Protein nutritional value of extrusion-cooking defatted lung flour

Abstract

The nutritional value of lung protein extruded at diverse conditions of feed moisture and process temperatures was determined by biological assay. No dependence of the nutritional quality of the proteins on process temperature was found in the extrusion of lung with 18% moisture content. Samples extruded at this low moisture (18%) presented a significant decrease in cysteine content and low biological value of the protein, although the decrease which has been observed in the chemical scores of total sulphur and other limiting amino acids was not enough to account for the observed decrease in biological value. Supplementation of this extruded protein with its limiting amino acids restored the initially observed nutritional value. Extrusion performed with 30% moisture lung flour protein resulted in a smaller loss of cysteine content after processing and bioassay comparable to non-processed samples or casein. Digestibilities of the lung samples decreased slightly after defatting and were not affected by their subsequent extrusion. In all lung samples digestibility was high, and thus could not explain the observed poor bioavailability of the protein extruded with 18% moisture content. Racemization could have occurred during the extrusion of this low moisture flour.