Cheese fermentation PDF

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Summary

Cheese Fermentation.1. Types of cheese. - Soft – e. Brie, Camembert, Mozzarella. - Semi-soft – e. Stilton, Roquefort. - Hard – e. Cheddar, Edam, Emmental. - Very hard – e. ParmesanCheese is a food made from the pressed curds of milk, complex mixture of water, protein, fat, ions, and chemical compoun...

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Cheese Fermentation. 1. 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 Cheese is a food made from the pressed curds of milk, complex mixture of water, protein, fat, ions, and chemical compounds which are produced during the ripening process. The ‘sensory’ characteristics of cheese relies on these compounds produced during ripening. -

Carbohydrates Phenolic compounds Organic acids Volatile aroma compounds

Evidence indicates that cheese has been made for at least 7,500 years. Possibly arose as animal stomachs were used to store food. 2. Key aspects of cheese production. Milk is clotted to produce curd. The main protein in milk is casein, which forms aggregates called micelles, which are negatively charged and repel each other. In cheese production, the protease rennin (also called chymosin) clots the milk by cleaving the side chain of casein. After cleavage, the micelles stop repelling each other and start to aggregate. The cut side chain can now bind to calcium ions, forming a bridge that holds the micelles together in a gel. Micelles are also held together by hydrophobic interactions. -

Chymosin.

Chymosin (rennin) is an aspartic endopeptidase. It is produced by (some) young mammals to curdle the milk that they eat. The natural substrate is kappa casein, which it cleaves between Phe105 and Met106. When cheese was first produced it was made directly using the curdled stomach contents of young animals (called the 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 using Kluyveromyces lactis). Identical rennins have been found in other organisms, e.g. Cryphonectrica parasitica, Mucor spp and Endothia spp. 3. Cheese production. 1

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Cheeses made without rennin. Lactic acid bacteria (LAB) - Lactococcus lactis, L. cremoris convert the main milk sugar, lactose, to lactic acid, decreasing the pH.

As the pH drops the milk curdles forming a light, wet curd. Cottage cheese is made this way. Lactic acid production.

Cheeses made with rennin. -

Pre-treatment of raw milk.

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Formation of solid curd. o Inoculate with starter cultures

Lactic acid bacteria (LAB) are added - Lactococcus lactis, L. cremoris, or Streptococcus thermophilus. A mixture of bacteria are often used in the starter culture. Defined starter cultures help with batch to batch consistency of the product. The temperature is held at 32oC for 10-75 minutes to ‘ripen’. This ripening allows the bacteria to start to grow and begin fermentation. During this process the pH drops, as lactose is converted to lactic acid, this helps with protein coagulation. The LAB also help to develop the cheese flavour. o

Addition of rennin.

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The rennin is then added, and this acts on the milk proteins to form the curd. The curd is not disturbed for at least 30 minutes so that a firm coagulum forms. The curd ferments until it reaches pH 6.4. The curd is then cut with cheese knives into small pieces and heated to 38oC. This temperature helps separate the curds from the whey. The whey is drained from the vat (and can be used in other processes, e.g. single cell protein production). -

Curd processing. o Cheddaring.

The curd mats are cut into sections, ‘loaves’, and placed on top of each other. They are turned frequently. The weight expels further whey and fermentation continues until a pH of 5.1-5.5 is reached. o

Salting and milling.

Subsequent steps vary a lot depending on cheese type. For cheddar: -

The curd mats are cut into smaller pieces and milled ( 1-2 cm pieces) 1-3% salt is added (this removes more whey and prevents further acidification) The cheese is packed into moulds and pressed.

Mozzarella is immersed in brine. Herbs, colouring or other microbes may be added. -

Ripening and ageing.

Ripening. Proteins and fats are modified by microbial proteases and lipases Proteases  creamy texture Lipases  complex flavours Commercial enzymes are often used Microbes may be added at different stages 4. Emmental cheese. The bacterium Propionibacterium freudenreichii secondarily ferments lactic acid to propionic acid, acetic acid, and carbon dioxide. The propionic acid contributes to flavour, whereas the carbon dioxide gets trapped, and we then find holes in the cheese. 5. Camembert cheese. An example of a bloomy-rind cheese Uses cow’s milk Curds are salted and the surface is sprayed with fungal spores and develops into a complex fungal community. Considered to be ‘surface-ripened’ Common commercial fungal strains are: a. Penicillium camemberti 3

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29/10/2021 b. Geotrichum candidum c. Kluyveromyces lactis d. Debaryomyces hansenii Some of the camembert flavoured compounds, which are often fatty acids and derivates.

6. Roquefort. Made from raw sheep's milk (Lacaune breed). Protected designated origin product (for 600 years-by King Charles VI in 1411) The mould used for the production is Penicillium roqueforti, which was isolated from soil in the limestone caves of Mont Combalou in Roquefort-sur-Soulzon In traditional production bread was left in the cave to go mouldy, and the spores were then used to inoculate the curds or added through holes made in the crust. P. roqueforti is now grown in the laboratory, so that there is more consistency in the flavour The cheese are shaped into round and then matured in the limestone caves for approx. 4-9 months. 7. Stilton. LAB are added to fresh pasteurised cow’s milk in an open vat along with spores of Penicillium roqueforti and rennet. Curds are cut into blocks and then milled and salted. This is then put into cylindrical moulds. The moulds are turned daily. The cylinders are removed, and the cheese coat is sealed by wrapping to prevent entry of air. After 5 weeks the crust is pierced with stainless steel needles. This allows air to enter and create the blue veins. It is not just the P. roqueforti which contributes to the flavour, there are other fungi, such as yeasts and also bacteria which all help to develop the complex flavour profile. It is the lipid content which contributes most of the complex flavour, as the P. roqueforti produces lipases. The extent of lipase activity depends on: -

Strain used Duration of ripening Amount of residual lipolytic activity in the milk Starter microflora (LAB) Homogenisation of cheese milk Surface microbes pH, temperature, and salt concentration

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29/10/2021 8. Comparison between cheese and beer production.

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