The determination of hydroxyl, ketone and ester groups in autoxidised fatty esters and related compounds by infra-red spectroscopy

645

380

Lipids become rancid as a result of oxidation, and this oxidative rancidity is a major cause of food deterioration. The acceptability of a food product depends on the extent to which this deterioration has occurred. Thus some criterion for assessing the extent of oxidation is required. This paper reviews the experimental techniques for the measurement of lipid oxidation. The spectrum of tests ranges from simple organoleptic evaluations to chemical and physical methods. There is no ideal chemical method which correlates well with changes in organoleptic properties of oxidized lipids throughout the entire course of autoxidation. The methods discussed each give information about particular stages of the autoxidative process, and some are more applicable to certain lipid systems than others. The method of choice depends on a number of factors including the nature and history of the oxidized sample, the type of information required, the time available, and the test conditions. Clearly, there is a need for a more thorough assessment of the available methods so that unreliable, cumbersome methods may be discarded and modifications made to the remaining methods to maximize the information obtained. The ultimate criterion for the suitability of any test is its agreement with sensory perception of rancid flavors and odors.

Section: Infrared Spectroscopymentioning

confidence: 99%

Measurement of lipid oxidation: A review

Gray

1978

645

380

“…Physical measurements of optical rotation (11) or infrared absorption (12) have proved applicable in instances when the structure of the hydroxy constituent is known, but these are not suitable for general application. Recently near-infrared methods for the determination of epoxy and vieinally unsaturated hydroxy components have been deseribed (13).…”

Section: Introduction Mmentioning

confidence: 99%

Quantitative estimation of esters by thin‐layer chromatography

Vioque

Holman

1962

134

A method for the analysis of fatty esters employing separation by thin-layer ehromatography and quantitative determination vitl their hydroxamie acids has been developed. Esters of different types are separated on silica gel plates, the spots or zones are scraped from the plates, the esters are extraeted from the silica gel, and the iron hydroxamie aeid complexes are formed. The latter are then measured by eolorimetry.The method is suitable for analysis of mixtures of ordinary, epoxy, monohydroxy, and dihydroxy fatty esters as well as for mixtures of mono-, di-, and triglyeerides.Used in conjunction with gas chromatography this method permits the fatty acid composition of seed oils containing oxygenated fatty acids to be measured in about 3 hours. The amount required for the total analysis is 1 to 10 rag. per determination, depending upon composition.

“…Although direct measurements of the spectra are fast and simple, the degree of hydrogen bond associations, and hence, the intensity of their absorption peaks varies markedly with the concentration and the nature of the sample making such measurements unreliable. It was suggested [16] that in very dilute solutions the degree of hydrogen bond association is negligible and under this condition, measurements of the intensity of the unassociated absorption peak could permit the determination of the OHV. Indeed, this method was used to determine the hydroxyl content of auto-oxidized fatty esters (e.g.…”

Section: Resultsmentioning

confidence: 99%

“…It is recognized that due to differences in the chemical environment of the hydroxyl groups in the various polyols, dislocations of the infrared absorption band related to the angular deformations are to be expected. These variations are most significant in polyols derived from the epoxidation of unsaturated fatty acids since the triglycerides in this case consist of distinct chains with double bonds at different positions [16]. As the double bonds are reacted and converted to hydroxyls, the absorption spectrum is affected.…”

Section: Structural Considerationsmentioning

confidence: 99%

A Spectroscopic Method for Hydroxyl Value Determination of Polyols

Chalasani

Dewasthale

Hablot

et al. 2013

A relatively simple method is described for routine determination of hydroxyl values for a wide range of hydroxyl containing compounds including soybean oil polyols, polyols derived from soy meal, polyether polyols and ethylene glycol as well as their blends. This method is based on reacting the hydroxyl compound with hexamethyldisilazane (HMDS) and determining the FTIR peak area of the silylated product at 1,251 cm−1. The method is simple, accurate and reproducible. It is not limited to a specific family of polyol compounds. It does not require any special equipment, hazardous chemicals and can be carried out by non‐technical staff as a rapid and convenient method for quantitative determination of hydroxyl values. An excellent linear correlation was obtained between this spectroscopic method and conventional titration methods for different polyols over a wide range of hydroxyl values. Furthermore, unlike the titration methods the current method is not affected by the presence of acid, base or small amounts of water in the test sample.