Elisa Luengo

Pulsed-electric-field-assisted extraction of anthocyanins from purple-fleshed potato.

The influence of pulsed electric field (PEF) treatment on the anthocyanin extraction yield (AEY) from purple-fleshed potato (PFP) at different extraction times (60-480 min) and temperatures (10-40°C) using water and ethanol (48% and 96%) as solvents has been investigated. Response surface methodology was used to determine optimal PEF treatment and optimise anthocyanin extraction. A PEF treatment of 3.4 kV/cm and 105 μs (35 pulses of 3 μs) resulted in the highest cell disintegration index (Z(p)=1) at the lowest specific energy requirements (8.92 kJ/kg). This PEF treatment increased the AEY, the effect being higher at lower extraction temperature with water as solvent. After 480 min at 40°C, the AEY obtained for the untreated sample using 96% ethanol as the solvent (63.9 mg/100 g fw) was similar to that obtained in the PEF-treated sample using water (65.8 mg/100 g fw). Therefore, PEF was possible with water, a more environmental-friendly solvent than ethanol, without decreasing the AEY from PFP.

Improving Mass Transfer to Soften Tissues by Pulsed Electric Fields: Fundamentals and Applications

The mass transfer phenomenon occurs in many operations of the food industry with the purpose of obtaining a given substance of interest, removing water from foods, or introducing a given substance into the food matrix. Pretreatments that modify the permeability of the cell membranes, such as grinding, heating, or enzymatic treatment, enhance the mass transfer. However, these techniques may require a significant amount of energy and can cause losses of valuable food compounds. Pulsed electric field (PEF) technology is a nonthermal processing method that causes permeabilization of cell membranes using low energy requirements and minimizing quality deterioration of the food compounds. Many practical applications of PEF for enhancing mass transfer in the food industry have been investigated. The purpose of this chapter is to give an overview of the state of the art of application of PEF for improving mass transfer in the food industry.

Improving carotenoid extraction from tomato waste by pulsed electric fields

In this investigation, the influence of the application of pulsed electric fields (PEFs) of different intensities (3–7 kV/cm and 0–300 μs) on the carotenoid extraction from tomato peel and pulp in a mixture of hexane:acetone:ethanol was studied with the aim of increasing extraction yield or reducing the percentage of the less green solvents in the extraction medium. According to the cellular disintegration index, the optimum treatment time for the permeabilization of tomato peel and pulp at different electric field strengths was 90 μs. The PEF permeabilization of tomato pulp did not significantly increase the carotenoid extraction. However, a PEF treatment at 5 kV/cm improved the carotenoid extraction from tomato peel by 39% as compared with the control in a mixture of hexane:ethanol:acetone (50:25:25). Further increments of electric field from 5 to 7 kV/cm did not increase significantly the extraction of carotenoids. The presence of acetone in the solvent mixture did not positively affect the carotenoid extraction when the tomato peels were PEF-treated. Response surface methodology was used to determine the potential of PEF for reducing the percentage of hexane in a hexane:ethanol mixture. The application of a PEF treatment allowed reducing the hexane percentage from 45 to 30% without affecting the carotenoid extraction yield. The antioxidant capacity of the extracts obtained from tomato peel was correlated with the carotenoid concentration and it was not affected by the PEF treatment.

C-phycocyanin extraction assisted by pulsed electric field from Artrosphira platensis

This paper assesses the application of pulsed electric fields (PEF) to the fresh biomass of Artrhospira platensis in order to enhance the extraction of C-phycocyanin into aqueous media. Electroporation of A. platensis depended on both electric field strength and treatment duration. The minimum electric field intensity for detecting C-phycocyanin in the extraction medium was 15kV/cm after the application of a treatment time 150μs (50 pulses of 3μs). However higher electric field strength were required when shorter treatment times were applied. Response surface methodology was used in order to investigate the influence of electric field strength (15-25kV/cm), treatment time (60-150μs), and temperature of application of PEF (10-40°C) on C-phycocyanin extraction yield (PEY). The increment of the temperature PEF treatment reduced the electric field strength and the treatment time required to obtain a given PEY and, consequently decreased the total specific energy delivered by the treatment. For example, the increment of temperature from 10°C to 40°C permitted to reduce the electric field strength required to extract 100mg/g dw of C-phycocyanin from 25 to 18kV/cm, and the specific energy input from 106.7 to 67.5kJ/Kg. Results obtained in this investigation demonstrated PEFs potential for selectively extraction C-phycocyanin from fresh A. platensis biomass. The purity of the C-phycocyanin extract obtained from the electroporated cells was higher than that obtained using other techniques based on the cell complete destruction.

The effect of temperature and bacterial growth phase on protein extraction by means of electroporation.

Different chemical and physical methods are used for extraction of proteins from bacteria, which are used in variety of fields. But on a large scale, many methods have severe drawbacks. Recently, extraction by means of electroporation showed a great potential to quickly obtain proteins from bacteria. Since many parameters are affecting the yield of extracted proteins, our aim was to investigate the effect of temperature and bacterial growth phase on the yield of extracted proteins. At the same time bacterial viability was tested. Our results showed that the temperature has a great effect on protein extraction, the best temperature post treatment being 4°C. No effect on bacterial viability was observed for all temperatures tested. Also bacterial growth phase did not affect the yield of extracted proteins or bacterial viability. Nevertheless, further experiments may need to be performed to confirm this observation, since only one incubation temperature (4°C) and one incubation time before and after electroporation (0.5 and 1h) were tested for bacterial growth phase. Based on our results we conclude that temperature is a key element for bacterial membrane to stay in a permeabilized state, so more proteins flow out of bacteria into surrounding media.

The Effect of Temperature on Protein Extraction by Electroporation and on Bacterial Viability

Extraction of proteins by electroporation from bacterial cells could provide a basis for significant reduction of downstream processing with low investment costs. Due to avoidance of using harmful chemicals for extraction, a significant improvement of the environmental footprint is also expected. In order to optimize extraction of proteins by electroporation, the optimization of electroporation protocol is needed (e.g. temperature). Thus the aim of our study was to optimize the temperature before and after electroporation in order to affect membrane permeabilization and to obtain maximum amount of extracted proteins, while preserving bacterial cells alive. Escherichia coli cells were incubated at different temperatures before and after electroporation, and the amount of extracted proteins and bacterial viability was assessed. Our results show, that the temperature has no effect on bacterial viability, while lower temperature (4 °C) seems to promote better protein extraction. We suggest that lower temperatures decrease lipid fluidity and facilitate slower resealing of electroporated membrane.

Comparison of the Efficacy of Pulsed Electric Fields Treatments in the Millisecond and Microsecond Range for the Extraction of Betanine from Red Beetroot

The efficiency of PEF treatments in the range of milliseconds (0.4 to 0.6 kV/cm; 10 to 60 ms) and in the range of microseconds (4 to 6 kV/cm; 30 to 150 μs) has been compared for the extraction of betanine from red beet. Both PEF-treatments in the milliseconds and in the microseconds range improved the extraction of betanine in comparison to the control. Similar betanine extraction was obtained with pulses of milliseconds and microseconds under the PEF conditions that resulted in the maximum betanine extraction. The more intense treatment conditions applied in the ms range (0.6 kV/cm; 40 ms) and the μs range (6 kV/cm; 150 μs) increased the BEYmax 6.7 and 7.2 times, respectively, compared with the control. However, lower specific energy was involved in the PEF-treatments applied in the range of μs (28.8 kJ/kg) than in the PEF-treatments applied in the ms range (43.2 kJ/kg).