High-pressure processing (HPP) is safe to use to destroy pathogens but it is not as effective on milk and some ready-to-eat foods, according to an EFSA opinion.

The European Food Safety Authority (EFSA) experts assessed the safety and efficacy of HPP on food, whether it can be used to reduce Listeria monocytogenes in ready-to-eat (RTE) foods, and as an alternative to thermal pasteurization of raw milk.

HPP is a non-thermal food preservation technique to kill microorganisms that cause foodborne diseases or spoil food. It uses pressure for a certain time period. Previous studies have shown minimal effects on taste, texture, appearance, or nutritional values. It is also known as high-hydrostatic pressure processing (HHP) or ultra-high-pressure processing (UHP).

The technique is not specifically regulated at the European Union level but establishments using it on products of animal origin are subject to approval. HPP is applied mainly to pre-packed juices, sauces, dips, fishery products, meat products and ready-to-eat meals at different points in the supply chain.

Reducing Listeria in RTE food
Based on a questionnaire to national authorities and industry, there is a large variability on the level of implementation of HPP in Europe with many sites in some countries but none in others.

The processing method reduces levels of Listeria monocytogenes in RTE cooked meat products. In general, the longer the duration and intensity of the pressure, the greater the reduction. HPP is also effective at tackling other pathogens, such as Salmonella and E. coli.

However, for other types of RTE foods like soft cheese and smoked fish, generic minimum HPP requirements could not be set and specific validation studies would be needed for each food, found the EFSA opinion.

In industry, pressures of between 400 and 600 megapascals are most often applied for microbial inactivation, with common holding times ranging from 1.5 minutes to 6 minutes.

The main factors that influence the efficacy of HPP are water activity and the pH of food, the pressure applied, holding time and temperature, and the target microorganism. Carbohydrates, proteins and lipids have a protective effect on microorganisms, which decreases microbial reduction.

Potential use on milk
There is a growing demand to allow HPP as an alternative to pasteurization as it is expected to keep the properties closer to those of raw milk. However, experts found HPP was not as good at killing microorganisms as pasteurization.

Pathogen reductions in milk with current HPP conditions used by industry are lower than those achieved by thermal pasteurization. However, minimum requirements for pressure and time combinations could be set to achieve lower reductions of hazards based on performance criteria proposed by standards agencies.

Alkaline phosphatase, the milk enzyme widely used to verify thermal pasteurization of cows’ milk, is relatively pressure resistant and use of HPP would be limited to being an over processing indicator.

Experts recommended conducting an analysis on the effect of HPP treatments on compounds in milk to verify their suitability as indicators of efficacy. They also called for more research on HPP inactivation of Listeria monocytogenes and other pathogens for RTE foods like smoked and gravad fish and soft/semi-soft cheese to help construct a predictive model to set the minimum requirements for HPP to ensure safety of these food products.

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