Optimisation of retention of Mangiferin in Cyclopia Subternata during preparation for drying and storage of green honeybush and development of Nir Spectroscopy Calibration models for rapid quantification of Mangiferin and Xanthone contents
Thesis (Msc Food Sc (Food Science))--Stellenbosch University, 2008.
Extraction efficiency of soluble solids (SS), total polyphenols (TP) and xanthones (AlCl3 assay) from dried, green Cyclopia subternata, as affected by mass-solvent ratio, extraction time and solvents, was investigated. In addition the effect of solvent composition on extraction of mangiferin and hesperidin was determined. Extraction of 5 g plant material as opposed to 0.5 and 1 g resulted in lower recoveries of SS, TP and xanthones (P<0.05). Extraction of SS and TP increased during the initial 20 min of contact time, where after it remained constant (P>0.05). Water, 33% acetonitrile, ethanol (50, 80 and 100%), methanol (50 and 100%) and 70% acetone were investigated as extraction solvents. Extraction for 30 min with 33% acetonitrile on a steam bath or 50% ethanol at 64°C on a water bath proved to be the most effective for extraction of SS, TP and xanthones, while 33% acetonitrile was most effective in extracting hesperidin from C. subternata. However, 70% acetone was most effective in extracting mangiferin. A poor correlation (r = 0.54) was observed for the total antioxidant activity (TAA) of C. subternata, as determined for water extracts and with the mangiferin content determined by HPLC. A moderate correlation (r = 0.85) was, however, obtained for TAA and TP content. The mangiferin content of green C. subternata can be determined using the aluminium chloride (AlCl3) colorimetric method. A moderate correlation (r = 0.87) was found for the xanthone content of the plant material determined using the AlCl3 colorimetric method and mangiferin content quantified by HPLC (y = 1.2x + 0.54) following extraction with hot water. For extraction using 33% acetonitrile a weaker correlation (r = 0.74; y = 1.3x + 0.87) was found between the xanthone and mangiferin contents. The xanthone content (determined by AlCl3) of the plant material as extracted by the two solvents, correlated well (r = 0.91). Good correlations were also obtained, when comparing extractions with water and 33% acetonitrile, for determination of the SS (0.94) and mangiferin contents (r = 0.97) of the plant material. Near infrared (NIR) spectroscopy was investigated as a rapid and more economical method for prediction of mangiferin and xanthone contents of dried, green C. subternata plant material. NIR spectroscopy calibration models can be used for screening purposes for the mangiferin and (SEP = 0.21 g.100 g-1; r = 0.82) and xanthone (SEP = 0.27 g.100 g-1; r = 0.81) contents. The effect of various pre-drying treatments and storage temperatures on the colour, soluble SS, TP, mangiferin and hesperidin contents of green C. subternata was investigated. By steaming green C. subternata directly after maceration, its colour retention can be improved. Good stability was shown for mangiferin and hesperidin during manufacture and storage of C. subternata.