Methods. Known throughout the world as the most comprehensive collection of for fats and oils, the Official Methods and Recommended Practices of the AOCS Find and purchase methods from the Official Methods and Recommended. cation of the AOCS Cd 3d method, through a statistical . Methods. AOCS Cd 3d Official Method . The acid number in oils and fats is determined. ufacturing, Kyoto, Japan) according to the AOCS Official. Method Cd 3d . All AV analysis results were expressed as mg KOH/g oil.
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This solvent mixture is previously neutralized with the standard KOH solution using phenolphthalein until the appearance of a slight pink color. Therefore, the determination of their concentrations throughout the refining process and during the storage is important for monitoring the occurrence of degradation reactions. In order to verify the stability of the basic titrant solutions, 0. AOCS Cd 3d official method 28 The acid number of oils and fats is determined through the titration of the sample with methox standardized 0.
Reagents, solutions and solvents. Figure 1 shows titrations curves obtained for the ethanol-water solvent by these two methods. The shorter time of the automatic procedure means, as an evident consequence, that the glass membrane remains in contact with the solution for a shorter time interval in comparison with the point-by-point titration.
Considering the above observations, the green method developed in this work can be proposed for the routine determination of the acid number of oils and fats. The acid number of oils and fats is determined through the titration of the sample with a standardized 0. The limits of confidence of the parameters a and b are calculated as confidence limits: The membrane must be frequently rehydrated or the electrode can be irreversibly damaged. AOCS Cd 3d official method The acid number of oils and fats is calculated through equation 1.
Mean relative standard deviation for the proposed procedure was 2. Knowledge related to this subject, acquired in developing earlier methods, was applied wocs the present work. Table 1 shows the acid numbers obtained for swine lard and for the vegetable oils canola, sunflower, linseed, castor, corn and soy applying the AOCS Cd 3d, the ABNT-NBRthe green visual 25 and the proposed potentiometric methods.
Soy, corn, canola, sunflower, linseed and castor oils and swine lard used in the present study were purchased at local markets. The quantity of wocs acids indicates how the feedstock was treated during industrial processing and during the storage. London, UK,p.
aocs official method cd 3d-63 pdf
Therefore, the present work has as objective to apply potentiometric detection to the titrimetric method aiming at low cost, operational simplicity and, especially, as environmentally friendly procedure.
April 4, Published online: According to this method, a quantity of the sample, which varies with its acidity, is dissolved in mL of a solvent that is a 1: The potentiometric method herein proposed was performed point-by-point and also using an automatic titrator in order to obtain the acid number of the solvents.
The automatic potentiometric titration is usually done in about 5 min, whereas the point-by-point procedure needs about 30 min. Oils and fats are compounds that are constituted of esters formed by fatty organic acids linked to a molecule of glycerol, forming triacylglycerols. In conformity with Table 2this disagreement is caused by the higher imprecision of the AOCS method with respect to the here proposed. As can be seen in the results presented in Table 2the calculated slopes and the intercepts are close to the ideal 1 and 0, respectively, in all cases.
A green potentiometric method for determination of the acid number of oils and fats
This non aqueous potentiometric titration presents as a disadvantage the use of organic solvents that, besides the toxicological 3d-663 environmental problems of the solvents, also causes the dehydration of the glass membrane of the electrode. Introduction Oils and fats are compounds that are constituted of esters formed by fatty organic acids linked to a molecule of glycerol, forming triacylglycerols. A green titrimetric method using potentiometry is proposed for determination of the acid number emthod vegetable oils and animal fats.
Distilled water was obtained from a glass distiller. The electrodes were calibrated as usual with aqueous buffer solutions of pH 7.
During the cooking of the food submitted to frying, the triacylglycerols are degraded as a consequence of the high temperature, of the loss of water and of exposure to the oxygen of the air. This situation not only reduces the time of the analysis, but also minimizes the possible effect of dehydration of the electrode as it remains for a shorter period in contact with the 1: It is expressed in mg of KOH per g of sample.
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Recently a green visual titrimetric method was presented for the determination of the acid number of oils and fats, using as titrant an aqueous 0. All the reagents and solvents were of analytical grade.
After each titration, carefully rinse the electrode with small portions of ethanol total of 15 mL to remove traces of oil or fat, followed by washing with distilled water, and immerse the electrode in distilled water for 1 min to rehydrate the glass membrane.
Potentiometrically titrate with 0. In the hydrolytic rancidity reactions, the carboxylic group suffers the action of enzymes of a microbial order commonly found in oleaginous seeds.
The acid number is calculated using equation 1. Reagents, solutions and solvents All the reagents and solvents were of analytical grade. The other methods present similar standard deviation among them with a little lower value for RSD for green visual procedure. The acid number is calculated using equation 1 where A is the titrant solution volume mL used in the titration of the sample, B is the titrant solution volume mL used in titration of the blank.
Solutions of sodium hydroxide and of potassium hydroxide were prepared by dissolving adequate masses of the bases in water. Despite the fact that the potentiometric methods can be more easily applied, in comparison to the visual method, as they do not depend on the color of the sample, in presence of organic solvents, the glass membrane of the electrode is dehydrated, a fact that results in instability of the measured electric potential.
With respect to the precision of the methods, it is clear that the green potentiometric procedure herein proposed presents the best performance. Collins for English revision of the manuscript.