Dairy Fermentation Flashcards
are all cheeses pressed?
no. some are “unpressed” because the draining process from gravity is enough to knit the curds together
pressing
-helps expel whey and knit the curds together.
knitting
the fusion of the curds together as the whey drains. Pressing achieves this
3 ways salt can be applied
- rubbed on the surface of the finished cheese
- submerged in a concentrated brine
- directly applied to the curd particles before knitting
purpose of salting
draws whey to the surface of the curd where it can be released. the greater uptake of salt, the greater expulsion of whey
what are the 2 distinct ripening zones?
the body, the surface
interior ripening
involves obligate aerobes like mold
cannot occur unless the cheese is broken
surface ripening
already exposed to air, so molds will grow naturally or can be added
interior ripening example
blue cheese
- not pressed
- needle pokes holes in it to promote o2 entry and co2 exit
- must be turned regularly to prevent moisture buildup and rind rot
optimal yogurt temp and pH
42-43C (a compromise between the 2 starter yogurt cultures)
pH of 4.2-4.6 if the pH drops below 4.2 wheying off will occur
what are the initial organisms in yogurt
Streptococcus thermophilus
Lactobacillus bulgarius
strained yogurt
Greek yogurt
Yogurt that is strained through cloth or paper to remove whey, giving a much thicker consistency and a distinctive tangy taste
set yogurt
a solid set where the layers are not disturbed. ie fruit on the top or bottom yogurt
dadiah
type of yogurt made from buffalo milk and fermented in bamboo tubes
drinking yogurt
stirred yogurt to which additional milk and flavours are mixed in
what are the 2 bacteria in yogurt
L. Bulgaricus, S. thermophilicus - symbiotic relationship.
what is crucial to the texture development?
heat treatment and acidification because of the way k-casein reacts/is converted
the taste in cheese is determined by
acetic acid, diacetyl, acetylaldehyde
the taste in yogurt is determined by
lactic acid, acetic acid, diaceytl, acetylaldehyde
diacetyl
buttery flavour
produced via the citrate metabolism
acetic acid
Bifidiobacteria - vinegary taste
acetylaldehyde
most important taste contributer, 40mg/kg
what is the importance to a starter culture in dairy fermentations
to monitor the decrease in pH. dairy fermentations need a consistent rate of pH decrease
what is the most significant spoilage organisms?
phage
how is lactose translocated into the cell?
- phosphoenolpyruvate phosphotransferase - lactose is phosphorylated and cleaved by phospho-B-galactosidase (lactose -> glucose and galactose-6-phosphate)
1a. glucose enters glycolytic pathway and GP enters the tagatose pathway to be converted to tagatose-6-phosphate - lactose antiport system - lactose is not phosphorylated. glucose enters the glycolytic pathway, galactose accumulates in the cell or is excreted.
Leloir pathway
pathway used by Lb. helveticus to metabolize galactose from the lactose antiport system (which wouldn’t have otherwise been useful).
detriments to galactose buildup in products
- heterofermentative bacteria will metabolize it causing CO2 and breaks in the cheese.
- galactose can react with amino groups and produce pink or brown colors
LAB are auxotrophs for which compound?
amino acids - so they need proteolytic systems to acquire them
PrtP
-degrades caseins into oligopeptides, which can be then transported into the cell via Opp
-casein cannot enter cells
-It is attached to the cell via an anchor sequence and
It has broad cleavage specificity (extracellular)
what is the effect that proteolysis has on flavour?
bitterness
coagulation
- first step in cheese making
- converts milk proteins into a nonpolar form in order to separate them from the water (whey)
chemistry of the casein micelle
- hydrophobic inside, polar outside
- Ca helps stabilize it
acid coagulation
- pH will decrease naturally and reach the isoelectric point of casein (4.6)
- hydrogen atoms force the casein into chains
- this network traps solid components
- coagulation occurs when micellar Calcium Phosphate is converted into a soluble form and leaves.
- the casein matrix has no MCP and is WEAK.
2. these cheeses have high water content - cottage cheese, cream cheese
heat/acid coagulation
- high heat = denaturation of whey proteins
- denatured whey proteins attach to the micelles and form aggregates that entrap fat globules
2. these cheeses are high in water content- ricotta, queso blanco
rennet
Rennet is a group of proteinases that cleave casein at the surface of casein micelles when added to milk
rennet coagulation
- occurs at a high pH 6.6-6.3, before any extensive acidification by starter LAB
- the casein matrix is rich in MCP and very strong
what are the 2 important differences between acid and rennet coagulation?
1- Rennet curd is more resilient (less fragile), and better able to expel whey
2- Rennet coagulation occurs quickly (30 -60 minutes)
