Detoxification of jackbean (Canavalia ensiformis L.) with pilot scale roasting.: II: Nutritional value for poultry

Experiments were conducted to investigate the relationships between various roasting conditions and the levels of antinutritional factors on the one hand and the nutritional value of jackbean (JB) samples on chicks on the other. Whole JB were roasted on a pilot scale coffee roaster as previously described (see part 1). Two animal experiments were performed 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 experiment was conducted with adult cockerels in order to determine the true metabolizable energy content, corrected for nitrogen balance (TMEn), as well as the true nitrogen digestibility (TND) of the JB samples using a digestive balance test according to a forced feeding method. A decrease in JB toxicity (feed intake and live weight) was observed in the roasted seeds. The best results in relation to chick feed intake were obtained when the JB were roasted at medium (164–168°C) or high (180–190°C) temperatures with a longer exposure time (24–26 min). The improvement in chick feed intake could be related to the decrease in the initial canavanine content and the total removal of the haemagglutination activity from roasted seeds. The most intensive treatments (high temperatures and long time exposure) resulted in a statistically significant (P<0.01) decrease in the TMEn when compared to raw JB values. Long heating times significantly decreased TND (P<0.01) only when they were combined with high temperatures (180–190°C), which could be associated with an increase in acid detergent fibre content. The best results on feed consumption and poultry growth were obtained when the JB were roasted at a medium temperature (164–168°C) with a long exposure time (24–26°C). Our trials demonstrated that roasting alone could significantly destroy the antinutritional factors without major adverse effects on the biological value of JB 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 the jackbean as an economic crop.