Effects of dried curry leaves and tea leaves on oxidative rancidity of rice bran

P.H.G.J. De Silva and N.S.B.M. Atapattu
Department of Animal Science, University of Ruhuna, Sri Lanka

Control of the rancidity of rice bran (RB) is difficult due to the oxidative rancidity that persists even after inhibiting lipolytic rancidity by heating. Anti-oxidants are widely used to control the oxidative rancidity. Leaves of some plants such as curry leaves (Murrya koenigi) and tea (Camellie sinensis) are reported to contain high levels of natural anti-oxidants (NAO). The objective of this study was to test whether curry leaves and tea leaves could be used to control the oxidative rancidity of RB. A 2 x 3 factorial experiment was conducted. Heat stabilized and nonheat stabilized RB were stored without NAO or with 4% dried curry leaves (CL) or tea leaves powder (TL).

Each of the six treatment combinations had four replicates. Peroxidase values (PV) of the samples were determined weekly for 8 weeks.  Heating alone reduced the PV only by 43%. The initial PV (Meq/kg) of nonheat stabilized RB stored without NAO increased linearly (PV = 0.756 + 1.48 x days; R2= 0.99) from 2.5 to 85 over the eight weeks of storage.  The PV of the heat stabilized  RB stored without NAO also increased linearly (PV = -1.00 + 0.820 x days,R2=0.97) from 2.3 to 48 over the eight weeks of storage. Throughout the eight weeks of storage period, the PV of heat stabilized RB were significantly lower than those of non-heat-stabilized rice bran. Storage of non-heat stabilized RB with CL and TL significantly reduced the PV compared to same type of rice bran stored without CL or TL.

Similarly, PV of heat-stabilized RB stored with CL and TL were significantly lower than those of heat-stabilized rice bran stored without CL or TL.  Though there was no significant difference, CL was more effective compared to TL. Use of both CL and TL was more effective when used with heat-stabilized RB than with non-heat stabilized RB. When CL was mixed with non-heat stabilized RB, the PV at 56th day of storage reduced by 45% (from 85-46).  Meanwhile, when heat stabilized RB was mixed with CL, the PV at 56th day of storage reduced by 72% (from 48-13). It was concluded that dried powders curry leaves and tea leaves reduced the oxidative rancidity of rice bran on storage.