[Effect of the extrusion process on the availability of proteins]

The extrusion process has grown rapidly as in the preparation of meat-extenders from vegetal proteins as in the fabrication of cocktail-snacks and food for breakfast. The nutritional modifications induced by the thermic shock during the extrusion affect: -the diminution of the content of nutrient: loss in vitamins, destruction and unavailability of amino-acids; -the structural modification of a few compounds: starch gelatinization; -destruction of antinutritional factors: essentially antitrypsic factor. We studied the effect of extrusion with a model-mixture on the availability of amino-acids and particularly lysin. We effected the systematic study of different factors which can interfer in the intensity of the Maillard reaction in relation to the composition of the mixture (presence and nature of sugar, etc.) and to the technological parameters (screw-section, moisture of the mixture, etc.) The model mixture composed of cereal flours shows a global loss of 32 p. 100 in lysin (destruction 18 p. 100, biological unavailability 16 p. 100) after extrusion. When this mixture is added up with 7,2 p. 100 of saccharose the total loss in lysin reaches 40 p. 100. If saccharose is substituted by a more reducing sugar (fructose) the lysin loss approaches 80 p. 100. The addition of 4 p. 100 water at the mixture containing saccharose (total moisture 14 p. 100) limits the lysin loss to 10 p. 100. The modification of other technological parameters does not improve significatively the level of available lysin. The moisture of the mixture before extrusion appears to be a preponderatting factor in the intensity of the Maillard reaction during extrusion.