• Jellying

  Food may be preserved by cooking in a material that solidifies to form a gel. Such materials include gelatin, agar, maize flour and arrowroot flour. Fruit preserved by jellying is known as jelly, marmalade, or fruit preserves. In this case, the jellying agent is usually pectin, either added during cooking or arising naturally from the fruit.

• Irradiation

  Irradiation of food is the exposure of food to ionizing radiation; either high-energy electrons or X-rays from accelerators, or by gamma rays. The treatment has a range of effects, including killing bacteria, molds, insects, pests, reducing the ripening and spoiling of fruits, and at higher doses inducing sterility. The technology may be compared to pasteurization; it is sometimes called 'cold pasteurization', as the product is not heated. Irradiation is not effective against viruses; it cannot eliminate toxins already formed by microorganisms, and is only useful for food of high initial quality.

• Modified atmosphere

  Modified atmosphere is a way to preserve food by operating on the atmosphere around it. Salad crops which are notoriously difficult to preserve are now being packaged in sealed bags with an atmosphere modified to reduce the oxygen (O₂) concentration and increase the carbon dioxide (CO₂) concentration. There is concern that although salad vegetables retain their appearance and texture in such conditions, this method of preservation may not retain nutrients, especially vitamins. Nitrogen gas (N₂) at concentrations of 98% or higher is also used effectively to kill insects. However, carbon dioxide has an advantage in this respect as it kills organisms requiring concentrations of only 80%.

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