Extrusion cooking of immature rice grain: under-utilized by-product of rice milling process

Immature rice grain is one of the by-products of paddy milling process. Due to being "whole grain", immature rice grains comprise the fat-rich bran layer which bring along high nutritional value as well as susceptibility to rancidity. Therefore, they are generally used as "feed" rather than "food". In this study, the potential of utilizing immature rice grain as a food ingredient was investigated. For this purpose, raw (unprocessed) and infrared (IR) stabilized immature rice grain flours (IRGF) were extruded at different exit-die temperatures (130 °C and 150 °C) and feed moisture contents (16%, 18%, 20%) and the effects of these parameters on chemical composition (moisture, crude fat, protein, ash, soluble and insoluble dietary fiber and phytic acid contents), physicochemical properties (solubility, water binding capacity, expansion index and bulk density), thiamine, riboflavin and tocopherol contents, textural and sensorial properties of the extrudates were investigated. Either thiamine or tocopherol contents of the extrudates made of unprocessed IRGF were higher than that of the extrudates made of IR stabilized IRGF (p < 0.05). Additionally, higher extrusion temperature and lower feed moisture content resulted in further loss in both vitamins. On the other side, riboflavins showed a relatively heat-stable behavior. Rancid flavor and bitter taste scores of the extrudates which were made of unprocessed IRGF were significantly higher than their counterparts made of IR stabilized IRGF (p < 0.05). Toothpack was the most dominant sensory attribute in all extrudates.