High Pressure Processing: Our Research & Overview

If you’re looking for a quick overview of HPP and answers to FAQs, see here, Or watch our webinar for a guided walkthrough of the topics below. 

We’ll be going much more in depth on the process, how it works, and our testing in this post. 

High pressure processing (HPP) is a food safety technique that uses pressurized cold water chambers to inactivate harmful microorganisms. The high pressure disrupts important components such as cellular membranes and structural proteins causing the cell to die [1]. High pressure is extremely effective at breaking weaker chemical bonds (hydrogen bonds, hydrophobic interactions) important to overall cell function but it does not affect nutrients such as amino acids, vitamins, minerals, and fatty acids since they are held together by stronger covalent bonds unaffected at pressure ranges achievable by HPP machines [2]. 

We have previously used pathogen eliminating probiotics as the main hurdle in our food safety process. Before we go into why we decided to add HPP to our process, it’s important to discuss two important philosophies we have about food safety.

Continuous Improvement: Here at Viva, we believe in making each batch of our food better than the last. This means that we’re always looking at the latest science, evaluating new technologies, and conducting our own testing. Our goal is to constantly improve our processes and that inevitably brings change. Before we implemented probiotics, we invested heavily in researching & testing other food safety technologies and our decision to adopt HPP is just the latest, but not the last, step in the evolution of our food safety systems.

Data Driven Decisions: We follow the science—and as we gather new information from research, expert opinions, and data from our own testing, our decisions evolve accordingly. From our testing and research on HPP, the benefits it brings to our food safety & quality are clear and we evolved our systems and processes alongside the new information we found. 

So, why did we adopt HPP? 

Consistent Application: A key aspect of probiotics is that it functions through a biological agent—the probiotics are living cells that produce antibacterial compounds and outcompete other microorganisms. This has numerous advantages such as the duration of protection it offers and being applicable in a wider variety of food types but one key tradeoff is consistency since living organisms are naturally more sensitive to environmental conditions. HPP acts through a mechanical process that is easier to control and replicate and this consistency is important for creating a more robust food safety system.

Greater Pathogen Reduction: While probiotics are highly effective at controlling potential pathogens, our goal has always been to continuously enhance the safety & quality of our products. Our testing shows that HPP can eliminate even larger quantities of bacteria cells and we are excited to adopt this technology to further strengthen our food safety systems. 

When it comes to the debate on HPP, you’ll commonly see concerns around nutrient loss, lipid oxidation, and beneficial bacteria levels. Rather than rely only on literature or the data of others, we did our own testing with accredited third party labs to evaluate if HPP impacts other aspects of our food’s quality. 

We’ve mentioned this before but every manufacturer is unique and there isn’t a one-size-fits-all approach. Your production processes, recipe formulation / product matrix, and environmental conditions can all affect the outcome and that’s why it’s important for each manufacturer to conduct their own testing. We’ll be sharing the data we saw in our products but results may be different for others. 

The short answer is: yes, and by a lot.

In microbiology, we’re usually dealing with large numbers of bacteria—think millions or even billions. Because of this, we use log scales (factors of 10) to make the numbers easier to visualize. Let’s say we start with 1,000 bacteria cells. Here’s what different log reductions actually look like in real numbers:

• 1-log reduction (90% reduced)

  • 1,000 → 100 left

• 2-log reduction (99% reduced)

  • 1,000 → 10 left

• 3-log reduction (99.9% reduced)

  • 1,000 → 1 left

As you can see, each additional log reduction dramatically decreases the bacterial load. For additional context, cooking meat and poultry typically achieves a 5 to 7-log reduction [3], while spraying a surface with Lysol results in about a 3-log reduction.

A 5-log reduction—representing a 99.999% reduction in pathogen load—has long been both our internal food safety goal and the gold-standard benchmark used by the FDA across several regulated food categories. It represents a dramatic reduction in both risk and pathogen prevalence [4].

Our Study Design

We partnered with the Institute for Food Safety & Health (IFSH) at the Illinois Institute of Technology to run HPP validation studies on our recipes. In the food safety world, a validation study is a controlled stress test. You intentionally load product samples with large numbers of pathogens, run it through your kill step (HPP in our case), and see how many survive to gauge how effective your intervention is.

There are a couple of important aspects to a well-designed validation study:

1. Triplicate sampling: For each of our unique “parameter sets” (i.e. HPP hold time, pressure, days that the sample has been held post-HPP), we had 3 independent samples. This is the gold standard for ensuring our study is more robust and that we aren’t blind to potential variability.

2. Replication: Running the validation study once and receiving good results is nice, but what if there was just something different about the particular raw materials or lot that was used for that study? This is why it’s important to run replications of our validation study with different lots (i.e. Chicken Lot #1 for Study 1, Chicken Lot #2 for Study 2) and ensure that our findings are replicated.

3. Pathogen cocktail: This often goes under the radar, but it’s incredibly important to ensure that the ‘test’ pathogens we are using to inoculate our product samples represent a diverse set of isolates. If we choose one isolate for our study and find it to be easily killed off, it could just be that the specific isolate is not very hardy and there may be other isolates that have characteristics that make them much more resistant. For this reason, we selected at least 5 different isolates for both Salmonella spp. & L. monocytogenes (different animal origin, different types of outbreaks or extracted from clinical cases). For E. coli, we ended up inoculating with not only E. coli O157:H7 but also other Shiga-Toxin Producing E. coli strains that are less common but could still potentially be found in raw materials.

All in all, we had hundreds of samples that we were testing for each replication in order to ensure that we were robust in representing the results of HPP on our products.

How the Testing Worked

Each sample was inoculated to a starting concentration of 8 log CFU/g, roughly 100 million pathogens per gram of food, for each of the three major foodborne pathogens:

• Salmonella spp.

• Listeria monocytogenes
  

• Shiga-toxin producing E. coli (STEC)

It’s important to note that these levels would never occur naturally in any environment, but inoculating at such extreme levels allows us to test the upper limits of our kill step. In real environments, pathogen levels are typically far lower—often just 2-3 logs [5]. That means if HPP can reliably achieve a 5-log reduction, we can be confident it will handle any realistic scenarios (and with additional buffer).

After inoculation, samples were processed at 586 MPa (~85,000 PSI) for 180 seconds and then frozen. Pathogen levels were measured over the next 10 days to confirm that the reductions weren’t just immediate but remained stable over time.

What We Found – Chicken, Beef, & Rabbit Results

The charts below show how pathogen levels in our chicken, beef & rabbit recipes responded to HPP.

At 586 MPa (~85,000 PSI) for 180 seconds, in Chicken, Beef, and Rabbit, all three target pathogens were reduced to levels below the lab’s ability to enumerate (< 10 CFU/g). 

We exceeded our goal of a 5-log reduction and, in some cases, achieved 6 to 7-log reductions, which is comparable to the microbial reduction of cooking. In plain terms, that’s taking 10 million bacteria cells per gram of food and reducing them to fewer than 10 cells. Pathogen levels also stayed suppressed through 10 days of frozen storage, indicating that there was no meaningful recovery of injured cells post treatment.

This is one of the most common questions we hear with HPP—after all, given the high amounts of pressure, it seems plausible that it would alter the food’s nutrient make-up. 

Before diving into the data, it’s important to explain why, from a scientific standpoint, HPP doesn’t have a large impact on nutrient levels within food. We all know that heat-based processing like cooking can degrade nutrients like sensitive vitamins, amino acids & fatty acids. Most nutrients are held together by covalent bonds, which require heat or other chemical reactions to break. Contrary to heat, pressure mainly affects non-covalent bonds like hydrogen bonds, meaning that even when applied at high levels, it doesn’t chemically affect nutrients.

Another way to think about this is that pressure & HPP will affect molecular structure and organization, but not composition. Proteins may partially unfold, but the amino acid sequence & covalent bonds still remain unchanged, meaning that any existing nutrients are left unaffected.

While from a scientific standpoint, all this made sense, we still wanted to test and measure HPP impact directly within our food.

How We Evaluated Nutrient Impact

We compared nutrient levels (macronutrients, minerals, vitamins, fatty acids, and amino acids) before and after HPP and to ensure that we accounted for natural variation, we averaged our nutrient measurements across 3 unique turkey samples before HPP and 3 unique turkey samples after HPP (remember the importance of triplicate sampling?). All 6 samples were pulled from the same batch to control for raw material variability.

In the tables below, we compare the before & after HPP values for each nutrient. All nutrient levels fluctuate somewhat when comparing the treatment to the control group, but this is expected due to natural variation. In order to isolate which of these nutrient differences are statistically significant, we employed a 2-sample t-test.

In layman’s terms, we want to know if the sample values are actually different (impacted by how different the averages & standard deviations are for treatment & control groups) or are falling within normal, expected natural variation. We’ve displayed this information in the rightmost column after measuring significance against a standard p-value of 5%. This means that we would only conclude that the before & after HPP results were meaningfully different if there was a < 5% chance of this observation if the samples weren’t actually different.

What We Found

Overall, we found very little to no impact of HPP on nutrient levels across the board. When comparing the before and after HPP samples, only 1 nutrient out of the 50 measured was significantly different—Vitamin B3 was elevated in the HPP group compared to the control. For us, this is not a cause for concern because 1) we’re not at risk of nutrient deficiency due to it being an increase after HPP, 2) it only increased by 10% and 3) there are no established AAFCO limits for toxicity for this nutrient. We are continuing to monitor this to understand if an increase in Vitamin B3 can be replicated in future tests.

Moisture levels also stayed the same before and after HPP. This is important because it’s often easy to misrepresent whether there has been an impact on nutrient levels due to a change in moisture content. For example, most brands will HPP the product, then regrind it before forming and packaging. This additional processing can reduce the moisture levels of the food, and it may look like nutrient levels have increased or had no change post HPP until you compare the nutrient levels on a dry matter basis (remove the impact of different moisture levels).

There were a few other nutrients that had a greater than 15% increase/decrease when comparing the HPP group to the control, but all were not significantly different from the control group (p-value > 5%), indicating that they still fall in the acceptable range of natural variation that can occur during sampling.

The data that we found on HPP’s impact on nutrients in our food is unsurprising, given that pressure does not act on nutrients the same way that heat does. This is another reason why HPP is an effective kill-step for raw pet food—it minimizes impacts to product quality & nutrient composition while effectively killing pathogens.

This is a concern that we’ve heard many times over the years with regard to HPP. When choosing to feed raw, most not only care about avoiding the “bad” bacteria, they also want to protect the “good” microbes that might support digestion.

This concern usually centers around lactic acid bacteria (LAB), the group most often associated with “good” or beneficial microbes in food [6]. LAB are common in fermented products and are often talked about in the same breath as probiotics, even though not every LAB strain is a true, studied probiotic. Still, they’re a useful indicator group for the kind of bacteria people are hoping to preserve.

So does this mean that HPP-ed food has less beneficial bacteria? The answer isn’t that simple.

It’s important to consider what dosage of probiotics is required in order to see health benefits. Most probiotics are formulated to deliver 1-10 billion CFUs (9-10 logs) of a specific strain per serving [7] However, our results above show that our recipes & raw meat in general typically contain only a few million CFUs of LAB in total [8] (more than 1000x less than what any probiotics deliver), not to mention that any specific beneficial probiotic strains within this quantity would be vastly lower in concentration.

Even though HPP does reduce beneficial bacteria in the food, when looking at non-HPP raw meat & its microflora, there was never enough naturally occurring probiotics present to make a difference in your pet’s health. The gut health benefits associated with raw food actually come from the overall structure of the diet itself: high-quality animal protein, high moisture content, intact fats, low carbohydrate content and the right balance of fiber and nutrients, all of which remain unchanged by HPP [9,10,11]. So yes, while HPP-ed food does have less beneficial bacteria than non HPP-ed food, the levels of beneficial bacteria in your non HPP-ed food were never the reason why your pet’s gut performed so well on the diet!

High pressure can break down lipid globules and cell membranes, but like much else, this all comes down to the amount of pressure, the time under pressure [12], and the exposure & opportunity to oxidize [13]. Due to our food being vacuum-sealed from the beginning to the end of the process and by using a shorter hold time (just enough to eliminate pathogens), we’re able to limit any opportunity for oxidation. 

We’ll be the first to admit that we’d love if HPP had no effect on the look & feel of our food, but the reality is that the slight changes are a compromise we’re happy to make in order to elevate the quality & safety of the food that we’re feeding your pets. It’s also worth noting that even if the food may look a bit different to us, these shifts won’t affect how your pet enjoys their meal (data shows that HPP does not affect palatability)!

No, and this is a very important detail.

Many people don’t realize that what happens after HPP matters just as much as the kill step itself. In almost all applications of HPP on raw pet food, food is reopened after HPP treatment for regrinding, forming, and final packaging. This puts the product at high risk of recontamination if the environment is not adequately controlled, sanitation is lacking, or employees fail to follow good manufacturing practices (GMPs).

By keeping our product fully sealed and not re-exposing it to the environment, we’re able to avoid this risk altogether, which is another reason why HPP works well in our product and manufacturing systems.

HPP is a powerful kill step, but an effective food safety culture is built on layers that overlap and reinforce each other. In addition to HPP, we focus on:

• Robust food safety plan & HACCP program implemented at our USDA manufacturing facility

• Test & hold release program to verify the effectiveness of HPP and other quality controls

• Daily environmental monitoring to verify sanitation effectiveness

• In-depth supplier approval program for all raw ingredient sourcing & ongoing testing to verify quality

• Strict cold chain controls & temperature monitoring from raw material receipt all the way to packing customer orders

You trust us with your pet’s health, and that’s a responsibility we don’t take lightly. Our goal has always been to make each batch of food better than the last, and bringing HPP into our process is just the latest step in our journey. 

We’ll continue working with researchers and scientists to gather the latest insights, evolve our systems, and we’ll be sharing our learnings along the way. 

If you have any questions, please reach out to us at info@vivarawpets.com.