Frequently Asked Questions

We’ve collected together some of the questions Learners asked about this Week’s content when the course was last run and provided some answers here. You may have different questions. If so, do post them in the comments section below. Your fellow Learners will have their own views and may well be able to point you in the direction of further information.

3.3. PEF

How does PEF work for different applications? What are the approximate settings that are used?

• PEF can be applied for different purposes. If you use high processing intensities and apply the process to liquid or semi-liquid food, it will result in inactivation of microorganisms and thus increase the shelf life of products such as juices. However, when applying the process at very low intensities on solid food products, irreversible electroporation will just result in softening of the tissue, better drying properties and increased extraction, for example, of juice from fruits, oil from olives or valuable components from side streams.
• PEF can be applied as a continuous process for both liquid and solid products and modern machines can process up to 10, 000 litres of juice per hour, or up to 60 tonnes per hour of potatoes. Typical settings for inactivation of microorganisms are: a field strength of 15 kV/cm with energy input of 100 kJ/kg. Typical settings for softening tissues in potatoes are a field strength of 1 kV/cm with energy input of 1-3 kJ/kg. However, these settings are strongly dependent on the precise aim of the process, the product properties (pH, conductivity, etc) and on the type of bacteria to be inactivated.

3.4. PEF Applications

Are there any negative aspects or limitations to PEF technology?

• Industrially, PEF is mainly applied in the potato industry for tissue softening and is used a little for microbial inactivation in juices. For these products, no negative aspects have been observed. However, research is ongoing into wider applications as, for example, a pre-treatment for drying, or microbial inactivation in other products. This research has shown that PEF does have limitations, and high fat and protein products are more difficult to treat.

What are the costs of PEF?

• The initial costs are, of course, related to the capital costs of the processing equipment. The treatment itself is slightly more expensive than pasteurisation for microbial inactivation. In the potato industry PEF pre-treatment replaces a traditional heating step in the process and results in cost savings compared to the energy required for heat pre-treatment.

What is the exact effect of PEF on the microorganism? How is it inactivated?

• Exposure of the microorganism to an electric field damages its membrane and renders it inactive. This damage is based on electroporation which is a direct result of electrical breakdown of the membrane. The membrane is perforated, the contents of the cell leak out and it dies. Normally a cell membrane has a potential difference of around 10 mV. However, when an electric field is applied via PEF, the charges in the cell are separated across the membrane, increasing the potential difference. When a critical value is exceeded pores are created in the membrane.

3.5. HPP

Is HPP widely used in the industry?

• Currently there are 420 machines in operation worldwide, mainly in Europe and North America, as well as in South America and Asia, especially Japan. Main products are juices & beverages, vegetable and fruit products (avocado), meat products (sliced ham, etc), seafood, ready-to-eat meals and baby food.

Is HPP treatment always stated on the label of the product?

• Labelling varies in different countries. It’s not compulsory at the moment to mention HPP treatment on the product label, however, it is often indicated and used as a marketing tool.

3.6. Acrylamide

What daily dose of acrylamide is harmful and might ‘potentially’ cause cancer?

• Here is the European Food Safety Authority’s risk assessment.