The FieldFOOD Project - Exploring the use of Pulsed Electric Field (PEF) technology in the food industry

Over the last two decades, scientists have done a lot of research into the use of PEF for foods which improves food quality and food safety, optimises process efficiency, reduces energy costs and stimulates the introduction of new products.

The technology is especially fit for small and medium sized food processing companies, however the lack of industrial-scale equipment and the high costs involved have limited its commercial use in the food industry.

Therefore, in April 2015, the 3-year FieldFOOD project was launched to provide innovative solutions to overcome these bottlenecks. Supported by the EU Horizon 2020 Research and Innovation Programme, the project brought together 12 entities from 8 European countries, including 5 SMEs.

As part of the initiative, modular, portable, low-cost PEF generators were installed in the processing plants of the partner SMEs to test and validate the technology in five applications: olive oil, fruit juices, tomato peeling, cider and red wine.

About the PEF technology

Short, high voltage electrical pulses are used to perforate cell membranes. Electroporation can be used to permeabilize biological membranes including to inactivate microorganisms, enhance raw material properties for subsequent processing or to modify the food structure. PEF treatment has similar effects in foods as conventional heating, but is gentler to the food matrix without a lasting thermal load. It can complement or replace existing traditional food processing technologies.

PEF treatment can also be used to modify the structure of food by breaking down the cell membrane barriers in plant or animal tissue. It leads to tissue softening, easier and lower energy cutting and increased process speed and capacity. This results in more efficient product handling and manufacturing, a higher quality product and exciting new product development.

Winemaking with PEF

During traditional red winemaking, fermentation of the grape juice occurs together with the grape skins. In this step called maceration-fermentation step, yeasts convert the sugars of the juice into ethanol while polyphenolic compounds are extracted from the grape skin. This polyphenolic extraction has a big influence on red winemaking process and the wine quality.

Traditionally, there are two ways to obtain wines with a high phenolic content. One is to extend the maceration time for 2-3 weeks, instead of 1-2 weeks that are needed for fermentation. Another way is to increase the fermentation temperature, which speeds up the process of polyphenolic extraction.

PEF technology permits to obtain the same objective with very low energy requirements and processing cost. PEF is a physical non-thermal method that induces the formation of pores in the cell envelopes of plant tissues. These pores accelerate and increase the extraction of phenolic compounds during maceration-fermentation.

Within the FieldFOOD project, PEF technology has been demonstrated and validated in a winery, producing wine from Grenache grapes treated by PEF with 3 days of maceration. At the end of the fermentation step, the PEF wine had the same colour and content of polyphenols as the control wine that was obtained after 6 days of maceration in a traditional process. After 6 months aging of the wines in bottles or oak barrels, the colour and polyphenol content remained, while the concentration of molecules related with fruity flavour notes was higher in the PEF wine.

Steam peeling of tomatoes

PEF can be easily integrated in the processing line of tomato fruit before the steam peeling stage. The exposure to the electric field promotes the mass transfer of water inside the fruit, enhancing the amount of water under the tomato skin. As more water is vaporized when heating the PEF-treated tomatoes with the steam, a greater pressure difference across the tomato skin occurs. This facilitates the formation of even more cracks in the tomato peels, which are then easily removed by the pinch roller system.

The PEF pretreatment is a mild process, with an energy expenditure lower than 0.0001 kWh/kg. Compared to conventional steam processing, the steam pressure, energy consumption and peeling time are reduced by about 20-30%. PEF processing is sustainable and has a lower environmental impact, particularly for indicators related to climate change, ozone depletion, and terrestrial acidification.

Fruit juice pre-treatment

During the project, various de-juicing systems were used to characterise the influence of PEF-treated fruit mashes on the extraction yield by pressing. On a pilot scale, a continuously working single-belt-press was used for apple juice pressing. Depending on the mash particle size, the yield increased between 3.8 - 6.6 % compared to the traditional process. PEF-treated strawberries pressed with a pneumatic filter press resulted an increase in extraction yield of almost 5%.

PEF can be used also as a low temperature method for the reduction of bacteria and yeasts in fresh fruit juices, without affecting taste and nutrients. PEF was found to be beneficial for juices from apples, cherries and strawberries. Initial microbe concentrations were up to 10,000 per mL in freshly squeezed juices. Depending on the fruit, PEF reduced concentrations by up to 6 Log10 cycles (1,000,000 times smaller) without the need for a thermal pre-treatment. Freshly squeezed factory juices could be free from bacteria and yeasts, even at low energy use (60 kJ/kg).

PEF and olive oil extraction

Although the extraction of olive oil is quite an efficient process, PEF can reduce processing-time and increase extraction yield of olive oil processing plants.

Disruption of the cell envelopes of the olive pulp that act as a physical barrier is required to facilitate the oil release during malaxation. Although the crushing step is a very effective process, in the current extraction process a percentage of the oil remains inside olive pulp cells. PEF is a physical non-thermal processing method that may complement the crushing step by the formation of pores in cell membranes that were not disrupted by the crusher.

During the FieldFOOD project, a PEF treatment chamber was located after the crusher in a line with a processing capacity of 4 Tn/h. PEF treatment improved the extraction between 4.6 to 5.6 g of extracted olive oil per kilogram of processed olives for a malaxation time of two hours. When the malaxation time was reduced to 1 hour, the application of a PEF treatment increased an average of about 10 g of extracted olive oil per kilogram of processed olives. The polyphenol content of the oil was increased between 10-50% compared to the oil obtained after 2 hours of malaxation. The PEF treatment neither affects the parameters legally established by EU Regulation (EEC/2568/91) to measure the level of quality of the virgin olive oil nor bad flavor or taste were detected in the oil obtained from olive paste treated by PEF.

Total cost including both investment and energy consumption to establish a PEF treatment in an olive oil extraction plant are estimated between 0.038-0.02 €/L of oil for plants that process between 30 to 60 Tn/day respectively.

EFFoST

Website: https://www.effost.org/default.aspx

References:

https://www.tasteofscience.com/articles/1297/pef-facilitates-polyphenol-extraction-during-red-wine-making.html

https://www.tasteofscience.com/articles/1309/steam-peeling-of-tomatoes.html

https://www.tasteofscience.com/articles/1313/fruit-juice-pre-treatment.html

https://www.tasteofscience.com/articles/1317/pef-enhances-olive-oil-yields.html