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Abstract:The in vitro radical scavenging capacity of the roasted and ground coffee is generally known as well as the published results of lowering the incidence of various diseases by regular intake of coffee. The antioxidant capacity of coffee is based mainly on the phenols, but during the roasting phenols are degraded and new products with antioxidant capacity are formed. A major contributor to the antioxidant activity was identified as N-methylpyridinium, which is formed during the roasting by degradation of trigonelline, the degradation is about 50% of trigonelline content and the concentration of N-methylpyridinium in roasted coffee is up to 0.25% on a dry weight basis. These literature data were verified within the processing plant experiment, during the usual roasting procedure of Robusta coffee the following parameters were analysed: humidity, water activity, total antioxidant capacity, total phenols, chlorogenic acid and trigonelline content, and colour (L*, a*, b*). The changes of the evaluated parameters were correlated to each other. During the roasting the total antioxidant capacity (TAC) decreased to about one half of original level in the beginning stages of roasting, another decrease continued during the storage of roasted coffee at about 10% within the year. The degradation of trigonelline, neither the content of chlorogenic acid or total phenols did not correlate with TAC in samples during the roasting and storage.

DART (direct analysis in real time), a novel technique with wide potential for rapid screening analysis, coupled with high-resolution time-of-flight mass spectrometry (TOF-MS) has been used for quantitative analysis of 5-hydroxymethylfurfural (5-HMF), a typical temperature marker of food. The DART/TOF-MS method was optimised and validated. Quantification of 5-HMF was achieved by use of a stable isotope-labelled 5-HMF standard prepared from glucose. Formation of 5-HMF from saccharides, a potential source of overestimation of results, was evaluated. Forty-four real samples (honey and caramelised condensed sweetened milk) and 50 model samples of heated honey were analysed. The possibility of using DART for analysis of heated samples of honey was confirmed. HPLC and DART/TOF-MS methods for determination of 5-HMF were compared. The correlation equation between these methods was DART = 1.0287HPLC + 0.21340, R(2) = 0.9557. The DART/TOF-MS method has been proved to enable efficient and rapid determination of 5-HMF in a variety of food matrices, for example honey and caramel.

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