Inactivation of rice bran lipase with metal ions

Abstract

Abstract:The inactivation of rice bran lipase was studied in vitro and in vivo using metal ions in methanol or HCI. Lipase was extracted from rice bran in 0.1 M potassium phosphate buffer, pH 7.0 and purified by ammonium sulphate fractionation. The 25-55 % ammonium sulphate fraction was subjected to DEAEcellulose ion exchange chromatography and the fraction (F6) eluted at V,/ V, of 14.37 was purified about 333-fold. In-vitro studies on F6 lipase showed that Fe3+ and Ni2+ completely inhibited the lipase activity at 5 x M concentration, while Zn2+ and Cu2+ did so at 2.5 x M. The results on in-vivo inactivation of rice bran lipase showed that Fe3+ and Ni2+ at 200 pg g-' significantly checked the release of free fatty acids (FFA) from rice bran for 6 days of storage when compared with using concentrated HCl (2 %, v/w) only. The triglyceride content of oil was also maximum with Fe3+ and Ni2+ treatment at 200 pg g-l. The present results suggest that Fe3+ and Ni2+ 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.

Effects of temperature, moisture, and metal salt content on dielectric properties of rice bran associated with radio frequency heating

“… Water/salt solution needed (mL) Concentration of salt solution (g/mL) Ref. NaCl 0.50 20 12.05 0.041 14 , 34 1.00 0.083 2.00 0.166 KCl 0.40 0.033 14 , 35 0.70 0.058 1.00 0.083 EDTAFeNa 0.05 0.004 13 , 34 0.10 0.008 0.15 0.012 Na 6 O 18 P 6 0.50 0.041 36 1.00 0.083 2.00 0.166 …”

“…For example, Munshi et al . 13 found that lipid rancidity of RB could be inhibited by spraying solutions of FeCl 3 or NiCl 2 over the bran during storage. Doblado-Maldonado et al .…”

Key issues and challenges in whole wheat flour milling and storage

“…Because the activity of lipase can be influenced by the presence of metal ions (Barros et al, 2010), Munshi et al (1993) treated rice bran with ZnCl 2 , NiCl 2 , FeCl 3 , or CuCl 2 , by dissolving each salt in HCl or methanol and spraying the solution in a fine mist over the bran. The salts were applied at 25e200 mg of the metal ion/g bran.…”