Polar γ-oryzanol, a new class of γ-oryzanol in RBO: Identification and monitoring of qualitative and quantitave alternations throughout the rice milling process

Rice Bran Oil (RBO) is cooking oil obtained from rice bran, a by-product of the rice milling process. In contrast to other vegetable oils, RBO contains high amount of γ-oryzanol (OZ). OZ has been reported to display health benefits including antidiabetic, antihyperlipidemic and anti-inflammatory effects. In the context of our studies of edible oils, RBO has been investigated and the identification of a new group of OZ hydroxylated derivatives called pollar γ-oryzanol (p-OZ) was recently reported.

The present work aims at characterizing of both OZ types using HPLC-DAD and UHPLC-HRMS/MS techniques in diverse samples. Specifically, different cultivars (Gladio, Ronaldo) and rice preparations (regular, parboiled) were qualitatively and quantitatively investigated in the 3 whitening steps of rice production. Initially, different extraction methods were assayed. Ultrasonic extraction using EtOAc was the optimum being specific for both OZ and p-OZ with yields up to 25% (w/w). Additionally, a targeted HPLC-UV method was developed for the separation and quantification thereof. 12 Different samples were analyzed and measured concentrations were in the range of 1 mg/g and 10 mg/g for OZ and p-OZ, respectively. Highest concentrations of OZ and p-OZ were found in the extracts from the first whitening step. In Gladio parboiled OZ and p-OZ levels were generally maintained during the process in contrast to other preparations. Furthermore, the same samples were studied using UHPLC-APCI(±)-HRMS/MS methods and selected extracts have been subjected to hydrostatic CCC for fractionation and purification. Both initial extracts and derived fractions were analyzed for further identification of minor constituents. This is the first time that detailed information regarding the p-OZ content in different RBOs is reported as well as the thorough characterization of its constituents. Moreover, purification thereof is ongoing as well as evaluation of p-OZ and OZ biological properties.