Adsorption of carotene from palm oil by acid-treated rice hull ash

Rice hull ash obtained by heat treatment and acid activated followed by washing was not effective as an adsorbent for carotene in palm oil in contrast to that reported for adsorption of soy oil lutein. However, unwashed acid-activated ash had activity much higher than carbon and silica but slightly less than a commercial bleaching clay. Heat treatment of raw rice hulls at temperatures below 300°C resulted in the most active adsorbent after acid activation. Drying the unwashed acid-activated ash at temperatures higher than 200°C reduced the activity. The activity of the acid ash was attributed to adsorbed acid. The results also suggested that the removal of carotene in palm oil was caused by chemical interactions involving the adsorbed acid and the carotene. The small amount of Fe³⁺ in the ash was not responsible for the activity.