A new method for determining free fatty acid content in edible oils by using electrical conductivity.

摘要

In the current study, a new method for determining free fatty acid (FFA) content in edible oils has been developed based on the electrical conductivity (EC) value change of a 0.04 M potassium hydroxide (KOH) solution during KOH-FFA mixed reaction. At ambient temperature, 4.000+or-0.001 g of edible oils (oils with a high melting point were melted first) was dispersed in 40.0+or-0.1 ml of KOH solution. The mixtures were stirred for 5 s and were held for 5 min. The EC value changes of the KOH solution layers were determined, and the FFA was predicted basing on the calibration. The analytical conditions studied include the concentration of KOH solution, holding time, the types of edible oils, setting temperature, and the ratio of oil to KOH solution (m/v). The calibration was validated by using the American Oil Chemists' Society (AOCS) titrimetric FFA method. The analytical conditions were found to have no significant effects on the results. When the ratio of oil to KOH solution was 1:10 (m/v), the calibration was y=12.04x-0.0769 (where x is the EC value change and y is the FFA content), R=0.9992, SD=0.0745, and a calibration with an SE of <0.0745% FFA over a range of 0% to 5% was obtained. The method was validated using standard addition and the AOCS method. The results show that the analytical performance of the EC procedure is as good as or better than that of the AOCS titrimetric procedure.