Investigating carotenoid loss after drying and storage of

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2. Assessment of Methods
2.4 OPTIMISATION OF EXTRACTION AND REPEATABILITY OF
CAROTENOID ANALYSIS
2.4.1 Optimisation of extraction on dried sweet potato
Extraction is a key stage for the accuracy of the carotenoid analysis. Seventeen European
laboratories assessed the accuracy of HPLC procedures for the determination of lutein,
zeaxanthin, lycopene, $-carotene, and !-carotene in a vegetable blend. Preliminary
conclusions were that the chromatographic system was not the main source of variance
but the extraction that may have represented about 13% of the overall variance of around
23% (Scott et al. 1996 quoted by Rodriguez-Amaya 2001). A good extraction should
release all the carotenoids from the matrix (Rodriguez-Amaya 2001, Rodriguez and
Kimura 2004).
While carotenoids extraction of homogenised puree made from fresh sweet potato roots
was really effective, extraction of flour made from dried sweet potato chips did not give
acceptable results: the residue was still coloured after several washings with the
extraction mix and carotenoids were visible in the residue after further soaking in the
mix during a couple of hours. Hence different pre-extractions treatments were tested on
sweet potato flour:
• no treatment;
• soaking in THF:Methanol extraction mix for one hour;
• re-hydration in distilled water for one hour (Table 2-2).
The re-hydrated sample presented significantly higher results than the directly extracted
sample. The re-hydrated sample gave the highest total carotenoid content and the
precipitate was colourless contrary to other treatments after 3 h in extraction mix at
ambient temperature. Re-hydration of dried samples therefore is the best way for
achieving a complete extraction of carotenoids from the dried food matrix.