The aim of this study was to analyse changes in chlorophyll a and b content, a*, b* and chroma colour parameters during microwave-convective drying of basil, lovage, mint, oregano, parsley and rocket leaves. Drying was conducted at 40°C in air flowing perpendicular to the mate-rial layer with velocity 0.8 m s -1 , and at 300 W of microwave power level. The results show that drying had a significant impact on chlorophyll degradation, however the level of its losses was different for each herb species. High retention of chlorophyll a was observed in lovage and basil, and chlorophyll b retention in mint, as well. Drying did not have any significant impact on chloro-phyll a content only in the case of lovage. On the other hand, chlorophyll b contents in basil, lovage and mint were statistically constant. The greatest chlorophyll a and b losses were observed in rocket leaves. Significant decreases of a*, b* and chroma values, as a result of drying, were observed in all herbs, except rocket leaves. The smallest changes were noted for Apiaceae (lovage and parsley) and rocket (Brassicaceae). Lamiaceae (oregano, mint, basil) herbs were characterised by less stable colour. The reason for colour changes was also dependent on taxonomic group. The changes of green and yellow colour resulted from significant chlorophyll a content changes in Apiaceae herbs. Nevertheless, chlorophyll degradation was not the only reason for colour changes in the other herbs. High relationship between degradation of chlorophyll a and a* parameter was observed in the case of all investigated herbs. Ke ywo rd s : herbs, microwave-convective drying, chlorophyll, colour INTRODUCTION
Rapid drying assures that plant pigments are well preserved; if the drying process is slow, chlorophylls will degrade, and leaves will appear yellow; flower pigments also fade badly with slow drying.
- Handbook of Molecular and Cellular Methods in Biology and Medicine
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