Pressurization technique: principles and impact on quality of meat and meat products

ABSTRACT

High-pressure processing as a unique technique of meat preservation is being widely used to preserve the meat and meat products by which a commercially feasible product’s production is possible to meet the consumer’s demand with no chemical preservatives and other harmful substances. Pressure treatment could have effects on colour, texture, protein denaturation, and meat microbial stability at ambient or low temperatures; it can help in minimizing the thermal exposure of the meat product to prevent the quality degradation, reduce microbial contamination and improve tenderness. This paper briefly reviews the attention of the high-pressure processing influence on meat product quality, namely texture, tenderness, colour, and microbial. The principles, HPP equipment, challenges, and future trends in high-pressure processing are also discussed.

KEYWORDS:

• Pressurization
• meat products
• texture
• tenderness
• colour
• microbial quality

1. Introduction

High-pressure processing (HPP) is known as cold pasteurization, which facilitates improvements in meat and meat products’ safety against microbial spoilage (Hugas et al., 2002). HPP is an important substitute with consumers’ higher acceptability (Nielsen et al., 2009) for hot pasteurization of meat products. The aim of industrial HPP is to stop pathogenic and perishable microorganisms’ growth and increase shelf life, while almost retaining the meat and its products with good characteristics and quality (Balasubramaniam et al., 2008; Jofré & Serra, 2016).

Heat treatment is the common method by which food processing and preservation are done. The continuous use of heat energy has transformed the food process industry and created a possibility for the long-term preservation of foods. Nevertheless, heat leads to objectionable variations in food nutritional and sensory quality. Therefore, today’s market favours preservation technologies that extend shelf life without harmful effects on the quality characteristics of foods. These types of technologies of food preservation are minimal processing methods. Minimal processing methods include processing procedures that cause a minimal change in the inherent fresh-like quality characteristics of a food item, but prolong the life stability of the food enough to be transported from the food industry to the customers. Among the many minimal processing methods, a non-thermal processing method e.g., high-pressure technology, is of great interest. HPP has gained great acceptance due to its effective commercial use on meat products (Patterson et al., 2007).

HHP is a process that is an emerging food processing technology without thermal impact wherein food is exposed to high hydrostatic pressures (200–700 MPa) by a non-compressible fluid (generally water) at reasonable temperatures (characteristically well lower than 100°C). This technology is important in the food manufacturing industry due to its deactivating microorganisms and biocatalysts at ambient or moderately low temperatures without a contrary impact on the flavour, colour and nutritive components of foods compared to thermal treatment (Hoover et al., 1989). HPT takes a short time with minimal effect on the sensory and physicochemical properties of food, and it increases safety, and shelf-life and reduces microorganisms to satisfactory levels. Thermal processing methods have been generally used in food processing technology. These methods generally decrease the properties of food to the most essential, but a non-thermal method reduces this damage. It is appropriate for foods containing moisture with vacuum in adaptable packaging. RTE products are good examples of HPP makes. HPP deactivates oxidative biocatalyst and pathogens in foods, and it increases storability to more than two times than other approaches (Abera, 2019). HPP extends the shelf-life of shared “lacón,” a cured cooked ready-to-eat product (Del Olmo et al., 2014).

Inevitably, sliced meat products suffer from microbiological recontamination throughout slicing and packaging. The evolution of microorganisms existing from this recontamination may limit the innocuous preservation and shelf-life of these products.

Usually, such preservation problems have only a reasonable effect on dry, cured, sliced products. However, it is a more serious concern for those products with high water activity, high pH, and almost no rival bacterial flora capable of delaying the spread of not good microorganisms. The presence and evolution of lactobacilli are among the main problems that cause advanced acidification of the product and limit product shelf-life to a comparatively short period (Gassiot & Masoliver, 2010). One of the important features of HPP is that it inactivates spoilage and harmful microbe vegetative cells at low and moderate temperatures without degrading the functional and nutritional food quality (Chen & Hoover, 2003; Hugas et al., 2002). HPP is mostly performed as a final hygienization step following production and/or packaging activities to promote food product safety and storage stability.

Keeping these issues in mind, HPP has been used to maximize the safety and freshness throughout the product's shelf-life.

2. HPP principles

According to Yordanov and Angelova (2010), there are three basic principles to control food behaviour during high-pressure treatment.

First Le Chatelier’s principle deals with changes in equilibrium due to applying pressure. It states that pressure enhances any process (phase transition, chemical reaction, variation of molecular configuration) followed by a reduction in volume.

Any process resulting in a reduction in volume like a chemical reaction, phase transition, change in permanent geometry of molecules, increased by pressure. Thus, the HPP in reactions favour the outcome of a volume reduction. When the frequency pressure changes, the equilibrium moves to reduce the volume. Thus, the system is moved to the lowest volume (Srinivas et al., 2018).

Second, the Isostatic principle, which assumes that a uniform application of pressure operates similarly in all directions (Figure 1), is the first concern when applying high pressure. When it decompresses food, the food gains its original shape. This special feature of HPP expands processes that are effectively commercialized (Abera, 2019; Kumar et al., 2018; Sehrawat et al., 2021). A good hydrostatic condition should be time- and space-independent. When a fluid is used to distribute pressure throughout the product, it can be determined. In high-pressure applications, irrespective of food shape or size, the pressure and, more crucially, their impacts are transmitted instantly and uniformly within the food product.

Figure 1. The isostatic processing principle (Yordanov & Angelova, 2010).

This distinguishing feature has facilitated the creation of commercially effective processes. This concept explains why pressure treatment does not cause macroscopical damage to non-porous products with high water content. Although air and water compress differently under pressure, foods with air pockets may have their structure and form altered by pressure treatment unless the food is elastic and composed of closed-cell foam out of which air could exit.

Third, in the microscopic ordering principle, an increase in pressure expands the degrees of the ordering of molecules of a particular substance at a constant temperature. The temperature and pressure exert opposing influences on molecule structure and chemical reactions (Yordanov & Angelova, 2010). It is necessary to consider the net combined pressure-temperature influence on the treated foods product to understand the impact of HPP on foods fully.

Food products undergo a decline due to pressure applied at the compression stage, as shown in Figure 2. Before decompression, the product is subjected to pressure for just a while. The product will normally return to its original volume when decompression of the product takes place (Farr, 1990). when the product is under pressure, the compression and decompression, could cause a transient temperature variation in the product. As an outcome of physical compression, the temperature rises in food.

Figure 2. Pressure and temperature effect profile during HHP of food (Muntean et al., 2016).

3. Pressure–temperature impact

Figure 2 shows the impact of pressure–temperature on the product. The temperature of the product at process pressure is not dependent on compression degree till heat exchange is reached as minimal or negligible between the product and the surroundings. When a properly insulated (adiabatic) system is decompressed, the product goes back to its previous temperature. However, due to heat losses during the compression phase, the product will revert to a temperature that is slightly lower than its initial temperature. The rapid heating and cooling caused by HPP processing provide a one-of-a-kind approach to enhance the temperature of the material mainly during the treatment and immediately cool it afterward. During room temperature, every 100 MPa of increased pressure raises the water temperature by around 3°C.

Fats and oils have a heat of compression value of 8–9°C per 100 MPa, while proteins and carbs have a heat of compression value of intermediate (Ganessingh et al., 2018; Juliano et al., 2012; Patazca et al., 2007; Rasanayagam et al., 2003).

4. HPP equipment

The HPP equipment consists of a high-pressure vessel and its closures, such as a pressure-generation system, a temperature monitoring device, and a material handling system (Figure 3) (Mertens, 1995; Van den Berg et al., 2001). The most significant component of high hydrostatic-pressure systems is the hydraulic vessel. When designing a vessel, several factors need to be considered. The vessel should be engineered to be dimensionally stable fail safely. If it fails, it should do so with a leak rather than a fracture. The pressure transmitting fluids are employed in the vessel to impart pressure to the products specimen equally and instantly. Water, inert gases, silicone oil, castor oil glycol solutions, sodium, ethanol solutions, and benzoate solutions have been the most often used fluids (Yaldagard et al., 2008).

Figure 3. A schematic diagram for working of the high-pressure technology equipment.

Flexible packaging should be used to pack the food items. The items are stacked and placed into the high-pressure chamber. The vessel is charged with a pressure-transmitting fluid and closed. To facilitate operation and suitability with food products, high pressure is frequently carried out with water as a hydraulic fluid. Compressing the water surrounding the item is the basis of applying high pressure to it. At room temperature, as pressure builds up, the volume of water drops. Because fluid compression creates a minimal volume change, high-pressure vessels that use water do not pose the same operational risks as vessels that use pressurized gases (Balasubramaniam et al., 2016).

When the desired condition is achieved, the pump or piston is turned off, the valves are closed, and the pressure may be maintained without any additional energy. The vessel subsequently is decompressed by removing the pneumatically fluid after keeping the item for the required time at the desired pressure. Most items are kept at 600 MPa for 3–5 min in most applications. It is feasible to cycle at a rate of 5–6 cycles every hour, permitting compression, holding, depressurization, filling, and discharging. After pressure treatment, the processed product is taken from the vessel and kept as usual. High pressures can be generated by direct or indirect compressionand heating the pressure fluid (Elamin et al., 2015; Heinz et al., 2009). Direct compression is achieved by pressurizing a fluid with a piston pushed by a low-pressure pump at its bigger diameter end. The high-pressure dynamic shield between the piston and the internal surface of the vessel limits this procedure to small-diameter laboratory or pilot plant systems, but it permits very speedy pressurization (Farkas & Hoover, 2000). Pumping a pressure medium from a storage tank into a sealed, high-pressure vessel until the appropriate pressure is achieved using a high-pressure intensifier is indirect compression (Figure 4). The pressure medium is heated by expanding the pressure fluid as the temperature increases to generate high pressure. When high pressure is combined with high temperature and very precise temperature control is required throughout the pressure vessel's internal volume, this approach is used (Palou et al., 2020).

Figure 4. Working principles of direct and indirect pressurization equipment.

5. Impact on quality of meat and meat products

5.1 Texture and tenderness

Many investigations have examined the effect of pressure on meat quality since the 1980s. Because of the interest in employing high pressure for beef tenderization, meat texture was the most researched quality feature in early studies (Simonin et al., 2012). Meat texture is strongly influenced by the connective tissue (principally collagen) and contractile (primarily actomyosin) systems. Collagen's triple helix is primarily balanced by hydrogen bonds, so, it is relatively inert to pressure under normal conditions. Indeed, pressure treatment at 150 MPa increased the thermostability of tendon collagen , from 58 to 64°C, as expected from the volume increase associated with the rupture of these bonds (Macfarlane, 1985). As a result, this baseline toughness is unlikely to be amenable to pressure treatment. The rupture of electrostatic and hydrophobic interactions within protein molecules following the re-development of intra- and intermolecular bonds within anf between protein molecules are the main causes of high-pressure impact on proteins (Galazka et al., 1995).

Tenderization of meat generally is caused by multiple transformations within the muscle during conditioning because of natural protease activity: Actin–myosin interactions are impaired, myofibrils are subdivided into smaller segments due to Zline disintegration, the connective tissue is weakened, and elastic filaments containing connectin are damaged (Koohmaraie, 1994). The study investigates the impact of high pressure on meat proteins and helps understand why raw meat changes texture and tenderness when subjected to pressure. The high pressure causes myofibril fragmentation to increase, as does ageing since myosin filaments dissociate and -actinin is released (Iwasaki et al., 2006). In addition, other changes occur in high pressure-treated meat proteins, which could explain the increase in hardness. When pressures of up to 300 MPa are applied to turkey meat, acto-myosin swells, increasing meat hardness (Scheibenzuber et al., 2002). Myofibrillar cross-sections are transformed under pressure of more than 300 MPa: myofibrils become unrecognizable forms, while myofilaments are fragmented (Jung, Ghoul, et al., 2000a; Scheibenzuber et al., 2002). To improve tenderness in the beef muscle, subject it for 20–30 min to 150–200 MPa at 60°C (Ma & Ledward, 2004; Macfarlane, 1973; Sikes et al., 2010). Jung, de Lamballerie-Anton, et al. (2000b) showed disorientation of myofibrils in post-rigor beef muscle exposed to high pressure (100–600 MPa, 10°C, 4.3 min); however, this did not lead to an increase in tenderness. It was determined that high pressurization of post-rigor beef was inadequate for getting better tenderness under the conditions tested.

Meat from several animal species changes texture resulting in a reduction in protein volume during HHP treatment. The solubilization of peptide bonds and amino acid-branched chains, volume of internal cavities, and the constitutive volume of atoms, all contribute to the volume of a protein in a solution. Because the interior cavities are compressed when high pressure is applied, the volume of a treated protein is reduced (Sun & Holley, 2010).

The structural and textural changes in HPP-treated meats are also associated with the denaturation of proteins (Khan et al., 2014; Yang et al., 2016). It has been often reported that the principal components of meat responsible for toughness are the myofibrillar and connective tissue proteins. The contribution of the myofibrillar component is greatly influenced by post-slaughter processing procedures, whereas that of the connective tissue proteins is largely determined during the life of the animal. The effects of HP on proteins, such as protein denaturation and aggregation, significant changes in actin–myosin interaction, -actinin release, and denaturation of myofibrillar proteins, could be directly associated with changes in meat texture (Chevalier et al., 2001; Guyon et al., 2016). HP causes tissue compression by creating new protein interactions (Jantakoson et al., 2012), resulting in fibre compression and connective tissue restructuring (Briones-Labarca et al., 2012; Hurtado et al., 2001). HP-induced tissue and fibre compaction may be attributable to sarcomere length reduction. A possible softening effect associated with the disintegration of myofibril structures has also been identified during HP processing (Ashie & Simpson, 1996).

Ma and Ledward (2004) observed the effects on the texture of beef meat and found that when increasing pressure up to 400 MPa causes an increase in hardness, after which there is a light decrease as the pressure is increased further at 20°C. Similarly, when pressure was applied to the cod muscle, the hardness increased up to 400 MPa but decreased (Angsupanich & Ledward, 1998).

In meat, the changes in product structure and texture occur due to proteolysis and the solubilization of myofibrillar proteins (Sikes et al., 2009). High pressure improves the tenderness of fresh meat (Macfarlane, 1973), but increases hardness up to 400 MPa of post-rigor meat (Ma & Ledward, 2004) Sikes et al. (2009) showed high pressure used to improve the texture of low-salt beef sausage batters. There was an increase in hardness and fracture strength with increasing pressure, significantly different from the non-pressure-treated control at 200 MPa (0.1 MPa). Hardness and fracture forces declined with increasing pressure between 200 and 400 MPa, and were not different from the control at 400 MPa. Pressure dramatically reduced cohesiveness, which differed from the control at 200 and 400 MPa. The increase in hardness of the duck meat samples treated with high pressure alone was attributed to muscle compaction, whereas the decrease in hardness of the samples treated with high pressure before or after thermal treatment than those of high-pressure-alone samples was attributed to the changes in muscle by modifications in meat protein conformation, protein denaturation, aggregation and gelation (Khan et al., 2014).

According to Fernandez et al. (1998), chicken batters treated under 200 MPa resulted in higher hardness and chewiness in the product compared to non-pressure-treated samples, whereas chicken batters treated under 400 MPa having coarser, more irregular, less compact, and aggregated structures. The springiness, cohesiveness, and chewiness were all reduced in these samples. This phenomenon might be described partly because high pressure protects meat proteins against heat denaturation (Fernández-Martín et al., 1997).

5.2 Meat colour

Discoloration of poultry, lamb, beef, and pork, is common after high-pressure treatment. The degree of colour change is determined by the meat's chemical and physical state, particularly myoglobin and the atmospheric effects before and after pressurization. The oxidation of the bright red oxymyoglobin or the purple deoxymyoglobin into the brown metmyoglobin, and myoglobin denaturation, are responsible for the diminished redness. Compared to white chicken flesh, beef has a higher myoglobin level, making it more susceptible to discoloration. Furthermore, HP treatment produces denaturation and aggregation of myofibrillar proteins, changing surface reflectance and increased lightness (Bak et al., 2019). Table 1 shows colour variations of different HP-treated meats and meat products at different pressures and temperatures. According to Raman spectroscopy of pork meat pressurized at 600–700 MPa, pressure caused oxymyoglobin to be converted into metmyoglobin, which can be further changed into a denatured ferrous. Because of its brownish appearance, such nonnative ferrous deoxy forms of myoglobin are highly undesirable and are likely to cause oxidative destruction of other such muscle constituents (e.g. lipids). In pork meat, deoxidation of myoglobin was also eventually beneficial since deoxymyoglobin seems to have a high-pressure resistance but can be transformed into a pressure-induced deoxymyoglobin (Buckow et al., 2013).

Table 1. Colour variations of different types of HP-treated meats and meat products.

Meat Products	Treatment conditions	Effect on Colour parameters			Causes of colour changes	Reference
		L*	a*	b*
Minced beef	Under 200, 300 MPa, 20°C for 20 min	Decrease	Decrease	Usual	Denaturation and oxidation	Hassan et al. (2002)
Fresh minced beef meat	Under different pressures of 50, 100, 150, 200, 250, 300, 350, 400, 450 MPa and temperature of 20°C for 10 min	L* increase under 150, 200, 250, 350 MPa but usual in L* value under 350–500 MPa	Usual from 50 to 300 MPa but Decrease in a* value under 350–500 MPa	Usual	Denaturation and oxidation	Carlez et al. (1993)
Beef carpaccio	Under 450 MPa and 12°C for, 5, 10, 15 min	Increase	Decrease	Decrease	Denaturation and oxidation, other structure and surface properties pretentious	De Alba et al. (2012)
Dry cured beef	Under 500 MPa and 18°C for 5 min	Usual	Usual	Usual		Rubio et al. (2007)
Fresh and cooked pork loin	(I) Under 414 MPa and 2°C, 9 min, (II) At 414 MPa and 25°C for 13 min	Increase	Usual	Increase		Ananth et al. (1998)
LD	At 200–800 MPa and 20°C for 10 and 5 min	Increase	Increase	Increase	Denaturation, oxidation, Ferrohemo chrome	Bak et al. (2012)
Minced pork	Under 600 MPa and 20°C for 30 min	Increase	Increase	Increase	Denaturation and oxidation	Goutefongea et al. (1995)
Fresh pork sausage	Under 414, 552 MPa and 25°C and 50°C for 0–16 min	Increase				Huang et al. (1999)
Ground pork patties	At 300 MPa and four different temperatures 5°C, 20°C, 35°C, 50°C for 15 min	Increase	Decrease	Decrease under 50°C but increase under 20°C and 35°C	Denaturation and oxidation	López-Caballero et al. (2002)
Meat batters and cooked emulsion sausages	At four different pressure, 100, 200, 300, 400 MPa and 10°C for 2 min	Increase	Decrease	Increase	Denaturation of protein and Oxidation	Yang et al. (2015)
Dry-cured pork loin	Under three different pressures, 300, 350, 400 and 20°C for 10 min	Increase	Decrease		Denaturation of protein and Oxidation	Campus et al. (2008)
Cooked ham	At 600 MPa and 20°C for 10 min.	Usual	Usual	Usual		Pietrzak et al. (2007)
Uncooked and cooked ham	Under 500, 600 MPa and 3°C for 1 min	Increase	Usual	Usual	Denaturation of protein	Pingen et al. (2016)
Chicken breast fillets	Under 300–600 MPa and 15°C for 5 min	Increase	Increase	Increase	Denaturation of protein and oxidation	Kruk et al. (2011)
Breast fillets	400 MPa and 5°C for 1–20 min + multiple cycles of 10 min	Increase	Increase	Increase	Denaturation of protein and oxidation	Del Olmo et al. (2010)

The application of pressure of more than 200 MPa has dramatically altered the appearance of red meat after only a few minutes of treatment at low temperatures (Bak et al., 2019; Ledward, 2000; Tintchev et al., 2010). Major structural proteins in the muscle denatured as pressure were increased (Cheah & Ledward, 1996; Zhang et al. 2015), leading to an opaque colour of the flesh and further decreasing the visibility of other meat colours. Usually, after pressure treatments exceeding 250 MPa, the lightness (L values) of red meat increases dramatically, while the redness (values) decreases, resulting in grey-brown meat with a cooked appearance (Jung et al., 2003; Tintchev et al., 2010). Numerous colour changes in cured meat have been observed because of HP treatment. Generally, L* usually increases or stays stable after HP treatment, but a* and b* tend to decrease or remain unaffected. Some studies attribute the increase in lightness to increases in the myofibrilla component, namely protein denaturation resulting in higher light reflectance, comparable to uncured meat. Due to the initial heat denaturation of proteins, no additional increment in L* is detected after HP treatment in cooked, cured meat (Goutefongea et al., 1995).

Undoubtedly, the conditions of the HP treatment (most importantly, pressure and temperature) will impact the influence of ham colour. Compared to higher pressures treatment, low pressures of about 300 MPa have minimal impact on colour. Nevertheless, also at low pressures, myoglobin denaturation could be seen in porcine longissimus dorsi (LD) (Bak et al., 2012).

Korzeniowski et al. (1999) observed that after 100 MPa HP treatment, 28% of myoglobin had been denatured, increasing to 66% denaturation of myoglobin after 400 MPa HP treatment. The observed colour variations were explained by a rise in the quantity of denatured myoglobin. Consequently, HP treatment at 100 and 200 MPa led to a slight increase in brightness, leading to a red-light colour, but then at 300 MPa, the colour turedn to pale pink, and at 400 MPa, the colour turned to greyish white. Massaux et al. (1999) noticed a change in colour parameters in the case of an increase in L* and a lowering in a* when pressurized the pork LD at low pressures (50, 100, and 200 MPa) Chun et al. (2014) was unable to detect any colour changes in LD successfully treated at pressures lower than 150 MPa. Many investigations have shown a lightness effect threshold pressure of approximately 300–400 MPa. As a result, again, no gain in lightness with increasing pressure could be evaluated beyond 400 MPa (Bak et al., 2012; Shigehisa et al., 1991; Tintchev et al., 2010). This is most probably due to myofibrillar and sarcoplasmic protein denaturation at pressures exceeding 300–400 MPa (Cheah & Ledward, 1996).

Minced beef meat is pressurized at 10°C for 10 min. L* colour values increased significantly in the range 200–350 MPa, the meat becomes pink, while a* values decrease at 400–500 MPa, the meat becomes grey-brown. The colour of minced beef meat was pink when pressurized at a pressure above 200 MPa and converted into grey-brown at above 400 MPa. L* values increased between 200and –350 MPa, and a* values decreased as pressure increased, particularly at above 400 MPa, whereas b* values persisted constantly. For minced beef meat pressurized at below 150–200 MPa and 20°C, there was no colour change, L* increased at 150–400 MPa, and a* decreased at above 350 MPa. Meat discoloration under pressure appears to be caused by “whitening” (200–350 MPa) and destruction of bright red (400–500 MPa). Critical pressure thresholds could be caused by various phenomena (Carlez et al., 1993, 1995).

Figure 5 shows that after treatment under pressures between 200 and 250 MPa and room temperature (20°C), beef, pork, turkey, and chicken meat only altered in brightness, whereas higher pressures led to a significant meat discoloration, ranging from intense red to pale pink (350 MPa) and white and grey colour (450 MPa) (Tintchev et al., 2010).

Figure 5. Colour variations of different type of meats under high pressure processing at different pressure (0–600 MPa) for 5 min at room temperature (20°C) (Bak et al., 2019).

5.3 Microbial meat quality

Pressurized treatment is a food preservation technique that is mild for food while efficiently inactivating spoiling bacteria and foodborne microorganisms in many foods (Argyri et al., 2018). This practice was adopted to inhibit the microorganism’s growth and enzymes in muscle foods with minimum impact on flavour, colour, and nutritional quality (Hygreeva & Pandey, 2016). On low-sodium sliced vacuum-packaged turkey breast treated with a natural antibacterial agent, a study was conducted to examine the optimization of high hydrostatic pressure (HHP) processing for microbial inactivation (carvacrol). The HHP factors influenced the mortality rates and syneresis of the products investigated (p > 0.05), but not the pH values and lipid oxidation. Treatment at 600 MPa/180 s (at 25°C) is suitable for the tested low-sodium product, according to the required operating conditions for Listeria post-lethality treatment (Oliveira de et al., 2019).

Escriu and Mor-Mur (2009) found that Salmonella Typhimurium and L. innocua levels in chicken breasts were reduced immediately after HPP treatment. Yuste et al. (2000) evaluated the effects of pressurization under the treatment of 500 MPa at 65°C for 5 and 15 min, respectively, and heating pasteurization at 80–85°C for 40 min on cooked poultry sausages. They have found that against lactic acid bacteria and Listeria spp., the pressure was more effective than heat, and both treatments were quite efficient against enterobacteria. During the 18-week refrigerated vacuum storage of compressed sausages, Listeria spp. and enterobacteria grew minimally or not at all. HPP is a technology currently adopted by the meat industries to assure the safety of numerous hams or sausages items, as meat-derived goods are increasingly offered vacuum and sliced packaged. High-pressure pasteurization of poultry products and cooked meat is a viable alternative to heat pasteurization.

In general, the higher the pressure and the longer the time, the greater the microbicidal effect. For psychrotrophs and mesophiles, the highest reductions in counts were observed in poultry meat-treated samples at 450 MPa as 6.0 and 2.8 log CFU per gram, respectively (Yuste et al., 2002).

Fernandez et al. (2007) discovered that pressurizing beef muscle (M. longissimus dorsi) under 650 MPa at 20°C for ten minutes reduced TVCs. Due to the low initial numbers, no changes in LAB counts were seen in this study, whereas no changes in Enterobacteriaceae counts were found. Considine et al. (2008) used a treatment of 400 MPa at 50°C for 15 min to inactivate a pressure-resistant E. coli. The rate of inactivation observed (5–6 log decline) could not be obtained with just 50°C or 400 MPa. When temperature and HPP are used alone, they can produce significant microbial inactivation, but when these two treatments are combined, inactivation rates are significantly increased, especially for bacterial spores. High-pressure effects on microorganisms are well known and acknowledged. Recent research suggests that cell membrane changes are the most common cause of cell death. At high pressure, ribosome fragmentation has decreased cell viability.

Molds and yeasts are more responsive to pressure than bacterial vegetative cells. Ascospores, on the other hand, could be highly tolerant to extreme pressure. The microorganism species and their growing environment have a great impact on cell sensitivity. It’s more difficult to destroy bacterial spores under pressure. To accomplish total spore inactivation, many combinations of temperature, time, pressure, and cycling treatments could be applied. Most food parasites, in other directions, may be killed by very low pressures (200–300 MPa). A high-pressure treatment under 400–600 MPa, 7–18°C, 5–10 min, is usually effective for falling the enterobacteria number below the detection level in products having high water activity, such as cooked ham, marinated beef loin, or blood sausages (Simonin et al., 2012).

The pressure treatment influence on microorganism inactivation and storage life extension of raw pork loin (smoked) and pork ham (cooked) was investigated. These samples were packed in bags (polyethylene) under vacuum and subjected to HPP at 300–600 MPa for 10–30 min. The findings demonstrate that applying 300–400 MPa pressure for 10 min had not prolonged the ham product shelf-life.

Microbiological variables, including total bacterial count, psychrophylic bacteria, acidophylic bacteria, and e. coli in samples tested kept in refrigerator environments for 4 weeks, were significantly reduced by applying 500 MPa for 10 min. The population of all pathogens tested was decreased by 105–106 fold when 600 MPa pressure was applied for 10 min (Karłowski et al., 2002).

Pseudomonas fluorescens, Citrobacter freundii, and L. innocua were effectively eradicated by compressing fresh beef products to 200, 280, and 400 MPa for 20 min, respectively. Low (4°C) and high (50°C) holding period temperatures resulted in the greatest inactivation. The same scientists discovered that microbial growth was slowed from 2 to 6 days at 200–300 MPa at 20°C while analyzing the development of bacteria during storage.

Pseudomonas sp., Lactobacillus sp., and coliforms had been totally inactivated during HPP treatment at 400–450 MPa, however, regained after storing at 3°C in the atmosphere. Only Pseudomonas survived storage under vacuum (after 9 days). Cooked beef products were treated under 408, 616, and 888 MPa (maximal temperatures during holding period ranging from 14.4°C to 28.4°C), respectively, with estimated microbiological spoiling durations of 27, 70, and >98 days. Salmonella and L. monocytogenes peaked at 2.5 log CFU/g were not eliminated completely by treating sliced ham at 400 MPa for 10 min at 17°C, although its concentrations were significantly reduced to >1 log CFU/g. Both pathogens were suppressed during the storage period at 1°C. But L. monocytogenes grew to 6 log CFU/g after 84 days at 6°C (Jofré & Serra, 2016). Linton et al. (2004) Studied the influences on the microbiological quality of vacuum-packaged, minced treated chicken meat under hydrostatic pressure, and they found a fast rise in the aerobic count of meats after 8 days of storage at 3°C. This demonstrates the potential for HP to enhance the microbiological safety of processed meats. Bover-Cid et al. (2017) reported that HPP affected the reduction of Salmonella enterica of dry-cured ham. When the applied pressure intensity was increased, the rate of elimination of S. enterica levels in dry-cured ham increased. S. enterica lethality was relatively minimal in research conducted at pressures up to 450 MPa, with log reductions ranging between 1.41 and 3.00 CFU per gram. At varying temperatures, 20°C and 40°C, meat samples were compressed under 200, 300, and 400 MPa. For monitoring, the safety of meat, microbiological quality of beef was tested HPP immediately and during 7 days storage period °C. Now after storage, all pressurized samples had bacteria counts that were well below the detection limit. HPP resulted in lower levels of TVCs, indicating a method for improving meat hygiene and increasing the storability of raw meat. At various pressure levels, HPP has been an excellent approach to minimize TVCs in meat. These results show that applying high pressure to meat at low or moderate temperatures enhances its microbial safety while minimizing the impact on the meat’s quality (McArdle et al., 2010).

Porto-Fett et al. (2010) evaluated that applying combined a pressure of 483 MPa and a temperature of 19°C for 5 min for dry-fermented Genoa salami, resulted in a 100% decrease of the initial 5 logs (CFU per gram) of E. coli incubated into dry-fermented Genoa salami (characterized by pH values between 4.56 and 4.66 and aw values between 0.884 and 0.940). Numerous studies have already shown that exposing meat and meat products to a pressure of 600 MPa at 20°C for 180 s can kill the causative agents of listeriosis (Listeriamonocytogenes) and inhibit other life-threatening microorganisms such as E. coli, Salmonella, Vibrio, often these types of mould fungi, and pathogenic bacteria with little effect on taste, flavour, texture, appearance, and nutritional value of food (Diachkova et al., 2019).

With increasing pressure and pressurization duration, L. innocua survival in chicken meat samples was reduced. The effect of temperature on bacterial survival was not linear, with larger reductions at 0°C and 40°C compared to treatments at 20°C. Pressure, time, temperature, and the interaction of pressure and temperature were all significant parameters. After 10 min of treatment at 400 MPa and 0°C, no bacteria were found. Nevertheless, over 35 days of storage at 3°C, Aerobic Counts grew and surpassed the original level of microbial load (108 cfu/g) in all chicken meat samples (Bulut et al., 2014).

In high-pressured chicken patties samples, a total reduction of psychrotrophic microorganisms and lactic acid-forming bacteria growth was identified and a substantial decrease of mesophilic bacteria. HPP treatment under 500 MPa, at 10°C for 10 min, increased the storability of chicken patties by up to 3 weeks (Pietrzak et al., 2011). The use of high pressure under 600 MPa at 20°C for 10 min extended the storage life of vacuum-packed ham significantly (Pietrzak et al., 2007). The effect of high pressure on the inactivation of microorganisms in different types of meat products is shown in Table 2.

Table 2. HHP influences on microorganisms’ inactivation in different types of meat products.

Meat product	Microorganisms	Treatment (MPa/min/°C)	Inactivation (log CFU/g)	Reference
Chicken breast fillet	Escherichia coli	300/ 5/ 15	1.69	Kruk et al. (2011)
Chicken breast fillet	Salmonella typhimurium	450/ 5/ 12	0.64	Kruk et al. (2011)
Chicken breast fillet	Listeria monocytogenes	300/ 5 /12	3.22	Kruk et al. (2011)
Sliced dry-cured ham	Salmonella Enteritidis	400/ 5/ 12	1.02	De Alba et al. (2012)
Sliced dry-cured ham	Salmonella Enteritidis	600/5/12	4.32	De Alba et al. (2012)
Sliced dry-cured ham	Salmonella Enteritidis	500/5/12	2.54	De Alba et al. (2012)
Dry-cured ham	L. monocytogenes	450/5/11	0.32	Bover-Cid et al. (2011)
Dry-cured ham	L. monocytogenes	347/9/16	0.05	(2011)
Minced beef	Pseudomonas flourescens	200/20/20	5	Carlez et al. (1993)
dry-fermented Genoa salami	E. coli	483/5/19	5	Porto-Fett et al. (2010)
Cooked ham	Staphylococcus carnosus	500 10 40	1.29	Hugas et al. (2002)
Cooked ham	Lactobacillus sakei	500/10/40	4	Hugas et al. (2002)
Cooked ham	L. monocytogenes	400/10/17	2.01	Aymerich et al. (2005)
Cooked ham	L. monocytogenes	600/5/15	≥ 3.79	Jofré et al. (2008)
Fermented sausages	L. monocytogenes	600/5/15	0.96	Rubio et al. (2013)
cooked chicken	Listeria survivors	600/2/20	0.02	Patterson et al. (2011)
Pork slurries	Pseudomonas aeruginosa	300/10/25	≤_6	Shigehisa et al. (1991)
Pork slurries	Candida utilis	400/10/25	≤_6	Shigehisa et al. (1991)
Pork slurries	Micrococcus luteus	500/10/25	≤_6	Shigehisa et al. (1991)
Pork slurries	St. aureus	600/10/25	≤_6	Shigehisa et al. (1991)
Raw chicken meat	Listeria monocytogenes:	375/15/18	5	Simpson and Gilmour (1997)
Mechanically recovered poultry meat	Aerobic mesophiles	450/15/20	3.7	Yuste et al. (2001)
Frankfurt sausages	Aerobic mesophiles	500/15/65	6.14	Yuste et al. (2000)
Raw beef	Aerobic mesophiles	560/4/10	2.5	Jung et al. (2003)
Marinated beef loin	Aerobicmesophiles	600/6/31	6.51	Garriga et al. (2004)
Sliced cooked ham	Aerobic mesophiles	400/20/7	2.34	López-Caballero et al. (1999)
Sliced cooked ham:	Aerobic mesophiles	300//15/20	0.3	López-Caballero et al. (2002)
Cooked ham	Aerobic mesophiles	600/6/31	>2.45	Garriga et al. (2004)
Fried minced pork meat	Bacillus stearothermophilus	400/6020	2	Moerman et al. (2001)
Dry fermented pork sausage	Listeria monocytogenes	400/10/17	0.6	Jofré et al. (2009)
Dry cured chorizo sausages	Aerobic mesophiles	350/15/20	<1	Ruiz-Capillas et al. (2007)

6. Challenges and future trends in HPP

Consumers are increasingly concerned about healthful food, particularly meat products low in salt, nitrite, and polyphosphates. We must evaluate how to balance customer demand with microbial contamination affecting food safety. yet HPP can make it feasible to create meat products with few food additives. The HPP technology boosts the value proposition of products by extending storage life by lowering the microbial load, and maintaining texture, tenderness, and colour. Furthermore, it increases the shelf-life of the meat and meat products, lowers the defect rate, and aids in expanding the meat and meat product's target markets. HPP technique is a popular manufacturing alternative for retaining meat product quality due to its non-thermal processing characteristics. In addition, there are some advantages of this technique: Meat product size and shape do not affect high pressure. High pressure is time-/mass-independent, which means it operates instantly, minimizing processing time. It may be used at room temperature, lowering the amount of heat energy required for meat processing in traditional methods. Meat product is kept uniformly throughout without any particles escaping the treatment because HPP is an isostatic process, and this method is environmentally beneficial because it uses just electricity and produces no waste. But there are some drawbacks: Bacterial spores in meat and meat products are extremely pressure-resistant and require extremely high pressure to be inactivated. Enzymatic and oxidative breakdown of particular meat product components is caused by persistent enzyme activity and dissolved oxygen. To maintain their organoleptic and nutritional properties, numerous pressure-processed foods require low-temperature storage and distribution, and the meat products lack a cooked appearance and can lose flavour quickly. The non-covalent link, covalent bond, and protein structure of myofibrillar proteins were also modified. To be accepted, a full understanding of the HPP principle and its implementation is required. Although it was noted in certain places that there is a distinct kind of meat with its HPP range, the meat suitable/unsuitable for HPP and the packaging material of HPP treated meat should be clearly stated and understood. Consumer approval should also be evaluated. As a result, establishing applicable legislation and regulations is a significant problem for the future expansion of HPP technology in the meat market. Well-defined process conditions will assure microbiological safety, product quality, and compliance with food hygiene rules and regulations in the countries where the manufacturers are situated. HPP technology may potentially be coupled with existing trends in the meat business to help the meat industry grow. For example, high-quality fresh meat and functional, healthy meat are future development prospects in HPP. However, the influencing factors on the qualities of meat under HHP are complicated, and further research is needed.

7. Conclusion

HHP treatment can be used as a promising technique for meat tenderizing and texturizing benefits and to preserve the meat products. The impacts are most typically found in more extreme. HP treatments are textural features changes and discoloration, with mechanisms exhibiting interdependence of processes. High-pressure treatment is a reliable method for inactivating microorganisms and controlling their activity in meat and meat products during storage. Based on microbial load and product nature, pressures from 400 to 600 MPa are usually required to ensure effective microbial inactivation. Much research is now being conducted on the use of high pressure to texturize meat products. It is now popular to adopt high pressure to specific products to achieve combined texturization and pasteurization. High pressure is no longer considered a simple substitute for normal pasteurization, but rather as a method to develop unique meat products. Finally, microbial inactivation with no significant meat colour changes and good texture using HP treatment could offer the meat industry an effective tool to prolong meat product storage life; therefore, market boundaries internationally.

Acknowledgements

We thank HOD, Chemical Engineering, Adigrat University for the assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).