Question

• Explain how bacteria can be used in Food production

• Explain the fermentation of Milk & Cheese

• Explain the use of starter cultures

• Explain the difference between foodborne infection & foodborne intoxication

Answer 1

1. Microorganisms are used by nature to carry out fermentation processes and for thousand of years mankind has used yeasts, moulds and bacteria to make food products such as bread, beer, wine, vinegar, yogurt and cheese.

Food typically contain a variety of bacteria of which some may be beneficial, such as those preserving foods through products of fermentation.

Lactic acid bacteria are among the most important groups of micro-organisms used in food fermentations.

Starter cultures, which are largely comprised of lactic acid bacteria, are food grade micro-organisms that are used to produce fermented foods of desirable appearance, body texture and flavour.

Types of fermented foods for which commercial starter cultures are used include dairy products ( cheese, sour cream, yogurt), meat products (sausages) and vegetable products (pickles, olives).

For starter cultures to be effective during food fermentations, they must dominate over naturally occurring microflora and produce the desired end products of fermentation.

Another application for beneficial microbes used in foods is adding probiotic organisms to provide a health benefits to consumers. Lactic acid bacteria are the most common types of probiotic microbes being used.

Probiotics have been largely delivered in fermented foods such as yogurt and fermented milk products.

2. Fermented milk products also known as cultured milk products are dairy foods that have been fermented with lactic acid bacteria such as lactobacillus and lactococcus.

The fermentation process increases the shelf life of the product, while enhancing the taste and improving the digestibility of the milk.

A range of different lactobacilli strains has been grown in laboratories allowing for a wide range of cultured milk products with different tastes.

So many different types of cultured milk products can be found around the world including milk, cheese, yogurt, other cultured daily foods, ice cream and more.

Cheese can be defined as a consolidated curd of milk solids in which milk fat is entrapped by coagulated casein.

Unlike fermented milk, the physical characteristics of cheese are far removed from those of milk because protein coagulation proceeds to a greater extent as a result of use of proteolytic enzymes and much of the water content of milk separates and is removed in the form of whey.

Cheese can be made using pasteurized or raw milk. Cultures for cheese making are called lactic acid bacteria.

Milk is often standardized before cheese making to optimize the protein to fat ratio to make a good quality cheese

Depending on the desired cheese milk may be pasteurized or mildly heat treated to reduce the number of spoilage organisms and improve the environment for the starter culture to grow.

Milk is cooled after pasteurization or heat treatment to bring it to the temp. needed for the starter bacteria to grow.

Then the starter culture bacteria are added to the milk and held at 32°C for 30 min to ripen. The ripening step allows the bacteria to grow and begin fermentation.

The rennet is the enzyme that acts on the milk protein to form the curd. After the rennet is added, the curd is not disturbed for 30 min so a firm coagulation forms.

The curd is allowed to fermented until it reaches the pH 6.4. The curd is then cut with cheese knives into small pieces and heated to 38°C. The heating step helps to separate the whey from the curd.

The whey is drained from the vat and the curd forms a mat.The curd mats are cut into sections and oiled on top of each other and flipped periodically. This step is called cheddaring.

Cheddaring helps to expel more whey, allows the fermentation to continue until a pH of 5.1 to 5.5 is reached and allows the mats to knit together and and form a tighter matter structure.

The curd mats are then cut into smaller pieces.

3. Starter cultures are those micro-organisms that are used in the production of cultured dairy products such as yogurt and cheese.

The natural microflora of the milk is either inefficient, uncontrollable and unpredictable or is destroyed all together by the heat treatments given to the milk.

A starter culture can provide particular characteristics in a more controlled and predictable fermentation.

The primary function of lactic starters is the production of lactic acid from lactose. Other functions of starter culture may include:

a. Flavour, aroma and alcohol production

b. Proteolytic and lipolytic activities

c. Inhibition of undesirable organisms

4. Foodborne infection is caused by the ingestion of food containing live bacteria which grow and establish themselves in the human intestinal tract.

Foodborne intoxication is caused by ingesting food containing toxins formed by bacteria which resulted from the bacterial growth in the food item. The live micro-organisms does not have to be consumed.