FFA
The efficiency of deodorization is usually quantified by the reduction of FFA. For most conventional-processed 1st-grade refined oils, the target residual FFA content is 0.03-0.05%, and the upper limit for FFA in past national standards for these oils in China was 0.10%. In order to conform to the development trend of minimal processing, the national standards for these oils in China have been revised and updated successively in recent years, and the upper limit for FFA is currently 0.25%. Fig. 6 shows the comparisons of FFA of four oils (soybean oil, rapeseed oil, maize oil and sunflower seed oil) obtained by conventional high-temperature deodorization or DCDT deodorization. The content of FFA of these deodorized oils are all less than 0.08%, not only meeting the internal quality standard for the trial-production (≤0.10%) but also meeting the national standards for 1st-grade refined oils. Since FFA contents of oils obtained by the DCDT deodorization were all slightly higher than the conventional ones due to the lower deodorization temperatures, the oil stability during the shelf life might be a concern and will be discussed later.