F A C U L T Y O F S C I E N C E U N I V E R S I T Y O F C O P E N H A G E N ANALYSIS OF AROMA COMPOUNDS OF ROSELLE BY DYNAMIC HEADSPACE SAMPLING USING DIFFERENT METHODS OF SAMPLE PREPARATION NURUL HANISAH JUHARI, Camilla Varming and Mikael Agerlin Petersen University of Copenhagen, Department of Food Science, Dairy, Meat and Plant Product Technology Section, Rolighedsvej 30, DK-1958, Frederiksberg C., Denmark. INTRODUCTION  Roselle (Hibiscus sabdariffa L.), is one of several underexploited food crops with nutritional and food processing potential. Utilization of Roselle flower as a food product is still meagre but has economic potential (Figure 1).  Sample preparation is often overlooked and is frequently considered as ‘a means to an end’. Nowadays, there has been impressive advancement in spectrometry and chromatographics instruments for analysis of aroma and flavour (Luthria & Mukhopadhyay, 2006).  Different sample preparation methods may lead to differences in the profile thus care must be taken to avoid sampling procedures which may alter the substances being studied.  Objective: to determine the influence of different methods of sample preparation on the aroma profiles of dried Roselle flower. MATERIALS AND METHODS  Samples were prepared by five different procedures: whole dry (WD), ground dry (GD), blended together with water (BTW), ground and then mixed with water (GMW), and ground and then mixed with water and kept in water bath (40°C/2hr) (GMWKB) (Figure 2).  Oven dried Roselle of the UMKL cultivar obtained from Malaysia was chosen to study aroma profiles by using dynamic headspace sampling (Figure 3), and GC- MS analysis (Figure 4). All samples were analysed in duplicate.  Multivariate analysis (principal component analysis) was applied to GC-MS data to evaluate the variation between the different sampling techniques (Figure 5). RESULTS AND DISCUSSION  A total of 125 compounds were identified using GC-MS.  Compounds identified included terpenes (32), aldehydes (20), esters (16), ketones (14), alcohols and furans (13), acids (9), sulphurs (3), lactones (2) and others (3) (Figure 6).  Different sample preparation of Roselle affected the amounts of aroma recovered (Figure 5). Least amounts of aroma compounds were recovered in WD followed by GD, BTW and GMW (Figure 6). The highest number of aroma compounds was found in Roselle treated as GMWKB, probably partly due to release of glycosidically bound volatiles.  This may be because the GMWKB treatment facilitates the swelling and hydration of plant materials, which improves the rate of mass transfer and breaks the cell walls, resulting in increased extraction efficiency (Vinatoru, 2001) but also the prerequisites for the enzymatic or chemically facilitated release of terpenes.  Furans (2-pentylfuran, 2-acetylfuran, furfural) may be produced from the drying process mainly the thermal processing.  GMW was chosen as the preparation method because it was shown to be an efficient extraction method without the possibility of excessive chemical changes of the sample. CONCLUSION  The ground and then mixed with water (GMW) sample is chosen to be the type of sample preparation for further analysis of aroma of Roselle.  Reasons: it gives efficient extraction, ease of handling, and ability to use internal standard. Figure 3: Dynamic headspace sampling setup. Figure 4: Chromatogram of Roselle prepared as GD (left) and GMW (right) determined by GC-MS. Figure 5: Principal component analysis (PCA) scores and loadings plot of Roselle volatiles. Figure 1: Photo of plants and Roselle flowers. Figure 2: Different methods of sample preparation. ACKNOWLEDGEMENT This study was financially supported by the Ministry of Education Malaysia and University Putra Malaysia. Figure 6: Total numbers of volatile compounds for each class in Roselle determined by GC-MS.