Category Archives: HPP

Research – The effectiveness and safety of high pressure food treatment


Definition and applicable regulations

Type of food treated and processing conditions

Intrinsic and extrinsic factors of food that influence the effectiveness of high pressure treatment

Possible chemical and microbiological hazards associated with high pressure treatment

High pressure treatment as an alternative to pasteurization of milk

Efficacy of high pressure treatment for the control of Listeria monocytogenes in ready-to-eat foods

USA – Microbiological Surveillance Sampling: FY17–19 Processed Avocado and Guacamole


The U.S. Food and Drug Administration collected and tested processed avocado, the main ingredient in guacamole, and finished guacamole as part of the agency’s proactive and preventive approach to deploying its sampling resources with the ultimate goal of preventing contaminated food from reaching consumers.

Assignment Overview

The assignment began in November 2017 and ended in September 2019. In total, the FDA collected and tested 887 samples of processed avocado and guacamole (domestic and imported product) for Salmonella spp. and Listeria monocytogenes. This total is smaller than the initial number of samples the agency set out to collect and test because the agency encountered factors that twice required a reduction of the collection target, as explained in the Sample Collection section of this report (page 6).

As to the design of the assignment, the FDA directed its field staff not to collect products that had undergone high-pressure processing (HPP) or products intended for HPP. HPP is a “kill step” validated to eliminate pathogenic microorganisms in food, and it is often used in the manufacture of processed avocado and guacamole. In seeking to exclude from the assignment products that had been HPP-treated, the FDA’s intent was to focus on products that posed the greatest risk to consumers.

The agency learned during its evaluation of the test results that some of the products collected had received HPP treatment but were not labeled as such. FDA staff worked retrospectively with industry to identify the HPP-treatment status of the samples collected but could not determine the status of a number of samples. Those samples were designated as “could not ascertain” for purposes of the data analysis.

Findings and Follow-up Actions

The FDA detected Salmonella two samples which were later determined to be distinct samples of the same brand of domestically manufactured guacamole from different lots. Neither sample had received HPP treatment. In addition, the agency detected Listeria monocytogenes in 15 samples from nine different firms. Of those 15 samples, eight had not been HPP treated. The HPP-treatment status of the other seven samples could not be ascertained.

When the FDA detected a pathogen in a domestic sample, agency personnel worked with the company that owned or distributed the affected product to conduct a voluntary recall in all cases in which product was available, or likely to still be available, to consumers. The FDA also conducted one follow-up inspection of a domestic facility, and state officials in Florida likewise conducted one domestic inspection. As to the imported samples, the agency refused to admit lots associated with the positives and placed the responsible companies on import alert. In all, the agency placed two firms on import alert. In addition, the agency conducted whole genome sequencing (WGS) analysis on the positives but was unable to determine whether processed avocado or guacamole were the food vehicle associated with any known human illnesses.

In addition to affirming that Salmonella spp. and Listeria monocytogenes may be present in processed avocado and/or guacamole, the assignment data show that the estimated prevalence of these pathogens in the non-HPP-treated samples was higher than in the HPP-treated samples. This finding appears to support other research that shows HPP is effective at neutralizing pathogenic microorganisms,[1] even as this assignment was not designed to compare possible differences based on HPP-treatment status. The findings also underscore the need for processors and others in the processed avocado and guacamole supply chain to comply with the FDA’s Preventive Controls for Human Food Rule[2] and for importers of these foods to comply with the FDA’s Foreign Supplier Verification Programs Rule.[3]

Research – High-pressure processing: food safety without compromising quality


High-pressure processing (HPP) of food is effective at destroying harmful microorganisms and poses no more food safety concerns than other treatments. These are two of the conclusions of a scientific opinion published by EFSA today.

EFSA experts assessed the safety and efficacy of HPP of food and, more specifically, whether it can be used to control Listeria monocytogenes in ready-to-eat (RTE) foods and as an alternative to thermal pasteurisation of raw milk.

HPP is a non-thermal food preservation technique that kills microorganisms that can cause diseases or spoil food. It uses intense pressure for a certain time and has minimal effects on taste, texture, appearance, or nutritional values.

HPP can be used at different steps of the food chain, usually on pre-packed products. It can be applied to raw materials such as milk, fruit juices, and smoothies but also to products that have already been processed, such as sliced cooked meat products and RTE meals. In the latter case, it reduces the contamination originating from the manufacturing environment, for example during slicing and manipulation of the products.

This processing method reduces levels of Listeria monocytogenes in RTE meat products, at specific time-pressure combinations defined in the scientific opinion. In general, the longer the duration and intensity of the pressure, the more reduction is achieved. This is an important finding because L. monocytogenes contamination of RTE foods is a public health concern in the EU. HPP also proved to be effective at decreasing the levels of other pathogens, such as Salmonella and E. coli.

For raw milk, experts identified the time-pressure combinations that can be considered to have the same effect as thermal pasteurisation. These vary depending on the pathogen considered.

HPP is not specifically regulated at EU level and EFSA’s advice will inform the possible decisions of risk managers in this field.

Research – High-Pressure-Induced Sublethal Injuries of Food Pathogens—Microscopic Assessment


High Hydrostatic Pressure (HHP) technology is considered an alternative method of food preservation. Nevertheless, the current dogma is that HHP might be insufficient to preserve food lastingly against some pathogens. Incompletely damaged cells can resuscitate under favorable conditions, and they may proliferate in food during storage. This study was undertaken to characterize the extent of sublethal injuries induced by HHP (300–500 MPa) on Escherichia coli and Listeria innocua strains. The morphological changes were evaluated using microscopy methods such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Epifluorescence Microscopy (EFM). The overall assessment of the physiological state of tested bacteria through TEM and SEM showed that the action of pressure on the structure of the bacterial membrane was almost minor or unnoticeable, beyond the L. innocua wild-type strain. However, alterations were observed in subcellular structures such as the cytoplasm and nucleoid for both L. innocua and E. coli strains. More significant changes after the HHP of internal structures were reported in the case of wild-type strains isolated from raw juice. Extreme condensation of the cytoplasm was observed, while the outline of cells was intact. The percentage ratio between alive and injured cells in the population was assessed by fluorescent microscopy. The results of HHP-treated samples showed a heterogeneous population, and red cell aggregates were observed. The percentage ratio of live and dead cells (L/D) in the L. innocua collection strain population was higher than in the case of the wild-type strain (69%/31% and 55%/45%, respectively). In turn, E. coli populations were characterized with a similar L/D ratio. Half of the cells in the populations were distinguished as visibly fluorescing red. The results obtained in this study confirmed sublethal HHP reaction on pathogens cells. View Full-Text

Research – Inactivation of Foodborne Viruses by High-Pressure Processing (HPP)



High-pressure processing (HPP) is an innovative non-thermal food preservation method. HPP can inactivate microorganisms, including viruses, with minimal influence on the physicochemical and sensory properties of foods. The most significant foodborne viruses are human norovirus (HuNoV), hepatitis A virus (HAV), human rotavirus (HRV), hepatitis E virus (HEV), human astrovirus (HAstV), human adenovirus (HuAdV), Aichi virus (AiV), sapovirus (SaV), and enterovirus (EV), which have also been implicated in foodborne outbreaks in various countries. The HPP inactivation of foodborne viruses in foods depends on high-pressure processing parameters (pressure, temperature, and duration time) or non-processing parameters such as virus type, food matrix, water activity (aw), and the pH of foods. HPP was found to be effective for the inactivation of foodborne viruses such as HuNoV, HAV, HAstV, and HuAdV in foods. HPP treatments have been found to be effective at eliminating foodborne viruses in high-risk foods such as shellfish and vegetables. The present work reviews the published data on the effect of HPP processing on foodborne viruses in laboratory media and foods. View Full-Text