The Science Behind High Pressure Pasteurization (HPP)

Scientific Evidence of Effects of HPP on Meat Products

High Pressure Pasteurization (HPP) claims to decrease the potential of pathogens such as Salmonella, Listeria, Campylobacter and E.Coli in raw meat pet food products while still maintaining the “raw” integrity.

How does HPP work?  HPP is a non-thermal, cold processing technique in which the food, in its flexible, plastic, oxygen rich packaging, is subjected to high levels of hydrostatic (water) pressure. In 2012, documents were published stating that pressure greater than 400 MPa is necessary to achieve efficient microbial inactivation. However, Staphylococcus Aureus, Spores, Protease Cathepsin, etc are resistant even above 600MPa (87,000 psi (pounds per square inch)).  HPP treatment at subzero temperatures (on frozen raw foods) is not effective in decreasing microbial counts in meats due to lack of plasticity of the product. (1)

How much real life pressure is 87,000psi?  When a Scuba Diver is exposed to underwater pressure Boyle’s Law states that effects are an increase in the absorption of nitrogen which can lead to oxygen toxicity, nitrogen narcosis, carbon monoxide toxicity and decompression sickness. (19) These physiological effects are usually reversible in a living being because a living being is capable of persistently working to metabolize excess nitrogen and strive for homeostasis, while dead tissue is not.  Of course, humans can’t survive the depths of the ocean (17,000 psi) without a submarine.  Even a submarine would not survive 30,000psi which bends steel. A Scuba Diver would have to reach 200,685 ft (6.3 times the depth of the Mariana Trench) to reach 87,000psi (21) thus it would take a diver 418 hours of active metabolizing to recover from the physiologic changes caused by the pressure. The tissues of deep water sea-life “brought to the surface… (They suffer) the congealing pressure off its lipids, it may start to ooze a bit internally… (and lose) integrity in their nerve cell membranes… (which get) quite leaky.” (23) Imagine the effects of an animal brought up from 6.3 times that depth!!! Yet that’s what HPP does to your pets’ food.

Mandating (or lack thereof) HPP.  USDA’s FSIS (Food Safety & Inspection Service) Directive 6120.1 on HPP inspection verification responsibilities has caused false rumors that HPP will become mandated. This documents wording implies that HPP requirement when, in fact, the document is simply stating the rules of a HACCP plan IF HPP were used by a company, not because it is mandatory. (26)  Since 2009 FDA has worked with the FSIS and FIC (Food Industry Counsel) to enforce HACCP plans (Hazard Analysis Critical Control Point) on food companies (canned food excluded) because the FDA does not have the authority to enforce specific pathogen stop-gap measures.  The 2016 USDA's FSIS HACCP enforcement program is designed to ensure food safety and quality control by requiring raw food companies, for human and pet consumption, to maintain a detailed tracking log of manufacturing and testing procedures. It does enforce specific stop gap methods such as HPP, irradiation or cooking. Legally, according to the FSIS authority HACCP, itself, is considered a “stop gap method,” as are irradiation, HPP, cooking and "other methods" that are "not yet researched” (like fermentation) if their efficacy can be proven. (25)

So why would a company choose to do HPP? Doesn't it cost more to do that? Why bother if they don't have to and it has negative side effects? If a company chooses to purchase lower quality meats that they are know are more likely to harbor bacteria then it is necessary to implement a "stop-gap" procedure to prevent recall. Companies that source higher quality, less processed or un-processed meats do not need to take expensive steps to kill existing pathogens prior to resale because the meat has been cared for in a way that has never allowed pathogens to proliferate in the first place.

Damage done by HPP… what does the science say?  HPP fractionates the protein molecule and delays rigor mortis, which is useful for tenderizing. It disassociates myosin, actin, albumin, myoglobin and causes coagulation, aggregation or gelation of sarcoplasmic proteins and myofibrils. (1)(12) Muscle proteins are also susceptible to oxidative reactions that involve the loss of essential amino acids and decrease protein digestibility, thus affecting the nutritional value of the meat. (1) HPP can affect protein conformation and lead to protein denaturation, aggregation or gelation. (10) The higher the fat or water content the greater the "whitening effect" caused by protein coagulation (loss of solubility of sarcoplasmic and myofibrillar protein and/or globin deterioration from heme (blood) group displacement).  Therefore, in addition to beef and other fatty meats (20-25%) being more susceptible to whitening, they are also more susceptible to lipid oxidations. (1) HPP induces meat protein modifications that result in varying effects on meat product texture and water retention.  Because of this the meat develops a cooked and sticky look after thawing. Because the muscle proteins and heme groups are displaced the thawing and freezing time is decreased and the meat doesn't freeze uniformly unless in oxygen depleted environments (vacuum sealed) (1) which may allow bacteria to re-proliferate and speeds oxidation of lipids. Glutamate/Glutamic Acid (not to be confused with gluten) are naturally present in amino acid rich proteins. Hydrolyzation is a process where proteins are broken down into their component amino acids (accomplished by many methods, including, obviously, HPP). Hydrolyzation releases natural glutamate into its “free form” which results in a by-product of 5-20% MSG(20)

Lipid oxidation (peroxide and cholesterol) is dramatically increased after HPP especially in oxygen rich environments. Oxidative reactions make meat susceptible to loss of amino acids and decrease protein digestibility. The only ingredients known to limit oxidative damage in HPP products are rosemary, sage, EDTA, or egg white powder. Tocopherols, most commonly used in raw pet foods, are specifically listed as being ineffective. (1) Lipid peroxidation is the oxidative degradation of lipids which results in cell damage and rupture of red blood cell membranes which may be mutagenic and carcinogenic. Tests of toxicity of lipid hydroperoxides done on mice showed they did not survive past embryonic day 8, indicating that the removal of lipid hydroperoxides is essential for mammalian life. (2,3) Considering that most pets stay on a diet of one brand or protein for their entire life an HPP damaged food, fed exclusively, could be life-threatening based on our HPP scientific research findings.  Studies showed that lipid oxidation was ONLY slowed if the meat was pressure treated at 500MPa or above for 30-60 minutes at 20-70* C (68-158* F) (cooked) and vacuum sealed at the time of processing. Raw Pet Foods HPP for only 3-5 minutes at lower temperatures at 600MPa and do not commonly vacuum seal. Additionally, HPP meats are only more stable and resistant to re-proliferation of pathogens ONLY if cooked prior to, or in conjunction with, HPP. (1)

Vitamin A has up to 100% loss at 87,000 psi. (1)  Vitamin C has 30-40% decrease at only 400MPa and up to 70% at 600MPa (87,000psi) that is only limited by lowering oxygen concentrations. (5) Synthetically supplemented B Vitamins have a 30x greater rate of decay after HPP, especially Thiamine Monophosphate (TMP). (8) TMP deficiency results in the disease called Beriberi which may result in difficulty walking/incoordination, mental confusion, pain, strange eye movements, tingling, vomiting, increased heart rate, shortness of breath, enlarged heart, congestive heart failure and swelling of the lower legs. Lycopene (11) and Carotiniods (7) are damaged by HPP. HPP decreases the pH of meat products. (1) Excessively low pH levels may cause metabolic acidosis, which leads to acidemia, resulting in fatigue, headache, loss of appetite, coma or death. Whether the decrease of pH caused by HPP is significant enough to cause acidemia is debatable but a pet with existing health concerns such as urinary stones/crystals, infections, cancer, etc caused by low pH may be exacerbated by HPP.

HPP can inactivate microorganisms and enzymes as well as degrade and denature nutrients. (6) While blood and muscle tissue are void of DIGESTIVE and food enzymes metabolic enzymes are found in other tissues, including blood and muscle.  These enzymes are still part of the natural process of carnivore digestion, and are therefore beneficial for health.  Just as cooking salad or fruit would remove many beneficial, nourishing nutrients from raw foods for people, HPP removes nourishing nutrients for your pets.

Studies have shown that polymer packaging material (plastic) that pet food is packaged in is modified by high pressure. A significant migration of compounds from the plastic material into the food product has been observed. Traces of n-hexanal and some hydrocarbons have also been found by Schindler and others in 2010. (1) The Ecology Center lists “product packaging and food wrap plastic” under the section for Phthalates (DEHP, DINP, and others) and states that they are Endocrine Disruptors, linked to asthma, developmental and reproductive effects, release of dioxins and mercury, including cancer, birth defects, hormonal changes, decreasing sperm counts, infertility, endometriosis and immune system impairment. (4) Plastic fragments have never been found in raw pet foods.  However, plastic fragments have also never been found in plastic water bottles that were left in a 100* car or frozen, though research is wide-spread proving the health detriments of drinking water from a plastic bottle that has been heated or frozen. (27)

Dogs and cats are designed to tolerate pathogens.  They have pathogen regulating, rather than digestive enzymes in their mouths. Their short digestive tracts pass foods quickly, before they can harbor pathogens. Their stomach acid is 1, far more acidic than a person. While a dog or cats system is fully capable of tolerating high levels of pathogens, in the case of illness is it damaging to force the immune system to endure pathogens when it could be using metabolic and immune resources to heal? Is truly raw or HPP safer for an immune compromised pet??? Studies show that HPP is only highly effective in short and long term pathogen regulation when products are cooked or cured first, and then HPP. HPP alone does not always provide sufficient regulation of pathogens. HPP increases oxidation and free radicals, decreases enzymes and antioxidant capacity and destabilizes the amine matrix. Therefore, an already taxed immune system would have an increased free radical load, decreased contribution of enzymes to regulate health and decreased antioxidants to assist in regaining health.  Additionally…

What if my pet is immune compromised??? Wouldn’t HPP make the food safer?  The FDA, FSIS and FIC implemented a Zero Tolerance Policy (24) and “War on Pathogens” in 2009 on ALL raw pet foods (though NO raw food recalls are listed on the FDA website prior to 2010, and only 22 EVER). This means that non-HPP, completely raw pet foods, as well as HPP or other “stop-gap treated” foods, are allowed to have 0% pathogens in the food.  Pathogen levels as low as .05% (far below levels that cause illness) will be recalled. For the consumer this means that untreated raw products are just as safe, if not safer than HPP. A non-HPP truly raw product must maintain superior standards because they must rely on the quality of well-sourced ingredients to be capable of testing negative for pathogens. Truly raw products would also maintain their natural bacterium that prevents pathogen proliferation once home with the consumer (22) while HPP pet food could purchase a Salmonella contaminated or 4D (dead, diseased, disabled, dying) product and test free of pathogens after HPP, though bacteria needed to regulate the RE-proliferation of pathogens were killed in the HPP process.  It’s therefore safer to feed an immune compromised pet a fully raw product (that is equally regulated for pathogens by FDA, FSIS and FIC) than it is to feed a HPP food product that burdens the body with lipid oxidation, decreased pH/metabolic acidosis, endocrine inhibitors, loss of Vitamin A, Thiamine, Vitamin C, Carotenoids, Enzymes, etc. Cooked foods (dry/kibble and canned) are excluded from testing, as well as these safety measures and regulations. (25) Pet food is legally required to have substantially lower levels of pathogens than even Grocery Store meats for human food consumption.  The FDA’s Regulatory Offensive “War on Pathogens” implemented microbiological sampling of over 2,000 raw pet food samples taken from retail stores between 6.1.2015-8.31.2015. FDA was instructed to enforce recalls on all products that tested positive for Salmonella, Listeria, E.Coli or Campylobacter. Despite the sampling of 2,000 raw (and HPP) pet food products only 5 (.002%) were recalled. 80% of the raw food recalls enforced in this time frame were popular HPP products.  Only 20% (1 product (.0005%)) was caused by non-HPP, truly raw pet food. Other bags from the same batch were tested, no others were positive.

Statistical likelihood of actual recalls (2007-2016 – 9 years). Since 2007 there have been 7 recalls on Raw, untreated pet foods (NO reported illnesses or death), 16 recalls on HPP pet foods (57% more than that of raw, untreated, non-HPP products), 2 recalls on Dehydrated raw pet foods, and nearly 300 recalls on Dry Kibble (Cooked Dog and Cat Food) and Cans (numerous reported illnesses and deaths), despite FDA’s active efforts to recall raw pet foods.  (14)

E.coli is highly responsive to HPP, however since 2007 there has only been ONE recall of pet food for e.coli (dry food), making it a moot point for pet food regulation. (17) Campylobacter – There is minimal reference to HPP’s ability to regulate Campylobacter. However, NO cases of campylobacter have ever been associated with pet food recall. (18) Listeria monocytogenes has been observed to have a higher survival rate in cooked and HPP meat than in raw meats. (Simpson and Gilmour 1997) (1) NO Listeria outbreaks have ever been caused by pet products. (15) Salmonella - In September of 2015 Dr. William James, a 28 year Chief Veterinarian of FSIS in charge of pathogen and residue sampling published a document showing his disappointment in FSIS’s ability to decrease Salmonella in food products since 2000 despite changes in policy.  He states that FSIS will not change their regulatory strategy for Salmonella, despite its failures. (13) Since 2006 there have been 60 outbreaks caused by Salmonella, TWO of which were caused by COOKED, DRY PET FOOD (none from raw). (16)


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Westchestergov – Bisphenol-A (BPA) by R.P. Astorino, Westchester County Executive