Study q Flashcards
Milk clotting may be divided into different phases. Which are these different phases?
1) enzymatisk split of the GMP
2) spontan aggregation
3) gel formation
4) syneresis och whey expelling
Which bond on kappa-casein is cleaved during phase 1 and which are the resulting products of the clotting reaction?
the phe (105) - Met (106) klipps av resultat: Para-casein + glycomacropeptid (GMP)
What is the driving force of the 2nd phase and which type of bonds are created?
sker när 70% av k.casein blivit avklippt
- sterisk och electorstatisk relpulsion minskar
aggregation hålls ihop m vdW kraft ca2+ är med och -minskar elecrostatisk repulsion -skapar bridges -minskar ph
What is initiating the 3rd phase?
aggregationen har gått så långt så det tar upp all yta
nätverket blir mer och mer dense för:
- mer miceller går in i gelen
- starkare junktions emellan
- modolus är max när steric hindrance inhibits further inrteraktions
How is the 1st phase of the clotting reaction influenced by
a. pH-decrease?
b. CaCl2 (Ca2+)-addition?
c. Cooling?
d. Heating
a) går upp pga change in charge - enklare att nå in
b) går upp pga ca jämnvikten - drar in casein i micellen (Ip oxå)
c) går ner pga minskad enzymatisk reaktion - optimal temp
d) upp sen ner pga optimal rörelse och enzymaktivitet för hög så denaturerar proteinerna
How is the 2nd and 3nd phase of the clotting reaction influenced by
a. CaCl2 (Ca2+)-addition?
b. Cooling?
c. Heating?
a) upp pga drar ut ca ut ur cellen och kan bidra till att skapa bindningar - troligen mer i steg 3
b) stops under 20 grader pga hydrofoba interactions blir för svaga (går ihop för de ej gillar vattenfasen)
C) ökar av heation - mer rörelse och fler hydrofoba interactions
Describe in what way mastitic milk influence the milk-clotting reaction
- minskad mängd caseiner färre som kan reagera, mer whey
- rennet clotting time delayed and minskar curd firmness - får ut mindre ost
How could bacteriophages decrease the clotting properties of cheese milk?
dessa är virus för bakterier - strain specefika
de kan förstöra starters - påverkar pH sänkningen
vilket ger sämmre clotting i speciellt yogurt
At which pH is an acid gel formed? Describe the mechanism of this reaction.
vid lägre pH så förlorar micellerna sitt cap och håller enast ihop med saltbryggor och hydrofoba interactioner.
de bond som då var i micellen hamnar utanför.
den negativa net charge av micellen neutraliseras av H+ vid pH 4,6 och caseinerna precipates (slutar va lösliga)
What are the characteristics of an acid gel compared to a rennet gel?
rennet gels är elastisca - hydrofoba interactions + cap bridgeses
acid gels är viscösa - hyrofoba inteactions och elctorstatisca inteactions
Which milk-clotting enzymes are found in bovine rennets? Varifrån kommer de?
chymosin (kalv) spjälkar ej imunoglobiner vilket pepsiner (ko) gör
Which are the pH-properties of these milk-clotting enzymes?
vid pH 6,6 har de samma effektivitet.
kar med minskad ph
ost 6,5-6,6 i pH
What is the probable reason for a special milk-clotting enzyme in young mammals?
för den bryter ej ner de viktiga imunoglubinerna
In order to understand and predict its performance in coagulation, what information is important to have when you use a bovine rennet?
ph, koncentration, innehåll
Which different heat treatments are applied in a dairy?
therminisatin LTLT HTST ESL UHT sterilisation in container
How do temp affect the different whey proteins and the caseins?
whey proteins är värmekänsliga
caseiner är ej känsliga för värme
vuht - mailard
vid pastörisering ökar ccp in micellerna, över 100 grader dissolution of part of k-casein
age gelation
What is the skin on boiled milk? What is cooked taste (flavour)?
denuturerar protein - whey
What happens with the equilibrium of CaP between casein micelles and the milk serum at moderate and heavy heat treatment respectively?
Vid uppvärmning går cap in i micellen ju varmare ju mer går in
What happens with the equilibrium of caseins between casein micelles and the milk serum at heat treatment?
de denaturerar urea och går ifrån varandra.
What happens with the equilibrium of CaP between casein micelles and the milk serum when milk is cold-stored for a short and long time, respectively?
dissoution of the ccp
- less ca bind till casinet
What happens with the equilibrium of caseins between casein micelles and the milk serum when milk is cold-stored?
dissolution of beta-cassein pg svaga hydrofoba bindningar - plasmin risk
andra caseiner dissolve oxå vilket ger högre vircositet
What are the consequences of a long cold storage of milk for cheese production (explain in detail and remember the connection with enzymes)?
då cassein micellerna blir svaga blir det svårt att binda ihop gelen samt att de kan bryta ner
- samma me ca, blir mindre bindningar
colloida stabilitet ökar vilket leder till poor renetability during cheese making.
What could be done to increase the cheese making properties of milk, which have been cold-stored (mention both reversible and irreversible reactions and the speed of the former)?
tillsätta ca för att få ihop micellerna igen
- värma innan användning för ta tillbaka de dåliga bitarna
- add chelatants skulle kanske få vatten att gå ut igen
What are the general steps in cheese manufacture?
pastörisering separering och standardnisering pre ripening renneting cutting press cheese salt
Which parameters are differing in the manufacture of soft versus hard cheeses?
utting, värme, ph acid/rennet
What differs between the manufacture of cheeses with round-eyed, granulareyed
and close texture?
hur de pressas - du kan detta
How is the fat content in the cheese regulated?
genom att bestämma fetthalt i mjölken
Why is the history of the milk very important when producing cheese?
för om tex lagrad längre innan kan det behövas annat, homogenisering påverkar tillgänglighet till caseiner
Give examples of factors that influence the cheese yield?
casein stabilitet
hur mycket finns i
(värme, rörande)
How do the different flavours of cheeses develop?
bakterier fr det mesta, nerbryt av komponenter i mjölken
How could the ripening of cheeses be accelerated?
temp, mer starters, optimal förhollande, andra bakerier som är snabbare
Give examples of factors that may result in abnormal milk composition, i.e.
situations and conditions when milk should not be delivered to the dairy?
antibiotica, första mjölken sopm ges, sjukdom, mouldy feed, mastit, late lactation
Which type of milk sample is used for raw milk quality assessment and thus basis for the milk price to the producer?
fett och protein
bakterie antal
Give examples of harmless and harmful bacteria in the raw milk.
lab och clostriium, tuberkulos
Which are the two most common types of spore forming bacteria in milk?
Describe the types of problems they cause
Bacillus cereus
clostridium thyrobutyricum
Which is the average concentration of proteins in milk? Give examples of
factors that influence upon protein concentration.
Caseiner 1120 mmol/m3 Milk
Globuliner ∼320 mmol/m3 milk
Affect koncentretion – feed , gener, laktationsstadium (colostridium), ungens behov
What could generally be said about the molecular structure of whey proteins
and to which property is this related?
De är globulärer och därmed heat sensetive – skinn på ytan av mjölken
Give examples of models of the casein micelle that have been discussed
during the last decades and describe them briefly. Give examples of
agreements and disagreements between models.
k-kasein på utsidan nanocluter av ca emellan caseinmicellerna grå grej – submicell blåa/röda – pretruding peptid chain nanokluster av cap i själva submicellen
What is colloidal calcium phosphate?
Cap som finns ine i micellen och som håller ihop – till ungen igen
What types of carbohydrates are present in milk? Major carbohydrate?
Lactos till 99,8%
Discuss the phenomena of lactose crystallisation; crystal forms, ways to
reduce problems associated with crystal formation in dairy products
(especially in connection with milk and whey powders)
Stoppa i en nuklei som bestämmer hur kristallen ska se ut – detta behövs alltid då svårt att få att kristallisera sig
Sker i oversaturated lösningar.
Alfa lactos är vanligare kristallen men ej den mest optimala – sandig
to avoid to big crystals:
• “seeding” of lactose crystals (slurry of lactose)
• resulting in >106 crystals per ml
• 95% <10μm and 100% <15μm
- Give examples of antibacterial enzymes in the milk
Lactoperoxidase
- Describe the activity of plasmin, its properties and influences on milk and
dairy products.
• Importance of plasmin in dairy products:
– PP lost in whey during cheese making,
resulting in lower cheese yield
– Plasmin contributes to gelation of UHT milk
+ Plasmin important during cheese ripening
• Flavor
• Reduction in ripening time
Kommer ifrån blod där det är med i blood clotting
. Milk fat is enclosed by a milk fat globule membrane (MFGM)
a. What is the origin of this membrane?
b. Briefly describe its composition and structure
c. What are the functions of the MFGM with regard to lipid stability?
huvud och svans
a)Proteiner eller polära lipider
• Phospholipids are amphilic
• MFGM makes the milk fat globule dispersible in water
environment
b)huvud och svans
c) • 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
- Highly bioactive surface; biological function?
In what way is partial coalescence different from true coalescence?
De går ej ihop helt, fettkristaller punkterar membranet och de går ihop men samtidigt så är kristallerna ivägen så de ej kan smälta ihop totalt.
Describe how the whipping properties of cream are influenced by the fatty
acid composition.
Smält p och kjristall formation
What is butter, according to definition?
Butter by definition
• >80% milk fat
– Existing regulations related to water content;
<16%
