PEF for fruit treatment

Product examples: Fruit compote, fruit puree, pre-cut fruits

Aim PEF treatment: Microbial inactivation for increased shelf life, cell disintegration and structure modification for enhanced extraction and refining efficiency.

Cold fruit extraction

PEF applied to solid whole fruits causes softening of the fruit tissue by permeabilization of the cell membranes. The tissue softening enhances subsequent fruit extraction at ambient temperature for the production of purees and compotes from fruits like mango, apricot, peach and apple, and for juice production. The enhanced extraction process also leads to higher refining yields and cost reduction. Cold refining processes are favorable in terms of product quality and retention of vitamins, flavor compounds, antioxidants, pigments and freshness in general.
Necessary field strengths for enhancing mass transport and release of juices go from 1,0 up to 3,0 kV/cm, corresponding with a energy delivery of 3 to 10 kJ/kg.

Structure modification of strawberry

Applied to strawberry PEF treatment leads to tissue softening by loss of turgor pressure. Required field strengths are 0,5 – 1,0 kV/cm; the energy delivery is 0,5 – 5,0 kJ/kg

Shelf life increase

Shelf life increase of liquid fruit products like purees, juices and smoothies requires a higher field strength and energy input of the PEF treatment, namely 10 – 20 kV/cm and 50 – 120 kJ/kg.

Other fruit applications

Extended shelf life of natural fresh juices and smoothies

Fruit juice sterilization by a combined heat and PEF treatment

Sterilization of low acid products

Sterilization by combined heat and PEF treatment can be used in low acid products like banana and kiwi puree to avoid color change and to inactivate spores and enzymes. For example, a standard thermal treatment of these purees is at 130-135°C (266-275 F); due to this temperature the puree color changes to pink for banana and to brown for kiwi at 90-95°C (194-203 F). Product and process can be improved by using a lower temperature followed by PEF treatment in less than a second.

Benefits PEF

  • Targeted and controlled structure modification
  • Enhanced product handling by tissue softening
  • Improved extraction and refining
  • Increased process capacity
  • For fruit juice production PEF results in higher extraction and refining yields, longer shelf life, higher process efficiency by large reductions in energy, labor and running costs
  • Vitamins, minerals, pigments, antioxidants, flavors and colors are retained producing a healthier, fresher and more appetizing final product
  • Proteins are hardly affected
  • Extended shelf life results in greater flexibility for production planning
  • Continuous process and rapid technique
  • Small equipment footprint, quick start-up of the process
  • Low energy requirement

More information

Limitations

For preservation of liquids (microbial inactivation) PEF is applicable to pumpable products with a particle diameter of less than 20 mm. The shelf life is comparable to that of thermally pasteurized foods.
For cell disintegration purposes (tissue softening) to enhance extraction and refining efficiency there are no size limitations for the raw products.

Equipment

Pulsemaster has developed industrial scale equipment – named Conditioner – with treatment capacities up to 5,000 l/h (1320 US gal./h) for microbial inactivation and up to 50,000 kg/h (110,000 lb/h) for cell disintegration.

Costs

On a commercial scale total costs of 1 Euro/ton (= 0.1 Eurocent per liter or kg) for treatment of plant cells and 10 Euro/ton (= 1 Eurocent per liter or kg) for microbial inactivation have to be expected. In US Dollar this is approximately 0.056 US Dollarcent per lb for cell disintegration of plant cells and 4.92 US Dollarcent per gallon for microbial inactivation of liquids.

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