Effect of the extraction method on the lignan yield from different plant materials
Lignans are natural bioactive polyphenols widely distributed in the plant kingdom. To determine the amount and composition of lignans in plant materials, you first separate them from the plant matrix using solvent extraction. The outcome of the analysis is highly dependent on the sampling procedure and pretreatment . Another crucial step is the extraction. Accelerated solvent extraction is usually sufficient for extracting lignans from different tree species. Lignans in some plant materials may require different techniques. Here we have investigated the role of the extraction method and of enzymatic hydrolysis on the lignan yield from different cereal, nut, and oilseed species. Four different extraction methods were compared: Alkaline extraction, mild acid extraction, a combination of these two, or accelerated solvent extraction . Twenty-four different plant lignans were analyzed as their free aglycones and quantified by HPLC-MS/MS analysis. The lignan yield depended very much on the chosen extraction method. 7-Hydroxymatairesinol was the dominant lignan in the bran of some species. This was a good example of how the wrong, destructive extraction method can cause artefacts and unwanted chemical transformation. The degree of esterification can be high for furofuran and furano type lignans and thus an alkaline hydrolysis step is advisable. For some plants or lignans, mere accelerated solvent extraction or a combination of alkaline and acid extraction is enough. Nevertheless, when determining several different types of lignans (total lignan yield), at least two different extraction methods should be applied.
Acknowledgements: Academy of Finland, Sansei Nishibe, Takeshi Deyama.
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