Freezing of plant products. Mastering the quality of frozen fruits

In recent years, the consumption of fruit and vegetables has been widely encouraged by promotional campaigns such as the 1 ^er Plan national de nutrition santé (PNNS), advocating the consumption of at least 5 fruits and vegetables a day in all their forms: raw, cooked, frozen or canned to eat "better". Although the consumption of fresh fruit and vegetables (8.496 million tonnes) still outweighs that of processed fruit and vegetables (15%), only the consumption of processed products is on the increase (up by around 2% a year) (2007 data).

Most fruit and vegetables are highly perishable, fragile plant organs which undergo marked physiological changes as soon as they are harvested. If the post-harvest stages are not controlled, the organoleptic and sanitary quality of fruit and vegetables can rapidly deteriorate. Processing methods such as appertizing, freezing (deep-freezing) and drying can significantly increase shelf-life. Freezing is one of the food preservation processes that has developed most rapidly over the last thirty years. It covers a wide range of products. Frozen fruit and vegetables offer a number of advantages in response to new consumer demands (convenience of use, year-round availability, good conversation value at home, appreciated taste quality).

The production of frozen fruit and vegetables in France, which nevertheless represents only 4% of all fruit and vegetables (2007 figures), is a high-potential market. Freezing enables us to deliver products whose nutritional quality is often considered superior to that of other processed foods. During freezing, the water contained in the cell structure is transformed into ice, reducing the triggering of microbiological and enzymatic processes leading to the development of unwanted colors and flavors. On the other hand, freezing causes physical and chemical changes that can lead to a loss of quality (texture, turgidity) after thawing. Freezing speed and final storage temperature in the frozen state are critical parameters for maintaining sensory, functional and biological properties of agricultural and organic products after freezing. The complex mechanisms involved in the degradation of plant tissue quality, associated with the mobility and transformation of water into ice, are still poorly understood, and difficult to characterize using simple methods.

Observations published to date remain very macroscopic. As a result, technological solutions for improving the quality of frozen plant products are still based on very empirical reasoning.