Karanjin and pongamol
Karanja oil cake, and particularly its lipid fraction, contains two furanoflavones, karanjin and pongamol, that are toxic and make the cake unpalatable. The oil also contains polyphenolic compounds. Many treatments have been tested since the 1970s to remove these undesirable substances, including physical treatments (autoclaving, pressure cooking, water soaking, water washing, solvent extraction and partial deoiling), chemical treatments (sodium hydroxide, lime, addition of binder) and microbiological treatments (S. cerevisiae and Aspergillus oryzae) (Scott et al., 2008; Nagalakshmi et al., 2011; Dutta et al., 2012). However, while some treatments such as deoiling or pressure cooking are more effective than others in reducing karanjin, none of them appeared to make the processed cake completely suitable, feasible and wholesome for animal feeding. Also, the cost of detoxification discourages the use of karanja oil cake (Nagalakshmi et al., 2011; Dutta et al., 2012).
Protease inhibitors
Karanja oil cake contains protease inhibitors. Different methods have been assessed to reduce their activity, as summarized in the following table.
Table 1: Effects of treatments on trypsin and chymotrypsin inhibitors of karanja (Rattansi et al., 1997)
Technological treatment | Trypsin inhibitor reduction | Chymotrypsin inhibitor reduction
Solvent-extraction | 34% | 15%
Autoclaving | 83% | 15%
Fermentation | 33% | 15%
Gamma radiation (1, 5, 10 and 50 kGy) | 4-83% | 3.7-78%
2.4% HCl | 100% | 100%
A more recent method consists in autoclaving the cake with lime, then refluxing with 2% HCl and finally neutralizing with NaOH. This treatment improves the protein digestibility of the cake (Scott et al., 2008).