ABSTRACT
In the food product under development, PSs were incorporated as fatty acid esters (PSEs). For optimization of the processing and preformulation studies, the need emerged for an accurate quantification of PSs and PSEs within one method, mainly to determine the conversion degree of the esterfication reaction. For example, to analyze C18 esters of PSs, high-temper-ature GC using cold on-column injection (COC) is required because of their high boiling point. With this technique PSEs and PSs can be separated and quantified within in the same GC run, though for maximal sensitivity and selectivity they need to be isolated from the fat (mainly TAG) matrix before that step. The common
approach of saponification with isolation and further analysis of the unsaponifiables could not be used here because information on PSE is lost when either saponification or transesterification methods are applied. Direct NPLC preseparation gives the problem of PSE eluting before the TAGs and PS eluting afterward. Moreover, for the latter fraction a strong sample dilution occurs. To circumvent the first problem samples were derivatised with TMS (see Table 8) in order to eliminate the polarity difference between PS and PSE. Subsequently NP-HPLC can be used to separate PSs and PSEs from TAGs and MAGs, which would otherwise interfere with the GC analysis (for details, see Table 9). The socalled HPLC polarity shift is illustrated in Fig. 11. All the PSs and PSEs are in the same elution fraction.
