Don’t discount the benefits of thermal pasteurisation

Pasteurisation is a process which reduces the microbial load in many food products, ensuring consumer safety and prolonging shelf life. There have been significant developments in non-thermal alternatives to traditional heat-based pasteurisation, such as high-pressure processing (HPP) or pulsed electric field (PEF) processing.

 

Before investing in any new technology, it is worth remembering that thermal pasteurisation remains the standard against which these alternative methods are judged. For many ingredients and products, thermal pasteurisation is still the most suitable, efficient and cost-effective solution, particularly now that it can be combined with newer heat sources such as ohmic heating and direct steam injection.

 

Non-thermal processing techniques

The most common alternatives to thermal pasteurisation are high-pressure processing (HPP) and pulsed electric field (PEF) processing, followed by ultraviolet (UV) light, ultrasound, cold plasma, and high-pressure carbon dioxide (HPCD).

Typical industrial HPP involves underwater pressurisation of the product at ambient temperature, usually to a specific pressure between 400-600 MPa, and then holding the product at this pressure for a specific time (usually one-to-five minutes). These high pressures induce changes in the functionality of the cell membranes, resulting in inactivation of vegetative cells and some enzymes.

In contrast, PEF processing uses short bursts of high voltage electric fields (up to 30,000 pulses per second) to achieve the desired microbial inactivation or modification of the food structure. This ruptures the cell membranes, causing the contents of the cells to leak out, effectively deactivating the microbes.

 

Limitations of non-thermal options

HPP is not the ‘silver bullet’ that some have suggested; it requires high capital costs and is not suitable for every application. For example, any product where the air content is important (whipped creams, mousses, sauces, etc.) needs extra caution if HPP treatment is being considered, as the pressure may force the air from the product, or be compressed (and subsequently released). Both scenarios have the potential to cause catastrophic product damage.

HPP is also unsuitable for dry products (such as powders, nuts, etc.), many whole fresh produce items (such as fruits or tubers), and there is uncertainty around its use on raw meat. In trials, it has also been shown to cause denaturation in key proteins in certain dairy products, such as raw milk and whey.

PEF processing has a number of roles in food processing, including dehydration; but there have been reports of a number of potential limitations, including corrosion and fouling of the electrodes, electrolysis of water, migration of electrode material components, and chemical changes in the food product.

In most situations, there are several key advantages to traditional thermal pasteurisation and sterilisation techniques using corrugated tube, or scraped surface, heat exchangers:

• They are proven and highly effective, killing 99.9% of pathogenic bacteria, yeasts and moulds, and deactivating enzymes which can spoil food and drink products.
• They require lower capital costs than most non-thermal alternatives.
• They are scalable and versatile, making them suitable for a wide range of products.
• They maintain nutritional value, particularly of many dairy and juice products.

HRS Heat Exchangers offers a variety of thermal treatment options (including corrugated tube and scraped surface heat exchangers, ohmic heating and direct steam injection), as well as experience of numerous products and access to comprehensive laboratory testing facilities, making us perfectly placed to help food and drink manufacturers choose the best pasteurisation or sterilisation options for their specific needs.