Summary 2

The text, “Enzymatic-spectrophotometric determination of sucrose in coffee beans”, Ángela Alcázar, J. Marcos Jurado, M^a Jesús Martin, Fernando Pablos, Gustavo Gonzáles (2005), describes a spectrophotometric method for determining sucrose in coffee beans. The flavour of coffee is developed during the roasting process form aroma precursors present in green beans. Sucrose is one of the most important precursors. There are several methods for determining sucrose. By using ion chromatography with pulsed amperometric detection sucrose has been quantitated in coffee beans. But there are too many handicaps and drawbacks when using ion chromatography. Another method is electrochemical detection with series of potentialpulse. This method involves a number of experimental factors: detection, oxidation and reduction times. But this method limits the robustness because of the numerous factors. Due to these handicaps there is another method to determinate sucrose in coffee beans. The aim of this text is to develop an enzymatic spectrometric method for determining in coffee beans. This method is easy to handle and cheaper than the methods with a chromatographic separation pulsed amperometric detection.

In this experiment an Unicam UV series 500 was used equipped with quartz-cell of 1.0 cm. This was used for the absorbance measurements. An IKA WERKE M20 grinder& cusher was used for processing coffee beans. A Techne TE-8D thermostat was used for controlling the temperature. At first, the coffee samples were prepared. In this experiment the temperature has been increased for two times. The first time was for the extraction of sucrose and the second time was to hydrolyse the sucrose. The samples were measured at 505 nm by a spectrophotometer. The percentage sucrose on dry base was measured.

The samples of green and roasted coffee were analysed. The method that was used, is based on that glucose is released by invertase activity. There could be interferences due to the presence of endogenously reducing sugars. These possible interferences were analysed following the normal method but without the hydrolysis step. There was no signal so it can be concluded that there was no interference from the endogenously reducing sugars. The values of the green coffee samples were between 7,6 and 4,6 %w(w) dry base. These results are similar with the reported values. There are several factors that affects the sucrose content. The factors: varietal and cultivar differences, state of maturity, processing and storage conditions. In the roasted coffee samples was not found any sucrose. The sucrose was lost during the roasting process.

The method that was described in this text is useful for determining sucrose in coffee beans.