Chapter 4 Methods of reducing deterioration

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A knowledge of deterioration factors and the way they act, including the rates of deterioration to a specific category of food, means that it is possible to list the ways of lowering or stopping the action and obtaining fruit and vegetable preservation.

In order to maintain their nutritional value and organoleptic properties and because of technical-economical considerations, not all the identified means against deterioration actually have practical applications for fruit and vegetable preservation.

4.1 Technical methods of reducing food deterioration

These technical means can be summarised as follows:

Physical Heating
Lowering of water content Drying/dehydration. Concentration
Sterilising filtration
Other physical means (high pressure, vacuum, inert gases)
Chemical Salting
Sugar addition
Artificial acidification
Ethyl alcohol addition
Antiseptic substance action
Biochemical Lactic fermentation (natural acidification)
Alcoholic fermentation

This classification of methods of reducing deterioration presents some difficulties because their preservation effects are physical, physico-chemical, chemical and biochemical complex phenomena which rarely act in isolation. Normally they take place together or one after the other.

From the whole list of possible methods of reducing deterioration, over the years, some procedures for fruit and vegetable preservation have found practical application.

4.2 Procedures for fruit and vegetable preservation

Procedures Practical applications
Fresh storage Fruits, vegetables
Cold storage Fruits, vegetables
Freezing Fruits, vegetables
Drying/dehydration Fruits, vegetables
Concentration Fruit and vegetable juices
Chemical preservation Fruit semi-processed
Preservation with sugar Fruit products/preserves
Pasteurization Fruit and vegetable juices
Sterilisation Fruits, vegetables
Sterilising filtration Fruit juices
Irradiation Fruits, vegetables

These preservation procedures have two main characteristics as far as being applied to all food products is concerned:

4.3 Combined preservation procedures

In practice preservation procedures aim at avoiding microbiological and biochemical deterioration which are the principal forms of deterioration. Even with all recent progress achieved in this field, no single one of these technological procedures applied alone can be considered wholly satisfactory from a microbiological, physico-chemical and organoleptic point of view, even if to a great extent the food value is assured.

Thus, heat sterilisation cannot be applied in order to destroy all micro-organisms present in foods without inducing non desirable modifications. Preservation by dehydration/drying assures microbiological stability but has the drawback of undesirable modifications that appear during storage: vitamin losses, oxidation phenomena, etc.

Starting with these considerations, the actual tendency in food preservation is to study the application of combined preservation procedures, aiming at the realisation of maximum efficiency from a microbiological and biological point of view, with reduction to a minimum of organoleptical degradation and decrease in food value.

The principles of combined preservation procedures are:

Research and applications in this direction were followed by microbiological and biochemical way, obtaining a serial of combination of preservation procedures with the possibility of application in industrial practice. [unclear]


4.3.1 Fresh fruit and vegetable storage can be combined with:

4.3.2 Cold storage can be combined with storage in an environment with added of carbon dioxide, sulphur dioxide, etc. according to the nature of product to be preserved.

4.3.3 Preservation by drying/dehydration can be combined with:

- freezing: fresh fruit and vegetables are dehydrated up to the point where their weight is reduced by 50% and then they are preserved by freezing.

This procedure (freeze-drying) combines the advantages of drying (reduction of volume and weight) with those of freezing (maintaining vitamins and to a large extent organoleptic properties).

A significant advantage of this process is the short drying time in so far as it is not necessary to go beyond the inflexion point of the drying curve. The finished products after defreezing and rehydration/reconstitution are of a better quality compared with products obtained by dehydration alone.

4.3.4 Preservation by concentration, carried out by evaporation, is combined with cold storage during warm season for tomato paste (when water content cannot be reduced under the limit needed to inhibit moulds and yeasts, e.g. aw = 0.70...0.75).

4.3.5 Chemical preservation is combined with:

4.3.6 Preservation by lactic fermentation (natural acidification) can be combined with cold storage for pickles in order to prolong storage time or shelf-life.

4.3.7 Preservation with sugar is combined with pasteurization for some preserves having a sugar content below 65%.

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