7- fermented dairy Flashcards
At the moment the most significant threat to the fermented milk products industry is ____
phage
why is homofermentative LAB important in the dairy industry?
because of the rapid drop in pH
T or F : The main function of LAB is to ferment lactose into lactic acid, it is not their only function, they also are involved in the development of flavor
true
____is the main metabolite at the end of a diary fermentation
Lactic acid
The main volatile and flavor components of fermented milks are____, ___ and _____
acetic acid, acetaldehyde, and diacetyl
What is a auxiotrophs?
organism (especially a bacterium or fungus) that requires a particular additional nutrient which the normal strain does not
How does LAB hydrolyse proteins?
with the PrtP proteinse attached to its cell wall.
____ is essential for uptake of peptides from the breakdown of casein via PrtP
Opp
What are the three way of making cheese coagulate
Rennet-coagulated Acid-coagulated Acid/heat-coagulated
How does acid coagulation works
As pH decreases, the isoelectric point of casein (pH 4.6) is reached, hydrogen atoms accumulate and neutralize the polar surfaces of casein micelles, forcing them into chains of micelles
What is the coagulum?
The soft fragile gel that is formed over the course of hours by the coagulation of the milk
How does the acid / heat coagulation works ?
However, if milk is moderately acidified (pH 6.2-5.4) it becomes susceptible to heat-induced coagulation at relatively low temperatures (85C)
How is make queso-blanco (type of coagulation)?
It is a pressed version of ricotta made from a acid / heat coagulation
What is the type of coagulation that expels more whey than the others
the rennet coagultion
How does the rennet coagulation works?
Rennet preferentially cleaves the K-casein at the surface of the micelles and initiates coagulation
What are two advantages of using rennet for the coagulation?
1- Rennet curd is more resilient (less fragile), and better able to expel whey 2- Rennet coagulation occurs quickly (30 -60 minutes)
Why isn’t LAB lost with the whey when you drain your curds
The LAB are trapped in the matrix of the curd
What are the goals in the cooking step in the cheese making?
- It promotes the curd contraction
- Cooking also influences the rate of lactic acid production by LAB, which also causes the curds to contract and expel more whey as the pH decreases
What are the two methods of separating the curds from the whey?
Dripping: where curd-whey mixture is scooped out and placed in a draining vessel (ceramic sieve, wicker basket, or actual plastic draining mold)
Draining: were there is a fitted valve or a strainer in the vessel used for coagulation and the whey is simply drained off
What is knitting?
it is the term used to describe the fusion of curds together as the whey drains to produce once continuous mass of fused cheese curd
What is pressing?
Pressing is closely related to knitting and involves the application of external pressure to the curd during knitting (or in some cases after knitting)
What is the goal of salting the cheese?
Thus salting is yet another step to expel moisture from the cheese, the greater the uptake of salt the greater the release of whey
Surface ripened cheeses include two groups, what are they
Low pH at surface (pH<5) High pH at surface (pH>5)
What are the microorgasnisms used in dairy fermentations
- molds 2. yeasts 3. LAB 4. AAB
what is the function of the LAB in the fermented dairy products
- ferment lactose into lactic acid 2. development of flavor
what is the name of the bacteria that is able to transport galactose and utillize the leloir pathway to metabolize it
the Lb. Helveticus
why can galactose be a problem?
it can cause several problems for the cheese if there is no strains able to metabolize it because it can :
- There can be production of CO2 and cracks in the cheese (by the heterofermentative)
- residual galactose can react with a.a. and form colored compounds
explain the proteolytic system in lab
•PrtP degrades ___ effectively into oligopeptides
caseins
PrtP is found in ____
lactococci
what determines the flavor development in dairy products
•The proteolytic enzymes present in the milk matrix determine which peptides and amino acids accumulate and how flavor develops
what is coagulation?
•is the first pivotal step in cheese making, where all of the proteins are converted into a non-polar form and when this occurs they separate from the water phase though a process that entraps fat and minerals (curd contraction and whey expulsion)
what is the disadvantage of the rennet-coagulated cheeses?
the rippening procdess is unforgiving.
what are the objectives that needs to be achieved when making cheese from rennet?
- the correct amound of whey needs to be expelled
- The rate of acification must be controlled
- The salt must be incorporated at the correct rate
what is the goal of the cooking step in cheese making?
•Cooking to a higher temperature, for a longer duration and with more stirring promotes curd contraction
why is there orange molds that can appear on cheese when you use penicilum camenmberti
•P. camemberti rapidly catabolizes lactic acid and results in deacidification of the cheese surface (making the cheese prone to contamination by some bacteria that produce orange or yellow pigments)
•The starting temperature of milk used in the the average yogurt fermentation is ______ when the inoculation of LAB occurs
42-43∘C
what is the optimal pH for the yogurt production
4.2-.4.6
what are the two LAB in yogourt production
L. bulgaris and S. Termophilus
•____ is known to have several cell-bound proteases (PrtP) that cleave proteins into amino acids extracellularly
L. bulgaricus
__ and ___ produced by S.thermophilus are growth factor of the L.bulgaris
Formic acid and CO2
What does the L.bulgaris that helps the growth of S.termophilus
it cleaves casein proteins into smaller peptides that the S.thermophilus can use
what is dadiah?
Dadiah: Made from water buffalo milk and fermented in bamboo tubes
what is strained yogourt?
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
What is set yogourt?
a solid set where the yogurt forms and is not disturbed
Fruit-on-the-bottom yogurt
Fruit-on-the-top yogurt
What is stirred yogourt
Yogurt is made in a large container and then spooned into a secondary serving container
*What are the key in texture development of yogourt?
Heat treatment and acidification
how can we explain the textural changes in yogourt?
During acidification, at pH 5.0, the calcium phosphate is completely released from the casein micelle, and the integrity of the micelle is reduced, the denatured whey proteins also interact with k-casein increasing hydrophobicity, consequently, when the micelles become unstable aggregation starts which leads to gelation
Taste in yogourt is determined by :
- Lactic acid
- Acetaldehyde
- Acetic Acid
- Diacetyl
in yogourt ___ is probably the most important contributor to taste and LAB have a variety of pathways to produce acetaldehyde
Acetaldehyde
____ produce a little more acetic acid than other LAB and will produce a more ”vinegary” taste
•Bifidobacteria
