Lecture 3/4 - milk fat Flashcards

Question

Vad är partial coalescence? - hur går det till? | Under vilken produktion är detta fenomen viktigt?

Answer 1

• 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

Answer 2

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

Answer 3

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

Answer 4

Oxidation och lipolys

Answer 5

Reaction between oxygen and PUFAs of MFGM

Answer 6

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

Answer 7

- 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

Answer 8

• 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)

Answer 9

• 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

Answer 10

• 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

Answer 11

• Lipoprotein lipase (LPL) - Endogenous enzyme found in blood, mammary and adipose tissue - Is only active at the oil-water interface

Answer 12

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

Answer 13

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

Answer 14

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

Answer 15

``` • 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 ```

Answer 16

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

Answer 17

• 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

Answer 18

* 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

Answer 19

• 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

Answer 20

emulsion till foam

Answer 21

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

Answer 22

* The percentage increase in volume due to gas inclusion | * High overrun desirable (fluffy, voluminous)

Answer 23

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

Answer 24

• 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

Answer 25

• 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

Answer 26

• 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

Answer 27

• 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

Answer 28

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

Answer 29

``` • Flavor – Off-flavors • Lipolysis and oxidation • Volatile contaminants • Shelf life – Microbiological spoilage – Off-flavors ``` * Texture * Color

Answer 30

``` • Texture important for acceptability of butter – Spreadability – Taste – Mouthfeel – Appearance – Suitability for various uses ```

Answer 31

• 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

Answer 32

• 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

Answer 33

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

Answer 34

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

Answer 35

• 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

Answer 36

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

Answer 37

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)

Answer 38

``` 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 ```

Answer 39

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

Answer 40

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