INACTIVATION OF RICE BRAN LIPASE WITH METAL-IONS

The inactivation of rice bran lipase was studied in vitro and in vivo using metal ions in methanol or HCl. Lipase was extracted from rice br an in 0.1 m potassium phosphate buffer, pH 7.0 and purified by ammoniu m sulphate fractionation. The 25-55 % ammonium sulphate fraction was s ubjected to DEAE-cellulose ion exchange chromatography and the fractio n (F6) eluted at V(e)/V(o) of 14.37 was purified about 333-fold. In-vi tro studies on F6 lipase showed that Fe3+ and Ni2+ completely inhibite d the lipase activity at 5 x 10(-5) m concentration, while Zn2+ and Cu 2+ did so at 2.5 x 10(-4) m. The results on in-vivo inactivation of ri ce bran lipase showed that Fe3+ and Ni2+ at 200 mug g-1 significantly checked the release of free fatty acids (FFA) from rice bran for 6 day s of storage when compared with using concentrated HCl (2 %, v/w) only . The triglyceride content of oil was also maximum with Fe3+ and Ni2treatment at 200 mug g-1. The present results suggest that Fe3+ and Ni 2+ could be effectively used to arrest the release of FFA in rice bran and thus contribute to improving the edible quality of rice bran oil.