水酸化アルミニウムゲルによるフライ油の脱酸について
1974 年 23 巻 5 号 p. 296-300
詳細
1974 年 23 巻 5 号 p. 296-300
As a result of the supplemental test of the Hoover's method (U.S. 3, 231, 390), in which magnesium oxide was used as an adsorption agent on the removal of free fatty acids in frying oils, the method was concluded to be unpractical because magnesium oxide formed a soap with free fatty acids in frying oils, and the soap could dissolve in the oils and promote their hydrolysis significantly.
When some reagents were examined for their effects on the adsorption of free fatty acids in the oils, dried aluminum hydroxide gel (AHG) was found to be the most exellent reagent as an acid adsorbent, that is, it had a strong ability of adsorbing free fatty acids and was almost insoluble in the oils. After the adsorption tests had been repeated ten times, the amount of aluminum dissolved in the oil was very small (max. 1.5ppm).
A practical test of AHG adsorption was carried out by using an automatic test fryer and the changes in the amounts of free fatty acids and of aluminum in the oils and in the properties of the oils were followed at varied time intervals. As a result of this experiment, it was revealed that the amounts of free fatty acids in the oils had been maintained at a very low level for a long time and aluminum did not dissolve into the oils so much (max., 15ppm). The properties of the oils were maintained in better conditions than those of frying oils which were not treated with AHG. Therefore, AHG was proved to be an excellent acid adsorbent even when used practically.
The difference between the preliminary and practical tests in the amount of aluminum in the oils seemed to be due to the incompletion of filtration (the oils were sucked by a pump through filter paper) and to the effect of moisture in the oils coming from frying materials (potato) in case of the practical test.
The mecanism of the adsorption of fatty acids on AHG was discussed. It seems that the adsorbed layer is monomolecular and the fatty acids are chemisorbed on the surface of AHG and further reaction between adsorbate and AHG (production of the metal soap which dissolves into the oil) does not occur. This is the major reason why the amount of aluminum dissolved in the oil is very small.
