Articles
Drying temperature alters the quality components of peppermint leaves
Article number
1458_46
Pages
349 – 356
Language
English
Abstract
The technical drying of medicinal and aromatic plants is an indispensable part of the processing chain in order to preserve the plants as well as the bioactive and flavouring compounds they contain.
The drying technique must be adapted to the specific crop being dried.
Drying at temperatures exceeding 45°C is not recommended for peppermint, a traditional and economically important medicinal plant, as it leads to volatilisation of compounds and a reduction in essential oil content.
However, little is known about convective drying at temperatures below 30°C. The aim of this study was to investigate the temperature effects in a range between 15 and 75°C about quality preservation of dried leaves of peppermint (Mentha × piperita ‘Multimentha’). Colour, microbial load, as well as the essential oil content and composition, were considered as quality parameters.
Drying temperatures of 75°C resulted in a lower essential oil content of the leaves, because of the evaporation of monoterpenoids.
The qualitative analysis of the essential oils revealed minor differences between drying temperatures and harvest intervals.
At 75°C, a quality improvement is observed due to a reduction in the content of value-decreasing components, such as pulegone or menthofuran.
Lower temperatures (15-45°C), in contrast, are beneficial for the retention of volatile compounds and the leaf colour in the plant material.
Low drying temperatures and long drying cycles can promote microbial growth; in this case, the threshold for moulds according to the DGHM (German Association for Hygiene and Microbiology) was exceeded at 25°C.
The drying technique must be adapted to the specific crop being dried.
Drying at temperatures exceeding 45°C is not recommended for peppermint, a traditional and economically important medicinal plant, as it leads to volatilisation of compounds and a reduction in essential oil content.
However, little is known about convective drying at temperatures below 30°C. The aim of this study was to investigate the temperature effects in a range between 15 and 75°C about quality preservation of dried leaves of peppermint (Mentha × piperita ‘Multimentha’). Colour, microbial load, as well as the essential oil content and composition, were considered as quality parameters.
Drying temperatures of 75°C resulted in a lower essential oil content of the leaves, because of the evaporation of monoterpenoids.
The qualitative analysis of the essential oils revealed minor differences between drying temperatures and harvest intervals.
At 75°C, a quality improvement is observed due to a reduction in the content of value-decreasing components, such as pulegone or menthofuran.
Lower temperatures (15-45°C), in contrast, are beneficial for the retention of volatile compounds and the leaf colour in the plant material.
Low drying temperatures and long drying cycles can promote microbial growth; in this case, the threshold for moulds according to the DGHM (German Association for Hygiene and Microbiology) was exceeded at 25°C.
Authors
L. Kahlert, K. Luhmer, S. Hillebrand, S. Brennecke, J. Ley, R. Pude
Keywords
low-temperature drying, Mentha × piperita, essential oil, volatile organic compounds, VOC
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