| The processed oil may become darker upon storage or in the course of sales, which affects the consumers’ preference, to some degree, even damaging business reputation. This darkening of plant oil during storage is called color reversion. It has long been a serious problem for the edible oil industry, especially for corn oil. The degree of color change upon storage depends on a number of factors, such as the nature of raw oilseed, moisture content of oilseed or refined oil, refining conditions and storage conditions. Though the phenomenon had been studied early, with certain results that the gama-tocopherol was the main color reverted substances, the color reversion occurred every now and then. What was more, the involved mechnisim and retarding measures were still unclear. Color reversion of oils might vary according to oil types. In this context, the aim of this study was to study the influencing factors and retarding measures. The main results were summarized as follows:The factors effects and the interactions among them were studied in the medium chain triacylglycerol(MCT) and the strripped corn oil. In order to study the influencing factors involved in color reversion, powder phospholipid, tocopherols, minor metals were added to medium chain triacylglycerol(MCT) and stripped corn oil to carry out oven test, then the color was measured with automated Lovibond colorimeter after 9hr heating. The results showed that the 10mg/kg phosphorus samples reached 0.25±0.07 Lovibond units, while the 50mg/kg phosphorus samples 1.15±0.07 Lovibond units. And for 2000, 5000 mg/kg MCT sample, R value merely reached to 0.15±0.07, 0.40±0.00 Lovibond units, respectively. The R value reached 0.15±0.07, 3.15±0.07 Lovibond units for 1, 10mg/kg Fe3+ samples, respectively.The results showed that significant increasing of R values were observed with the concentrations went up(p<0.05). When different contents of phytosterols added into MCT, no R values were detected after 9 hours heating. These results indicated phytosterols was not the reasons for increasing R value. At the basis of the above researches, the spiked test, including phosphorus, tocopherols and minor metals, needed conducting in the stripped-corn oil for studying the color reversion in corn oil. The results showed that the 50mg/kg phosphorus samples reached 3.10±0.14 Lovibond units. For 5000 mg/kg tocopherols sample. R value merely reached to 0.80±0.00 Lovibond units, and the R value reached 3.60±0.00 Lovibond units for 10mg/kg Fe3+ samples. The three factor above tried again in stripped-corn oil had been tested to be the factors influencing corn oil color reversion. In order to study the interactions among factors, orthogonal test L27(313) were adopted.Judging from results analyzed with univariate analysis of variance, The interaction between phospholipids and Fe3+ had pronounced effect on R values(p<0.05) after 9hr heating in MCT.The content of phospholipids, tocopherols and metals at the course of oil refining were determined, as well as the color reversion. The correlation analysis of the above indexes was conducted. The results showed that oil refining significantly decreased the phospholipids content, with degumming significantly reducing it by 89.43%. The content of tocopherols decreased gradually, with deodorization evidently reducing it by 41.37%. After the whole refining process, the metals, including iron, content decreased by 44.78%. As for the color reversion properties, the deodorized oil was more susceptible to it. The content of metals significantly affected the red color. The content of phospholipids was positive correlated with color reversion properties(0.77). And the metals, including iron, had a significant positive correlation with the R value, with which the content of tocopherols and phospholipids were positive correlation.With further study into the measures of retarding corn oil color reversion, we found that: 001-7 Cationic ion exchange resins was found to be effective in delaying the oils color reversion. Compared with untreated oil samples, the samples stirred with cationic ion exchange resins and the ones passaged through a colomn packed with cationic ion exchange resins were different. R value of the stirred samples was 2.15±0.07 Lovibond units, higher than untreated sample(1.80±0.00 Lovibond units) and the one passing through coloum(1.50±0.00 Lovibond units). What is more, the tocopherols content of all samples showed no significant difference. After 9 hours heating at 100oC, the R of the samples stirred with cationic ion exchange resins was 3.50±0.14 Lovibond units, and the R of the samples passing through coloum was 3.60±0.00 Lovibond units, while the untreated ones was 4.60±0.00 Lovibond units. We also tried to use antioxidants-T-butyl hydroqumone(TBHQ) and L-ascorbyl palmitate(AP) to retarding color reversion. As for TBHQ treated samples, the ΔR gradually decreased with the content of TBHQ increasing up to 200 mg/kg. After 9hr heating, the untreated samples’ ΔR was 2.20±0.00 Lovibond units, which was much higher than that of the one treated with 200mg/kg TBHQ(1.45±0.07 Lovibond units);When samples added with 150mg/kg AP, the ΔR was 1.75±0.07 Lovibond units, which was much lower than the untreated samples(2.60±0.00 Lovibond units). TBHQ seemed to play better than AP in this research. All these results indicated that antioxidants can retard oils color reversion. |
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