Application of a supercritical carbon dioxide extraction unit - Extraction of Iris germanica L. and Rosmarinus officinalis L.

This dissertation deals with the investigation and optimization of new and existing extraction methods in regard to the principles of “green extraction” and “green chemistry”. The thesis consists of three major topics. In the first part, the application of a supercritical fluid extraction unit is described, whereas in the second part the unit is used to extract odorants from iris (Iris germanica L.) rhizomes. The third part deals with the extraction and application of antioxidants from rosemary (Rosmarinus officinalis L.) leaves. Over the last years, new sustainable and green extraction methods became more and more important. Supercritical fluid extraction (SFE) with carbon dioxide is an alternative technique to conventional methods for plant extraction. The first topic deals with the planning and installation of a new supercritical fluid extraction unit. In detail, this unit was purchased from Separex/France and is a major part of the new research topic “plant extractions” at the “Institute of Physical and Theoretical Chemistry” of the University Regensburg. This device enables extractions with supercritical carbon dioxide up to 1,000 bar and 150 °C. Also pressurized solvent extraction with water, ethanol, and other solvents up to 400 bar and 250 °C, are feasible. In addition, a combination of both techniques can be performed. Furthermore, the fractionation of the extract can be achieved by two separators. The construction with the different components of the extraction unit is described in Chapter 5. This section is considered to be a handbook and instruction manual for the handling of the unit for future PhD students. Besides, some troubles with the unit and the corresponding troubleshooting will be described. The main aim of the second part of this thesis was the establishment of a new extraction method to obtain iris butter, the essential oil of iris rhizomes. Supercritical fluid extraction with carbon dioxide was used as an alternative technique to conventional extraction methods. The research was focused on a fast, selective, and environmentally friendly extraction of irones, the main odorants in iris rhizomes. Preliminary experiments by SFE showed that the extraction of irones from iris rhizomes is a very complex process. For this reason, a design of experiments (DoE) was used in order to investigate the importance and best values of several extraction parameters on the irone yield. In detail, the extraction time, the flow of CO2, and both the temperature and pressure in the extraction vessel, the first separator, and the second separator of SFE were investigated. However, the result of DoE showed that the extraction of irones by SFE is not exhaustive and selective enough. Only one third of the actual irone content in the rhizomes were extracted. For this reason, the parameters obtained by DoE were used as the basis of further experiments in order to improve the extraction efficiency and selectivity. It was determined that an extraction pressure of 100 bar and a temperature of 60 °C increase significantly the selectivity of irone extraction from iris rhizomes. In fact, SFE-extracts were obtained which contain up to 30% of irones. This is three times the amount compared to conventional iris butter obtained by steam distillation. The only disadvantage of this procedure is the non-exhaustive extraction efficiency of irones. Further attempts to enhance the irone yield were not successful. In addition, appropriate methods to determine the residual moisture and irone content of iris rhizomes are described. The third part of this thesis deals with antioxidant compounds in rosemary leaves. The importance of natural sources of antioxidants has significantly increased in the last years. The reason is that artificial antioxidants are prohibited as food additives because of the potential toxic and carcinogen properties. The main antioxidants in rosemary are rosmarinic acid (water soluble) and carnosic acid (not water soluble). First investigations were performed in order to determine the influence of hydro distillation on these antioxidants. Hydro distillation is a common way to extract essential oil from rosemary leaves. It was found that large amounts of antioxidants get lost during hydro distillation. On the one hand, antioxidants, especially rosmarinic acid, are solubilized in the hydro distillation water residue. The antioxidant activity in the residual water, determined by radical scavenging experiments with DPPH, reaches a maximum value after 2.5 h of hydro distillation. On the other hand, the long exposure of heat during distillation also influences the residual antioxidants, especially carnosic acid, in the leaves. Actually, 76% of the initial rosmarinic acid and 36% of the initial carnosic acid get lost during hydro distillation. In regard to the concept of biorefinery, it would be desirable to see the hydro distillation water residue as co-product of the extraction and not as waste product. Therefore, this residue was taken and introduced in different microemulsions. It was shown that the hydro distillation water residue can enhance the antioxidant activity of drinkable microemulsions. Thus, this antioxidant water residue can be an alternative to common antioxidants, like ascorbic acid, in conventional beverages. In the final part of the rosemary chapter, an alternative green extraction method of antioxidants from rosemary leaves is presented. In particular, micellar extractions with different salts of fatty acids were performed. It is shown that almost the total amount of rosmarinic acid and three-quarter of the water insoluble carnosic acid can be extracted by means of a 4 wt% sodium myristate within 5 min. In addition, an alternative processing method of the extract was invented in order to recover selectively the carnosic acid. This is the first process used to obtain carnosic acid by extractions of rosemary leaves with aqueous solutions. To sum up, two new green extraction methods were established for the extraction of odorants from iris rhizomes and antioxidants from rosemary leaves. In addition, an approach is presented to valorize the hydro distillation water residue of rosemary leaves. These methods enhance the extraction techniques in regard to the principles of green extraction and biorefinery.