Study to Solve the Problem of Color Reversion in Refined Soybean Oil

Abstract

This study carried out on the soybean oil samples taken from the processing lines during refining process (degumming, neutralization, bleaching and deodorization process) for crude soybean oil as well as on color reversed oil after deodorization step during storage for several hours to study the physical and chemical properties (color, refractive index (RI), free fatty acid (FFA), peroxide value (PV), p-Anisidine value (p-AV), total oxidative (TOTOX) value, oxidative stability (OS), saponification value (SV), iodine value (IV), unsaponifiable matter (unsap. %), soap content, minerals, waxes, total phenols content, K 232 and k 270 nm), the fatty acids composition, sterol compound, total tocopherols and their components ( <i> α , β , γ </i> and <i> δ </i> tocopherol) and tocored compound for these oils and to find out the reason for the color reversion after a short period from storage for the deodorized soybean oil. Citric acid has been added (0.2%) to each color reversed and neutralized soybean oils, then procedure of bleaching and deodorization process on them, and studied its effect on the physical and chemical properties for them specially the color units (red and yellow), tocopherols contents and tocored compound. The results showed that refining process for soybean oil caused to a gradual decrease in values of AV, oxidative stability, IV, wax, % Unsapo., K 232 and K 270 nm, total polyphenols, minerals (P, Ca and Mg), total tocopherols and their compounds ( <i> α , β , γ </i> and <i> δ </i> tocopherol) and also caused decrease in all sterol components, but they show ed a few differences in percentages of fatty acids as result refining process. Color values (red and yellow unites) recorded gradually decrease d during refining process, but these values were increased in deodorized soybean oil after storage (color reversed soybean oil). Reduction of <i> α , β , γ </i> and <i> δ </i> tocopherol contents w as found to be linearly with the increase of red and yellow color units (color darking). The tocored is responsible for the color reversion phenomenon, where as maximum amount of tocored was in crude soybean oil 169.2 ppm, which gradually decreased during refining process 120.35, 99.82, 20.25, and 8.46 ppm, respectively, but it was found to be 46.5 ppm in color reversed soybean oil. Addition of citric acid (0.2%) related to the removal of tocored from soybean oil during the bleaching and deodorization process of soybean oil before and after color reversion in parallel with the significant decrease in the color values.