Purification and Antioxidant Properties of Rice Bran (Gamma)-Oryzanol Components.

A high purity $\gamma$-oryzanol was obtained from crude rice bran oil using a normal phase preparative scale HPLC. It was used in implementing a reverse phase HPLC method for separating each individual component of $\gamma$-oryzanol present in rice bran oil. Ten fractions were isolated in the reverse phase HPLC method. The ten components of $\gamma$-oryzanol were identified. Three of these, cycloartenyl ferulate, 24-methylene cycloartanyl ferulate, and campesteryl ferulate, were major components of $\gamma$-oryzanol. The yield of $\gamma$-oryzanol without saponification was significantly higher than that with saponification in solvent extraction. The solvent mixture with 50% hexane and 50% isopropanol (v/v.) at an temperature of 60\sp\circC for 60 min produced the highest yield of $\gamma$-oryzanol among test solvents and conditions. However, the yield of $\gamma$-oryzanol in supercritical fluid extraction under temperature 50\sp\circC, pressure 680 atm, and time 25 min was approximately four times higher than the highest yield of solvent extraction. Also, high concentration of $\gamma$-oryzanol in extract (50-80%) was obtained by collecting the extract between 15-20 min of extraction under this optimized condition. A quantitative method for determining four hydroperoxide isomers of linoleic acid, 9HPODE(t,c), 9HPODE(t,t), 13HPODE(c,t), and 13HPODE(t,t), using a normal phase HPLC with a UV detector was developed. The sensitivity and specificity of the HPLC method were sufficient to measure the production of the four hydroperoxide isomers when linoleic acid was incubated at 37\sp\circC with constant air flow. $\alpha$-Tocopherol and ferulic acid showed significant antioxidant activity via low productions of hydroperoxides, compared to control. Based on the relative production of each hydroperoxide, the mechanisms of antioxidants, scavenging singlet oxygen or scavenging peroxyl free radicals, were also determined. Different profiles of production of each hydroperoxide in the linoleic acid model with $\alpha$-tocopherol and ferulic acid indicated that they possess different mechanisms of antioxidation. The three components of $\gamma$-oryzanol evidenced significant antioxidant activity when they were mixed with linoleic acid in a molar ratio of 1:100 and 1:250 but not in a molar ratio of 1:500. The antioxidant mechanisms of the three major components of $\gamma$-oryzanol were similar to that of ferulic acid

Linear Convergence of Adaptively Iterative Thresholding Algorithms for Compressed Sensing

This paper studies the convergence of the adaptively iterative thresholding (AIT) algorithm for compressed sensing. We first introduce a generalized restricted isometry property (gRIP). Then we prove that the AIT algorithm converges to the original sparse solution at a linear rate under a certain gRIP condition in the noise free case. While in the noisy case, its convergence rate is also linear until attaining a certain error bound. Moreover, as by-products, we also provide some sufficient conditions for the convergence of the AIT algorithm based on the two well-known properties, i.e., the coherence property and the restricted isometry property (RIP), respectively. It should be pointed out that such two properties are special cases of gRIP. The solid improvements on the theoretical results are demonstrated and compared with the known results. Finally, we provide a series of simulations to verify the correctness of the theoretical assertions as well as the effectiveness of the AIT algorithm.Comment: 15 pages, 5 figure

Analysis of Recovery Type A Posteriori Error Estimators for Mildly Structured Grids

Some recovery type error estimators for linear finite element method are analyzed under O(h1+alpha) (alpha greater than 0) regular grids. Superconvergence is established for recovered gradients by three different methods when solving general non-self-adjoint second-order elliptic equations. As a consequence, a posteriori error estimators based on those recovery methods are asymptotically exact