Total sterols

Table 2. Occurrence of the Provitamins D in Selected Plants and Animals, Parts per Thousand of Total Sterol...

Fig. 1. Relative composition of root microsomal membranes from 24 land races, varieties and breeding lines of rice which differ in their salt resistance. Campesterol, Stigmasterol and Sitosterol as % of total sterols 16 0, 18 1, 18 2 and 18 3 fatty acids as % of total fatty acids Na transport on a relative scale from (1) lowest to (9) highest. Data of D.R. Lachno, T.J. Flowers A.R. Yeo (unpublished).

No class reaction has been proposed for the measurement of total sterols. Instead, various fractionation methods, usually derived from the biochemical litreature, have been adapted to the concentrated materials collected from seawater. Certain of the more important sterols, particularly those used in the evaluation of water quality, have been determined by the use of a compound-specific reaction, after concentration from solution. Thus Wann et al. [405,... 

In addition to more rapid absorption of lipids in animals fed casein, another mechanism that may be operative is decreased clearance of circulating lipids. Rabbits fed a casein-based semipurified diet excreted significantly less cholesterol but more bile acids in their feces than animals fed a commercial diet (18). The total sterol excretion in feces of the animals fed the casein diet was half that of the rabbits fed the stock diet. Huff and Carroll (19) found that rabbits fed soy protein had a much faster turnover rate of cholesterol and a significantly reduced rapidly exchangeable cholesterol pool compared with rabbits fed casein. Similar studies performed in our laboratory revealed that the mean transit time for cholesterol was 18.4 days in rabbits fed soy protein, 36.8 days in rabbits fed casein, 33.7 days in rabbits fed soy plus lysine, and 36.3 days in rabbits fed casein plus arginine. These data suggest that addition of lysine to soy protein... 

Cholesterol (Appendix 3C) is the principal sterol in milk (>95% of total sterols) the level ( 0.3%, w/w, of total lipids) is low compared with many other foods. Most of the cholesterol is in the free form, with less than 10% as cholesteryl esters. Several other sterols, including steroid hormones, occur at trace levels. 

Since the invasive form of Candida in vaginal mycosis is the pseudo-mycelium, we also looked at this morphologically specialized material. We observed that bifonazole causes an accumulation of dihydrolanosterol exclusively, whereas clotrimazole causes the normal accumulation of 24-methylenedihydrolanosterol, dihydrolanosterol, and lanosterol (Figure 18). However, after bifonazole application, the rate of total sterol synthesis is lowered by a factor of two, a result which will be discussed later. 

The results with bifonazole, in contrast to clotrimazole, show that the sterol pattern could not completely explain the rate of sterol biosynthesis. Torulopsis glabrata is another example where both compounds show the expected accumulation of 24-methylenedihydrolanosterol and dihydrolanosterol (Figure 19). The accumulation of dihydrolanosterol, after application of 2.5 pg/ml bifonazole, does not explain why the total sterol content is decreased so markedly. A "feed-back" control of the HMG-CoA-reductase appears an unlikely explanation. 

The above shows that rapeseed oil can easily be detected, or eliminated, as a contaminant by sterol analysis. It is also, at least in Europe, the oil most likely to be used to dilute another oil. Although low levels (as a percentage of the total sterols) have been reported in some other oils (Desbordes etal., 1993), the presence of brassicasterol in an oil is good evidence of contamination in any oil from a non-Brassica species. It is likely that the traces reported as present in some other oils arise from contamination of the sample with rapeseed oil, or from some other Brassica species, or from traces of some similarly behaving non-sterol not fully separated from the sterol fraction during the work-up of the sample (Desbordes et al., 1983). 

Sterol analysis can be useful other than for detecting rapeseed oil. Accepted ranges for many oils and all major oils, given as a percentage of the total sterols, are available (Codex Alimentarius, 1997 FOSFA, 1994 AOCS, 1997). In all... 

Acid composition Sum of the trans-oleic isomers Sum of the trans-linoleic and trans-linolenic isomers (%) Chole- sterol (%) Brassica- Campesterol sterol Stigma- sterol (%) p- sitosterol apparent (%) 8-7- Stigma- stenol (%) Total sterols (mg/kg) Erytro- diol + uvaol (%)... 

Adapted from Reina et al. (1997) each result represents die average of three oils tested absolute composition calculated for each identifiable sterol as mg/100 g oil relative% composition calculated as ratio of each sterol peak/total sterol peak area. 

Naturally, if no animal fat can be detected after cholesterol analysis, then it can reasonably be concluded that pork fat is not present. If cholesterol is present, either as a low percentage of the total sterols or as a major or only component of the sterols, then other approaches have to be employed. If the product is likely to contain any DNA material, then DNA analysis would probably be the best approach (Montiel-Sosa el al., 2000). This might include rendered fat if the fat had not been highly refined, though no work appears to have been done to determine whether this would be possible. 

Standard methods of analysis of total sterol content of oils involve saponification of the oil, followed by extraction and isolation of total sterols from the unsaponihable fraction by thin layer chromatography (TLC) (AOCS, 1998). Quantification of individual sterols involves silylation of the sterol fraction and analysis by gas chromatography (GC). Sterols and steryl esters in oils and fats can be analysed by LC-GC after silylation or acylation of the free sterols (Artho et al., 1993). An alternative approach to the analysis of intact steryl esters involves separation of sterols and steryl esters by solid phase... 

Phospholipids account for only 0.8% of milk lipids. However, they play a major role in milk due to their amphiphilic properties. About 65% of them are found in the milk fat globule membrane (MFGM), whereas the rest remain in the aqueous phase. Phosphatidyl choline, phosphatidyl etha-nolamine and sphingomyelin are the major phospholipids of milk, which together comprise about 90% of the total. Sterols are also a minor component, comprising about 0.3% of the fat cholesterol, being the principal sterol, accounts for over 95% of the total sterols. 

Triarimol almost completely suppressed the biosynthesis of ergosterol by Ustilago maydis,162 although total sterol production was unaltered, and (88), obtusifoliol (93), and 14a-methylergosta-8,24(28)-dien-3j8-ol accumulated. These three sterols may be the first intermediates in ergosterol biosynthesis in this organism, although alternative interpretations of the inhibition effects are possible. 

The main shortcoming of the current analytical methods is the fact that none of them is streamlined to analyze all classes of phytosteryl conjugates separately in one analysis. The methods currently used focus on, and are highly optimized to analyze, one or two groups of the sterol classes but not all of the classes in the same analysis. This multiplies the number of samples to be analyzed and creates some overlaps in the data. On the other hand, analytical procedures for total sterol analysis (without information on the conjugation) are easily available. 

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