Experiment of Cheese Production by Fermentation and Enzymatic Coagulation of Milk Proteins

Aim

To prepare cheese Production by fermentation and enzymatic coagulation of milk proteins using starter culture and rennet.

Principle

Cheese production is based on lactic acid fermentation and enzyme-mediated coagulation of milk proteins.

Lactic acid bacteria convert lactose into lactic acid, lowering the pH.
Rennet (proteolytic enzyme) cleaves κ-casein, causing milk proteins to coagulate.
The solid portion (curd) is separated from the liquid (whey) and processed to form cheese.

Theory

The principal objective of this investigation is to create cheese under laboratory conditions by utilising the process of lactic acid fermentation and the enzyme, lactase, for coagulating milk proteins. Cheese production is among the most important uses of biotechnology in the dairy industry, which relies on the combined effects of microorganisms and enzymes acting on milk.

Cheese is produced by coagulating the casein protein in milk. Casein protein may be coagulated by decreasing the acidity of the milk using lactic acid bacteria and their enzymes. The lactic acid bacteria in wine are responsible for producing lactic acid from fermented sugar, which causes a decrease in pH of the milk. The enzyme rennet acts specifically on κ-casein, causing it to displace its hydrogen ions and reduce the casein micelles' stability. When this occurs, a solid curd is formed while the remaining liquid is whey.

Requirements

Materials

Fresh pasteurized milk – 500 mL
Starter culture (lactic acid bacteria / fresh curd)
Rennet solution
Calcium chloride (CaCl₂) – optional
Common salt

Apparatus

Beaker (1 L)
Hot plate / water bath
Thermometer
Glass rod
Muslin cloth / cheesecloth
Measuring cylinder

Procedure

Take 500 mL of fresh pasteurized milk in a clean beaker.
Heat the milk gently to 72°C for 15 seconds to pasteurize it.
After heating, allow the milk to cool down to 35–37°C.
Add 2–3 mL of starter culture (or 1 teaspoon of fresh curd) to the milk and mix gently using a sterile glass rod.
Cover the beaker and incubate the milk at 37°C for 30–45 minutes to allow lactic acid fermentation.
Dilute 0.5 mL of rennet in about 10 mL of distilled water.
Add the diluted rennet solution to the fermented milk and stir slowly for 30 seconds.
Leave the milk undisturbed at 37°C for 30–40 minutes until a firm curd is formed.
After curd formation, cut the curd into small cubes (1–2 cm) using a sterile knife or spatula.
Allow the curd to rest for 10 minutes so that whey begins to separate.
Transfer the curd into a muslin cloth and allow the whey to drain for 30–60 minutes.
Tie the cloth tightly and press the curd under light weight for 1–2 hours to remove excess whey.
Remove the pressed curd and add 1–2% common salt uniformly.
The formed cheese is now ready for observation and further analysis.

Image Source: Natural cheese

Observations

Observation	Result
Appearance of curd	White, firm
Whey color	Pale yellow
Texture	Semi-solid
Odor	Mild sour smell

Result

Cheese was successfully prepared in the laboratory by fermentation and enzymatic coagulation of milk proteins.

Biology Notes

Experiment of Cheese Production by Fermentation and Enzymatic Coagulation of Milk Proteins