Effects Of Free Fatty Acids On The Quality Of Soybean Oil, Rapeseed Oil

At present, consumers have a misunderstanding in the choice of vegetable oil, they think the clearer the color is, the better the quality is. The current process aims to maximize fatty acids and pigments which impact the quality of vegetable oil; Excessive refining process conditions easily lead to a large loss of micronutrients in vegetable oil, such as tocopherols, sterols, etc., but also generate the trans fatty acids, triglycerides and glycidyl aggregation which is harmful to human health. As people increasingly focus on nutrition and health, as well as response to the call of "energy saving", we put forward the concept of moderate refining. Under the current refining process, energy consumption and waste generation are mainly in deacidification and deodorization process, the new national solicit draft is primarily to relaxed the acid value. Therefore, this paper studied the effect of tocopherol and sterol in each step of refining segment firstly. As acid value is the main classification criteria in currently standard grading standards of vegetable oil, we studied the effects of free fatty acids about storage stability and oxidation stability on soybean oil, rapeseed oil, by exogenous addition of free fatty acids. And we also studied its thermal stability during cooking, the impact of smoke point. Eventually we identified the acid value that without reducing the current shelf life, and we also established a mathematical equation between the free fatty acid and smoke point. The main findings are as follows:(1) Seven representative manufacturer’s sample were collected from different segments of soybean oil, rapeseed oil, then the content change of free fatty acids, tocopherols and sterols were analyzed. Results showed that free fatty acids mainly removed in the deacidification process; The content of tocopherol in soybean oil has a significant loss in deodorizing stage, while content of tocopherol in rapeseed oil has a significant loss in decolorization and deodorization stage. While the loss of sterol mainly happen in the degumming and deacidification stage. It can be seen that appropriate refining, relax the acid value, can significantly reduce the loss of tocopherols and sterols, improve the nutritional value of vegetable oils.(2) The evaluation about the effects of free fatty acids on oxidation stability and storage stability were studied by Rancimat method (oxidative stability index under 110 ℃) and Schall oven method (under 65℃ storage) in soybean oil, rapeseed oil. The methods mainly reflected its shelf stability and oxidation stability of soybean oil and rapeseed oil.At 65℃ accelerated storage experiment,we analyzed the significant difference between the peroxide value, conjugated diene and TOTOX value which stored in different days through SPSS software. The results showed that the acid value can be extended to 0.50 mg KOH/g oil for soybean oil, added oleic acid,0.60 mg KOH/g oil for rapeseed oil.The oxidative stability index at 110℃ conditions showed that the acid value can be extended to 0.2826 mg KOH/g oil for soybean oil added oleic acid,0.3836 mg KOH/g oil, for soybean oil added linoleic acid,0.9255 mg KOH/g oil for rapeseed oil added oleic acid. (3) In order to study the influence of vegetable oil cooking characteristics after relax the free fatty acids, especially the impact on smoke point of thermal stability, the subject firstly use different levels of soybean oil and rapeseed oil to conduct the complex experiment according to mass ratio.Then we received 49 soybean oil and 39 rapeseed oil samples. The effects of acid value, peroxide value, residual solvent, phosphorus, water and volatile on the smoke point of the samples were measured. The results showed that the phosphorus content and acid value were the biggest influence factors of smoke point, followed by solvent residues, peroxide value and moisture and volatile.To adapt to the appeal on current moderate refining process to relaxed the acid value, the subject further to study the effects about relaxed the acid value on smoke point, also establish the regression equation. The acid value and the corresponding smoke point were measured, by adding oleic acid or linoleic acid to soybean oils and vegetable oils. Next we analyzed the experimental results based on the different batches of vegetable oil. Eventually we found that a good mathematical relationship occured between the reduce percentage of smoke point and the content free fatty acid. So this issue established a mathematical equation between the percentage of free fatty acid and the decrease percentage of smoke point, corresponding to Y=9.87981nX+32.976 (R2=0.9753) and Y= 11.0391nX+32.058 (R2=0.8995) for soybean oil and rapeseed oil.