e. Use of Enzymes in Cheesemaking. In order to make cheese, the casein of
the milk must be coagulated by natural souring or by the use of rennet, a commercial
preparation of the enzyme rennin that is extracted from the calf's stomach. After the
curd is coagulated, it is then acted upon by microorganisms to produce the desired
f. More Examples of Enzyme Action. After death, the tissues of the animal
undergo a partial autolysis by enzymes contained in the tissues. Tenderizing of the
meat is accomplished by the action of these autolytic enzymes. Papain, a proteolytic
enzyme of papaya, is used as a meat tenderizer. Bromelin, a similar enzyme in fresh
pineapple juice, is equally effective as papain and has a more desirable odor.
a. The Action of Microorganisms. Many kinds of microorganisms are most
desirable for the part they play in preserving and processing foods. On the other hand,
some microorganisms attack food. Microorganisms such as bacteria, molds, and
yeasts damage or destroy foods. Bacteria produce certain enzymes that have either a
beneficial or a destructive effect on some foods. Bacterial growth in or on foods often is
extensive enough to make the food unattractive in appearance or objectionable in some
other way. Some bacteria cause food poisoning, some produce bitter flavor, and others
cause foods to spoil in one way or another. Molds cause some foods to decompose.
The fermentation effect of yeasts causes spoilage among many kinds of foods.
b. Microorganisms and Enzymes. Microorganisms include bacteria, molds,
yeasts, rickettsiae, and viruses. Enzymes are not included among the microorganisms.
An enzyme is an organic catalyst.
Section II. MICROBIAL GROWTH
Many species of bacteria increase in numbers very rapidly under ideal
conditions. Many scientists believe that the rapid growth of bacterial cells is because of
their large surface-to-volume ratio. In order to maintain their small size and the
favorable surface-to-volume ratio, cell division must occur rapidly. Most living
organisms have a cellular structure and grow by an increase in the number of cells per
organism. Bacteria, however, retain their unicellular structure and growth is reflected in
an increase in the number of individual cells, or organisms. Cell division of unicellular
bacteria appears to follow a very similar pattern and occurs in four steps.
a. Step 1. The cell nucleus divides before the cell division occurs.
b. Step 2. The second step is the division of the cytoplasm into two equal parts
separated by an inward growth of the cytoplasmic membrane forming a cross plate. In
cylinder-shaped bacteria, this division is generally at right angles to the long axis.