Shelf-life extension by heat preservation

The various forms of microbiological spoilage are preventable to a large degree by a wide range of preservation techniques, most of which act by preventing or inhibiting microbial growth.

Canning involves packing a food in a container and supplying sufficient heat treatment to kill spoilage organisms or pathogens that may present. It is a method of  preserving where food is placed in airtight, vacuum-sealed containers and heat processed at 121 °C.

Thermal processing like canning process is a suitable method to prolong the shelf life of fruits, such as date fruit, which has some benefits, including: artificial maturation, destroying insects, reducing the microbial load, inactivation of enzymes (e.g. pectinase), and reducing tannin.

Commercial canning is done under tightly controlled conditions — careful sanitation and the necessary time and temperature under pressure, but there are still limits to how long it will preserve food. There are several factors that limit the shelf life of canned foods. First, cans can rust over time. Shipping accidents, where cans fall and dent or are crushed, also cause container problems.

Heat preservation (canning) provides a shelf-stable product, but usually at the cost of colour, flavour, and texture. Heat treatment, however, leads to destruction of freshness and nutrient losses.
Shelf-life extension by heat preservation

Process of canning effects on vegetables

From the textural standpoint, vegetables may be divided into those that are eaten raw and valued primarily for their crispness, those that are eaten cooked and valued for their softness and those that can be consumed in either form such as cauliflower and carrots.

Vegetables like peas, beans, greens are sometimes canned. The retention of original color is of great importance effecting the marketability and consumer response.

In the process of canning, vegetables are heated to destroy spoilage disease causing microorganisms.

Such heat treatments also produce a number of of undesirable chemical and textural changes in the vegetables. The textural changes are due to partial destruction of the cell wall and cell membrane.

Blanching, plus the strong heat treatments applied to nonacid vegetables, appears to be responsible for the large vitamin losses in canning.

Heat treatments also cause chemical alteration of the green pigment chlorophyll, thus resulting in a processed vegetable with less green color.

During canning chlorophyll gets converted to pheophytin due to the high temperature used. Sometimes to retain the color and to neutralize the acid, alkali is added.
Process of canning effects on vegetables