Lim Chin Chin*, Chia Poh Ling, Irene Tan, Su W.J, Michael Tay Ming Kiong
59th AAFS, San Antonio, Feb 2007, abstract no. B112 (oral presentation)
In forensic investigations, unknown stains are sometimes found on non-porous surfaces such as floor tiles, furniture, knife blades, cutting boards, utensils and kitchenware. Porous materials such as clothes, carpets, upholstery, facial tissues and papers may also be stained with unknown substances. Techniques are readily available for stains containing biological materials (blood, seminal and vaginal fluids, urine), and stains of various organic and inorganic substances.
The detection and identification of fruit stains and residues pose a significant analytical challenge. Whole fruit juices are usually 80-90% water. Juice expressed from fruit during cutting and squeezing contains natural sugars, vitamins, minerals, phytochemicals, organic acids and aroma flavour compounds. Many fruit flavour and fragrance compounds are volatile or semi-volatile. Aroma volatile compounds have been reported in the literature to be influenced by various factors including the species, cultivars, locations, fruit maturity at harvest, processing, storage and ripening conditions. On exposure to air, cut or bruised fruit begins to darken and turn brown with oxidation, fermentation and chemical reaction. Microbes and other micro-organisms cause rapid spoilage in our hot climate. Small volumes of juice leave little residue on drying. Fruit residues in the stomach undergo digestion and chemical changes, are mixed with gastric secretions and other food, resulting in dilution and alterations to the composition of the original fruit constituents.
The aim of this research was to characterize different types of stone fruits using phase contrast microscopy, Raman microscopy, Fourier Transform-Infrared (FT-IR) microscopy and gas chromatography-mass spectrometry (GC-MS). More than 5 different types of stone fruits were analyzed. The microscopic characteristics of the flesh of these fruits were obtained using phase contrast microscopy. Our findings indicate that Raman microscopy and FT-IR microscopy were able to identify fresh fruit stains from furniture surfaces, but could not differentiate the different species of stone fruits. The flavour and fragrance compounds of stone fruits were extracted using both solvent extraction and passive headspace carbon strip adsorption techniques. A number of different aroma volatile compounds including organic acids, alcohols, aldehydes, terpenes, esters, ketones and lactones were detected using GC/MS. In our project, we were able to compare the chromatographic profiles of the aroma volatile compounds for the different fruit species. We further studied the effects of pH and decomposition on the volatile constituents of mango.