Fatty acid measurements

The fatty acids measured by these techniques have all been small monomeric molecules. Lamar and Goerlitz [ 125] studied the acidic materials in highly coloured water and found that most of the nonvolatile material was composed of polymeric hydroxy carboxylic acids, with some aromatic and olefinic unsaturation. Their methods included gas, paper, and column chromatography with infrared spectrophotometry as the major technique used for the actual characterisation of the compounds. 

Maefarlane, G.T., Gibson, G.R., Beatty, J.H., and Cummings, J.H., Estimation of short-chain fatty acid production from protein by human intestinal bacteria based on branched-chain fatty acid measurements, F M5 Mfcroftfo/. Ecol., 101 81-88 (1992). 

Free fatty acids can be separated on a Ci8 column based on carbon number using 50% MeOH/water pH 2.5 at UV, 280 nm a fatty acid column (actually a phenyl column) will also separate them based on the number of double-bonds. Fatty acids have also been analyzed at UV, 210 nm, or by refractive index. For high-sensitivity work, they are derivatized with bromophenacylbromide and separated on Ci8 in a 15-80% AN/water gradient at 254 nm. Increase in early running C2 and C4 fatty acids measured by HPLC is used as an indicator of bacterial action. Krebs cycle acids are di- and tricarboxylic acids involved in metab-... 

Woo, A.H., Lindsay, R.C. 1983a. Statistical correlation of quantitative flavor intensity assessments and individual free fatty acid measurements for routine detection and prediction of hydrolytic rancidity off-flavors in butter. J. Food Sci. 48, 1761-1766. 

Polyunsaturated Fatty Acids, Measurement of (Holman) Porphyrins in Biological Materials, Determination of (Schwartz, Berg, 4 99... 

Four groups of workers have independently reported total fatty acid measurements in microlayer and subsurface seawater samples. Their results are collected in Table VII. In surface slicks of Narragansett Bay, adjudged by visual observation to be heavy, continuous but moderate and light respectively, Quinn and Wade (1972) found that microlayer fatty acid concentra-... 

Fig. 9 a-c. Carbon isotope composition of individual fatty acids measured across the 1996 spring bloom in Conception Bay, Newfoundland, a Horizontal net-tow b 80 m depth, HgClj-poisoned sediment trap and c 220 m depth, HgCb-poisoned sediment trap. (After [117])... 

WH, whole homogenate SR, sarcoplasmic reticulum. Short chain fatty acids (14 0, 14 1 and 16 1) did not represent more than 10% of total fatty acids measured. 

In the course of our previous investigations it has become clear, that there is an interaction between membrane sterols and saponins an increased ergosterol content was measured after saponin-treatment, but there was no difference between sensitive and non-sensitive strains [3]. Fatty acid measurements showed, that resistance to saponin is accompanied with higher unsaturation and with the increase of the relative amount of certain fatty acids [4]. 

A USDA report indicates that between 1967 and 1988, butter consumption remained stable at 2 kg per capita, margarine dropped from 5.1 to 4.7 kg, and measured total fat intake per day dropped from 84.6 to 73.3 g (14). This study also projects that the reduced consumption of tropical oils is only temporary and will return to former use levels, possibly even higher. One reason for this projected rise in tropical oil consumption is the knowledge of the beneficial effects of medium-chain length acids high in lauric oils. There is a keen interest in omega-3 fatty acids, as well as linoleic acid, contained in fish oils. 

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

Evidence for consistent, positive metaboHc effects of feeding antibiotics is fragmented and inconclusive. Direct measurement of increased uptake of nutrients, ie, in vivo amino acids, glucose, or volatile fatty acids in mminants, have not been reported. 

Potentiometry is another useful method for determining enzyme activity in cases where the reaction Hberates or consumes protons. This is the so-called pH-stat method. pH is kept constant by countertitration, and the amount of acid or base requited is measured. An example of the use of this method is the determination of Hpase activity. The enzyme hydroly2es triglycerides and the fatty acids formed are neutralized with NaOH. The rate of consumption of NaOH is a measure of the catalytic activity. 

Schmid et al. studied in detail the sulfonation reaction of fatty acid methyl esters with sulfur trioxide [37]. They measured the time dependency of the products formed during ester sulfonation. These measurements together with a mass balance confirmed the existence of an intermediate with two S03 groups in the molecule. To decide the way in which the intermediate is formed the measured time dependency of the products was compared with the complex kinetics of different mechanisms. Only the following two-step mechanism allowed a calculation of the measured data with a variation of the velocity constants in the kinetic differential equations. 

Okane et al. measured the CMC values of a-sulfonated fatty acid higher alcohol esters. These molecules can be regarded as double-chain amphiphiles, but the CMC values are about three to six orders of magnitude larger than expected for double-chain amphiphiles that can spontaneously form vesicles in water [60]. 

The surface and interfacial tension of a great number of ester sulfonates has been measured by Stirton et al. [26-28,30]. The values of the surface tension of 0.2% solutions at 25 °C are in the range from 25 to 50 mN/m and from 2 to 20 mN/m for the interfacial tension. In the group with the same number of C atoms the pelargonates and laurates have the lowest values. Among the esters of the same a-sulfo fatty acid, the surface and interfacial tension decreases with increasing molecular weight of the alcohols. Surface tension values also depend on the cation. For the alkali salts the values decrease from lithium to sodium to potassium. 

The Gibbs equation allows the amount of surfactant adsorbed at the interface to be calculated from the interfacial tension values measured with different concentrations of surfactant, but at constant counterion concentration. The amount adsorbed can be converted to the area of a surfactant molecule. The co-areas at the air-water interface are in the range of 4.4-5.9 nm2/molecule [56,57]. A comparison of these values with those from molecular models indicates that all four surfactants are oriented normally to the interface with the carbon chain outstretched and closely packed. The co-areas at the oil-water interface are greater (heptane-water, 4.9-6.6 nm2/molecule benzene-water, 5.9-7.5 nm2/molecule). This relatively small increase of about 10% for the heptane-water and about 30% for the benzene-water interface means that the orientation at the oil-water interface is the same as at the air-water interface, but the a-sulfo fatty acid ester films are more expanded [56]. 

---