Hoteles de 2 estrellas

After harvesting, chamomile is a very perishable product during storage. This applies equally for the harvested whole herbs and, to an even greater extent, for the flowers. The main deterioration phenomena are:

• Dropping of the external quality traits, especially the natural green color of the leaves and stems and the light colors of the flowers

• Loss of particularly valuable ingredients due to material conversions, wilting due to transpiration, and physically induced escape

• Increased formation of grit through the decay of the flowers and separation of the leaves from the herb, both triggered by aging (senescence) processes

• A rise in the microbiological contamination of the product to be dried through warming and heating, especially in combination with mechanical damages and pressure points • A marked shortening of the subsequent storability of the dried product

The very high respiration rate of harvested chamomile, which reaches a mean value of 999 W t-1 _{for flowers at 10˚C (Section 7.1.1), accelerates these changes and leads, without ventilation,}

to an extremely fast rise in the stack temperature. On the other hand, chamomile reacts very easily to various external factors. For this reason, chamomile flowers and herbs should be regarded as very drying-sensitive crops.

Rapid, sufficient lowering of the water content in the harvested crops is the most important and — besides extraction — most frequently used option for preservation to avoid these changes. However, the drying conditions in question also determine the quality and stability of the dry product to a large extent. These are characterized by:

• The maximal occurring product temperature during the drying process • The dwell time of the crops in the hot air section

• The saturation deficit of water vapor in the drying medium (hot air), and also by the movement of air in the drying facility

• The coverage density (pile height and density) of the harvested product

The aim of drying must be to remove both the water that is physiologically bound in the harvested product and also the external moisture (precipitation, dew) in the shortest possible time, in order to reduce the water content of the dry product to 8–10%.

This will then cut off the ongoing respiration processes, the fermentative breakdown, and conversion reactions and the physical changes, since these can easily cause changes to the natural plant colorants (component of the external quality traits) and lead to a considerable loss of valuable active substances. The water content quoted of 8–10% for chamomile dried to a high quality is thus below the physiological water activity aw < 0.60, which prevents the dried product from being

affected even by the most xerophilic types of harmful microorganisms, the Aspergillus and Peni- cillium molds, during subsequent storage.

A sufficiently high drying temperature and a fast drying process have a decisive effect on the quality of the dry product. These factors are difficult to achieve with drying in the outdoor air (drying sheds, drying shelves, etc.), even if the chamomile is picked primarily in the months with the most favorable weather (June and July). It is thus necessary to improve the efficiency of air as the drying medium. This is done in practice either by adding thermal energy to the drying air (heated air-drying) or by lowering the moisture level in the drying medium through the use of a chilling machine such as a dehumidifier. The latter option, however, is less commercially viable in terms of both energy consumption and economics.

The permitted temperature of the product being dried is physically very limited, since increased evaporation of various components in the essential oils during the drying process can lead to an increased loss of the active substances or shifts in the spectrum of active substances. For chamomile flowers with particular, but also for the chamomile herb, which both naturally have a low level of resistance to transpiration with respect to water vaporization, this is a particularly high risk, requiring particular caution. The boiling points of the main components in the essential oils are not that low (chamazulene 160˚C, bisabolol 121˚C) [1], but in combination with the large quantities of water present in the freshly harvested plants, a further reduction in the partial steam pressure occurs in the resultant oil and water mixture, which thus lowers the vaporization to temperatures below 100˚C, as Rinder and Bomme [4] proved for the conditions for water vapor distillation for plants containing essential oils. In addition, the particular thermolability of the

covering membranes of the secretion containers for the essential oils are greater for chamomile than for other medicinal plants. This can cause considerable evaporation losses during drying, even at lower temperatures.

Thus Schilcher [5] attributes the rising losses that may occur particularly at high drying temperatures and a high air humidity (>60%) to “a type of micro water vapor distillation of the essential oil from the glandular scales,” which primarily affects the low-boiling fractions (including farnesene).

Constant checks must be carried out to ensure that the flower base of the chamomile is

completely dried, since it has a fairly high resistance to transpiration and thus takes longer to dry. Basically, the aim should be to achieve short drying times in order to minimize any changes in color, odor, and tissue structure and reduce the increasing microbiological contamination and the loss of important active substances during drying. This applies particularly to outdoor air drying. Smaller quantities of the harvested product can also be preserved using a well-designed outdoor air-drying system, making use of suitable outside air conditions. A good forced-air ventilation system through the chamomile flowers that are spread flat on hurdles is important to achieve sufficiently fast drying within 5 to 6 days.

But the physiological characteristics of the harvested chamomile also affect drying and quality [3]. One element that is extremely important is the crushing of the flowers (gritting, or crushing of the flower heads, which leads to the separation of the different parts of the heads) during drying. This crushing process is of most relevance for large flowers in which more than three quarters of all the tubular blossoms are open [2]. For tetraploid genotypes, values between 75 and 88% were measured, with values of 64% for diploid genotypes. If the flowers are plucked at the “medium mature” stage (second circle of tubular blossoms opened), the tendency to decay for tetraploids is only 14 to 27% and for diploids 11%. If they are picked even earlier, the small flowers (buds opened to first ring), there is hardly any decay (< 0.8%). In addition to the favorable influence of the ambient temperature, the tetraploid genotypes are another positive factor [2].

Harvested chamomile should be taken to drying basically without any preliminary wilting, as fresh as possible in order to guarantee that the dried medicinal product is of the highest possible quality. Drying has to be started within 2 hours after harvest, unless the stack is not ventilated (Section 7.2).

The cleaning and maintenance of the drying equipment should be such that microbiological contamination and pollution are avoided. During drying, the Guidelines for a Good Agricultural Practice (GAP) of Medicinal and Aromatic Plants [6] should be complied with at all stages.

REFERENCES

1. Gildemeister, E., Hoffmann, F. (1960) Die ätherischen Öle. Band IIIa. Akademie-Verlag, Berlin. 2. Letchamo, W. (1991) Vergleichende Untersuchngen über die nacherntetechnisch bedingten Einflüsse

auf die Wirkstoffgehalte in der Droge bei Kamille-Genotypen. Drogenreport. Sonderausgabe zur Fachtagung in Erfurt, pp. 129–134.

3. Marquard, R., Kroth, E. (2001) Anbau und Qualitätsanforderungen ausgewählter Arzneipflanzen. Agrimedia Verlag, Bergen/Dumme.

4. Rinder, R., Bomme, U (1998) Wasserdampfdestillation ätherischer Öle aus frischen und angewelkten Pflanzen. Bayerische Landesanstalt für Bodenkultur und Pflanzenbau, Freising-München, pp. 1–12. 5. Schilcher, H. (1987) Die Kamille — Handbuch für Arzte, Apotheker und andere Naturwissenschaftler.

Wissenschaftl. Verlagsgesellschaft, Stuttgart, Germany.

6. O.V. (1998) Guidelines for Good Agricultural Practice (GAP) of Medicinal and Aromatic Plants. Z. Arznei-und Gewürzpflanzen, 3, S. 166–174.

8.2 DRYING OF CHAMOMILE FLOWERS (MATRICARIA RECUTITA L.)