Lecture 11: Cheese Flashcards
What are different types of cheese?
- Soft e.g., brie, camembert, mozzarella
- Semi-soft e.g., stilton, roquefort
- Hard e.g., cheddar, edam, emmental
- Very hard e.g., parmesan
What is cheese?
Food made from pressed curds of milk
Complex mixture of: water, protein, fat, ions, and chemical compounds produced during ripening process
Sensory characteristics of cheese relies on compounds produced during ripening:
1. Carbs
2. Phenolic compounds
3. Organic acids
4. Volatile aroma compounds
What is the history of cheese?
- been made for at least 7,500 years
- Possibly arose as animal stomachs were used to store food
What are the key aspects of cheese production?
- Milk clotted to produce curd
- Main protein in milk, casein, forms aggregates called micelles,
which are negatively charged and repel each other - Protease renin (also called chymosin) clots milk by cleaving side
chain of casein - After cleavage, micelles stop repelling and aggregate. Cut side
chain can bind to calcium ions, forming a bridge between the
micelles - Micelles also held together by hydrophobic interactions
What is chymosin
- Aspartic endopeptidase
- Produced by (some) young mammals to curdle milk they eat
- Natural substrate is kappa casein, cleaving between Phe105 and
Met106
What is rennet
Commercial rennet is a mixture of several enzymes extracted from stomach of butchered veal calves
Most cheese now uses bovine chymosin, produced in heterologous hosts (E. coli, Aspergillus niger, or Kluyveromyces lactis)
How is cheese made without rennin
- Lactic acid bacteria (LAB) - Lactococcus lactis, L. cremoris convert
the main milk sugar, lactose, to lactic acid, decreasing pH - pH drop curdles milk forming a light wet curd. Cottage cheese is
made this way
How is cheese made with rennin
- Pre-treatment of raw milk
- Formation of solid curd
- Curd processing
- Ripening and ageing
How is solid curd formed
Inoculate with starter cultures
1. LAB added
2. Defined starter cultures help with batch to batch consistency
3. Temperature held at 32C for 10-75 minutes to ‘ripen’. Ripening
allows bacteria to start to grow and begin fermentation
4. During this process, pH drops, as lactose is converted to lactic acid,
aiding protein coagulation
5. LAB also helps develop cheese flavour
Addition of renin
1. Acts on milk proteins to form curd
2. Curd is not disturbed for at least 30 minutes allowing firm coagulum
formation
3. Curd ferments until it reaches pH 6.4. Curd then cut with cheese
knives into small pieces and heated to 38C (seperating curds from
whey)
4. Whey is drained from vat (can be used for other processes e.g.,
single cell protein production)
How is curd processed?
Cheddaring
1. Curd mats are cut into sections (‘loaves’) and placed on top of each
other, and turned frequently.
2. The weight expels further whey and fermentation
3. Continues until pH 5.1-5.5
Salting and milling
1. Subsequent steps vary depending on cheese type
2. Cheddar: curd mats cut into smaller pieces (1-2cm) and milled. 1-
3% salt added (removes more whey and prevents further
acidification). Cheese packed into moulds and pressed
3. Mozzarella immersed in brine
4. Herbs, colouring, or other microbes may be added
How is cheese ripened and aged?
Ripening
1. Proteins and fats are modified by microbial proteases and lipases
a. proteases = creamy texture
b. Lipases = complex flavours
2. Commercial enzymes often used
3. Microbes may be added at different stages
What is emmental
- Bacterium Propionibactierum freudenreichii secondarily ferments
lactic acid to propionic acid, acetic acid, and CO2 - Propionic acid adds flavour, whilst CO2 gets trapped to make holes
What is camembert
- Bloomy-rind cheese
- Cows milk
- Curds salted and surface is sprayed with fungal spores and
develops into complex fungal community - Considered to be ‘surface-ripened’
- Common commercial fungal strains
a. Penicillium camemberti
b. Geotrichum candidum
c. Kluyveromyces lactis
d. Debaryomyces hansenii
What are the flavour compounds of camembert
Often fatty acid derivatives
- Isovaleric acid (cheesy smell)
- Oct-1-en-3-one (metallic smell)
- Diacetyl (buttery taste)
- Methional (potato crisp flavour)
What is Roquefort
- Raw sheep’s milk
- Mould used for production is Penicillium roqueforti, which was isolated from soil in limestone caves
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