High-Pressure Processing (HPP) is revolutionizing the dairy industry by offering a nonthermal method to ensure food safety and extend shelf life while preserving the sensory and nutritional qualities of dairy products. Unlike traditional heat pasteurization, HPP effectively inactivates pathogens and spoilage microorganisms without compromising product quality. This technology is gaining traction for its ability create added-value products, and meet consumer demands for clean-label foods. In this post, we explore the various applications of HPP in dairy, including milk preservation, cheese production, and other potential uses.
Dairy products are an excellent source of proteins, minerals, and vitamins. Heat pasteurization has traditionally ensured food safety and extended the shelf life of milk and derived products such as cheese and yogurt. However, post-pasteurization environmental contamination by pathogens such as Listeria monocytogenes has led to an increasing number of recalls and foodborne outbreaks. Additionally, the process can negatively affect the delicate sensory and nutritional characteristics of fresh milk.
High-Pressure Processing (HPP) has emerged as the most widely implemented nonthermal food preservation technology in the food industry, offering two key advantages: (i) already packaged products are subjected to the process, eliminating any chance of environmental contamination and effectively inactivating microorganisms, and (ii) the nonthermal nature of the process preserves the quality attributes of dairy products.
Factors such as regulatory constraints, intellectual property issues, or throughput may account for the limited adoption of the process by the dairy industry. However, some companies are already taking advantage of the process to ensure safety and preserve the quality of raw milk, extend the shelf life of fresh cheese, and delay spoilage and eliminate pathogens in hard and semi-hard cheeses.
The availability of more productive equipment that allows bulk processing of liquids before packaging, along with recent scientific advances, supports the potential of HPP technology to deliver added-value dairy products and even create new product categories. Keep reading to learn how the dairy industry can leverage the use of HPP.
HPP Applications in the Dairy Industry
Milk
Since scientists at the West Virginia Agricultural Experiment Station used milk as the first food matrix to explore the effect of HPP in 1898, numerous investigations and assessments by food safety authorities have confirmed that the process is suitable for preserving milk. Figure 1A shows that processing raw milk at 6000 bar (87,000 psi) for 3 min extended the shelf-life of raw milk up to 30 days at 4 °C (39 °F) and kept Enterobacteriaceae counts below the detection limit (<1 CFU/ml). The same processing conditions yielded a 5-log10 reduction of Escherichia coli, L. monocytogenes, and Salmonella spp. (Figure 1B).
Other reports show that processing raw milk at 6000 bar (87,000 psi) for 10 min yielded a 4-log10 reduction of total plate counts, and counts remained steady below 102 CFU/ml through 60 days of storage at 6 °C (43 °F) (Lim et al. 2023). According to Chen et al. (2007), processing artificially inoculated UHT milk at 6000 bar (87,000 psi) for 6 min achieved a >3-log10 reduction for Staphylococcus aureus and E. coli O157:H7 and a >6-log10 reduction for S. Enteritidis and L. monocytogenes.
Although there is limited scientific research on whether pathogen inactivation is maintained throughout storage, agencies like New South Wales government in Australia (Szabo et al. 2016) and EFSA in Europe have evaluated and confirmed that HPP can produce safe milk. In this regard, EFSA concluded that processing raw milk at 6000 bar (87,000 psi) for 8 min is required to achieve the performance criteria for pertinent pathogens such as Mycobacterium bovis, L. monocytogenes, STEC, Salmonella spp., Campylobacter spp. and S. aureus (Koutsoumanis et al. 2022).
Moreover, the process respects the quality attributes of fresh milk. The concentrations of vitamins A, C, D, E, K, and all B-group vitamins were not significantly affected after processing fresh milk at 6000 bar (87,000 psi) for 10 min (Lim et al. 2023). The same processing conditions did not affect the viscosity of raw goat milk, whereas heat pasteurization at 70 °C (158 °F) for 5 min to 15 min decreased viscosity by 7% to 17% (Razali et al. 2021). Color is affected by processing conditions: HPP destabilizes casein micelles, causing them to lose their colloidal stability. This changes light scattering properties, resulting in a yellowish coloration depending on the level of casein dissociation. In this regard, Stratakos et al. (2019) reported that HPP at 6000 bar (87,000 psi) for 3 min had a lower impact on color attributes (DE = 2.3) compared to thermal pasteurization at 72 °C (161.6 °F) for 5 min (DE = 3.3), which resulted in a significant decrease in L* and b* color components.
Companies such as Villa de Patos in Mexico or Made by Cow in Australia have adopted HPP to ensure food safety and preserve quality attributes of non-homogenized raw milk.
Fresh Cheese
Heat pasteurization of milk is required for the manufacture of derived products such as fresh cheese. However, environmental contamination can be introduced during curdling, curd cutting, molding, brining, or packaging. This significantly reduces commercial shelf-life and potentially introduces hazards such as L. monocytogenes. Traditionally, chemical preservatives have been used to extend shelf-life, but an increasing number of companies are adopting HPP to inactivate microorganisms resulting from environmental contamination and reduce the use of preservatives to deliver “clean label” products.
Subjecting artificially inoculated Queso Fresco at 6000 bar (87,000 psi) for 3 min yielded a 4.1-log10 reduction of L. monocytogenes (Tomasula et al. 2014) (Figure 2A), but researchers observed recovery of the surviving fraction during storage at 4°C (39 °F). This highlights the importance of adequate Cleaning and Sanitation programs that ensure the absence of the pathogen at high concentrations in food contact surfaces. Interestingly, the growth of mesophilic aerobic bacteria was significantly delayed, which extended the shelf-life of the product up to 90 days at 4 °C (39 °F) (Figure 2B).
Examples of products in this category that enjoy extended shelf-life and increased food safety include fresh cheese, mozzarella, and paneer. The presence of a governing liquid in the package is usually required to ensure the absence of residual air and to uniformly transmit pressure.
Ripened Cheese
Similar to the manufacture of fresh cheese, ripened cheeses that require aging to develop their characteristic texture and flavor can introduce hazards that may persist until the end of the ripening process. Additionally, some jurisdictions allow the manufacture of cheese from raw milk, which is a well-known source of pathogens. High Pressure Processing emerges as a valuable tool to process whole cheeses or cheese portions, ensuring the absence of pathogens of concern in the final product.
A study in which raw milk was purposely inoculated with L. monocytogenes for cheese production revealed that the pathogen persisted throughout 60 days of ripening at 12 °C (53.6 °F) (Figure 3). However, processing the cheeses at 5000 bar (72,500 psi) for 5 min after 50 days of ripening reduced the counts to undetectable levels (<1 CFU/g). This reduction was maintained through the remaining ripening period until day 60 (Arqués et al. 2005).
Similarly, Carminate et al. (2004) demonstrated that HPP at 6000 bar (87,000 psi) for 15 min can achieve L. monocytogenes reduction levels between 2.4 and 5 log10 units in deliberately contaminated Gorgonzola cheeses with water activity (aw) values ranging 0.91 to 0.95. This makes HPP an attractive tool for ensuring the absence of L. monocytogenes in markets with zero tolerance for the pathogen. It also helps meet new regulatory requirements, such as the update to Regulation (EC) 2073/2005 in the European Union, which demands the absence of the pathogen in ready-to-eat products that can support its growth if food business operators cannot demonstrate that the pathogen will not exceed 100 CFU/g throughout the product’s shelf life.
Emerging Applications of HPP for the Dairy Industry
The effect of HPP at the molecular level on milk constituents expands the range of potential applications for the dairy industry. Scientific research outlines several ideas that deserve consideration by the food industry, as their implementation may result in enhanced productivity or added-value products.
- Increased yield in cheese production: Subjecting either raw or heat-pasteurized milk to HPP prior to curdling results in an enhanced yield. The process dissociates casein micelles and promotes the interaction of β-lactoglobulin from the whey with the micelle subunits. This also allows for higher moisture retention, resulting in curd and cheese with a higher yield (Molina et al. 2000; Voigt et al. 2010; Inácio et al. 2021).
- Accelerated cheese aging: Subjecting cheese to HPP after molding, but before the ripening process begins, can accelerate proteolysis and other reactions. This can shorten ripening time and also modulate flavor and texture attributes (Saldo et al. 2000; Costabel et al. 2016).
- Whey valorization: Subjecting pre-concentrated whey with the appropriate acidity to HPP enables the separation by centrifugation into a liquid phase rich in α-lactalbumin with high purity, and a solid phase rich in β-lactoglobulin. These fractions are valuable for use in infant formulas or sports preparations (Romo et al. 2023a; Romo et al. 2023b).
HPP stands out as a versatile technology addressing major challenges in the dairy industry. By effectively controlling pathogens and spoilage microorganisms from environmental contamination, HPP helps manufacturers meet food safety regulations while aligning with health-conscious consumer demands. Do not hesitate to contact us if you want to learn more or to request free trials in our HPP Incubators!
