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PEF processing of fruits and vegetables

Mark de Boevere

Major Advantages of PEF Processing in Fruits and Vegetables

  • PEF

On Thursday, December 4th, 2014, the potential of pulsed electric field (PEF) treatment was highlighted as a versatile technology offering mild food preservation, improved extraction processes, higher concentrations of bioactive compounds, and enhanced drying processes. PEF is a mild process that generally leaves valuable compounds unaffected, often leading to product and process improvement and energy reduction.

This raises the question: what are the potential applications of this technology in fruit and vegetable processing?

PEF treatment is an outstanding technique for the mild preservation of liquid foods and beverages. By permeabilizing the cell membranes of micro-organisms at relatively low temperatures, PEF enables a targeted shelf life increase, retaining product quality and freshness. Micro-organisms are killed through a series of microsecond, high-voltage pulses, while the pulsed electric field does not affect, for example, vitamins and proteins.

PEF processing improves the shelf life of fresh fruit and vegetable juices, smoothies, and other fruit or vegetable-based food products, such as purees and compotes. For the preservation of liquids, a field strength of 10-20 kV/cm and energy delivery of 50-120 kJ/kg are appropriate.

The shelf life of cold pasteurized drinks and foods is comparable to that of thermally pasteurized foods. However, enzymes are not fully inactivated after PEF treatment, necessitating cooled storage. Sterilization combining heat and PEF treatment is also possible, with challenges including the effect on enzymes, spores, and aseptic filling.

Pulsemaster has developed industrial-scale equipment – named Conditioner – with treatment capacities up to 5,000 l/h (1320 US gal/h) for microbial inactivation. On a commercial scale, the total costs are expected to be around 10 Euro/ton (approximately 4.92 US Dollar cents per gallon).

Plant Structure Modification

A distinct application of pulsed electric field processing or electroporation is cell disintegration of plant tissue, enhancing mass transport processes and improving product quality for various applications. It improves the extraction of oils, juices, and bioactive components and increases extraction yields. Cutting and peeling processes are also enhanced, and drying is accelerated.

Pulsemaster’s Conditioner range for cell disintegration purposes has treatment capacities up to 50,000 kg/h (110,000 lb/h). The estimated commercial-scale cost is around 1 Euro/ton (approximately 0.056 US Dollar cents per lb).

Examples

Tomato peeling is a prime example. The physical treatment with pulsed electric fields at ambient temperature softens tomatoes and improves peeling efficiency, potentially replacing the standard thermal treatment required before potato peeling. Compared to traditional heating, PEF treatment requires less energy and reduces energy costs.

Another interesting application is lycopene extraction from tomatoes, where PEF technology increases the extraction yield. Targeted structural modification also allows the use of new raw materials, such as tough and inconsistent produce like sweet potatoes, turnips, and beetroot, making them easily processable with PEF.

Disintegrating (softening) vegetable tissue before drying with pulsed electric fields improves water mass transport. This is beneficial in the manufacturing of dried sweet peppers. The field strength of the treatment may range from 1.0 to 3.0 kV/cm, with energy delivery of 5 to 10 kJ/kg.

Stress Response

Stress induction by electroporation is an emerging research area. PEF treatment can induce the formation of secondary metabolites in plants. For example, in broccoli, this may lead to higher concentrations of health-promoting glucosinolates. In this application, the field strength is relatively low: 0.1 to 0.5 kV/cm, with energy delivery of 0.1 to 1.0 kJ/kg.

More information:

PEF products: beverages, vegetable products, fruit products
PEF Pulsemaster: food preservation, product and process improvement