Forms, analysis and stability of selenium and vitamin E in flour and Asian noodles

摘要

Grains represent a major group of commodities that are important food sources for most of the world’s population. Asian noodles are gaining popularity worldwide and representing a major end use of wheat globally. Although research has developed the understanding of processing of noodles there is need to better understand the potential contribution of these to health and wellbeing. Particular areas that have not been studied include vitamin E and selenium (Se), both essential nutrients with antioxidant properties and known to occur in multiple molecular forms. Accordingly, the purpose of this project has been to investigate the analysis, forms as well as stability of these two significant components in wheat flours and Asian noodles. Suitable extraction and analysis procedures were investigated and developed for the various chemical species of Se and also for the eight vitamer forms of vitamin E. This involved adaptation and optimisation of advanced instrumental methods for the particular samples being studied. The resultant procedures were then applied to samples of noodles prepared in the laboratory and the objective was to evaluate the stability of these micronutrients during noodle processing. In the analysis of Se in cereal foods, both total Se and speciation analyses were studied. For total Se, extraction procedures by microwave-assisted digestion and quantitation by inductively coupled plasma mass spectrometry (ICP-MS) have been evaluated. For the determination of Se species, the use of high performance liquid chromatography (HPLC) coupled with ICP-MS provided reliable and sensitive analyses. Enzymatic approaches were found to be suitable for extraction of the species of Se and for the E vitamers, accelerated solvent extraction was utilised in conjunction with chromatographic separation on a variant of HPLC known as UPLC (ultra performance liquid chromatography). Wheat flour biofortified with Se contained a high level of total Se with more than eleven-fold higher contents than the unfortified flours. Selenomethionine was identified as the predominant form of Se in both the unfortified and biofortied wheat flours with smaller quantities of selenocystine and relatively minor traces of other species in some flours. Comprehensive analyses of the Se species in samples of each form of noodles showed that the organic forms of Se are relatively stable during each of the processing stages of the noodles.. The E vitamers were less well retained during processing of white salted and yellow alkaline with the retention being higher in the latter indicating a previously unreported effect of pH. Different patterns of loss were observed for different vitamers. In contrast, there was considerable uptake of vitamin E compounds during deep frying of instant noodles. In conclusion, reliable enhanced procedures have been developed for quantitation of the individual species of Se as well as the E vitamers. These have been applied to wheat flour and Asian noodles showing that these are significant contributors of bioavailable dietary Se and vitamin E for health and wellbeing, although the retention of the various components vary.