Lesson 11  FOOD PRESERVATION BY FERMENTATION

   Microorganisms no doubt outnumber other living entities on this planet and can be found existing actively or passively wherever living organisms occur. While the energy for on this planet is captured by green plants in the photosynthetic process, microorganisms are generally responsible for the final decomposition of the photosynthetic products. Animals play a minor role in the cycle.

   Inasmuch as bacteria, yeasts and molds are to be found throughout the environment of man, it is to be anticipated that these microorganisms are in direct competition with other living entities for the energy for life. Whenever the conditions of nutrients and environment are favorable for microbial activity, it will be found.

    Man must compete with all other living entities on earth. In order to retain food supplies for himself, he must interfere with natural processes. Through his study, and as a fruit of his curiosity, man has evolved a number of control systems. One is the preservation of food by controlling, yet encouraging, the growth of microorganisms. Under such a condition, man may employ microorganisms to create unfavorable conditions for other microbes, yet retain in the foodstuffs the nutrients desired.

    While microorganisms were not identified as the important agents in food spoilage until a century ago, wine making, bread baking, cheese making and salting of foods have been practiced for more than four thousand years. For all those years mankind practiced food preservation using unknown, invisible, active, living organisms.

While food preservation system in general inhibits the growth of microorganisms, all such organisms are not detrimental. In fact some are commonly utilized in food preservation. The production of substantial amounts of acid by certain organisms creates unfavorable conditions for others.

 

To review terms for a moment, respiration is that process whereby carbohydrates are converted aerobically into carbon dioxide and water with the release of large amounts of energy. Fermentation is a process of anaerobic, or partially anaerobic, oxidation of carbohydrates. Putrefaction is the anaerobic degradation of proteinaceous materials.

Sodium chloride is useful in a fermentation process of foods by limiting the growth of putrefactive organisms and by inhibiting the growth of large numbers of other organisms. Yet some bacteria tolerate and grow in substantial amounts of salt in solution.

                                              

   

 Fermentation of Carbohydrates

    

The word fermentation has undergone evolution itself. The term was emplyed to describe the bubbling or boiling condition seen in the production of

wine. prior to the time that yeasts were discovered. However. after Pasteur's

discovery, the word became used with microbial activity, and later with enzyme

activity. Currently the term is used even to describe the evolution of carbon

dioxide gas during the action of living cells. Neither gas evolution nor the presence of living cells is essential to fermentations where no gas is liberated, and in

fermentations accomplished solely with enz3'mes. s)

 

    There is a clear difference between fermentation and putrefaction. Fermentation is a decomposition action on carbohydrate materials; putrefaction relates

to the general action of microorganisms on proteinaceous materials. Fermentation

processes usually do not evolve putrid odors. and carbon dioxide is usually

produced. In putrefaction the evolved materials may contain carbon dioxide, but

the characteristic odors are hydrogen sulfide and sulfur-containing protein decomposition products. A putrid fermentation is usually a contaminated  fermentation. Putrid kraut or pickles result from microbial growths decomposing protein, rather than the normal fermentation of carbohydrates to produce acid.

    

Industially Important Organisms In Food Preservation

    

There are three important characteristics microorganisms should have if

they are to be useful in fermentation and pickling. (1) The microorganisms must

be able to grow rapidly in a stuiable substrate and environment. and be easily

cultivated in large quantity. (2) The organism must have the ability to maintain

physiological constancy under the above conditions, and yield the essential

enzymes easily and abundantly in order that the desired chemical changes can

occur. (3) The environmental conditions required for maximum growth and reproduction should be comparatively simple.

     The application of microorganisms to food preservation practices must be

such that a positive protection is available to control contamination.

     The microorganisms used in fermentations are notable in that they produce

large amounts of enzymes. Bacteria, yeasts and molds, being single cells, contain the functional capacities for growth reproduction, digestion. assimilation

and repairs in a cell, that higher forms of life have distributed to tissues.

Therefore. it is to be anticipated that single cell complete living entities(such as yeasts) have a higher enzyme productivity and fermentative capacity than found

with other living creatures.

     Enzymes are the active substances which control chemical reactions in fermentation. The microorganisms of each genus and species are actually a warehouse of enzymes, with its own special capacity to produce and secrete enzymes.

Man has yet to learn to synthesize them.

     A dry gram of an organism endowed with high activity lactose fermenting

enzymes is capable of breaking down 10,000 g of lactose per hour. This great

chemical activity is associated  with the single life-process requirements of the

organisms, the ease with which they obtain energy for life, their great growth

capacity and reproduction rate, and their great capacity for maintenance of the

living entity. One generation may occur in a matter o{ minutes.

     But there is a balance in effect. In living, the organisms consume energy.

The product of their actions is a substrate of lower energy than that native

material upon which they were planted. However. the product of the activity in

the instance of wine is one which man generally enjoys more than the native

juice from which the wine was produced.

                      

 Order of Fermentation

     Microorganisms have available carbohydrates, proteins, fats. minerals and

minor nutrients in native food materials. It appears that microorganisms first

attack carbohydrates, then proteins, then fats. There is an order of attack even

with carbohydrates; first the sugars, then alcohols, then acids. Since the first

requirement for microbial activity is energy, it appears that the most available

forms, in order of preference, are the CH2, CH, CHOH, and COOH carbon

linkages. Some linkages such as CN radicals are useless to microorganisms.

    

Types ,of Fermentations of Sugar

     Microorganisms are used to ferment sugar by complete oxidation, partial

oxidation, alcoholic fermentation , lactic acid fermentation, butyric fermentation

and other minor fermentative actions.

     (l) Bacteria and molds are able to break down sugar (glucose) to carbon

dioxide and water. Few yeasts can accomplish this action.

     (2) The most common fermentation is one in which a partial oxidation of

sugar occurs. In this case, sugar may be converted to an acid. The acid finally

     may be oxidized to yield carbon dioxide and Water, if permitted to occur. For

example, some molds are used in the production of citric acid from sugar solutions.

     (3) Yeasts are the most efficient converters of aldehydes to alcohols. Many

species of bacteria, yeasts and molds are able to yield alcohol. The yeast,

Saccharomyces ellipsoideus. is of great industrial importance in alcoholic fermentatioas. The industrial yeasts yield alcohol in recoverable quantities. While

other organisms are able to produce alcohol, it occurs in such mixtures of aldehydes, acids and esters that recovery is difficult. The reaction from sugar to

alcohol is many stepped.

     (4) Lactic acid fermentation are of great importance in food preservation.

The sugar in foodstuff may be converted to lactic acid and other end products,

and in such amounts that the environment is controlling over other organisms.

Lactic acid fermentation is efficient, and the fermenting organisms rapid in growth. Natural inoculations are such that in a suitable environment the. lactic acid

bacteria will dominate, as in souring of milk.

     (5) Butyric fermentations are less useful in food preservation than those

noted previously. The organisms are anaerobic and impart undesirable flavors and

odors to foods. The anaerobic organisms capable of infecting man causing disease are commonly butyric fermenters. Carbon dioxide. hydrogen. acetic acid and

alcohols are some of the other fermentation products.

     (6) In addition to the above there is a fermentation which involves much

gas production. It is useful ;n food preservation. although gas production has

disadvantages. Energy-wise it is less efficient to produce gases (carbon dioxide

and hydrogen) which have little or no preserving power in concentrations found

in comparison with lactic acid. Also, the important food spoilage organisms are

capable of growing in such environments. In gassy fermentations sugar molecules

are altered to form acids, alcohols and carbon dioxide. It is usually necessary

to include some other controlling influence, such as adding sodium chloride to

a substrate, with this form of fermentation.

     (7) There are many fermentative actions possible in foods which are detrimental to the acceptability of treated foods. Generally the organisms capable of

attacking higher carbohydrates such as cellulose, hemicelluloses, pectin, and

starch will injure the texture, flavor and quality of treated foods.

    

Fermentation Controls

     Foods are contaminated naturally with microorganisms and will spoil if

untended. The type of action which will develop is dependent upon the conditions

which are imposed. The most favorable to a given type of fermentation under

one condition will be altered by slight changes in a controlling factor. Untended meat will naturally mold and putrefy. If brine or salt added, entirely different organisms will take over.

     The pH Value of Food is a Controlling Factor-Most foods in native,

fresh form which man consumes as food are acid. Vegetables range in pH value from 6.5 to 4.8. Fruits range from 4.5 down to 3.O. Animal flesh when

killed is approximately neutral (7.2) but within two days the pH value will

be approximately 6.0. Milk has a pH value near 6.4.

     In as much as the two important fermentation in such foods are oxidative

and alcoholic, the growth of organisms will be controlled by the acidity of the

medium. In fruits and fruit juices, yeasts and molds will quickly establish

themselves. In meats yeasts are less active than bacteria. In milk, an acid fermentation is established in the matter of a few hours.

     Source of Energy-Inasmuch as the immediate need of microorganisms is a

source of energy, the soluble, readily available carbohydrates influence the

microbial population that wiLI dominate. In milk the sugar is lactose; those organisms which quickly mount in numbers are the lactose formenting organisms.

Because suitable energy sources are generally available to microorganisms in man's

foods, energy sources are not usually a limiting factor, with certain exceptions

(such as milk).

     Availability of Oxygen-The degree of anaerobiosis is a principal factor

controlling fermentations. with yeasts. when large amounts of oxygen are present, yeast cell production is promoted. If alcchol production is desired, a very

limited oxygen supply is required.

     Molds are aerobes, and are controlled by the absence of oxygen, Bacterial

populations which will dominate a substrate may be manipulated by their oxygen

requirements and its availability. .

     The end product of a fermentation can be controlled in part by the oxygen

tension of the substrate, other factors being optimum.

     Temperature Requirements-Each group of microorganisms has an optimum

temperature for growth; the temperature of a substrate therefore exerts a positive

control on their growth. To obtain the maximum performance during fermentation, the optimum temperature for the organisms must be created.

     The temperature at which a food is held will determine within certain limits

the nature of the organisms capable of either yielding the desired fermentation

or spoilage, whichever the case may be.

     The action of Sodium Chloride in Controlling Fermentations-Salts is one

of the most important food adjuncts in food preservation. In drying it has been

shown to have beneficial. In fermentations salt can exert a role in sorting

the organisms permitted to grow.