Characterzation Of Extracts Of Coffee Arabica And Some Of Theier Synthetic Analogues

Abstract

The composition of coffee beans’ extracts were analysed to indentify the individual constituents present and specify the component(s) that impart(s) to roasting coffee its remarkable characteristic odour. Crushed and uncrushed beans were treated, separately in soxhlet extractors, with plain water, 1molar aqueous solutions of HCl, H2SO4, and NaOH, ethanol, acetone, cyclohexane, petroleum ether, and heptane in this descending order of polarity. In a second set of experiments this order of treatment was reversed. The extracts were found to be complex mixtures of the known classes of organic compounds (aldehydes, ketones, esters, carbohydrates, and cellulose (fibers). 1 molar H2SO4 extracts on standing deposited a black coloured product with the characteristic scent of honey. The odour and colour of the product left imply a close relationship between the smells of honey and roasting coffee beans. The initial brown colour turning black on standing suggests that it is a derivative of furfuraldehyde since this compound is known to undergo such colour readily. It is expected to have the structure The tendencies of sodium sulphide, sodium hydrogen sulphide, and sodium thioxide to act as nucleophiles have been investigated. They all react with aldehydes in general; and products with characteristic colours and odours were obtained when acetaldehydes, butryldehydes, 3-nitrobenzaldehyde, and 4-nitrobenzaldehyde were treated with such regents in aqueous media. The corresponding reactions may be described by the following eqations: Similar products were obtained using, butryldehydes, 3-nitrobenzaldehyde, and 4-nitrobenzaldehyde instead of acetaldehyde. The products so obtained have been characterized by their melting points, boiling points, and infrared spectra. The characteristic aroma of coffee beans was evolved (smelled) immediately when furfuraldehyde was treated with either Na2S, NaHOS or NaHS aqueous solutions. This implies that the aroma associated with roasting coffee may be associated, with 2-furylhydroxythiol: The fatty acids present in coffee beans’ oil have been extracted, identified, and their percentages have been estimated. Efficient extractions, giving high yields, were achieved with least polar solvent; heptane. Plamitic acid is the most abundant fat (32%), followed by stearaic acid (5%), oleatic acid (10%), linoleic acid (23%), arachidic acid (30%