Author: Matthias Schulz
Fruit Juice pre-treatment
On-site, pulsed electric field (PEF) treatment can enhance the yield and
effectively preserve fresh juices prior to tank storage. In addition, PEF uses
low temperatures, little energy and shortens processing times.
Pulsed electric field (PEF) treatment
is a promising technology for fruit juice producers to complement conventional
production methods. It can be implemented in existing processing lines as a
pre-treatment, serving two goals: it enhances extraction yields and/or is a gentle
preservation method, as an alternative to thermal pasteurisation, retaining
nutrients and taste. PEF enables safer daily production and helps to reduce the
energy costs for steam generation used in pasteurisation.
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).
At the moment, PEF can be implemented in the production line in two places: after the crushing to facilitate juice extraction and after the pressing to preserve the juice. A different PEF chamber is needed for each application.
The incorporation of PEF into the juice process was also tested on an industrial scale. Regarding the yield improvement, a larger scale PEF system, developed by the FieldFOOD partner Energy Pulse Systems, reached a fruit capacity of up to 14 tons per hour. Regarding microbial reduction, a continuously operating PEF pilot plant was designed, assembled and equipped with a novel low-cost pulse modulator (PEF-MI, EPS). As intended, this new low cost generator allows for small producers to use this technology renting it at a running cost as low as Euro 2c per litre.
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.
FieldFOOD focussed on practical challenges like the implementation of PEF in existing pilot and industrial processing lines, adjustment of pre-treatment and subsequent processing steps. Here, both research institutions and SME benefited from a close collaboration during the last months. 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 installed 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 2014 to April 2018.
Funded by: European Commission (635632-FieldFOOD-H2020).
The type of press used in the juicing process controls the pressure and pressing mechanism individually, which can additionally influence the extraction yield.
Moreover, the properties of the apples that are treated with PEF can also play a role. Softer apples result in lower yields while harder apples tend to produce more juice compared to conventional processes. The combination of PEF-treated hard apples processed with a belt press seems to be the most effective.
In addition to increasing the extraction yields, the PEF treatment of apples results in juices with a higher total polyphenol content. Independent of the types of apples tested, PEF treatment resulted in an average polyphenol increase of at least 20% relative to the control product.
The final clear juice yield increased by 6,4% by using an industrial twin belt press for the extraction and by 2,2% by using a hydraulic HPX filter press. The selected juice quality parameters such as Brix, total acids, pH, total phenols remained constant.
A turbular treatment chamber was designed for direct application of microsecond pulses with electrical field strengths up to 20kV/cm and specific energy intakes od maximum up to 2100kJ/kg. The treatment chamber was constructed considering common standards of safe operation and hygienic design