PEF can be easily integrated in the processing line of tomato fruit before the steam peeling stage. PEF pre-treatment, performed at very mild conditions, reduces the surface resistance of tomato skin and its adhesiveness to the pulp, facilitating peel removal. This results in reduced peeling loss, improved quality and functionality of the end product, and reduced water and energy consumption.
Industrial peeling of tomato
Steam peeling coupled with vacuum cooling and pinch roller is a physical alternative to hot lye peeling of tomatoes. Heating the tomatoes for a few seconds to 1 min with pressurized steam weakens the tomato skin through the flash vaporization of water under the skin. During vacuum cooling, the increased vapor pressure under the skin promotes peel cracking. This is required for the effective mechanical removal of peels with the pinch roller.
Unlike hot lye peeling, steam peeling with vacuum cooling does not cause serious environmental problems. However, it can result in a loss in product firmness, reduced peeling yields, and excessive water and energy consumption.
How does PEF improve peelability?
PEF is a non-thermal technology for food processing based on the application of repetitive short pulses of electric field to the biological cells of plants. PEF increases the permeability of the cell membranes, allowing to improve the mass transport of water and other valuable intracellular compounds
In tomato processing, PEF is used before the steam peeling process. 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.
High quality and functionality
PEF-assisted steam peeling of tomatoes facilitates peel removal, avoiding the need to overheat the fruit. Under these mild conditions, peeling losses are reduced and the shape and texture of the tomatoes are well preserved.
The peeling process can also be carried out at relatively lower temperatures and reduced time. This is particularly beneficial for preserving thermo-sensitive compounds such vitamins C and A and other antioxidant compounds. Interestingly, exposing the tomatoes to PEF increases the bio-availability of lycopene in the canned product, adding value and health benefits.
The implementation of PEF treatment of tomatoes was demonstrated on a pilot and industrial scale within the Horizon 2020 project, FieldFOOD. In this project, a 300 kg/h pilot-scale treatment chamber and a 30 tons/h industrial-scale treatment chamber for PEF-assisted tomato peeling have been developed by ProdAl Scarl. It was shown that PEF can be used to treat tomatoes in a 30 tons/h industrial tomato processing plant.
Within FieldFOOD project, PEF technology was tested and validated for five applications: olive oil, fruit juices, tomato peeling, cider and red wine. Benefits derived from the introduction of the PEF technology depended strongly on the specific application. Modular, portable, low cost PEF modulators developed during the project allow companies to evaluate this technology in the above-mentioned sectors or for new applications. For more information visit the FieldFOOD website or contact the project coordinator Javier Raso.
FieldFOOD an EU funded initiative
FieldFOOD stands for: Innovative food processing technologies.
For whom: Food processors of plant-based food such as Wineries, Olive oil companies, Tomato products companies, Fruit juices companies and Cidery.
Objective: Provide innovative solutions to overcome existing bottlenecks that prevent the implementation of Pulsed Electric Fields (PEF) in the food industry.
Reason: Effects deriving from PEF processing are very attractive to the food industry in order to improve food quality and process efficiency, reduce energy inputs and enhance eco-friendly processes.
How: By conducting a systematic process analysis of the processing lines of the different companies for a successful integration of the PEF technology in order to replace or complement the existing processing and by designing modular portable low-cost pulse generators to be install in the processing plant of the companies involved in the project.
Areas of interest: Food processing, Equipment manufacturing, Food safety, food quality, sustainability.
When: From April 2015 to April 2018.
Funded by: European Commission (635632-FieldFOOD-H2020).
 Rock, C.; Yang, W.; Goodrich-Schneider, R.; Feng, H. Conventional and alternative methods for tomato peeling. Food Eng Rev 2012, 4, pp. 1-15. DOI: 10.1007/s12393-011-9047-3.
 Raso, J., Frey, W., Ferrari, G., Pataro, G., Knorr, D., Teissie, J., Miklavcic D. (2016). Recommendations guidelines on the key information to be reported in studies of application of PEF technology in food and biotechnological processes. Innov Food Sci Emerg Technol, 37, 312–321. http://dx.doi.org/10.1016/j.ifset.2016.08.003.