Hardened palm oil was found to deteriorate with an abnormal increase in acid value (AV) during storage. Therefore, a study was carried out to determine the causes of this and how to prevent it.
1) The increase in AV of hardened palm oil depended on the degree of hardening and storage temperature. The increase was marked when the oil had an iodine value of 1030 and contained more elaidic acid than oleic acid. Also it was more marked during storage at 25°C than that at 15°C or 37°C.
2) The addition of lipophilic sucrose fatty acid ester (SE-1) or soybean lecithin was effective for the most part in preventing deterioration. However, no effects were observed by the addition of monoglyceride or polyoxyethylene sorbitan fatty acid ester.
3) Hardened palm oil without emulsifiers storage at 25°C showed a rough crystal surface with a pile of irregular crystal size under scanning electron microscope. The surface of palm oil samples emulsified with SE-1 or soybean lecithin was smooth.
