**5. Application**

#### **5.1 Extraction**

A facilitated extraction of valuable components, like sucrose from sugar beet, red colorants from red beet roots and polyphenols from wine as well as juice from fruits, can be achieved by using PEF as a pre treatment.

The traditional sucrose extraction process is a thermal one treating the cossettes at 70 to 75 °C for 1 to 1,5 h. The heating process permits a denaturation of the sugar beet cells and facilitates the sugar extraction. This process uses a significant amount of energy and water and assists the growth of spoilage microorganisms. Lopez et al. (López et al., 2009) studied the influence of PEF on the extraction yield dependent on the electric field strength and pulse number as well as temperature. As a result applying 20 pulses with a field strength of 7 kV/cm allows a temperature reduction from 70 °C to 40 °C in a 60 min extraction process with yield of 80 %. The related thermal energy consumption is lowered by more than 50 %. In addition the extraction is dependant on the field strength, specific energy as well as temperature and independent from pulse shape and pulse duration (López et al., 2009). Agitation during extraction leads to an increase of the sucrose yield (El-Belghiti&Vorobiev 2004). In this study the sugar beets were treated with 0,9 kV/cm and 250 pulses in a cylindrical batch treatment chamber. For an extraction yield of 30 %, an extraction time of 120 min with 100 rpm agitation is required in comparison to 500 min extraction time without agitation. The sugar extraction process assisted by PEF can be improved by additional agitation, as well as by applying pressure. Using a pressure of 30 MPa during the extraction process the extraction yield can be increased by 20 % (Eshtiaghi&Knorr 2002).

Besides the yield of the PEF assisted extraction process, the quality of the sucrose was analysed. The treatment of sugar beets with an electric field strength of 0,6 kV/cm and 500 pulses with a pulse duration of 100 µs at 30 °C leads to comparable results of thermal process at 70 °C (Loginova et al., 2011).

The thermal treatment at 70 °C leads to a sucrose content of 14 % and a purity of more than 90 %. Equal values have been reached using a PEF treatment at 30 °C. The energy consumption required by PEF treatment is 5,4 kWh/t versus 46,7 kWh/t for the thermal treatment. In conclusion, the application of PEF lowers the energy consumption without influencing the sucrose content or the purity of the extracted sucrose solution (Loginova et al., 2011). Increasing the temperature of the PEF treatment leads to a reduction of the required electric field strength without decreasing the important quality parameters. Another study of Loginova et al. (Loginova et al., 2011) shows an increased sucrose content and °Brix values of extracted product assisted by PEF in a parallel stainless steel electrode with a gap of 7 cm applying 0,6 kV/cm at 50 °C. The end result is a higher purity and

concentration gradient. To rupture the cells, PEF can be used. Using PEF a disintegration of the cells could be observed at moderate temperatures. Consequently, the heat load could be minimized and no change of quality of the extract could be detected. In addition to that, the extraction yield could also be increased. In summary, the result of using pulsed electric fields instead of high temperature treatment is a reduced temperature and distillation time. A possible application being the treatment of roses to gain a higher yield of rose oil while

A facilitated extraction of valuable components, like sucrose from sugar beet, red colorants from red beet roots and polyphenols from wine as well as juice from fruits, can be achieved

The traditional sucrose extraction process is a thermal one treating the cossettes at 70 to 75 °C for 1 to 1,5 h. The heating process permits a denaturation of the sugar beet cells and facilitates the sugar extraction. This process uses a significant amount of energy and water and assists the growth of spoilage microorganisms. Lopez et al. (López et al., 2009) studied the influence of PEF on the extraction yield dependent on the electric field strength and pulse number as well as temperature. As a result applying 20 pulses with a field strength of 7 kV/cm allows a temperature reduction from 70 °C to 40 °C in a 60 min extraction process with yield of 80 %. The related thermal energy consumption is lowered by more than 50 %. In addition the extraction is dependant on the field strength, specific energy as well as temperature and independent from pulse shape and pulse duration (López et al., 2009). Agitation during extraction leads to an increase of the sucrose yield (El-Belghiti&Vorobiev 2004). In this study the sugar beets were treated with 0,9 kV/cm and 250 pulses in a cylindrical batch treatment chamber. For an extraction yield of 30 %, an extraction time of 120 min with 100 rpm agitation is required in comparison to 500 min extraction time without agitation. The sugar extraction process assisted by PEF can be improved by additional agitation, as well as by applying pressure. Using a pressure of 30 MPa during the extraction process the extraction yield can be increased by 20 % (Eshtiaghi&Knorr 2002).

Besides the yield of the PEF assisted extraction process, the quality of the sucrose was analysed. The treatment of sugar beets with an electric field strength of 0,6 kV/cm and 500 pulses with a pulse duration of 100 µs at 30 °C leads to comparable results of thermal

The thermal treatment at 70 °C leads to a sucrose content of 14 % and a purity of more than 90 %. Equal values have been reached using a PEF treatment at 30 °C. The energy consumption required by PEF treatment is 5,4 kWh/t versus 46,7 kWh/t for the thermal treatment. In conclusion, the application of PEF lowers the energy consumption without influencing the sucrose content or the purity of the extracted sucrose solution (Loginova et al., 2011). Increasing the temperature of the PEF treatment leads to a reduction of the required electric field strength without decreasing the important quality parameters. Another study of Loginova et al. (Loginova et al., 2011) shows an increased sucrose content and °Brix values of extracted product assisted by PEF in a parallel stainless steel electrode with a gap of 7 cm applying 0,6 kV/cm at 50 °C. The end result is a higher purity and

reducing the distillation time (Dobreva et al., 2010).

**5. Application 5.1 Extraction** 

by using PEF as a pre treatment.

process at 70 °C (Loginova et al., 2011).

Fig. 6. Influence of temperature and PEF on the sucrose concentration and the purity of the sucrose solution (Loginova et al., 2011)

improved filter capability of the product in comparison to the thermally treated product at 70 °C.

The thermal treatment is dependent on the holding time (equal with treatment time for the extraction process) and aiming on an almost complete thermo-break. The application of PEF reduces the treatment time resulting in a high cell disintegration index of approximately 0,95 in several milliseconds in contrast to a cell disintegration index of 0,85 in more than 100 s for a thermal treatment. A higher cell disintegration index can be reached by using a higher electric field strength (Lebovka et al., 2007). The researchers Eshtiaghi et al. (Eshtiaghi&Knorr 2002) indicated a cell disintegration index of approximately 0,7 by treating the slices with an electric field strength of 2,4 kV/cm and 20 pulses at 20 °C. The same cell disintegration index can be achieved by a heat treatment at 72 °C for 15 min.

In addition to the extraction of sucrose from sugar beet the extraction of industry relevant colorants from red beet roots can be improved. Red beet concentrate can be used as a food additive to color food. Betalains are the major colorants, and are composed of the red –violet substance betacyanin and the yellow-orange betaxanthin. The main function of betalains beside the color, is antiviral and antimicrobial activity (Azeredo 2009). Most extraction processes contains a thermal treatment leading to a lower extraction yield and high color degradation, because of the sensitivity of the betalains towards high temperature. For example a thermal treatment at 30 °C for 5 h leads to a degradation of 20 % of the betalains. In comparison an extraction at 80 °C for 1 h results in a complete degradation of the betalains (Loginova et al., 2011). The extraction assisted by PEF lowers the temperature without decreasing the extraction yield and destruction of the color (Fincan et al., 2004; Loginova et al., 2011). The same extraction rate can be achieved using a pre-treatment with PEF at 30 °C of the red beet using a field strength of 1,5 kV/cm and 20 pulses with a duration of 100 µs in comparison to a thermal treatment at 80 °C for 40 min and in addition with less color degradation (Loginova et al., 2011).

Another main product function is the solid-liquid juice extraction process assisted by PEF. The effects of PEF on the extraction of apple juice will be described. The left side of the Fig. 7. below shows a current process for apple juice extraction.

Mass Transport Improvement by PEF –

(Guderjan et al., 2007).

these substances is possible.

yield and distillation time.

after 0,5, 1, 1,5 and 2,5 h (Fig. 8.).

reference extraction method.

specific energy of 10 kJ/kg and a distillation time of 2,5 h.

**5.2 Distillation** 

Applications in the Area of Extraction and Distillation 223

The oil extraction process also contains a solid-liquid extraction step, which can be improved by PEF application. Guderjan et al. (Guderjan et al., 2005) studied the effect of PEF on the oil yield of maize and olives. Pulsing the maize with an electric field strength of 0,6 kV/cm and a specific energy of 0,62 kJ/kg at 20 °C yields an extraction of 43,7 % in comparison to a yield of 23,2 % of the untreated maize. The same effect of increased extraction yield is observed when treating olives with 1,3 kV/cm and 100 pulses. An increase of 7,4% with PEF in contrast to an increase of 5,3 % for a heat treatment (50 °C for 30 min) was determined (Guderjan et al., 2005). Beside olive and maize, rape seed can be treated to enhance the extraction yield and the quality of the oil. In that case, an improved oil yield was observed as well as an increase of the polyphenol-, phytosterol and tocopherol content. The rape seeds were pulsed with field strength of 7 kV/cm and 120 pulses

Distillation is a separation process, where the product is exposed to a defined temperature for a specific time. Because of the different boiling point of the components, a separation of

The traditional rose oil distillation process is characterized by exposing a product to a high temperature for a defined time. The temperature causes a denaturation of the cell membrane and substances diffuse out of the cells. Due to the temperature sensitivity of the rose oil during the distillation process, the critical threshold should not be exceeded as the quality of the rose oil will be reduced. A lower temperature results in reduced disintegration of the rose cells and in a low extraction yield. To improve the rupture of the cell membrane, the cells can be exposed to pulsed electric fields. The electric field induces a polarization with a resulting breakdown of the cell membrane and an increased permeability. The process can be used for the rose oil production. Dobreva et al. (Dobreva et al., 2010) studied different PEF treatment conditions varying the specific energy and different distillation times. The aim was to detect the influence of PEF on the extraction

The PEF treatment was performed in parallel treatment chamber with a gap of 5 cm. The white oil-bearing roses (*Rosa alba* L.) were pulsed with an electric field strength of 4 kV/cm and a specific energy of 10 and 20 kJ/kg at room temperature. The distillation time using high temperature for cell rupture was 2,5 h. For the analysis the oil yield was determined

After a distillation time of 1 h equivalent oil yields for the PEF and control samples were found. An increase of energy input from 10 to 20 kJ/kg causes an increase of oil yield of 20 %. Treating the roses with a specific energy of 10 kJ/kg, the yield was increased by 35 % compared to the control. In conclusion, using PEF as a pre-treatment the distillation time can be reduced resulting in lower energy consumption and a higher productivity of the distillation process. A higher yield can be achieved by treating the roses with PEF and a

Besides the improvement of yield and the distillation time, the quality of the oil analysis also showed no undesirable changes of any of the essential components in comparison to the

Fig. 7. Left side the traditional apple juice process, right side the process using PEF (adapted from (Toepfl 2006))

The current extraction process contains an enzymatic treatment to rupture the apple cells. This step can be replaced by a PEF treatment (see right side of Fig. 7.) in order to increase the extraction yield without a destruction of the juice quality (Bazhal&Vorobiev 2000; Bazhal et al., 2001; Toepfl&Heinz 2011). The extraction yield can be increased to 1,7-7,7 % using field strengths of 1 and 5 kV/cm and 1 to 30 kJ/kg using a decanter centrifuge. In comparison, an increased extraction yield of 4,2 % can be achieved using enzyme treatment (Schilling et al., 2007). For the enzymatic treatment the apples were treated with a pectolytic enzyme for 1 h at 30 °C , the pectin is degraded using an enzymatic treatment for increasing the extraction yield. After the PEF treatment, native pectin can be produced from the pomace. An increase of the nutrient content of the juice was not observed (Schilling et al., 2007). Grimi et al. (Grimi et al., 2011) studied the extraction yield, clarity, polyphenol content and the antioxidant activity of the pre-treated apples. Additionally they differ between the treatment of whole apples and sliced apples. Treatment of sliced apples with a field strength of 0,4 kV/cm and a treatment time of 0,1 s, resulted in a higher extraction yield than the treatment of whole apples using the same conditions. The cell disintegration index, clarity of the juice, polyphenol content and the antioxidant activity showed no difference between the two different apple type treatments.

The studies of Grimi et al. (Grimi et al., 2011) show an increase of the polyphenol content in apple juice in comparison to the non PEF treated sample. Similar results were reported by Puertolas et al. and Corrales et al. (Corrales et al., 2008; Puertolas et al., 2010) studying the extraction of polyphenols from red wine grapes. The polyphenols are the most important components for the color and the quality of the red wine. A rupture of the grape skin, where the polyphenols are located, leads to a release of the polyphenols resulting in a facilitated extraction. A PEF induced cell disintegration using an electric field strength of 3 kV/cm and 10 kJ/kg results in an increase of the phenolic compounds as well as a higher antioxidant content (7841 µmolTE g-1DM in comparison to 187 µmolTE g-1DM thermal treatment at 70 °C for 1 h) (Corrales et al., 2008).

The oil extraction process also contains a solid-liquid extraction step, which can be improved by PEF application. Guderjan et al. (Guderjan et al., 2005) studied the effect of PEF on the oil yield of maize and olives. Pulsing the maize with an electric field strength of 0,6 kV/cm and a specific energy of 0,62 kJ/kg at 20 °C yields an extraction of 43,7 % in comparison to a yield of 23,2 % of the untreated maize. The same effect of increased extraction yield is observed when treating olives with 1,3 kV/cm and 100 pulses. An increase of 7,4% with PEF in contrast to an increase of 5,3 % for a heat treatment (50 °C for 30 min) was determined (Guderjan et al., 2005). Beside olive and maize, rape seed can be treated to enhance the extraction yield and the quality of the oil. In that case, an improved oil yield was observed as well as an increase of the polyphenol-, phytosterol and tocopherol content. The rape seeds were pulsed with field strength of 7 kV/cm and 120 pulses (Guderjan et al., 2007).

## **5.2 Distillation**

222 Distillation – Advances from Modeling to Applications

Fig. 7. Left side the traditional apple juice process, right side the process using PEF (adapted

The current extraction process contains an enzymatic treatment to rupture the apple cells. This step can be replaced by a PEF treatment (see right side of Fig. 7.) in order to increase the extraction yield without a destruction of the juice quality (Bazhal&Vorobiev 2000; Bazhal et al., 2001; Toepfl&Heinz 2011). The extraction yield can be increased to 1,7-7,7 % using field strengths of 1 and 5 kV/cm and 1 to 30 kJ/kg using a decanter centrifuge. In comparison, an increased extraction yield of 4,2 % can be achieved using enzyme treatment (Schilling et al., 2007). For the enzymatic treatment the apples were treated with a pectolytic enzyme for 1 h at 30 °C , the pectin is degraded using an enzymatic treatment for increasing the extraction yield. After the PEF treatment, native pectin can be produced from the pomace. An increase of the nutrient content of the juice was not observed (Schilling et al., 2007). Grimi et al. (Grimi et al., 2011) studied the extraction yield, clarity, polyphenol content and the antioxidant activity of the pre-treated apples. Additionally they differ between the treatment of whole apples and sliced apples. Treatment of sliced apples with a field strength of 0,4 kV/cm and a treatment time of 0,1 s, resulted in a higher extraction yield than the treatment of whole apples using the same conditions. The cell disintegration index, clarity of the juice, polyphenol content and the antioxidant activity showed no

The studies of Grimi et al. (Grimi et al., 2011) show an increase of the polyphenol content in apple juice in comparison to the non PEF treated sample. Similar results were reported by Puertolas et al. and Corrales et al. (Corrales et al., 2008; Puertolas et al., 2010) studying the extraction of polyphenols from red wine grapes. The polyphenols are the most important components for the color and the quality of the red wine. A rupture of the grape skin, where the polyphenols are located, leads to a release of the polyphenols resulting in a facilitated extraction. A PEF induced cell disintegration using an electric field strength of 3 kV/cm and 10 kJ/kg results in an increase of the phenolic compounds as well as a higher antioxidant content (7841 µmolTE g-1DM in comparison to 187 µmolTE g-1DM thermal treatment at

difference between the two different apple type treatments.

70 °C for 1 h) (Corrales et al., 2008).

from (Toepfl 2006))

Distillation is a separation process, where the product is exposed to a defined temperature for a specific time. Because of the different boiling point of the components, a separation of these substances is possible.

The traditional rose oil distillation process is characterized by exposing a product to a high temperature for a defined time. The temperature causes a denaturation of the cell membrane and substances diffuse out of the cells. Due to the temperature sensitivity of the rose oil during the distillation process, the critical threshold should not be exceeded as the quality of the rose oil will be reduced. A lower temperature results in reduced disintegration of the rose cells and in a low extraction yield. To improve the rupture of the cell membrane, the cells can be exposed to pulsed electric fields. The electric field induces a polarization with a resulting breakdown of the cell membrane and an increased permeability. The process can be used for the rose oil production. Dobreva et al. (Dobreva et al., 2010) studied different PEF treatment conditions varying the specific energy and different distillation times. The aim was to detect the influence of PEF on the extraction yield and distillation time.

The PEF treatment was performed in parallel treatment chamber with a gap of 5 cm. The white oil-bearing roses (*Rosa alba* L.) were pulsed with an electric field strength of 4 kV/cm and a specific energy of 10 and 20 kJ/kg at room temperature. The distillation time using high temperature for cell rupture was 2,5 h. For the analysis the oil yield was determined after 0,5, 1, 1,5 and 2,5 h (Fig. 8.).

After a distillation time of 1 h equivalent oil yields for the PEF and control samples were found. An increase of energy input from 10 to 20 kJ/kg causes an increase of oil yield of 20 %. Treating the roses with a specific energy of 10 kJ/kg, the yield was increased by 35 % compared to the control. In conclusion, using PEF as a pre-treatment the distillation time can be reduced resulting in lower energy consumption and a higher productivity of the distillation process. A higher yield can be achieved by treating the roses with PEF and a specific energy of 10 kJ/kg and a distillation time of 2,5 h.

Besides the improvement of yield and the distillation time, the quality of the oil analysis also showed no undesirable changes of any of the essential components in comparison to the reference extraction method.

Mass Transport Improvement by PEF –

Composition of the OD solution [%salt/%sucrose]

from (Amami et al., 2007b))

solution with the highest efficiency (Fig. 9.).

in Table. 1.

Applications in the Area of Extraction and Distillation 225

Besides the use of PEF as a pre-treatment for red pepper, reports have shown that it can be used for treating carrots in order to increase the drying efficiency. Amami et al. (Amami et al., 2007a; Amami et al., 2007b) treated the sliced carrots with an electric field strength of 0,6 kV/cm and a specific energy of 19 kJ/kg as well as a pulse duration of 100 µs. After the PEF treatment different osmotic dehydration trials were performed to evaluate the influence of salt and sucrose concentration as well as the additional effect of a centrifugal instead of a static osmotic dehydration process. The water loss and °Brix of the solution was determined after defined time periods. For the OD process the ratio of carrots to solution was 1:3 and the duration was 240 min at 20 °C. The water loss of the untreated carrots after 2 h static OD process was 42 %. A pre-treatment of the carrots with PEF induces a water loss of 38 % and a sugar concentration of 45 °Brix. Consequently, the PEF treatment positively affects the mass transfer process. Besides the analysis of the effect of PEF on the water loss, the effect of the addition of sucrose and additional salt concentration was determined. As the sugar concentration is increased, the water loss was also increased. The addition of salt (NaCl) to the sucrose solution leads to different water loss values. An overview of the results is shown

> water loss [%] untreated

0%/65% 48,5 50 5%/60% 50,9 54,6 15%/50% 54,5 58,8 Table 1. Water loss of untreated and PEF treated (0,6 kV/cm, 19 kJ/kg) carrots slices using different salt concentrations for the osmotic solution in a OD process after 4 h (summarized

By increasing the salt concentration a higher water loss can be obtained and the water loss can be improved even more by using PEF as a pre-treatment. A higher salt concentration leads to a higher diffusion gradient and combining a higher salt concentration with a PEF process, which induces an improved mass transfer, leads to a better diffusion with regard to the dehydration process. The addition of NaCl lowers the water activity, which increases the driving force for the drying process. Using a centrifugal OD process the water loss of the untreated carrot slices can be increased from 48,5 %, 50,9 % and 54,5 % in 0%/65%, 5%/60% and 15%/50% to 56,5 %, 58,1 % and 61,9 %. As a result, centrifugation leads to an improved OD. The best result for an OD can be reached using PEF, a salt/sucrose solution as osmotic solution and centrifugation. The temperature influence was also evaluated with the result of an improved OD using 40 °C in comparison to 20 °C (Amami et al., 2007a; Amami et al., 2007b). Similar results could be obtained using the PEF pre-treatment of apples. The mass transfer of apples is increased by the PEF treatment (Chalermchat et al., 2010) and the kinetics of water and solute transfer were accelerated during the convective and diffusion stages of OD process (Amami et al., 2006). Also the treatment of strawberries with PEF leads to an improvement of the OD process. Taiwo et al. (Taiwo et al., 2003) treated strawberries placed in tap water in a parallel stainless steel electrode with a gap of 3 cm, 5 pulses with a duration of 350 µs were applied to the product using an electric field strength of 1,2 kV/cm and 100 J/pulse. For the OD different osmotic solutions were tested to find out the best

water loss [%] PEF treated

Fig. 8. Oil yield after a PEF pre-treatment of the roses in comparison to untreated after different distillation times (Dobreva et al., 2010)

#### **5.3 Drying/Freezing**

Drying is regarded to be an important preservation step. Temperature, relative humidity and time are the most important processing paramters. The drying process can be separated into three main parts. The first describes the evaporation from free surface, which is mostly influenced by heat and mass transfer. The second part includes the liquid flow from the capillaries and the third the diffusion of liquid or vapour (Sharma et al., 2000). The mass transfer, which is important for the first step of drying, is determined by the structure of the cellular material. By influencing the structure for example a disintegration of the cells, a facilitated mass transfer can be obtained. A cell disintegration of biological cell membranes can be induced by exposing the material to an electric field. The application of pulsed electric fields induces structural changes that leads to a rapid cellular breakdown and an increased permeability resulting in an enhanced mass transfer. The idea to use the PEF process in order to facilitate the drying process is described by several researchers and food products.

One product example using PEF as a pre-treatment before drying is red pepper. Ade-Omowaye et al. (Ade-Omowaye et al., 2000) investigated an increased water loss using the PEF process. For drying, a fluidized bed was used with a temperature of 60 °C for 6 h. The researchers examined the influence of the electric field strength and pulse number on the efficiency of the drying process. After 1,5 h drying the moisture content of the untreated red pepper sample was 2,06 kg/kg, of the sample treated with 1 kV/cm it was 1,45 kg/kg and the moisture content of the red pepper sample treated with 2 kV/cm it was 1,09 kg/kg. That corresponds to a decrease of moisture of 47 % at the same drying time. In summary an increasing electric field strength leads to a higher reduction of moisture content. In comparison to that shows the pulse number not that high influence so that a high pulse number has only a minimal effect on the electro permeabilisation (Ade-Omowaye et al., 2003). The same effect is reported by Knorr 1998 (Knorr&Angersbach 1998). Regarding the distillation time, after 3 h drying the drying rate was not higher as compared to the rate at 1,5 h. The reason for that is based on the fact, that nearly all water was evaporated at that time and the driving force was reduced.

Fig. 8. Oil yield after a PEF pre-treatment of the roses in comparison to untreated after

to facilitate the drying process is described by several researchers and food products.

One product example using PEF as a pre-treatment before drying is red pepper. Ade-Omowaye et al. (Ade-Omowaye et al., 2000) investigated an increased water loss using the PEF process. For drying, a fluidized bed was used with a temperature of 60 °C for 6 h. The researchers examined the influence of the electric field strength and pulse number on the efficiency of the drying process. After 1,5 h drying the moisture content of the untreated red pepper sample was 2,06 kg/kg, of the sample treated with 1 kV/cm it was 1,45 kg/kg and the moisture content of the red pepper sample treated with 2 kV/cm it was 1,09 kg/kg. That corresponds to a decrease of moisture of 47 % at the same drying time. In summary an increasing electric field strength leads to a higher reduction of moisture content. In comparison to that shows the pulse number not that high influence so that a high pulse number has only a minimal effect on the electro permeabilisation (Ade-Omowaye et al., 2003). The same effect is reported by Knorr 1998 (Knorr&Angersbach 1998). Regarding the distillation time, after 3 h drying the drying rate was not higher as compared to the rate at 1,5 h. The reason for that is based on the fact, that nearly all water was evaporated at that

Drying is regarded to be an important preservation step. Temperature, relative humidity and time are the most important processing paramters. The drying process can be separated into three main parts. The first describes the evaporation from free surface, which is mostly influenced by heat and mass transfer. The second part includes the liquid flow from the capillaries and the third the diffusion of liquid or vapour (Sharma et al., 2000). The mass transfer, which is important for the first step of drying, is determined by the structure of the cellular material. By influencing the structure for example a disintegration of the cells, a facilitated mass transfer can be obtained. A cell disintegration of biological cell membranes can be induced by exposing the material to an electric field. The application of pulsed electric fields induces structural changes that leads to a rapid cellular breakdown and an increased permeability resulting in an enhanced mass transfer. The idea to use the PEF process in order

different distillation times (Dobreva et al., 2010)

time and the driving force was reduced.

**5.3 Drying/Freezing** 

Besides the use of PEF as a pre-treatment for red pepper, reports have shown that it can be used for treating carrots in order to increase the drying efficiency. Amami et al. (Amami et al., 2007a; Amami et al., 2007b) treated the sliced carrots with an electric field strength of 0,6 kV/cm and a specific energy of 19 kJ/kg as well as a pulse duration of 100 µs. After the PEF treatment different osmotic dehydration trials were performed to evaluate the influence of salt and sucrose concentration as well as the additional effect of a centrifugal instead of a static osmotic dehydration process. The water loss and °Brix of the solution was determined after defined time periods. For the OD process the ratio of carrots to solution was 1:3 and the duration was 240 min at 20 °C. The water loss of the untreated carrots after 2 h static OD process was 42 %. A pre-treatment of the carrots with PEF induces a water loss of 38 % and a sugar concentration of 45 °Brix. Consequently, the PEF treatment positively affects the mass transfer process. Besides the analysis of the effect of PEF on the water loss, the effect of the addition of sucrose and additional salt concentration was determined. As the sugar concentration is increased, the water loss was also increased. The addition of salt (NaCl) to the sucrose solution leads to different water loss values. An overview of the results is shown in Table. 1.


Table 1. Water loss of untreated and PEF treated (0,6 kV/cm, 19 kJ/kg) carrots slices using different salt concentrations for the osmotic solution in a OD process after 4 h (summarized from (Amami et al., 2007b))

By increasing the salt concentration a higher water loss can be obtained and the water loss can be improved even more by using PEF as a pre-treatment. A higher salt concentration leads to a higher diffusion gradient and combining a higher salt concentration with a PEF process, which induces an improved mass transfer, leads to a better diffusion with regard to the dehydration process. The addition of NaCl lowers the water activity, which increases the driving force for the drying process. Using a centrifugal OD process the water loss of the untreated carrot slices can be increased from 48,5 %, 50,9 % and 54,5 % in 0%/65%, 5%/60% and 15%/50% to 56,5 %, 58,1 % and 61,9 %. As a result, centrifugation leads to an improved OD. The best result for an OD can be reached using PEF, a salt/sucrose solution as osmotic solution and centrifugation. The temperature influence was also evaluated with the result of an improved OD using 40 °C in comparison to 20 °C (Amami et al., 2007a; Amami et al., 2007b). Similar results could be obtained using the PEF pre-treatment of apples. The mass transfer of apples is increased by the PEF treatment (Chalermchat et al., 2010) and the kinetics of water and solute transfer were accelerated during the convective and diffusion stages of OD process (Amami et al., 2006). Also the treatment of strawberries with PEF leads to an improvement of the OD process. Taiwo et al. (Taiwo et al., 2003) treated strawberries placed in tap water in a parallel stainless steel electrode with a gap of 3 cm, 5 pulses with a duration of 350 µs were applied to the product using an electric field strength of 1,2 kV/cm and 100 J/pulse. For the OD different osmotic solutions were tested to find out the best solution with the highest efficiency (Fig. 9.).

Mass Transport Improvement by PEF –

thaw process (Jalté et al., 2009)

**5.4 Process and equipment design** 

PEF (Schilling et al., 2007; Toepfl&Heinz 2011).

shown in Fig. 11.

Applications in the Area of Extraction and Distillation 227

Fig. 10. Cellular structure of a untreated (a) and a PEF treated (b) potato after freeze and

Most of the PEF applications described as a pre-treatment in order to increase the extraction yield, to decrease the distillation time and/or process temperature, were performed with discontinuous PEF systems using a parallel or cylindrical electrode configurations for the treatment chambers. A parallel electrode configuration of the treatment chamber allows a homogenous electric field distribution. All tests with the different food types and systems were performed on a lab-scale. Toepfl et al. (Toepfl&Heinz 2011) studied a scale up from pilot plant to production scale for the apple juice production. They showed nearly the same increase of juice yield compared to the lab scale trials without influencing the taste or nutritional content. An increase of total acids, glucose, fructose and saccharose as well as total polyphenols was observed. Because of the high quality of the juice and the accordance of all quality parameters within the Europrean Code of Practice for Fruit Juices (AIJN 1996), the production including the PEF process step is equal to the common used process without

A continuous treatment up to an industrial scale has been realized by DIL. At the moment three different systems are available for laboratory scale, semi-industrial scale and industrial scale. The 5 kW system has a maximum voltage of 30 kV and maximum current of 200 A. The pipe diameter ranges from 10 to 30 mm. Due to the small pipe diameter it is not possible to treat tubers or whole fruits. An increased pipe diameter can be used in 30 kW systems with a maximum voltage of 30 kV and a maximum current of 700 A. The pipe diameter can be increased up to 100 mm and for the application cell disintegration the capacity is 10.000 kg/h. A further increase of capacity up to 50.000 kg/h can be realized using the 80 kW systems with a maximum voltage of 60 kV and a maximum current of 5.000 A. The pipe diameter of these systems is in range of 200 mm, as an alternative belt type chambers

can be used. At a belt width of 1 m the processing capacity can be up to 50.000 kg/h.

The 30 kW system and the belt system and a PEF system with a pipe diameter of 50 mm are

The PEF treatment consumes less energy compared to for example thermal treatments. For the treatment of sliced apples, the energy consumption is 12,5 ±0,5 kJ/kg and for whole apples 7,9±0,4 kJ/kg (Grimi et al., 2011). The typical energy requirement is in a range of

Fig. 9. Extent of water loss from PEF pre-treated strawberries during OD process in different osmotic solutions (Taiwo et al., 2003)

From the above examples it can be said that pre-treatment with PEF increases mass transfer during the OD. When considering different osmotic solutions containing glucose, sucrose or salt/sucrose results show that the salt/sucrose solution shows the best result regarding the water loss.

In addition to PEF treatment of carrots in order to improve the OD, potatoes can also be regarded as suitable products for a PEF pre-treatment. The application of PEF on potatoes with an electric field strength of 1,5 kV/cm induces an enhanced drying process, because of the disintegration of the potato cells induced by PEF. The comparison of a freeze dried potato without PEF and a PEF freeze dried potato shows less structure damage (Lebovka et al., 2007). Besides the structure also the diffusion characteristics in potatoes can be improved using PEF. For example a PEF treatment using 1,5 kV/cm and 20 applied pulses leads to a release of glucose and fructose, which are precursors for Maillard reaction, and a facilitated uptake of sodium chloride (Janositz et al., 2010). A reduced browning and acrylamide formation has been reported (Lindgren et al., 2002). A comparison of the treatment of potatoes and apples shows different diffusion coefficients during OD for these two different food products. The treatment of apples showed an increase of diffusion coefficient. The treatment of potatoes by PEF showed that the diffusion coefficient could be improved. The reason for this difference is based on the morphological structure of potato and apple. The tissue of potato is more tightly packed in contrast to the apple tissue (Arevalo et al., 2004).

Using PEF as a pre-treatment the drying and freezing rate can be improved. With increasing cell disintegration the freezing rates increased. Regarding the freezing process cellular water flows easily out of the cell and ice nucleation outside the cell starts. SEM pictures show the impact of PEF on the freezing process (Jalté et al., 2009).

The untreated potato cells show perturbation of the original polyhedral arrangement of the cells and also disrupted cell walls. The structure of PEF treated potato indicates a structural damage in order to a partial destruction of the polyhedral shape. Fig. 10. (right) shows voids, which can be explained by the formation of ice crystals outside the cell (Jalté et al., 2009).

Fig. 9. Extent of water loss from PEF pre-treated strawberries during OD process in different

From the above examples it can be said that pre-treatment with PEF increases mass transfer during the OD. When considering different osmotic solutions containing glucose, sucrose or salt/sucrose results show that the salt/sucrose solution shows the best result regarding the

In addition to PEF treatment of carrots in order to improve the OD, potatoes can also be regarded as suitable products for a PEF pre-treatment. The application of PEF on potatoes with an electric field strength of 1,5 kV/cm induces an enhanced drying process, because of the disintegration of the potato cells induced by PEF. The comparison of a freeze dried potato without PEF and a PEF freeze dried potato shows less structure damage (Lebovka et al., 2007). Besides the structure also the diffusion characteristics in potatoes can be improved using PEF. For example a PEF treatment using 1,5 kV/cm and 20 applied pulses leads to a release of glucose and fructose, which are precursors for Maillard reaction, and a facilitated uptake of sodium chloride (Janositz et al., 2010). A reduced browning and acrylamide formation has been reported (Lindgren et al., 2002). A comparison of the treatment of potatoes and apples shows different diffusion coefficients during OD for these two different food products. The treatment of apples showed an increase of diffusion coefficient. The treatment of potatoes by PEF showed that the diffusion coefficient could be improved. The reason for this difference is based on the morphological structure of potato and apple. The tissue of potato is more tightly packed

Using PEF as a pre-treatment the drying and freezing rate can be improved. With increasing cell disintegration the freezing rates increased. Regarding the freezing process cellular water flows easily out of the cell and ice nucleation outside the cell starts. SEM pictures show the

The untreated potato cells show perturbation of the original polyhedral arrangement of the cells and also disrupted cell walls. The structure of PEF treated potato indicates a structural damage in order to a partial destruction of the polyhedral shape. Fig. 10. (right) shows voids, which can be explained by the formation of ice crystals outside the cell (Jalté et al.,

osmotic solutions (Taiwo et al., 2003)

in contrast to the apple tissue (Arevalo et al., 2004).

impact of PEF on the freezing process (Jalté et al., 2009).

water loss.

2009).

Fig. 10. Cellular structure of a untreated (a) and a PEF treated (b) potato after freeze and thaw process (Jalté et al., 2009)

### **5.4 Process and equipment design**

Most of the PEF applications described as a pre-treatment in order to increase the extraction yield, to decrease the distillation time and/or process temperature, were performed with discontinuous PEF systems using a parallel or cylindrical electrode configurations for the treatment chambers. A parallel electrode configuration of the treatment chamber allows a homogenous electric field distribution. All tests with the different food types and systems were performed on a lab-scale. Toepfl et al. (Toepfl&Heinz 2011) studied a scale up from pilot plant to production scale for the apple juice production. They showed nearly the same increase of juice yield compared to the lab scale trials without influencing the taste or nutritional content. An increase of total acids, glucose, fructose and saccharose as well as total polyphenols was observed. Because of the high quality of the juice and the accordance of all quality parameters within the Europrean Code of Practice for Fruit Juices (AIJN 1996), the production including the PEF process step is equal to the common used process without PEF (Schilling et al., 2007; Toepfl&Heinz 2011).

A continuous treatment up to an industrial scale has been realized by DIL. At the moment three different systems are available for laboratory scale, semi-industrial scale and industrial scale. The 5 kW system has a maximum voltage of 30 kV and maximum current of 200 A. The pipe diameter ranges from 10 to 30 mm. Due to the small pipe diameter it is not possible to treat tubers or whole fruits. An increased pipe diameter can be used in 30 kW systems with a maximum voltage of 30 kV and a maximum current of 700 A. The pipe diameter can be increased up to 100 mm and for the application cell disintegration the capacity is 10.000 kg/h. A further increase of capacity up to 50.000 kg/h can be realized using the 80 kW systems with a maximum voltage of 60 kV and a maximum current of 5.000 A. The pipe diameter of these systems is in range of 200 mm, as an alternative belt type chambers can be used. At a belt width of 1 m the processing capacity can be up to 50.000 kg/h.

The 30 kW system and the belt system and a PEF system with a pipe diameter of 50 mm are shown in Fig. 11.

The PEF treatment consumes less energy compared to for example thermal treatments. For the treatment of sliced apples, the energy consumption is 12,5 ±0,5 kJ/kg and for whole apples 7,9±0,4 kJ/kg (Grimi et al., 2011). The typical energy requirement is in a range of

Mass Transport Improvement by PEF –

materials are eligible for a PEF treatment.

the industry.

**7. References** 

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and distillation time. Industrial scale PEF systems are available and can be implemented in

Other products as described in the chapter can be analysed as well. Many different studies showed an increased extraction yield, cost reduction and improvement of product quality. Consequently, the PEF process can be used for other product fields, like the extraction of essential oils from plants. Besides products mentioned in that chapter, many other raw

Ade-Omowaye, B. I. O., A. Angersbach, N. M. Eshtiaghi and D. Knorr (2000). Impact of high

Ade-Omowaye, B. I. O., A. Angersbach, K. A. Taiwo and D. Knorr (2001). Use of pulsed

Ade-Omowaye, B. I. O., N. K. Rastogi, A. Angersbach and D. Knorr (2003). Combined

Álvarez, I., J. Raso, A. Palop and F. J. Sala (2000). Influence of different factors on the

Amami, E., A. Fersi, L. Khezami, E. Vorobiev and N. Kechaou (2007a). Centrifugal osmotic

Amami, E., A. Fersi, E. Vorobiev and N. Kechaou (2007b). Osmotic dehydration of carrot

Amami, E., E. Vorobiev and N. Kechaou (2006). Modelling of mass transfer during osmotic

Angersbach, A. and V. Heinz (1997). Elektrische Leitfähigkeit als Maß des

Angersbach, A., V. Heinz and D. Knorr (2000). Effects of pulsed electric fields on cell

Arevalo, P, Ngadi, O. M, Bazhal, I. M, Raghavan and V. G. S (2004). *Impact of pulsed electric* 

Azeredo, H. M. C. (2009). Betalains: properties, sources, applications, and stability - a review. *International Journal of Food Science & Technology* Vol.44, pp. 2365-2376.

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intensity electric field pulses on cell permeabilisation and as pre-processing step in coconut processing. *Innovative Food Science & Emerging Technologies* Vol.1, No.3, pp.

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Fig. 11. (a) 30 kW belt system for the treatment of tubers or whole fruits, (b) PEF system with a pipe diameter of 50 mm

3 kWh/ton for a complete tissue disintegration. Compared to other cell disruption methods (mechanical: 20-40 kJ/kg; enzymatic: 60-100 kJ/kg; heating, freezing/thawing: >100 kJ/kg) the energy consumption is very low (Toepfl 2006). For tissue softening, where a lower extent of cell disintegration is required, the typical specific energy input for a PEF treatment is in a range of 1 kJ/kg. The same effect can be observed during the sugar extraction process. More than 50 % of the thermal energy can be saved using a PEF treatment (temperature: 40 °C) instead of a thermal treatment (70 °C) in 60 min extraction process with a yield of 80 % (López et al., 2009).

In conclusion the application of PEF offers the possibility to decrease the energy consumption and a continuous scale up is possible.

### **6. Conclusion**

Food processing is a wide field containing many different process steps and techniques based on the principles of process engineering. The industry is searching for new and innovative techniques to improve the quality of the food and to introduce new products with a simultaneous cost reduction. One of the most promising new novel food processing techniques is the application of pulsed electric fields (PEF). This non-thermal treatment is based on the application of pulses with a certain voltage and short duration times (µs) to the product located between two electrodes. The product is located between the electrodes and is exposed to the electric field. The cells and the microorganisms in the product are affected by PEF. Membranes of the cells are destroyed.

For some food processing steps, especially extraction, dehydration and distillation, a rupture of the tissue is required. Many different cell rupturing techniques are available based on mechanical, chemical or thermal treatments, but they often induce a quality loss of the product or the rupture is not sufficient resulting in a low product yield. Using PEF a more efficient rupture of the cells can be achieved. PEF leads to a poration of the cell membrane resulting in a facilitated diffusion out of the cell. The application field has a very wide range such as the extraction yield of juices, oils, sugar and the reduction of drying time and distillation time. Industrial scale PEF systems are available and can be implemented in the industry.

Other products as described in the chapter can be analysed as well. Many different studies showed an increased extraction yield, cost reduction and improvement of product quality. Consequently, the PEF process can be used for other product fields, like the extraction of essential oils from plants. Besides products mentioned in that chapter, many other raw materials are eligible for a PEF treatment.
