FOOD FERMENTATION

Decomposition of carbohydrates by microorganisms or enzymes is called fermentation. Fermentation of food results in the production of organic acids, alcohol, etc., which not only help in preserving the food but may also produce distinctive new food products.

The term fermentation has come to have somewhat different meanings as its underlying causes have become better understood. The term was first applied to the production of wine more than a thousand years ago. Fermentation means the breakdown of sugar into alcohol and carbon dioxide. Pasteur later demonstrated the relationship of yeast to this reaction, and the word fermentation became associated with microorganisms, and still later with enzymes.

Further, many of the microorganisms and enzymes studied also had the ability to break down non-carbohydrate materials such as proteins and fats, which yielded carbon dioxide, other gases, and a wide range of additional materials.

The term fermentation refers to breakdown of carbohydrate and carbohydrate like materials under either anaerobic or aerobic conditions.

• Conversion of lactose to lactic acid by Streptococcus lactis bacteria is favored by anaerobic conditions and is true fermentation;

• Conversion of ethyl alcohol to acetic acid by Acetobacter aceti bacteria is favored by aerobic conditions and is more correctly termed an oxidation rather than fermentation.

The term fermented foods is used to describe a special class of food products characterized by various kinds of carbohydrate breakdown. Most fermented foods contain a complex mixture of carbohydrates, proteins, fats, and so on, undergoing modification simultaneously, or in some sequence, under the action of variety of micro- organisms and enzymes.

Those reactions involving carbohydrates and carbohydrate like materials (true fermentations) are referred to as "fermentative".

• Changes in proteinaceous materials are designated proteolytic or putrefactive.

• Breakdowns of fatty substances are described as lipolytic.

When complex foods are "fermented" under natural conditions, they invariably undergo different degrees of each of these types of change. In specific food fermentations, control of the types of microorganisms and environmental conditions to produce desired product characteristics is necessary.

Fermentations occur when microorganisms consume organic substrates as part of their own metabolic processes. Such processes lead to the decomposition of natural materials.

Natural fermentations have played a vital role in human development and are probably the oldest form of food preservation. Although the growth of microorganisms in many foods is undesirable and considered spoilage, some fermentation is highly desirable.

• Fruit and fruit juices left to the elements acquired an alcoholic flavor;

• milk on standing became mildly acidic and eventually became cheese;

• Cabbage turned to sauerkraut.

Fermentation encourages the multiplication of microorganisms and their metabolic activities in foods. But only selected organisms are encouraged, and their metabolic activities and end products are highly desirable.

Acetic, lactic and alcoholic are the three important kinds of fermentation involved in fruit and vegetable preservation. The keeping quality of vinegar, fermented pickles and alcoholic beverages depends upon the presence of acetic acid, lactic acid and alcohol, respectively.

Care should be taken to exclude air from the fermented products to avoid further unwanted or secondary fermentation. Wines, cider, vinegar, fermented pickles and other fermented beverage, etc., are prepared by these processes.