Suitability for various uses
Vad beror the texture av smör på
• 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
Vilka varianter på smör finns?
• 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
Process of cultured butter making - hantering av mjölken
- Cream (35% fat)
- 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) - Aroma forming lactic acid bacteria added
- Alternatively sweet-cream butter grains worked together with a concentrated lactic acid starter permeate - 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
Hur fås olika hårdhet på smöret?
Hur påverkar orginal fett compositionen detta?
(extra koll)
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
Ripening (ageing) of cream
jag förstår ej vad jag menar
• 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
Hur går churning till?
Varför görs detta?
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
varför tvättas smör kornen?
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)
Varför knådas smörkornen?
Finns det några alternativ till den här behandlingen+
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
Hur förvaras smör?
- Cold storage
- Stored for 1-3 days before selling
- Shelf life typically 12 weeks in cold storage
- Longer storage time stored frozen (-20°C)
Hur produceras low fat brebara smör?
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
