**1. Introduction**

210 Distillation – Advances from Modeling to Applications

materials can be clarified by microscale fractional bulb-to-bulb distillation. To determine important components in natural materials with complex compositions, the method presented in this chapter is useful not only for perfumery chemicals but for many substances

I would like to thank Hideo Yamada at Yamada-matsu Co., Ltd., for providing plant specimens and contributing to sensory evaluations and fruitful discussions. I also would

Hamm, S; Bleton, J; Connan, J.; Tchapla A. (2005) *Phytochemistry*, pp. 1499-1514, ISSN 0031-

Hasegawa, T.; Kikuchi, A.; Yamada, H. (2011) *The Journal of Essential Oil Research, 2011 ISEO* 

Hasegawa, T.; Toriyama, T.; Ohshima, N.; Tajima, Y.; Mimura, I.; Hirota, K.; Nagasaki, Y.;

Mertens, M.; Buettner, A.; Kirchhoff, E. (2009) *Flavour and Fragrance Journal* Vol. 24, pp. 279-

Nabeta, K.; Kawauchi, J.; Sakurai, M. (1993) *Development in Food Science*, Vol. *32*, pp. 577-589,

Singh, M.; Sharma, S.; Ramesh, S. (2002) *Industrial Crops and Products*, Vol. *16*, pp. 101-107,

Weyerstahl, P.; Marschall, H.; Splittgerber, U.; Wolf, D.; Surburg, H. (2000) *Flavour and*

Yamada, H. (2011) *Flavour and Fragrance Journal,* Vol.26, pp. 98-100, ISSN 0882-5734.

like to thank Shohei Tamada for work in early experiments on vetiver.

Anonis, D. P. (2004) *Perfumer & Flavorist*, Vol. *29*, pp. 30-36, ISSN 0272-2666.

*Fragrance Journal* Vol. 15, pp. 395-412, ISSN 0882-5734.

in natural products chemistry.

**4. Acknowledgments** 

**5. References** 

9422.

*Abstracts*, p. 8, ISSN 1041-2905.

300, ISSN 0882-5734.

ISSN 0167-4501.

ISSN 0926-6690.

Mass transport processes in the food industry are mostly based on the diffusion of soluble products out of food tissue. The main barrier for the diffusion is the biological membrane separating the inner cellular material from the outside. A rupture of the membrane results in an enhanced diffusion rate resulting in a higher yield of the product located in the cell. Most methods used for disintegration of cellular material are mechanical, chemical or thermal based treatments. A new promising technique for cell rupture is the application of pulsed electric fields (PEF). The product is treated with pulses of microseconds at a high electric field strength. The electric field affects the cell membrane of the biological tissue in order to increase the permeability resulting in pore formation. Pore formation facilitates the diffusion process. Moderate PEF settings are used to achieve a disintegration of the cellular material. Some researchers define a moderate PEF treatment by applying a field strength of 0,5 to 1,0 kV/cm and treatment times in a range of 100 and 10.000 µs. The same effects were obtained by other researchers using electric field strengths of 1 to 10 kV/cm and shorter treatment times in the range of 5 to 100 µs (Schilling et al., 2007; Corrales et al., 2008; López et al., 2009).

It has been reported that PEF induces an increase of the mass transfer process resulting in a higher extraction of different intracellular materials, such as sucrose from sugar beet, betalains from red beetroot or polyphenols from grapes during the wine production. An increase in the extraction yield of juices from different fruits and vegetables has also been noted. The drying process can also be improved by PEF application. The reduction in the drying time yields a better end product quality. For example an accelerated osmotic dehydration and drying was reported for different fruits and vegetables, such as potatoes and pepper. An improvement of the distillation processes by PEF, for example distillation of rose oil was also reported.

The following chapter describes in detail the effect of PEF on the mass transfer and the related application fields.

#### **2. Principle of action of cell disintegration using PEF technology**

The application of PEF using short pulses of a high voltage affects the membrane of a cell resulting in a permeabilisation of the biological membranes.

Mass Transport Improvement by PEF –

of cellular material by PEF (Dobreva et al., 2010).

**3. Determination of cell disintegration index** 

(Dimitrov 1984).

1988).

disintegration.

Applications in the Area of Extraction and Distillation 213

as a process condition leads to a lower critical potential if long pulse durations are applied

The induced pore formation by the external electric field leads to an increase of the permeability of the membrane. Due to the intensity of the pulses reversible and irreversible pores can be formed. Reversible pores are formed, applying less energy than the critical potential. Using that intensity of the electric pulses stress reactions in plant cells can be induced and the production of secondary metabolites can be stimulated (Schilling et al., 2007). If the intensity of the electric pulses exceeds the critical potential irreversible pores are formed, which causes lethal cell damages. This potential can be applied to inactivate pathogen and non-pathogenic microorganisms or to facilitate the mass transfer and to improve the diffusion of intra- and extracellular liquids. The result of a facilitated mass transfer and improved diffusion is a facilitated distillation process due to the disintegration

Consequently applying PEF using intensities higher than the critical value two different effects can be observed. On the one hand inactivation of microorganisms (Heinz et al., 2001; Toepfl et al., 2007) and on the other hand the cell disintegration (Angersbach&Heinz 1997; Angersbach et al., 2000). The difference between these two effects is the applied intensity of the electric field and the specific energy, which represents two of the main process parameters of a PEF treatment. The electric field strength is defined as the electric potential difference (U) for two given electrodes in space divided by the distance (d) between them, separated by a non-conductive material (Zhang et al., 1995). The specific energy describes the intensity of the treatment with high intensity pulses and is expressed in kJ/kg. Because of the small size of the microorganisms and the composition of their membranes, a high energy input is required for a successful inactivation (Glaser et al.,

For a microbiological inactivation of different vegetative microorganisms, which has been widely demonstrated by various researchers (Álvarez et al., 2000; Toepfl et al., 2007) an electric field strength of 15 to 20 kV/cm and a specific energy of 40 to 1000 kJ/kg is required. In contrast for a disintegration of cellular material lower values for electric field strength (range of 0,7 to 3 kV/cm) and a specific energy (range of 1 to 20 kJ/kg) is required (Corrales et al., 2008). The comparison of the values shows less energy is required for cell

The application of PEF induces a polarization of the cellular membrane resulting in an increased trans membrane potential. The increase leads to a rapid electrical breakdown and to local structural changes in the membrane. The result of the applied external electric field is the formation of pores related to an increase of permeability of the membrane. A permeabilisation influences the diffusion processes, for example increasing the extraction yield and shortening the distillation time. To make the best use of the permeabilisation, a maximum of cell disintegration is required. But it has to be noted that cell permeabilisation by PEF leads to a softer structure. An optimum for the PEF settings (process parameters) has to be defined as for some liquid solid separation techniques a too soft texture may be limiting. Up to now different methods are available to measure the permeability of membranes. Microscopic methods can be

The membrane acts as a semi permeable barrier for the intra- and extracellular transport of ions and macromolecules. The membrane can be considered as a capacitor filled with dielectric material of low electrical conductance and a dielectric constant in the range of 2 (Castro et al., 1993; Barbosa-Cánovas et al., 1999). The accumulation of the free charges in- and outside the cell leads to the formation of a concentration gradient, which is called trans membrane potential. The resulting voltage varied in a range from 20 to 50 mV (Wilhelm et al., 1993).

The exposure of the cell to an electric field with a specific intensity causes a movement of the charges along the electric field lines, which results in an induction of an additional potential. The trans membrane potential increased due to the electric field up to a value of 1 V (Zimmermann et al., 1976; Weaver 2000). The action of polarizing the cell is illustrated in Fig. 1.

Fig. 1. Induction of cell polarization caused by PEF application (adapted from (Dimitrov 1995))

The polarization of the membrane is related to an increase of conductivity of the membrane in the range of more than 1 S/cm² (Dimitrov 1984; Tsong 1991; Wilhelm et al., 1993). Due to this increase the resistance of the membrane decreases and results in dramatic change in permeability for potassium and sodium (Pliquett et al., 2007). The higher permeability leads to a dielectric breakdown of the cell, which occurs at different electric potentials depending on the electrical pulse duration (Dimitrov 1984).

Due to the polarization of the membrane, which is related to the movement of free charges, forms electro compressive forces causing the local dielectric rupture of the membrane. Dielectric rupture is the formation of pores and a drastic increase of permeability, which can be termed as dielectric breakdown (Zimmermann et al., 1976). This electro mechanical process is still the most accepted explanation for describing the effect of applying an external electric field on biological cells. Other theories describe the membrane as a viscoelastic model with fluctuating surfaces. The external applied electric field induces reorientation and deterioration of the membrane molecules resulting in pore formation and also the expansion of the pores leading to mechanical breakdown of the membrane (Dimitrov 1984).

The electric breakdown occurs if the applied electrical potential exceeds a critical value, which is termed the critical potential. Temperature, cell size and shape as well as medium and process conditions are influencing factors for the critical potential. The pulse duration

The membrane acts as a semi permeable barrier for the intra- and extracellular transport of ions and macromolecules. The membrane can be considered as a capacitor filled with dielectric material of low electrical conductance and a dielectric constant in the range of 2 (Castro et al., 1993; Barbosa-Cánovas et al., 1999). The accumulation of the free charges in- and outside the cell leads to the formation of a concentration gradient, which is called trans membrane potential. The resulting voltage varied in a range from 20 to 50 mV (Wilhelm et al., 1993).

The exposure of the cell to an electric field with a specific intensity causes a movement of the charges along the electric field lines, which results in an induction of an additional potential. The trans membrane potential increased due to the electric field up to a value of 1 V (Zimmermann et al., 1976; Weaver 2000). The action of polarizing the cell is illustrated in

Fig. 1. Induction of cell polarization caused by PEF application (adapted from (Dimitrov

on the electrical pulse duration (Dimitrov 1984).

The polarization of the membrane is related to an increase of conductivity of the membrane in the range of more than 1 S/cm² (Dimitrov 1984; Tsong 1991; Wilhelm et al., 1993). Due to this increase the resistance of the membrane decreases and results in dramatic change in permeability for potassium and sodium (Pliquett et al., 2007). The higher permeability leads to a dielectric breakdown of the cell, which occurs at different electric potentials depending

Due to the polarization of the membrane, which is related to the movement of free charges, forms electro compressive forces causing the local dielectric rupture of the membrane. Dielectric rupture is the formation of pores and a drastic increase of permeability, which can be termed as dielectric breakdown (Zimmermann et al., 1976). This electro mechanical process is still the most accepted explanation for describing the effect of applying an external electric field on biological cells. Other theories describe the membrane as a viscoelastic model with fluctuating surfaces. The external applied electric field induces reorientation and deterioration of the membrane molecules resulting in pore formation and also the expansion of the pores leading to mechanical breakdown of the membrane

The electric breakdown occurs if the applied electrical potential exceeds a critical value, which is termed the critical potential. Temperature, cell size and shape as well as medium and process conditions are influencing factors for the critical potential. The pulse duration

Fig. 1.

1995))

(Dimitrov 1984).

as a process condition leads to a lower critical potential if long pulse durations are applied (Dimitrov 1984).

The induced pore formation by the external electric field leads to an increase of the permeability of the membrane. Due to the intensity of the pulses reversible and irreversible pores can be formed. Reversible pores are formed, applying less energy than the critical potential. Using that intensity of the electric pulses stress reactions in plant cells can be induced and the production of secondary metabolites can be stimulated (Schilling et al., 2007). If the intensity of the electric pulses exceeds the critical potential irreversible pores are formed, which causes lethal cell damages. This potential can be applied to inactivate pathogen and non-pathogenic microorganisms or to facilitate the mass transfer and to improve the diffusion of intra- and extracellular liquids. The result of a facilitated mass transfer and improved diffusion is a facilitated distillation process due to the disintegration of cellular material by PEF (Dobreva et al., 2010).

Consequently applying PEF using intensities higher than the critical value two different effects can be observed. On the one hand inactivation of microorganisms (Heinz et al., 2001; Toepfl et al., 2007) and on the other hand the cell disintegration (Angersbach&Heinz 1997; Angersbach et al., 2000). The difference between these two effects is the applied intensity of the electric field and the specific energy, which represents two of the main process parameters of a PEF treatment. The electric field strength is defined as the electric potential difference (U) for two given electrodes in space divided by the distance (d) between them, separated by a non-conductive material (Zhang et al., 1995). The specific energy describes the intensity of the treatment with high intensity pulses and is expressed in kJ/kg. Because of the small size of the microorganisms and the composition of their membranes, a high energy input is required for a successful inactivation (Glaser et al., 1988).

For a microbiological inactivation of different vegetative microorganisms, which has been widely demonstrated by various researchers (Álvarez et al., 2000; Toepfl et al., 2007) an electric field strength of 15 to 20 kV/cm and a specific energy of 40 to 1000 kJ/kg is required. In contrast for a disintegration of cellular material lower values for electric field strength (range of 0,7 to 3 kV/cm) and a specific energy (range of 1 to 20 kJ/kg) is required (Corrales et al., 2008). The comparison of the values shows less energy is required for cell disintegration.
