DETOXIFICATION OF JACKBEAN (CANAVALIA-ENSIFORMIS L.) WITH PILOT-SCALEROASTING - II - NUTRITIONAL-VALUE FOR POULTRY

Experiments were conducted to investigate the relationships between va rious roasting conditions and the levels of antinutritional factors on the one hand and the nutritional value of jackbean (JB) samples on ch icks on the other. Whole JB were roasted on a pilot scale coffee roast er as previously described (see part 1). Two animal experiments were p erformed on nine roasted JB samples differing in the intensity of the roasting treatment. The first experiment was carried out over a period of five days using an acceptability test for chicks. The second exper iment was conducted with adult cockerels in order to determine the tru e metabolizable energy content, corrected for nitrogen balance (TMEn), as well as che true nitrogen digestibility (TND) of the JB samples us ing a digestive balance test according to a forced feeding method. A d ecrease in JB toxicity (feed intake and live weight) was observed In t he roasted seeds. The!,est results in relation to chick feed intake we re obtained when the JB were roasted at medium (164-168 degrees C) or high (180-190 degrees C) temperatures with a longer exposure time (24- 26min). The improvement in chick feed intake could be related to the d ecrease in the initial canavanine content and the total removal of the haemagglutination activity from roasted seeds. The most intensive tre atments (high temperatures and long time exposure) resulted in a stati stically significant (P<0.01) decrease in the TMEn when compared to ra w JB values. Long heating times significantly decreased TND (P<0.01) o nly when they were combined with high temperatures (180-190 degrees C) , which could be associated with an increase in acid detergent fibre c ontent. The best results on feed consumption and poultry growth were o btained when the JB were roasted at a medium temperature (164-168 degr ees C) with a long exposure time (24-26 degrees C). Our trials demonst rated that roasting alone could significantly destroy the antinutritio nal factors without major adverse effects on the biological value of J B seeds. However, the process has to be optimised within a very short. range of roasting conditions, which assumes a precise control of the process conditions. Roasting increases the feasibility of developing t he jackbean as an economic crop. (C) 1998 Elsevier Science B.V.