Color
Besides a bland odor and taste, a light color is also a quality parameter for most refined oils. In the refining process, the color components can be removed during the bleaching process by adsorption onto a suitable bleaching earth or by thermal degradation during deodorization. Heat bleaching is a purely time-temperature-dependent reaction. Literature data on heat bleaching of palm oil indicate that the rate of carotene breakdown doubles per 20°C increase in temperature and heat degradation of carotene takes a few hours at 210°C but only a few minutes at 270°C (Shahidi, 2005). Similarly, to conform to the trend of minimal processing, specific restrictions of R value have been revoked and replaced with descriptive words in the newest Chinese national standards for these refined oils.
Fig. 8 shows the comparisons of R-values of four oils (soybean oil, rapeseed oil, maize oil and sunflower seed oil) between conventional high-temperature deodorization and the DCDT deodorization. The majority of oils have an R-value below 1.5R. For DCDT deodorized oils the R-value of sunflower seed oil was the lowest (≤1.0R), followed by soybean oil, rapeseed oil and maize oil. Except sunflower seed oil, R values of the other zero-TFA oils were all slightly higher than corresponding conventional ones.