FOOD7024
SPECIAL STUDIES IN FOOD SCIENCE AND TECHNOLOGY
ASSIGNMENT 1
HIGH PRESSURE PROCESSING
DUE ON 18/03/2024
WORD COUNT: 2750
STUDENT NAME STUDENT
NUMBER
CONTENTS
1. INTRODUCTION
2. HIGH PRESSURE PROCESSING
3. EFFECT OF HPP ON FOOD QUALITY AND SAFETY
4. EFFECT OF HPP ON THE CHEMICAL COMPOSITION OF FOOD
5. APPLICATION OF HPP
5.1. Vegetables and fruits
5.2. Cereal
5.3. Diary
5.4. Meat
6. ADVANCED TRENDS
7. CONCLUSION
8. BIBLIOGRAPHY
FIGURE 1: Pressure, temperature and time during a HPP process.
FIGURE 2: A. An illustration of the protein elliptic phase diagram demonstrating pressure, heat and
denaturation.
B. An illustration of denatured egg.
1. INTRODUCTION
The quality of food, encompassing attributes such as colour, texture, flavour, and nutritional
content, holds significant importance in both food preservation and processing. The
characteristics of food play an important role in influencing the customers to purchase a product
and the overall product acceptability. Meanwhile, the nutritional content, including vitamins,
minerals, and other health-related components, represents the hidden quality aspects of food.
In traditional thermal processing methods, optimizing the process involves minimizing the
impact of heat on food quality while ensuring that food safety is maintained. However, in
response to consumer preferences for fresher, healthier, and more natural food options, high-
pressure technology emerges as a novel and alternative approach in food processing and
preservation operations.
2. HIGH PRESSURE PROCESSING
High-pressure processing (HPP) is a food preservation method that utilizes high hydrostatic
pressure continuously and simultaneously from all sides to extent the longevity of the product
while preserving the nutritional and sensory properties. By applying pressure typically ranging
from 100 to 1000 megapascals (Mpa) to both liquid and solid foods, regardless of packaging
(Khaliq et al., 2021). This non-thermal pasteurisation approach deactivates enzymes and
bacteria that cause spoiling, without the use of high heat. It has a limited impact on flavour,
appearance, texture, and nutritional value. Treatment temperatures can be specified below 0°C
or above100°C. Specially designed vessels are employed to endure these pressures across
multiple cycles. Pressure is applied quickly and evenly in an isostatic manner, subjecting every
component of the food to the same pressure at the same time. Regardless of size, shape and
food composition, HPP acts instantaneously and uniformly through a mass of food. When HPP
is applied to food, its effectiveness is influenced by three main extrinsic parameters: P and t;
intrinsic parameters: pH and water activity; and microorganism-related parameters: type,
taxonomic unit, strain, and physiological condition. It also a small effect the molecular weight
component, such as vitamins, colour pigments, and extremely volatile flavouring chemicals
than ultra-heat treatment does.
In HPP, food safety is achieved by treating food with intense pressure. The two main systems
used are batch and continuous. Batch systems are the most common type that can handle both
solid and liquid foods (Tao et al., 2014). Food goes into a sealed chamber filled with a special
pressurizing liquid. By pumping liquid in or by shrinking the chamber pressure is applied.
Factors like corrosion resistance and the type of food being processed must be considered while
choosing the right pressurizing liquid. Food must be packaged in a flexible container which
can tolerate a 10 -20% volume less during the pasteurization process and return to its former
volume after the pressure is removed in order for it to withstand the process (Ting & Marshall,
2002). Materials like polypropylene (PP), polyester tubes, polyethene (PE) pouches and nylon-
cast polypropylene pouches are commonly used (Muntean et al., 2016). After treatment, the
system depressurizes, unloads and reloads for the next batch. Processing time depends on the
cycle time and how efficiently the chamber is filled. A semi-continuous system is used for
pumpable like juices. These systems use a special chamber with a separator to keep the food
separate from the pasteurizing liquid. Pressure on the liquid compresses the food. After
treatment, the lighter food is transferred to the sterile tank aseptically. Multiple units can be
used for continuous processes (Palou et al., 2002). The pressure used in HPP affects both the
initial cost and maintenance of the equipment. Higher pressure capabilities come at a higher
pressure but can increase the lifespan of the equipment.
Le Chatelier's concept, isostatic pressing (also known as Pascal's principle), and the
microscopic ordering principle are the basic principles guiding how foods behave under
extreme pressure. According to Le Chatelier's principle (Le Chatelier, 1884) a chemical system
in equilibrium will adapt its reaction to changes in pressure, usually leading to a reduced
volume when pressure is rised and vice versa (Jaeger et al., 2012). The material returns to its
former shape upon decompression, ensuring uniform pressure transmission in all directions by
isostatic pressing (Benet, 2005). According to the principle of microscopic ordering, while
temperature remains constant, applying more pressure to a substance results in better molecular
ordering, as temperature and pressure have opposite effects on molecule structure (Yordanov
& Angelova, 2010).
3. EFFECT OF HPP ON FOOD QUALITY AND SAFETY
HPP is renowned for its ability to deactivate microorganisms while maintaining the nutritional
value and sensory attributes of foods such as colour, appearance, and texture. These sensory
qualities are pivotal factors influencing consumers’ food preferences, making them crucial
considerations in food processing, particularly in the fruit and vegetable industry (Norton &
Sun, 2008; Rastogi et al., 2007). Scholars have extensively explored the impact of high
pressure on various enzymes in fruits, notably pectin methyl esterase (PME) and
polygalacturonase (PG), using instrumental methods ( Perera et al., 2010). In meat processing,
elevated pressures have been found to alter muscle protein structure, consequently affecting its
functional properties and texture. Similar effects have been observed in seafood, where
pressure exceeding 450MPa results in undesirable texture attributes like gumminess, chewiness
and hardness (Yagiz et al., 2007).
Studies have also investigated the influence of HPP on the colour of muscle foods (Andres et
al., 2006). While HPP processing tends to reduce redness in meats, it is associated with
increased lightness in fish, contributing to a processed look (Ramirez-Suarez & Morrissey,
2006). Similar effects have been noticed in cow’s milk, where HPP includes colour changes
attributed to structural changes in protein muscle. Interestingly, these colour changes are less
pronounced in HPP-processed fruits, regardless the effect of HPP plant pigments (Patras et al.,
2009).
Initially, it was believed that HPP had minimal effects on food flavours. However, some studies
showed that a combination of HPP and enzyme immobilization aids in de-bittering grapefruit
juice (Ferreira et al., 2008).Specifically, applying a pressure of 160 MPa at 37°C for 20 minutes
reduces the naringin content in grapefruit juice, thereby diminishing the bitterness.
Combining pressure and temperature treatments maximizes the efficiency of pressure therapy
in suppressing growth of microbial cells. A moderate treatment (440–600 MPa) succeeds
against pathogenic microorganisms like yeasts, vegetative bacterial cells, and molds, whereas
different microorganisms show variable resistance to pressure treatment. Nevertheless,
pressure (400–600 MPa) and heat (≥70°C) together work better for bacterial spores (Khaliq et
al., 2021).
When compared to Gram-positive bacteria, gram-negative bacteria often show less resilience
to pressure. Different strains of bacteria also exhibit differences in pressure resilience; in the
experimental phase, vegetative microbial cells exhibit lesser resistance than stationary phase
cells.

Different mechanisms of microbial inactivation are engaged in both pressure and heat treatment
controls, and there doesn't seem to be any relationship between them. As with conventional
thermal processing, water activity, pH, and food composition all affect how quickly microbes
reduce under pressure. Therefore, while conducting experimental trials involving pressure-
thermal applications, food processors must work in conjunction with experts in high-pressure
control.

The efficiency of pressure treatments alone in destroying spores at room temperature has been
found to be slightly limited. Generally, nutrient germinant receptors are activated by pressure,
which causes the onset germination of spores (Farkas & Hoover, 2000). Spore germination can
be started by applying mild pressure (100–400 Mpa) and temperature treatments (20°C–50°C).
To successfully inactivate the resulting vegetative cells after germination, modest pressure-
heat treatments or other less-lethal treatment regimens may be required (Black et al., 2007).

There are issues in ensuring full germination of spores while pressure treatment and ensuring
product lifespan. It may not be economically feasible to sterilize low-acid food using the first
attempts at mild pressure (the Tyndallization process, 300–400 MPa at standard temperature)
for the germination of spores followed by thermal pasteurization (Daryaei et al., 2013).

When pressure and temperature exceed certain thresholds (400-600 MPa and 90°C-120°C,
respectively), the process is called pressure assisted thermal sterilization (PATP). PATP
treatments have been shown effectively target microbes such as clostridium botulinum.
Bacillus sterothermophilus, used as surrogate microbes, is more sensitive to be combined
effects of thermal-pressure processing compared to heat processing alone. However,
identifying surrogate microbes for PATP sterilization remains a challenge (Skinner et al.,
2014).

The tailing in inactivation curves of thermal-pressure combination treatments is distinct from
the typical linear profile of spore inactivation seen after heat processing (Rajan et al., 2006).
The non-linear behaviour of the material requires the application of irregular kinetic models in
order to account for the combined impacts of heat and high pressure on vegetative cells and
spores. This phenomenon has been described using a variety of empirical non-linear models,
such as the biphasic model, log-logistics, Weibull distribution, and nth order kinetics (Nguyen
et al., 2014).. It has also been proposed to use an integrated process lethality model that takes
into account how temperature and pressure affect spore killing.

4. EFFECT OF HPP ON THE CHEMICAL COMPOSITION
OF FOOD

HPP uses pressure, but there is a natural warming effect during treatment due to adiabatic
heating which is depended on the targeted food and chemical composition. Water heats up
a little (3°C for every 100MPa), but fat heats up much more because fat is easier to squeeze.
In figure 1 a representation of the pressure and temperature profile of a typical HPP
treatment is shown (Muntean et al., 2016).

Fig. 1. Pressure, temperature and time during a HPP process.
(Source: (Muntean et al., 2016))
Although there’s some heat, it’s not as harsh as traditional food processing with high
temperatures. This gentler approach means vitamins, flavours, and colours stay put, making
the food more nutritious and tastier. However, HPP can change some things: pressure alone
can gelatinize carbohydrates and high pressure can denature proteins at high temperatures.
Figure 2 shows the pressure-temperature relationship.
The figure 2 shows eggs processed in HPP and using heat. The HPP-treated egg tasted similar
to a raw egg, where the temperature infected had a change in flavour and texture.
Fig. 2. A. An illustration of the protein elliptic phase diagram demonstrating pressure, heat and cold
denaturation.
B. Picture of denatured egg.
(Source: (Smeller, 2002))
5. APPLICATIONS OF HPP
In 1899 Hite pioneered the application of HPP for the preservation of milk and meat, followed
by its application in the preservation of fruits and vegetables.
5.1. Vegetables and fruits
High pressure is primarily employed in fruits and vegetables to deactivate microorganism and
enzymes, thereby extending shelf life while preserving optimal organoleptic, sensory, and
nutritional qualities. Compared to thermal processes, HPP demonstrates enhanced retention of
phenolic compounds, contributing to the preservation of valuable nutritional and functional
characteristics in fruit and vegetables. Along with it, HPP effectively retains the colour and
flavour compounds of these products (Gopal et al., 2017). Combining HPP with thermal
treatment proves to be highly effective strategy against enzyme inactivation, while also
creating textures unattainable through thermal processing alone.
5.2. Cereal
High pressure initiates starch gelatinization through mechanisms distinct from those of thermal
gelatinization. It triggers starch swelling while maintain granule integrity. Starches treated with
pressure exhibit altered thermal properties, with reductions observed in both gelatinization
temperature and enthalpy, along with decreased crystallinity and increased susceptibility to
aggregation within starch granules. At lower pressures, awakening effect on gluten is observed;
however, elevated pressure and temperature conditions (800 MPa, 60°C) induce a
strengthening effect on gluten due to the formation of disulphide bonds facilitated by high
pressure (Bárcenas et al., 2010).
5.3. Dairy
The introduction of high pressure in milk processing aimed to offer an alternative to traditional
pasteurization methods. High pressure processing indirectly affects the coagulation process and
cheese-making properties of milk through various effects on milk proteins, including the
reduction in the size of casein micelles and denaturation of α- lactoglobulin, potentially leading
to interactions with miscellar χ-casein and alterations in colour. HPP also results in increased
pH, decreased rennet coagulation time, and enhanced cheese yield, while accelerating the
ripening process of Mozzarella cheese. Its application to milk is as much for its impact on
functional properties as it is for preservation process. Although cheese made from raw milk is
favoured, it poses a risk of Listeria monocytogenes contamination. Research indicates that HPP
effectively eliminates L. monocytogenes from soft cheese made from raw milk (Clark, 2006).
5.4. Meat
HPP causes alterations in muscle enzymes, meat proteolysis, and myofibrillar proteins, leading
to changes in the structure and texture of meat products. Additionally, high pressure effects
tenderization, gelation, colour, and the extent of lipid oxidation in meat. The inactivation of
microorganisms in meat can also be achieved through high-pressure application, with the
effectiveness depending on various factors such as the type of microorganism, pressure
intensity, processing temperature and duration, pH level, and the composition of the food
matrix or dispersion medium (Rastogi et al., 2007).
6. ADVANCED TRENDS
HPP is making waves in the food industry, with exciting new applications emerging from the
lab. In the next decade, we can expect to see these innovations reach commercial scale. One
area of promise is replacing heat treatment in meat processing. German researchers have shown
that HPP can achieve the same protein gelling and firmness as traditional heat methods while
preserving texture and flavour. This translates to tastier, more nutritious meat products.
Additionally, HPP opens doors for new functional food products.
Another exciting development is meat tenderization. Australian and North American scientists
have discovered that applying HPP shortly after slaughter can significantly improve tenderness.
This is achieved by impacting enzymes involved in the tenderizing process. This technology
offers immense potential for adding value to cheaper cuts of meat (Balda et al., 2012).
Meanwhile, research in US has yielded a different approach. Hormel foods patented a method
using HPP to prevent rigor mortis in meat (Sikes et al., 2010). This leads to juicer, more
flavourful meat by inhibiting post-mortem changes in muscle structure.
Overall, HPP is poised to revolutionising meat processing. It offers the potential for safer,
tastier and mor nutritious meat products, while also creating opportunities to utilize previously
undervalued cuts. These advancements are expected to reach consumers within the next few
years, significantly impacting the meat industry.
However, the technology possesses the following drawbacks:
• Because pressure treatment at room temperature or a lower temperature can effectively
reduce a range of vegetative pathogens by more than five logs, the majority of HPP
goods need to be refrigerated during storage and transit (Huang et al., 2017). Pressure
treatment alone is required to inactivate Harmful spore like Clostridium botulinum.
Low acid HPP products may pose potential microbial risks due to the survival of
clostridium spores.
• HPP requires packaging materials with a compressibility of at least 15%, limiting
suitable options to plastic packaging materials. Therefore, a crucial aspect for the future
advancement of HPP technology in the food sector lies in establishing pertinent laws
and regulations in the countries where manufactures operate.
• This technology is unsuitable for several food types such as low-water-content flour
and powdery flavours or products containing numerous air bubbles, as HPP necessitates
the use of water as pressure transfer from medium and products with air bubbles will
deform under pressure (Naveena & Nagaraju, 2020)
7. CONCLUSION AND FUTURE ASPECTS
HPP emerges as a promising technology with profound implications for various industries,
particularly the food industry. Throughout this report, we have delved into the principles,
applications, advantages and challenges associated with HPP, aiming to provide a
comprehensive understanding of its significance in modern processing technologies. It presents
numerous opportunities for innovation and diversification within the food industry. From
extending the shelf life of fresh juices and ready-to-eat meals to enhancing the safety of raw
seafood and deli meats, the applications of HPP are vast and diverse. Additionally, its potential
extends beyond the realm of food encompassing pharmaceuticals, cosmetics, and material
modification.
However, despite its advantages, HPP is not without challenges. Technical constraints, such as
the need for specialized equipment and packaging materials, limit its widespread adoption,
particularly among small-scale producers. Furthermore, regulatory compliance and consumer
acceptance pose additional hurdles, necessitating concerted efforts to standardise protocols and
educate stakeholders about the benefits of HPP.

Looking ahead the future of HPP appears promising, with ongoing research and technical
advancements poised to address existing limitations and unlock new opportunities. Optimizing
process parameters, exploring novel applications, and integrating HPP with complementary
processing techniques represents avenues for further innovation and growth. Moreover, as
consumer preferences continue to evolve towards healthier, fresher, and more sustainable food
options, HPP is well-positioned to meet these demands, driving market expansion and industry
transformation.

HPP stands at the forefront of modern food processing technologies, offering a sustainable,
efficient, and versatile solution for enhancing food safety, quality and innovation, BY
embracing the potential of HPP and overcoming existing challenges, stakeholders across
industries can harness its benefits to meet the evolving needs of consumers and pave the way
for a more resilient and sustainable future.





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