Kreis test

There are also methods based on the detection of aldehydic substances, for the typical odor and flavor of rancidity seem to be associated with the liberation of aldehydic materials during the oxidative deterioration. The Kreis test (18), perhaps the best known of these methods, consists of treating the fat with concentrated hydrochloric acid and a solution of phloroglucinol. The red color formed is attributed to a condensation product of epihydrin aldehyde with phloroglucinol. Historically, the chief difficulty with this method has been that fats which are not rancid will often give a positive Kreis test. It has been shown that if this test is quantitatively correlated with the induction period... 

Various tests for rancidity, such as the Kreis test, may be used in stability determinations if the intensity of reaction is plotted against time. The curves so obtained will give an indication of the length of the induction period. However, the plotting of a curve for each sample is somewhat laborious. 

Other traditional methods available for monitoring the extent of lipid oxidation include the Anisidine value, the Kreis test (Mehlenbacher, 1960), methods based on the carbonyl content of oxidized fats (Henick et al., 1954 Lillard and Day, 1961), and measurement of oxygen uptake either by manometry or polarography (Tappel, 1955 Hamilton and Tappel, 1963). 

In addition to organoleptic assessment, several chemical/physical methods have been developed to measure lipid oxidation. These include peroxide value, thiobarbituric acid (TBA) value, ultraviolet absorption (at 233 nm), ferric thiocyanate, Kreis test, chemiluminescence, oxygen uptake and analysis of carbonyls by HPLC (see Rossell, 1986). 

The most popular method involves 2-thiobarbituric acid (TBA) two molecules of 2-thiobarbituric acid are condensed with malonaldehyde. The emergent chromogen — the two tautomeric structures of the red TBA-malonaldehyde adduct — is determined at 532 nm, and also often at 450 nm, to determine aUcenals and aUcanals, respectively. The qualitative Kreis test was based on a similar principle it involved detection of the epihydrine aldehyde — a tautomeric malondialdehyde — in a color reaction with resorcine or phloroglucinol. The popularity of the TBA test stems from a correlation between the results and sensory evaluations. Paradoxically, this is related to the most important drawback of the TBA technique — its lack of specificity. In addition to the reaction with malonaldehyde, TBA forms compounds of identical color with other aldehydes and ketones, products of aldehyde interaction with nitrogen compounds, and also with saccharides, ascorbic acid, creatine, creatinine, trimethylamine oxide, trimethylamine, proteins, and amino acids. For this reason, the TBA test may even be treated as a proteolysis indicator (Kolakowska and Deutry, 1983). Recently, TBA-reactive substances (TEARS) were introduced, primarily to stress that the reaction involves hydroperoxides in addition to aldehydes. Due to the nonspecificity of the TEARS test, its results reflect the rancidity of food better than other conventional methods, especially off-flavor, which is caused by volatiles from lipids as well as being affected by products of lipids interaction with nitrogenous compounds. 

Mainly with the idea of overcoming these objections to the peroxide value as a measure of rancidity, various tests have been developed for decomposition products of oxidized fats. The widely used Kreis test, which depends upon the development of a red color when rancid fats are treated with phloroglucinol, has recently been shown to be given by malonic dialdehyde and other closely related constituents of oxidizing fats (Patton et al., 1951). The test has been greatly improved in recent years by solution of all reactants in a single phase and colorimetric estimation of the color produced (Walters et al., 1938 Pool and Prater, 1945 Watts and Major, 1946). 

The reaction of oxidation products of linolenic acid with thiobarbituric acid to give an orange red color has been used by Abramson (1949), Wilbur et al. (1949), and others to follow unsaturated fat oxidation in various tissues. Patton et al. (1951) present evidence that this test, like the older Kreis test, also measures malonic dialdehyde. 

Watts, B. M., and Major, R. 1946. Comparison of a simplified, quantitative Kreis test with peroxide values of oxidizing fats. Oil Soap 23, 222. 

The extent of prior oxidative activity in a fat sample may be estimated by the following peroxide value (PV), thiobarbituric acid test (TEA) (which measures the presence of malonaldehyde), anisidine value—Totox, Kreis test, oxirane test, total and volatile carbonyl... 

In distillation systems, the improvement of tray efficiency due to taller weirs is small (5). Koch Engineering (8), Kreis and Raab (28), and Kalbassi et al. (184) observed little effect of weir height on distillation tray efficiency for weirs 1.5 to 3 in, 1 to 2 in, and 0.5 to 1 in tall, respectively. Finch and Van Winkle (185) reported an efficiency increase of the order of 5 to 10 percent as weir height is raised from 1 to 3 in a similar increase was reported by Prado and Fair (110,144) in humidification and stripping tests. 

Fractional hole area. Efficiency increases with a reduction in fractional hole area (23,28,110,144,186). Yan and Sakata (23), experimenting with commerdal-scale towers, show a 10 to 15 percent increase in tray efficiency when firactional hole area was lowered from 14 to 8 percent of the bubbling area (Fig. 7.10a). Kreis and Raab (28j show an identical increase for N2/O2 separation, and an even larger increase (20 to 25 percent) when fractional hole area was lowered from 8 to 5 percent of the bubbling area. Prado and Fair (110,144) showed an efficiency increase of the Older of 5 percent as fractional hole area was reduced from 11 to 6 percent of the bubbling area in humidification and stripping tests. The above data were collected both in the froth and spray regimes. 

Kreis, A., Kurz, A., Klein, M., Deloo, P., 1996. Static and dynamic modelling of diaphragm tanks. In Proceedings of International Conference on Spacecraft Structures, Materials and Mechanical Testing, vol. 2, pp. 845-852. 

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