Milk is one of the most nutrient-dense everyday foods, providing high-quality proteins, minerals, and vitamins. Yet, when consumed raw, it can also carry biological hazards, with outbreaks historically linked to pathogens such as Listeria monocytogenes, Salmonella spp., Campylobacter spp., and Shiga toxin-producing Escherichia coli (STEC).
For over a century, the dairy industry has relied on thermal pasteurization to ensure safety, but heat can also drive quality trade-offs and contribute to sensory alterations. This is why emerging nonthermal technologies are gaining momentum. Among them, High-Pressure Processing (HPP) stands out as a promising route to reduce microbial risk while preserving a more raw-like sensory profile and much of milk’s nutritional value. Turning that promise into routine commercial practice, however, still depends on meeting regulatory expectations for validation and verification.
Milk and Nutritional Properties
Recent data in raw cow milk suggest that nutritional value can be largely preserved immediately after HPP, with vitamins and minerals remaining comparable to untreated milk under intense conditions (6000 bar/87 kpsi, 10 min) (Figure 1). Importantly, vitamin stability is still governed by storage: some vitamins (A, B3, B5, B6, C) decline gradually over refrigerated storage after HPP, but untreated raw milk can degrade even faster.
The Potential of HPP to Inactivate Pathogens and Ensure Safety
Raw milk safety remains a public-health concern. A US analysis (2013–2018) reported around 75 outbreaks linked to raw milk, with most occurring where sales were permitted, especially where retail sale was allowed (Koski et al. 2022).
Multiple challenge studies indicate that HPP at 6000 bar (87 kpsi) can deliver several log reductions of key vegetative pathogens, including L. monocytogenes, Salmonella spp., and E. coli (Figure 2). However, a recurring limitation in published research is that post‑process pathogen evolution during storage is often not monitored, and some studies use UHT milk for inoculation, which may not fully represent raw milk behavior.
HPP may also help address emerging hazards such as avian influenza. While its effectiveness against H5N1 in milk remains uncertain, results for other subtypes (e.g., H7N7) in other matrices suggest that sufficiently intense pressure treatments can markedly reduce viral titers (Isbarn et al. 2007).
The Potential of HPP to Extend Shelf Life by Controlling Spoilage Microorganisms
Beyond safety, HPP can meaningfully reduce spoilage microbiota in milk. For example, 6000 bar (87 kpsi) for 3 min achieved a 4 log reduction of total viable counts and >2.7 log reduction of Enterobacteriaceae, followed by delayed growth under refrigeration compared with untreated milk, which extended shelf life up to 21 days under refrigeration (Figure 3).
Across studies, shelf life outcomes vary with conditions and initial microbiota, but reports include:
- Up to 60 days at 6 °C (43 °F) after 6000 bar (87 kpsi) for 10 min, with an initial total viable count (TVC) in raw milk of 5 log cfu/mL (Huey Lim et al. 2023).
- More than 30 days at 6 °C (43 °F) after 6000 bar (87 kpsi) for 15 min, with an initial TCV of 4.5 log cfu/mL (Yu et al. 2022).
- More than 22 days at 8 °C (46 °F) after 6000 bar (87 kpsi) for 3 min, with an initial TVC of 5 log cfu/mL (Fern Tan et al. 2020).
The Potential of HPP to Retain Sensory Quality
HPP is often presented as a way to deliver “raw-like” milk because it avoids many of the flavor changes associated with heat treatment. Sensory studies report only minor differences between untreated and pressure-treated milk across several attributes, and panelists generally preferred HPP-treated milk to pasteurized milk (Figure 4).
That said, appearance can shift in raw, unhomogenized milk: HPP may increase the yellow color component b*, likely linked to micellar changes that increase light interaction with the lipid fraction. Notably, color differences (DE) can be smaller than heat treatment under some conditions (e.g., 6000 bar / 87 kpsi for 3 min vs 72 °C / 161 °F for 5 min) (Stratakos et al. 2019).
Regulatory Situation
Several agencies and expert groups acknowledge the potential of HPP but also highlight gaps. New Zealand’s review concluded there is no “safe harbor” (no default parameters usable without further validation), and pointed to challenges with verification indicators (e.g., alkaline phosphatase is pressure‑resistant and not a suitable performance indicator for HPP).
European risk-based assessments have proposed time/pressure combinations to meet performance criteria for multiple pathogens, while also warning about challenges with process verification.
In the United States, the situation is particularly stringent because pasteurization equivalence traditionally links to inactivation of Coxiella burnetii (historically used as the benchmark organism). Alternative processes must demonstrate equivalence and consider revalidation when hazards and/or processes change. This raises practical challenges regarding reference organism selection and robust protocols for process validation.
Take-home Message
HPP can enable safe, extended‑shelf‑life, “raw‑like” milk, but the industry needs better-defined validation playbooks. Evidence shows strong pathogen and spoilage reductions and promising sensory retention, yet gaps remain around benchmark targets, post‑process behavior during storage, and universally accepted verification indicators.
One possible approach is to use HPP as a shelf‑life‑extension step for milk that has already undergone a validated lethal treatment for pathogen control, such as Long-Temperature Long-Time (LTLT), which is claimed to minimally affect milk quality compared with other pasteurization treatments at higher temperatures.
