Ingredients, morphology and color changes of herbal drugs and spices after mechanical saturated steam decontamination

Abstract

Today spices and medicinal plants are used by many different industries. For instance spices are widely used by the food or fragrance industry or as raw materials for medicinal products. It is very important in all the different applications that the raw plant materials are free of microorganisms. In Germany saturated steam decontamination is the most common method for reducing germs on herbal drugs and spices as the use of ionizing radiation is not allowed. This study tested a new method of mechanical saturated steam decontamination called “Lemgo process” which is used for tearing off microorganisms from the surface of spices and medicinal plants. This method of saturated steam decontamination is characterized by an explosion-like evaporation of a condensate film on the plant material caused after the sudden vacuum creation. This process leads to a prompt and gentle decontamination by saturated steam. As a first example Tropaelum majus L. (nasturtium) was treated with the “Lemgo process” in a small laboratory scale (0,7 L). Due to this effect and in contrast to the classical applied saturated steam procedures it could be shown that this treatment decreased the microbial drug contamination of nasturtium up to 4 decades, along with an only small loss in the content of glucotropaeoline (13 %). Further investigations respectively focused on measuring the effects of steam temperatures at 120 °C and 100 °C, for a duration of 20 s with a subsequent flash vacuum of 20 s. Control treatments, flash-vacuum as well as saturated steam heated at 120 °C were tested separately. The impact of these incubation parameters on essential oil content and on the surface of different medicinal plants were analyzed using gas chromatography and scanning electron microscopy. During this study the following plant materials were used as an example: Foeniculum vulgare Mill. (fennel), Majorana hortensis L. (marjoram), Origanum vulgare L. (oregano), Thymus vulgaris L. (thyme), Eucalyptus grandis (eucalyptus), and Mentha x piperita L. (peppermint). Especially in herbal drugs with peltate glandular hairs, such as marjoram and peppermint, a heavy loss in essential oil content is observed (93% for marjoram and up to 97% for peppermint). Oregano and thyme, however, have peltate glandular hairs that are embedded into the leaf surface and therefore less loss of oil occurs (59-64%). The oil loss of  pharmaceutical plants like fennel and eucalyptus was very low. Application of saturated steam  decontamination did not only destroy the oil-including peltate glandular hairs, it also clotted the existing wax layer of the eucalyptus afterwards. In another studie five different pharmaceutical drugs were investigated: Linum usitatissimum L. (linseed), Foeniculum vulgare Mill. (fennel), Origanum majorana L. (marjoram), Tropaeolum majus L. (nasturtium), Allium cepa L. (onion). These herbal drugs were chosen because of their different morphologies and ingredients. The analysis considered applications in a 5 L ploughshare stirrer of the “Lemgo process” with saturated steam temperatures of 110 °C and 125 °C and an exposure time of 20 s followed by the mechanical displacement of the condensate film. A double treatment, comprising of a repeated vaporization and evacuation was also examined. The total plate count and aerobic spore count was reduced up to 4 decades. Valuable ingredients such as the essential oil of fennel and marjoram were measured before and after the treatment. The results showed a heavy loss of essential oil from marjoram (93%) and the analysis of the essential oil components indicated a dehydration of cis-sabinene hydrate, cissabinene hydrate acetate and sabinene into terpinen-4-ol, γ-terpinene and α-terpinene. In contrast fennel only showed a small essential oil loss (7%) and no modifications in its percentage composition. Distinct color changes of the plants were apparent: whereas marjoram looked dry and pale after the treatment, fennel did not undergo any changes in its appearance. Linseed is the only medicinal plant in this study that suffered no loss of value-adding ingredients, i.e. no changes of the fatty acid spectrum and no change in flavor and color. Both onion and nasturtium have ingredients which can be enzymatically degraded. As soon as the plant material has contact with saturated steam, it begins to swell and cell disrupture occurs. As a consequence the enzymes myrosinase (nasturtium) and alliinase (onion) degrade the value-adding ingredients. Onion loses 18% of cysteine sulfoxide. The percentage ratio of methiin, propiin and alliin stay the same but the color changes from white to reddish brown. Nasturtium appears darker after the “Lemgo process” treatment and loses 17% of glucotropaeoline.