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Study of changes in the chemical composition of coffee during roasting
Kohoutová, Lenka ; Vítová, Eva (referee) ; Diviš, Pavel (advisor)
This bachelor thesis deals with monitoring of changes in acrylamide and hydroxymethylfurfural levels in coffee during the process of roasting. Green coffee was roasted using two separate roasting modes (medium roast: temperature 210 °C for duration of 14 minutes, City roast: temperature 220 °C for 17 minutes). Concentration of acrylamide and hydroxymethylfurfural for various roasting durations was determined by high performance liquid chromatography. For the determination of acrylamide, linear growth of the concentration was observed. The final levels of acrylamide corresponded with levels given by the literature, although the characteristic trend of acrylamide formation was not observed. Typical trend of hydroxymethylfurfural formation was observed in samples roasted with City roast mode, while the first part of the trend was also apparent in samples roasted with medium roast mode. Final levels of hydroxymethylfurfural in roasted coffee were within the limits given by the literature.
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Control of careless heating of honeys using HPLC and MAS techniques
Radvanová, Tereza ; Punčochářová, Lenka (referee) ; Diviš, Pavel (advisor)
Honey is a popular natural food. Liquid honey without any trace of crystalization is much more desirable. Therefore, honey undergoes heat treatment to dissolve formed crystals. Exposure to high temperetures can cause chemical changes of honey components and formation of undesirable reaction products. When honey is heated 5-hydroxymethylfurfural can be formed and activity of enzyme diastase lowers. In this bachelor thesis, 5-hydroxymethylfurfural content was analyzed by HPLC-MS and activity of enzyme diastase was determined with commercial Phadebas method followed by MAS in 11 honey samples. Analysis determined 5 honey samples with above the limit content of 5-hydroxymethylfurfural and 1 sample with insufficient diastase activity. 5-hydroxymethylfurfural content in honey correlated well with diastase activity values (r = 0,612).
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Monitoring process contaminants in coffee roasting using LC-MS
Ilyushchenkova, Alexandra ; Juglová, Zuzana (referee) ; Diviš, Pavel (advisor)
The bachelor thesis focuses on monitoring changes in the concentration of process contaminants during coffee roasting using liquid chromatography with mass detection. Green coffee was roasted at 220 °C for 14 minutes with two-minute intervals. Samples for analysis were taken from 10. by 24. minutes of roasting. Practical monitoring of the acrylamide’s formation during coffee roasting was not carried out, since it was not possible to detect acrylamide in coffee using a mass detector, even after its derivatization with thiosalicylic acid. The relevant data were taken from other scientific articles, which reported a linear increase in concentration with the roasting time up to the maximum value and a subsequent exponential decrease at the end of roasting. By monitoring 5-hydroxymethylfurfural, it was found that during roasting, this substance is gradually formed in coffee due to the decomposition of carbohydrates, however, with increasing roasting time, the degradation of this substance occurs quite quickly. The concentration of 5-hydroxymethylfurfural was also determined in coffee samples purchased in the trade network. Concentrations of 5-hydroxymethylfurfural in these samples ranged from 0,3 to 0,38 mg/kg, which are corresponded to those reported in other expert studies.
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Control of careless heating of honeys using HPLC and MAS techniques
Radvanová, Tereza ; Punčochářová, Lenka (referee) ; Diviš, Pavel (advisor)
Honey is a popular natural food. Liquid honey without any trace of crystalization is much more desirable. Therefore, honey undergoes heat treatment to dissolve formed crystals. Exposure to high temperetures can cause chemical changes of honey components and formation of undesirable reaction products. When honey is heated 5-hydroxymethylfurfural can be formed and activity of enzyme diastase lowers. In this bachelor thesis, 5-hydroxymethylfurfural content was analyzed by HPLC-MS and activity of enzyme diastase was determined with commercial Phadebas method followed by MAS in 11 honey samples. Analysis determined 5 honey samples with above the limit content of 5-hydroxymethylfurfural and 1 sample with insufficient diastase activity. 5-hydroxymethylfurfural content in honey correlated well with diastase activity values (r = 0,612).
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Study of changes in the chemical composition of coffee during roasting
Kohoutová, Lenka ; Vítová, Eva (referee) ; Diviš, Pavel (advisor)
This bachelor thesis deals with monitoring of changes in acrylamide and hydroxymethylfurfural levels in coffee during the process of roasting. Green coffee was roasted using two separate roasting modes (medium roast: temperature 210 °C for duration of 14 minutes, City roast: temperature 220 °C for 17 minutes). Concentration of acrylamide and hydroxymethylfurfural for various roasting durations was determined by high performance liquid chromatography. For the determination of acrylamide, linear growth of the concentration was observed. The final levels of acrylamide corresponded with levels given by the literature, although the characteristic trend of acrylamide formation was not observed. Typical trend of hydroxymethylfurfural formation was observed in samples roasted with City roast mode, while the first part of the trend was also apparent in samples roasted with medium roast mode. Final levels of hydroxymethylfurfural in roasted coffee were within the limits given by the literature.
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