Valorization of used rice bran oil for the production of hard and liquid soap

Abstract

Used rice bran oil (URBO) represents a potential non-food feedstock for value-added soap production. This study evaluated URBO for formulating hard and liquid soaps, along with activated-carbon pretreatment to improve the spent oil's visual quality. URBO with 26% total polar materials was filtered and treated with activated carbon at 10, 20, and 40 g/100 mL. The 20 g/100 mL treatment produced the greatest improvement in visual clarity and CIELAB colour and was selected for subsequent soap preparation. Hard soaps were prepared by the cold-process method, whereas liquid soaps were produced by the hot-process method. The formulations were evaluated for total fatty matter (TFM), total alkali, pH, moisture content, foam height, and preliminary sensory acceptability. For hard soap, TFM, total alkali, pH, moisture, and foam height ranged from 25.10 – 69.46%, 1.85 – 2.69%, 9.79 – 11.45, 8.90 – 14.86%, and 7.50 – 17.50 cm, respectively. T5 showed the highest TFM and foam height and the lowest total alkali, while its pH remained within the cited acceptable range. For liquid soap, TFM, total alkali, pH, and foam height ranged from 36.03 – 67.99%, 1.33 – 2.18%, 9.25 – 12.57, and 13.00 – 18.33 cm, respectively; T3 showed the highest TFM and foam height and the lowest alkali and pH. Sensory scores indicated generally favorable preliminary acceptability. These findings demonstrate the laboratory-scale feasibility of valorizing URBO in soap formulations, while further chemical characterization, control formulations, and broader consumer testing are required before conclusions on cleansing efficacy, skin safety, or commercial applicability. The work supports circular-economy approaches for redirecting degraded frying oil toward useful non-food products.