Optimization of Bleaching Parameters for Soybean Oil

204 D. [KEVIN et al.: Soybean Oil Bleaching Parameters, Food Technol. Biotechnol. 50 (2) 199–207 (2012)neutralized oil occurring in only 4 samples. This indicatesthat the clay used is suitable for soybean oil bleaching.The Friedman-type rank test showed that soybeanoil bleached for 20 min at 95 °C using 1 % clay had thebest oxidative stability. Fisher’s LSD for ranking the sumsshowed statistically significant differences among thesamples (p£0.05), due primarily to the influence of temperatureand secondarily to the influence of clay content.PCA was also performed on parameters of oxidativedeterioration. The first two PCs had an eigenvalue >1and together they explained 80 % of the total variance.Score plot (parameters of oxidative deterioration and FFA)and loading plot (samples of bleached oil) as a functionof PC1 and PC2 are shown in Figs. 2a and 2b, respectively.Fig. 2a shows a high negative correlation of PC1with the indicators of secondary oxidation products,while PC2 has a good positive correlation with primaryoxidation products. Fig. 2b shows that although thesamples do not fall into non-overlaping groups based onthe oxidative deterioration, soybean oil samples bleachedwith 1 or 1.5 % clay at 115 °C fall to the left side alongthe PC1. These samples have higher values of AV andK 270 . No clustering of samples is evident along PC2.These findings suggest that clay amount and bleachingtemperature had a strong influence on the secondary oxidationproducts, but no effect on the primary oxidationproducts.The Friedman-type rank test was applied to all resultsin Tables 2 and 3. It indicated that sample 5 showedthe most efficient bleaching with minimum oxidativedeterioration of the oil; this sample was bleached for 20min at 95 °C using 1 % clay.The influence of bleaching conditions on the contentand composition of bioactive components of soybean oilwas also examined. These analyses were carried out ona subset of samples bleached at different temperaturesusing different clay amounts, since statistical tests of theresults showed that the duration of bleaching had nosignificant influence on bleaching efficiency or oxidativedeterioration of oil. Of course, the sample bleachedusing optimal parameters of 1 % clay, 95 °C and 20 minwas also included.Bioactive compounds in vegetable oil, including soybeanoil, contribute to their oxidative stability and nutritionalvalue. The most important bioactive componentsare tocopherols, strong antioxidants with a significant biologicaleffect. Levels of total and individual tocopherolsdecrease during neutralization, bleaching and deodorization(6,36). Table 4 presents the content and compositionof tocopherols of selected soybean oil samples. Thedominant tocopherol is g-tocopherol, as reported in previousstudies (8,36,37). It is obvious that the levels of a-and g-tocopherol in the neutralized oil decreased duringbleaching. This reduction was greater when increasingclay content and bleaching temperature. The levels of d--tocopherol and total tocopherols also decreased, butthere was no significant association with clay content ortemperature. The Friedman-type rank test showed thatthe sample bleached at 105 °C using 1 % clay had thehighest levels of individual and total tocopherols. TheFisher’s LSD for ranking the sums confirmed that thesamples with different clay content and bleaching temperatureshowed significant differences (p£0.05). In fact,the bleaching parameters found to be optimal based onthe bleaching efficiency and oxidative deterioration of soybeanoil (1 % clay, 95 °C and 20 min) did not give opti-Table 4. Tocopherol content and composition of bleached soybeanoil samplesw(tocopherol)Samplemg/kga-tocopherol g-tocopherol d-tocopherol TotalNS 87.1 431.7 202.8 721.62 c 62.6 405.1 167.9 635.63 b 54.0 403.6 199.5 657.15 d 47.6 388.2 171.3 607.17 a 51.9 410.6 210.2 672.611 c 42.4 399.2 201.5 643.012 d 41.3 376.1 198.3 615.7NS=neutralized soybean oilBleaching parameters for each sample are given in Table 1Samples with different letters in superscript differ significantly(p£0.05)Fig. 2. PCA loading (a) and score (b) of the plots of the data on oil deterioration during the process of bleaching. Samples in b aredescribed in Table 1