Analysis of sterol content and composition in fats and oils by capillary-gas liquid chromatography using an internal standard. Comments on the German sterol method

Abstract

The German method for the determination of sterols in oils and fats, which was originally developed by Homberg with the cooperation of Bielefeld [1][2][3], has been used with very good results for many years in Germany. On the other hand the German text sometimes led to misunderstandings because no authentic English translation, and no further explanations were available regarding the rationale (the pros and cons) of the various steps used in the analytical procedure. The fact, that such misunderstandings had occurred also surfaced in discussions around international standardization efforts, for example in ISO. There are at least two remarks in footnotes [in the Italian NGD method [4] and in the European method [5] for sterols in olive oils], that also point to possible misunderstandings of the reasons for the use of an alumina column in the German method.Following these discussions, an authentic English language version of the German sterol method was now prepared. At the same time, the method was reformulated and a number of minor variations, which had been tested in the laboratory, were included in the present protocol. For example, the internal standard is now added one step earlier.The present method is also faster than the older one, because by the full use of the advantages of an internal standard procedure, a number of steps, which aimed at a more quantitative recovery of the sterol fraction, could be omitted. As a result of this work, we now present a reformulated English version of the German method for sterol determination in fats and oils. In this English text, which is reproduced below (see below under "3 Description of the Method"), a number of additional explanatory comments were added. A full chapter has been added describing the pros and cons of the various steps and the major differences between this method and some other established methods. This chapter precedes the actual method protocol.The authors believe that the method described here is more widely applicable than other methods using other internal standards such as cholestanol, sitostanol or cholestane. In particular, the method is also applicable to cereal lipids, to animal fats, and to fat mixtures containing partially hydrogenated animal fats, where sitostanol and/or cholestanol may naturally occur [6]. In these cases, methods using cholestanol or sitostanol as internal standards require a second determination -without cholestanol or sitostanol -to obtain reliable quantitative results. This second determination can be avoided when betulin is used in the way as described here. Major Differences between the German Sterol Method and some other MethodsAdmittedly, the German sterol method requires some training and perhaps more detailed information before a newcomer can obtain useful results. There are a few very important points, plus a number of minor points, where the German sterol determination method ([3], and also the improved German language protocol) differs from some of the other methods of sterol determination. The advantages and...

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