METHOD INVOLVING PEF TREATMENT AND DRYING

Abstract

The present invention describes a method for treatment of biological soft tissue, said method comprising a step involving pulsed electric field (PEF) treatment to open up the stomata in tissues and a subsequent drying step, wherein the PEF treatment is performed in an electrical field with a field strength in the range of 0.4-1.5 kV/cm to provide enhanced rate of moisture removal during dehydration without irreversible damage on epidermal cells, wherein the PEF treatment is performed with reversible electroporation and wherein the temperature in the drying step is held within the range of 20-55 C.

Claims

1. A method for treatment of biological soft tissue, said method comprising a step involving pulsed electric field (PEF) treatment to open up the stomata in tissues by electroporation of guard cells and a subsequent drying step, wherein the PEF treatment is performed in an electrical field with a field strength in the range of 0.4-1.5 kV/cm to provide enhanced rate of moisture removal during dehydration without irreversible damage on epidermal cells, wherein the PEF treatment is performed with reversible electroporation and wherein the temperature in the drying step is held within the range of 20-55 C.

2. The method according to claim 1, wherein the stomata is kept open during the PEF treatment and during at least part of the subsequent drying step.

3. The method according to claim 2, wherein the stomata is kept open during the entire method.

4. The method according to claim 1, wherein the PEF treatment is performed so that the metabolic activity is kept when drying to at least a moisture level of 20% moisture content.

5. The method according to claim 1, wherein the drying step is maximum performed down to a moisture level of 20% moisture content to keep metabolic activity in the cells.

6. The method according to claim 1, wherein pulses applied have a field strength in the range of 0.4-1.0 kV/cm.

7. The method according to claim 6, wherein pulses applied are monopolar pulses having a field strength in the range of 0.6-1.0 kV/cm.

8. The method according to claim 1, wherein the method also comprises measuring the conductivity.

9. The method according to claim 8, wherein the conductivity is measured after a first pulse and after a last pulse, and wherein the applied field strength is selected so that the conductivity has increased at least 5% between the first pulse and the last pulse.

10. The method according to claim 1, wherein the pulse width being applied is in the range of 80-150 s.

11. The method according to claim 1, wherein the pulse space being applied is in the range of 500-1000 s.

12. The method according to claim 1, wherein the number of pulses being applied is in the range of 65-300 pulses.

13. The method according to claim 1, wherein the number of pulse trains is in the range of 1-10.

14. The method according to claim 1, wherein the temperature in the drying step is held within the range of 20-50 C.

15. The method according to claim 1, wherein the temperature in the drying step is held within the range of from room temperature to 40 C.

16. The method according to claim 1, wherein the drying is performed by convective air drying.

17. The method according to claim 1, wherein the method also involves a vacuum impregnation step.

18. The method according to claim 1, wherein the method involves a step of conservation of aroma in a herb.

Description

EXAMPLES AND DESCRIPTION OF THE DRAWINGS

[0032] In FIG. 1 there is shown graphs on the effect of PEF parameters on the convective air-drying of basil leaves. Convective drying of the samples was carried out at 50 C. and 2 m/s air velocity. Both samples were exposed to light for 1 h and either immediately dried (control) or PEF-treated before drying.

[0033] In FIG. 2 there is shown graphs on the combined effect of vacuum infusion (VI) with trehalose and PEF treatment on the convective air-drying of basil leaves.

[0034] It should be noted that FIGS. 1 and 2 show background examples showing the effects discussed above, and not graphs on trials performed within the evaluation work of the present invention.

[0035] Furthermore, in FIG. 3 there is shown graphs showing the variation of rehydration ratio with time. The following treatments are shown: (B) The control (untreated), (C) Reversibly electroporation with opened stomata not electroporated, (D) Reversible electroporation of opened stomata, (E) Irreversible electroporation of epidermal cells, (F) Vacuum impregnation with trehalose before PEF treatment with PEF parameters as in D, (G) Vacuum impregnation of the control with trehalose was applied prior to drying. Data points are averages of three replications.

[0036] In FIG. 4 there is shown a table providing the weight after rehydrating to constant weight at room temperature for different treatments, which are: (A) The control, (B) reversibly electroporation with opened stomata not electroporated, (C) Reversible electroporation of opened stomata, (D) Irreversible electroporation of epidermal cells, (E) Vacuum impregnation with trehalose before PEF treatment with PEF parameters as in C, (F) Vacuum impregnation of the control with trehalose was applied prior to drying.

[0037] Furthermore, in FIG. 5 there is shown the drying curves at 50 C. convective air-drying of control (untreated) basil leaves and the effect of PEF treatment on the convective air-drying of basil leaves.

[0038] In FIG. 6 there is depicted the drying curves at 40 C. convective air-drying of control (untreated) basil leaves and the effect of PEF treatment on the convective air-drying of basil leaves.

[0039] Moreover, in FIG. 7 there is shown the drying curves for room temperature of control (untreated) basil leaves and the effect of PEF treatment on the convective air-drying of basil leaves.

[0040] Furthermore, in FIG. 8 there is shown the calorimetric results of fresh PEF-treated and dried, untreated and dried basil leaves. (i) the upper curve corresponds to the fresh, untreated, non-dehydrated basil, (ii) Rehydrated basil leaves treated with PEF prior to drying up to 20% moisture content (iii) the last curve (close to 0) corresponds to the leaves that were dried without PEF treatment (untreated control). FIG. 8 shows the positive effect of maintaining the metabolic activity in the cells according to the present invention. Below there is provided yet another example where vacuum impregnation was used as a first step before a PEF step.

PEF PARAMETERS AFTER VI

[0041] Below there is provided a suggested protocol for basil and dill. The protocol is as follows:

TABLE-US-00001 STEP STEP STEP STEP STEP STEP STEP STEP STEP STEP 1 2 3 4 5 6 7 8 9 10 Pressure (mbar) 700 650 600 500 400 250 170 100 50 150 Time (s) 10 5 10 5 5 10 5 30 1 1 Time 8 (min) 0 0 0 0 0 0 0 0 1 1 STEP STEP STEP STEP STEP STEP STEP STEP STEP STEP 11 12 13 14 15 16 17 18 19 20 Pressure (mbar) 250 300 350 400 450 500 550 600 700 1000 Time (s) 1 30 30 30 30 30 30 30 30 50 Time 8 (min) 1 0 0 0 0 0 0 0 0 1

[0042] The solution used for the impregnation of dill is 10 g/100 ml of trehalose. Basil is impregnated with isotonic trehalose solution (4.5 g/100 ml).

Basil

[0043] The voltage in which basil presents stomata electroporated with no VI treatment is 0.6 kV/cm. After VI treatment, the voltage in which there is electroporation of stomata is 0.47 kV/cm. The rest of the PEF parameters is not changed (65 pulses, 150 s of pulse width, 760 pulse space).

Dill

[0044] The voltage in which dill presents stomata electroporated with no VI treatment is 1.0 kV/cm. After VI treatment, the voltage in which there is electroporation of stomata is 0.88 kV/cm. The rest of the PEF parameters is not changed (400 pulses, 100 s of pulse width, 1000 s pulse space).

Metabolic Activity of Basil During Drying

[0045] Fresh (untreated) basil leaves metabolic activity was measured with calorimetry and it was compared with the treated (irreversible electroporation of stomata and reversible electroporated of other cells) and untreated basil leaves metabolic activity during drying process. The results show that PEF has irreversibly damaged the stomata and reversibly electroporated the other cells, keeping viability during the drying process.

[0046] In FIG. 9 there is shown the conductivity change in basil. The conductivity increases in cells after electroporation has started. FIG. 9 shows the relationship between the conductivity and electrical field. In this case, electroporation starts at around 500 V/cm. The chosen electrical field to get the best survival shall be when the conductivity has increased with more than 5% between the first and the last pulse of the treatment. As may be understood from the graph, measuring the conductivity may be of interest to be utilized in a PEF treatment of biological soft tissue, such as according to one embodiment of the present invention. Furthermore, according to yet another embodiment of the present invention the conductivity is measured after a first pulse and after a last pulse, and wherein the applied field strength is selected so that the conductivity has increased at least 5% between the first pulse and the last pulse.

[0047] Furthermore, in FIG. 10 there is shown drying curves for reversible, irreversible electroporation and an untreated leaves (control). As disclosed above, the present invention is directed to a method involving PEF treatment to open up the stomata, and which PEF treatment is performed with reversible electroporation and a subsequent drying step. In FIG. 10 there is shown the drying curve for such treatment, but also drying curves for untreated control as well as irreversible electroporation, the latter two not being part of the scope of the present invention.