Potential of high-pressure homogenization (HPH) in the development of functional foods

ABSTRACT

The main problem on a global scale is the demand for functional foods among consumers in terms of healthy diets and wellbeing. In this context, high-pressure homogenization (HPH) is a new technology with a variety of potential uses in the food industry, such as the modification of food biopolymer structures to direct their functionalities, the creation of nanoemulsions, the inactivation of microorganisms and enzymes, and the disruption of cells for the extraction of intracellular components. Furthermore, new opportunities for homogenization processing have been opened up by recent developments in high-pressure homogenization technology. This has made it possible to produce novel products that can be recognized from traditional ones by sensory, structural, or functional attributes. The fact that the product experienced heavy mechanical stresses during the process, such as cavitation and shear forces, is the cause of all these consequences. It has been suggested that HPH may have a role in the creation of functional probiotic dairy products and other beverages with enhanced sensory qualities in the functional food industry. Additionally, it has been demonstrated that HPH can change the volatile-molecule profiles of milk and beverages, increase specific cellular enzymatic activities, inhibit microbial growth, strengthen the probiotic properties of bacterial strains, extend shelf-life through microbial inactivation, and extend shelf-life with minimal effects on nutritional value and sensory qualities. Therefore, this review compiles and summarizes the workings, benefits, and applications of HPH in the food industry.

KEYWORDS:

• Consumer’s interests
• Homogenization
• High pressure processing
• Functional foods
• Probiotics

Introduction

Food industries have long relied on homogenization for stabilizing food emulsions and breaking macromolecule globules in liquid foods^[1]. Nowadays, the new tendency of macromolecule modifications focuses on the utilization of “green” physical treatments including pulsed electric field microwave, ultrasonic, homogenization and high-pressure processing.^[1,2] These emerging technologies are also often investigated as a replacement of conventional methods to minimize the effect of heat on food components while ensuring microbial safety and preserving nutrients as well as sensorial properties, and, in some cases, improve techno-functional properties.^[3] High-pressure homogenization (HPH) represents a potential non-thermal approach to develop new functional applications, easily implementable at industrial level.^[4] This technology has recently undergone a considerable modification, aiming at investigating new application areas for the food processing business, allowing the building of larger emulsions and the alteration of not just macromolecule aggregates but also some food constituents.^[4] HPH is the process of rapidly increasing the speed of a fluid through a narrow space valve with extreme pressure intensifiers, culminating in depressurization and high shear stress. Subsequently, the fluid cells, particles and macromolecules are exposed to enormous mechanical pressure, twisting and deforming them into nano-sized particles.^[5–7] It also causes a decrease in air pressure, leading to more turbulence, shear stress, temperature rise and cavitation. HPH offers interesting possibilities to restructure food proteins, affecting protein conformation, leading to protein denaturation, gelation or aggregation and, consequently, creating new products with new/improved texture.^[4,8] Dynamic high-pressure (DPH), a new form of high-pressure homogenization technique, combines forces of high-velocity impact, high-frequency vibration, immediate pressure drop, cavitation, strong shear and ultra-high pressures up to 200 MPa. Numerous food sectors utilize dynamic high-pressure treatments ranging from 15–200 MPa to break fat droplets, stabilize emulsions and disrupt microbial cells.^[9] Between 100 and 250 MPa, pH-induced inactivation of the Gram-negative bacteria was reported.^[10]

Functional foods are those that have been licensed to carry label claims that a person using them may expect to achieve enhanced health through their intake. These foods are concerned with the relationship between foods or food components and health and are believed to confer particular health advantages. Due to growing knowledge of how the gut microbiota affects the host, consumer health consciousness, and worries about the nutritional value of food, producers now place a strong emphasis on the promotion of functional foods.^[11] According to Jiang et al.^[12] and Brown et al.,^[13] these functional foods can be either natural or processed and fortified with active ingredients that have been shown to have bioactivity and therapeutic effects. According to Champagne et al.,^[14] probiotic meals and supplements are getting more and more well-liked. It is essential to preserve food quality through the application of innovative technologies because customer tastes, needs, and acceptances change over time.^[15] According to Guerrero et al.^[16] and Martin-Rios et al.,^[17] consumer cultural background, customs, and even sustainability factors can all affect the technological advancements used in the food manufacturing industry. Although probiotic cultures are present in naturally fermented foods, many people rely on manufactured items (including supplements) due to mouth feel issues or perhaps a requirement for a specific starter culture.^[18]

Commercial operations have to be able to provide adequate beneficial microbes, get them isolated from the growing medium, and store them as a base for future use.^[19] Industry and researchers are looking at new evolving technologies and biotechnological approaches to develop functional but innovative food items that are safe, high-quality, and nutritionally helpful in response to the growing interest for valuable health beneficial foods. The ones that involve non-thermal product treatment are the most essential as they retain much of the nutritional characteristics of the food besides providing them extended shelf stability.^[20–22]

Ultra high-pressure homogenization (UHPH), a part of high-pressure processing, often referred as dynamic high pressure (DHP), is a continuous process that is better suited to liquids^[23] that operate at a pressure of up to 400MPa. The pressure range has since been increased to 50 MPa by traditional homogenization. Modern high pressure homogenizers support pressure ranges between 300 and 400 MPa and permit pressures 10–15 times greater than conventional ones. The move toward UHPH has also given rise to novel possibilities for sterilizing, such as the HPH-mediated inactivation of spores. The temperature achieved during the UHPH treatment is determined by the inlet temperature of pumpable products and the level of pressure, which have both been identified as the primary determinants of microbial inactivation.^[24] Several HPH systems are currently accessible for laboratory work; however, they are also available for industrial scale processing and design of innovative foods with enhanced functions compared to HPP.^[10,25] Keeping into consideration the benefits of HPH in the field of food processing especially novel functional foods, the current review focusses on the background, principles and applications of HP in food industry with special emphasis on the development of novel functional or nutraceutical-rich food products.

Mechanism

A positive hydraulic pump, nozzle, and a homogenizing valve are the three main components of a homogenizer, as shown in Figure 1.^[26] The homogenizing valve assembly contains a small opening between the valve and the valve seat through which the fluid is forced under pressure. An impact disk becomes clogged with the fluid as it exits the aperture in the form of a tangential stream. Finally, it leaves the homogenizer with a low velocity and ambient pressure. The effluent from a homogenizer is often chilled to avoid overheating the product because frictional heating caused by high fluid velocity increases product temperature by 2.0 to 2.5°C for every 10 MPa increase in pressure.^[27] The working pressure is maintained by controlling the distance between the valve and the seat during homogenization because the fluid in front of the injector has a high velocity that is converted to kinetic energy when it enters the nozzle.^[27] The process’s pressure and temperature readings are the two most crucial variables that affect how big the food particles and how many microbes are present in them. Cavitation, flow conditions, and pressure all have an impact on droplet disruption. The globules are exposed to a strong impulsive force when a pressure drop (cavitation) and HPH are present.

Figure 1. High-pressure homogenizers: schematic pathway (Adapted from Vinchhi et al., 2021).

A novel homogenization chamber design and a replacement method for producing fine emulsions were launched in the early 1980s, enabling the delivery of machinery capable of producing and managing extremely high pressures in fluids exceeding 100 MPa up to 300–500 MPa. Any traditional homogenizer system uses a high-pressure generator, such as a positive-hydraulic pump, in conjunction with a high-pressure intensifier to push the process liquid through a specifically designed homogenizer valve assembly.^[28] The material is pressured and pushed through two spatially arranged micro-channels at a high rate, similar to the usual valve homogenizer, causing unfavorable distortion and disintegration of microorganisms and other cell structures. The tertiary or quaternary structures of macromolecules may be affected by mechanical stresses produced during high-pressure homogenization treatment. Any modification to a molecular structure may trigger a mechanism that repairs some of the features that high temperatures have harmed. The piston valve (Figure 1) is useful for destabilizing cell structures, creating nanosuspensions and nanoemulsions, creating solid lipid nanoparticles, and inactivating microorganisms.^[29,30]

Background

According to Saricaoglu et al.,^[31] homogenization is a unit process that reduces particles or droplets to micron sizes to produce a stable emulsion or dispersion. It comprises of a high-pressure pump that pushes particles through narrow tubes, greatly shrinking and evenly dispersing them. Inside the fluid, gas-filled bubbles (or voids) develop and grow. The collapse of such holes could cause a variety of localized stresses to be transmitted to interfaces or particles, particularly microorganisms, when the local pressure is lowered without changing the temperature.^[32]

Turbulence, cavitation, and impingement are the three main ways that homogenization pressure affects fluid.^[33] Homogenization causes the proteolysis, lipolysis, and glycolysis of microbial cell walls (Martinez et al., 2017). According to Donsì et al.,^[34] homogenization pressure is the result of the intensifier’s (homogenizer’s) internal pressure building up as it passes through the system’s pipes and fittings and effectively stresses bacterial populations. The HPH has been recognized as an efficient approach for microbial cell denaturation due to the ability of microbial spores to endure extreme conditions, typically in conjunction with additional physical-chemical barriers for cell survival and/or reproduction.^[35] HPH also improves the accessibility of bioactive components, the microstructure, and the rheological properties of food.^[7,31,36] According to Zamora and Guamis,^[24] and Donsì et al.,^[37] UHPH is a continuous process procedure that optimizes pressure effects and homogenization cavitation, producing shear forces and turbulence, in order to sterilize and physically stabilize pumpable fluids, food, or other types of fluids under aseptic circumstances. In comparison to conventional homogenizers, HPH or dynamic HPH can withstand pressures that are 10–15 times higher and has an operating pressure range of 100–400 MPa with a maximum pressure range of 300–400 MPa.^[38] The EU Craft project “UHPH 512,626, Development and Optimisation of a Continuous Ultra High-Pressure Homogeniser for Application on Milk and Vegetable Milk” and national sponsored initiatives created two innovative concepts allowing UHPH treatment at 9 L/h and 120 L/h. According to Zamora and Guamis,^[24] the initiatives looked into UHPH technologies for the production of safe foods, the eradication of hazardous microorganisms, the removal of carcinogenic or poisonous substances, and the improvement of operating pressure of prototypes produced. The highest pressure level attained, which depends on the homogenizer system and factors like valve design, gap size, and seals, differs significantly between UHPH and HPH. According to Balasubramaniam et al.^[39] and Zamora & Guamis,^[24] UHPH may achieve pressures of up to 400 MPa while HPH can reach pressures of 50 to 200 MPa. The dynamic UHPH treatment had a considerable impact on the whey protein structure and greatly improved the surface hydrophobicity. Additionally encouraged was the exchange reaction between the sulfhydryl group and the disulfide bond. This obviously had an effect on the solubility, frothing, emulsifying, and thermal properties of whey protein.^[40] HPH alters the solubility, interaction characteristics, viscosity, and other physico-chemical properties of macromolecules by reducing their particle size and structure. HPH at 100 MPa and one pass enhanced the functioning of proteins from the hazelnut sector, according to Saricaoglu et al.^[31] The homogenization pressure raised the zeta potential and water solubility of proteins while reducing their particle size. By using HPH at 100 MPa and 10 passes, Hua et al.^[41] showed how tomato waste fibers underwent a microstructural change. The authors converted 8% or so of the insoluble fibers into soluble fibers.

Since thermal processes frequently have undesirable side effects like nonenzymatic browning, cooked flavor, or the loss of essential components, HPH treatment has been used as an alternative to thermal methods for inactivating enzymes and microbes in recent years.^[39] The use of HPH to lower the microbial load in fruit juices has been the subject of extensive research. According to Tabanelli et al.,^[42] the number of passes and the addition of citral had an effect on the bacteria that cause deterioration. They discovered that the number of passes had a linear relationship with the viability of yeast cells, with the number of passes decreasing as the number of passes increased. Additionally, the addition of citral enhanced the effects of HPH, extending storage by 6–8 days. The same authors evaluated how HPH treatment at 100 MPa affected the viability loss of S. cerevisiae 635 inoculated at a level of roughly 6.0 Log10 cfu/mL in apricot juice and various foods. Apricot juice was just 2.2 logarithmic cycles per mL after four passes at 100 MPa, a significant reduction. Eight passes at 100 MPa were insufficient to completely render the implanted cells inert in carrot juice. Due to the apricot juice’s higher viscosity and sugar content, they arrived to the conclusion that more HPH treatment runs were required to reduce the yeast load.^[43]

HPH in food industry

More nutrient-dense meals are in demand from consumers, as are methods that are more microbiologically effective without compromising the nutritional and sensory characteristics of food (Figure 2). The use of high-pressure processing is environmentally sustainable since it doesn’t require the addition of chemicals and addresses specific difficulties with food product quality and productivity without affecting the product’s overall characteristics.^[44,45] HPH Applications for improving the technological functionality of food components and inactivating enzymes have been studied. Depending on the circumstances of the reaction, high pressure treatments can change the secondary, tertiary, and quaternary structures of enzymes to increase the number of hydrophobic sites, reveal amino acid and sulfhydryl groups, and induce modifications in enzyme functionality. Additionally, recent research has focused more on the direct and indirect effects of HPH on bioactive molecules.^[4] In many aspects, the majority of HPH use is still in laboratories or on a small scale. Commercially accessible HPH units have a limited industrial usage due to operating at maximum feasible pressure levels with flow rates below industrial requirements and, in some cases, significant energy consumption.^[46]

Figure 2. Schematic illustration representing attributes of high pressure homogenization in the food sector.

Dairy products

Homogenization has been widely employed in the dairy industry since mid-nineteenth century, mostly to stabilize the food emulsions and rupture lipid globules. Homogenization at higher pressure values not only results in the generation of fine emulsions but also in the reconfiguration of either lipid globules or food components. In addition, it results in the partial inactivation of intracellular microorganisms due to the mechanical disruption of cells.^[47] HPH was envisioned as a one-of-a-kind integrated process milk approach that combines various advantages of traditional milk homogenization and sterilizing into a sequential manner.^[48] As a result, it is comprehensible that several studies targeted on the HPH process of dairy and dairy-based product (Table 1).

Table 1. Effect of HPH on dairy products.

Dairy product	Processing conditions	Treatment	HPH units	Interpretations	References
Hazelnut milk	Hazelnut cake was grounded for 10 min; 100 g were homogenized in 1 L of water for 10 minutes at 10,000 rpm in an Ultra Turrax homogenizer.	25–150 MPa; inlet temp = 15°C	GEA NiroSoavi, Panda PLUS 2000	With a monomodal particle size distribution, particle size is reduced. Microstructure and rheological characteristics have been enhanced; Increased flow behavior index from 0.15 to 0.36 and reduction in consistency from 91.82 to 0.51 Pa.s” friction loss; Greater values of G′ than G′depicting that samples could be described as a soft-gel network.	Gul et al.^[Citation49]
Whole milk	Using a Hyperjet 94i-S pump system, the milk was HPH processed from 125 to 500 MPa in 125 MPa intervals.	125–500 MPa; Inlet temp = 5°C, 55°C	Flow Internationals Corp., Hyperjet 94i-S pump system	Fat content reduction in the supernatant fraction and consequent rise in the percentage of precipitate; When entire milk was treated utilizing HPJ (High pressure jet) processing at 375 MPa, viscosity elevated from about 2 to 5 mPas. Foam inflation rose from about 80 to 140% after processing at > 125 MPa.	Tran et al.^[Citation50]
Condensed Skim milk (CSM)	High-pressure jet (HPJ) processing of condensed skim milk (CSM) at 100–500 MPa yielded skim milk powders, which were then spray dried.	100–500 MPa; Inlet temp = 25–30°C	Flow International Corp., Hyperjet 94i-S waterjet pump System	Increased apparent particle density (1.25 g cm^−3) and less solubility (93.2%) at 500 MPa; Greater foam inflation index and volume stability index at 400 and 500 MPa; At 500 MPa, the highest emulsion stability index is achieved.	Hettiarachchi et al.^[Citation51]
Skim milk	ND	100–500 MPa; Inlet temp = 10°C	Flow International Corp., Hyperjet 94i-S waterjet pump system	Increase in viscosity at pressure > 300MPa; Emulsion activity Foam inflation, stability indexes, and foam volume at pressures of 300 MPa and above; At 400 and 500 MPa, milk has a bimodal particle size distribution. Formation of uniform and non-uniform Protein aggregates higher than molecules	Hettiarachchi et al.^[Citation52]
Yogurt	homogenization in a single – phase at 15 MPa, supplemented with 3% SMP (Skim Milk Powder)	200, 300 MPa; Inlet temp = 30°C, 40°C	Stansted Fluid Power Ltd. homogenizer, model FPG 11,300	Yogurt made from milk processed at 300 MPa and thermally treated milk have equivalent organic acid and volatile carbonyl compound profiles; Yogurt made from milk processed at 300 MPa and thermally treated milk have equivalent organic acid and volatile carbonyl compound profiles;	Serra et al.^[Citation53]

Milk

According to Patrignani et al.^[54], HPH is frequently used in fermented milk for a number of reasons, including (1) regulating sensory attributes without sacrificing shelf life and nutritional quality; (2) enhancing the probiotics’ technical performances; and (3) altering the functional characteristics of Lactic Acid Bacteria (LAB). HPH is advised for usage to sterilize and homogenize milk in a single step since it reduces the microbial load of milk. According to several studies,^[48,55,56] using high pressure (>150 MPa) and high temperature (>40°C) effectively reduces bacterial load. Researchers have looked at how conventional homogenization (20 MPa, 60°C) and HPH at 100 MPa at various temperatures (4–60°C) affect the size of milk fat aggregates and the amount of proteins and phospholipids. According to the findings, when the temperature and pressure increased, more milk proteins were able to bind to the milk fat globule membrane (MFGM). Additionally, it has been demonstrated that HPH lowers the phosphatidylcholine in MFGM and raises sphingomyelin levels in milk.^[57]

Additionally, it has been discovered that HPH of milk increases the coagulation properties of the milk due to a switch between insoluble and soluble phosphorus, nitrogen, and calcium components.^[58] Pereda et al.^[59] studied the impact of ultra-high-pressure homogenization (UHPH) on the quality and shelf-life of milk while stored at 4°C. Applications of high pressure included 100, 200, and 300 MPa (single stage) with a milk input temperature of 40°C and 200 and 300 MPa (single stage) with a milk inlet temperature of 30°C. The UHPH-treated milks and high-pasteurized milk (90°C for 15 s) were contrasted. The milk treated at 200MPa at 30°C had the longest shelf life (about 21 days), indicating that the thermal effect on milk was less than that of the high pasteurization treatment. The pH of milk did, however, noticeably decline at 200 MPa and 30°C. Other UHPH treatments resulted in a shelf-life of 14 to 18 days, which is comparable to the time period seen for highly pasteurized milk. After treatment, UHPH was found to be just as effective at reducing total bacteria and psychrotrophic lactococci as high-pasteurized milk, lowering the microbial load to 3.50 log cfu/mL.^[59]

Yoghurt

In the production of milk products and a variety of other acid-coagulated farm products, homogenizing is a frequent process. It plays a crucial part in creating an intriguing mouthfeel texture and stability by reducing the size of the fat globule and allowing milk proteins to bind to the fat globule interface. This is because cavitation and high shear forces cause the fat globule to disintegrate into smaller fat globule particles. It has been demonstrated that HPH alone, even at 350 MPa, is unable to consistently increase gel strength as compared to traditional heat treatment, such as at 90°C.^[60] Serra et al.^[53] discovered that the milk supplemented with 3% skim milk powder homogenized traditionally (15 MPa) and thermally treated at 90°C for 90 s had significantly lower structural integrity than the set yoghurt gels made from homogenized milk at 200–300 MPa at 30 or 40°C inlet temperature (3.2% protein, 3.5% fat). Raising the homogenization pressure reduced the particle size, allowing for the creation of finer, whiter emulsions with improved physical segregation resilience. The yoghurt substitute had a gel-like consistency and had the same temporal span as yoghurt manufactured from milk. The pressure stability of the yoghurt substitute revealed the least amount of phase separation with an increase in homogenization (200 MPa). Similar to commercial yoghurt prepared from plant replacements, it has a similar water retention capacity and lightness value.^[61] The protein molecules undergo a brief period of high pressure, cavitation, shear, turbulence, and temperature rise during HPH. Plant substitutes such soybean globulins were able to unfurl and aggregate as a result of HPH treatments. The proteins’ ability to emulsify was enhanced by an ideal treatment pressure (150–200 MPa).^[61] Additionally, adding probiotic (health-promoting) microorganisms to various yoghurt- or fermented milk-based products can enhance their already well-known health benefits. Although, Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus, the traditional starter cultures of yoghurt, are not typically a part of the native microbiota of the mammalian intestine and have limited survival after oral intake, they actually improve the nutritional content and digestibility of yoghurt.^[26]

Cheese

Zamora et al.^[62] looked into the impact of single or two stage ultra-high-pressure homogenization (UHPH; 100 to 330 MPa; 30°C inlet temperature) on the cheese-making qualities of bovine milk. The study’s findings demonstrated that treating milk with UHPH lowered the size of the fat globules, increased the wet yield and moisture content of the curd, and decreased the protein content of the whey. Single-stage UHPH at 200 and 300 MPa improved the rennet’s coagulation capabilities. The effects of raw, heat-pasteurized (72°C for 15 s), and traditional homogenized-pasteurized (15 + 3 MPa, 72°C for 15 s) treatments were compared. According to Zamora et al.,^[62] the combined effects of heat and homogenization may have altered the protein-fat structures of milk, improving its ability to produce cheese. According to Patrignani et al.,^[54] HPH has the potential to produce probiotic fermented milk, bio-yoghurt, and probiotic cheeses with increased sensory or functional qualities. The nutritional value of fermented milk, as well as other characteristics including acidity, lipid content, the presence of diacetyl, acetaldehyde, and acetoin, are significant and have an impact on customer acceptance.

Lodaite et al.^[63] evaluated the impact of HPH on the rennet coagulation properties of reference and skim milk using model systems. HPH-induced changes to casein molecules and fat globules resulted in a noticeably different gelling process even in milk with little to no fat. Natural spoilage organisms like Listeria monocytogenes in cheese-making brines were rendered inactive after five passes of low HPH treatment (150 MPa).^[64] Traditional homogenized milk (15 MPa 1st stage/3 MPa 2nd stage at 60°C), pasteurized milk (300 MPa at 30°C) treated milk, without starter fresh cheese, and pasteurized milk all demonstrated greater lipolysis, proteolysis, and moisture loss.^[65] Furthermore, sublethal HPH (50 MPa) treatment of Lactobacillus paracaseiA13 cells led to the production of short-ripened probiotic caciotta cheese. This led to the expansion of sustainable and clean label products thanks to decreased cheese maturing costs (during chilled storage).^[58]

Ice cream

We looked at the usage of HPH and micro fluidization for making frozen sweets. The method holds potential for the creation of frozen desserts since the scale, stability, and shape of the droplet size are crucial for creating an appealing texture, stability, and organoleptic characteristics of the completed product. HPH has enhanced the frozen dessert’s texture quality. It was discovered that ice cream prepared from a 5% fat combination homogenized at 100 MPa had a texture similar to ice cream made from an 8% fat mixture homogenized at atmospheric pressure (18 MPa). As a result, HPH offers a lot of potential for enhancing the textural characteristics of frozen sweets with lower fat^[66,67]

Probiotics

According to studies, HPH technology may be used in the production of probiotic cheese. According to Gobbetti et al.,^[68] crescenza cheese can be stored at low temperatures and doesn’t require extensive ripening, making it a good probiotic bacteria carrier. The organoleptic qualities of the cheese suffered as a result of the probiotic bacteria’s inclusion. According to Patrignani and Lanciotti^[26] and Bevilacqua et al.,^[69] HPH can positively affect and modulate the metabolic activity of microorganisms. Probiotic microorganisms have undergone HPH (50 MPa) treatments to change functional characteristics like hydrophobicity, interaction with the small intestine, resistance to simulated gastric conditions, auto-aggregation, and stomach-duodenum passage, as well as higher microbial viability over refrigerated product storage^[33]Asithambi et al.,^[70] Recent research (Table 2)^[73] suggest that HPH regulates and enhances the fermentative and probiotic activities of several Lactobacillus species. By using this technique, Tabanelli et al.^[42] were able to enhance a number of the functional properties of well-known probiotic strains. The fermented milk was subjected to a pressure of 60 MPa in order to maintain the probiotic strain’s high viability during preservation and enhance its rheological properties. The milk’s dry matter and fat content were 3 and 1.5%, respectively. During homogenization, temperature and shear stress reduce the size of milk fat globules, break down casein micelles into tiny particles, and thermally degrade various whey proteins, particularly lactoglobulin. This makes it easier for probiotic bacteria to grow and thrive with the remaining ingredients.^[74,75] found that HPH treatment of milk increased the viability of Streptococcus thermophilus and Lactobacillus delbrueckii ssp, while refrigeration of yoghurt promoted the development of S. thermophilus vs. L. delbrueckii ssp. bulgaricus supported the development of S. thermophilus, lowering the risk of post-acidification. According to Tabanelli et al.,^[76] when given to BALB/c mice, sub-lethal HPH processed cells of L. paracasei A13 elicited a stronger IgA response. By producing free fatty acids and free amino acids, which are crucial for probiotic bacteria’s growth and viability, increasing homogenization temperature (50–70oC) and pressure (100–200 bar) simultaneously has a significant impact on the sensory qualities and survivability of probiotic bacteria in yogurt during storage.^[15,77] Bacterial cells are one of the most frequent causes of failure dairy fermentations, and raw milk is a substantial source of phages in milk products.^[78] (1996, Cogan and Accolas). Probiotic bacteria counts increased as a result of the inhibition of probiotic phages at 100 MPa (Suarez and Reinheimer, 2007).^[43] One of the most pressure-sensitive targets is the cell membrane, which helps isolate bacteria from their environment. Cell membranes can react in a number of ways to lessen sub-lethal stress. Changes in membrane composition result in changes in the physical properties of cell surfaces.^[79,80]

Table 2. The utilization of HPH in probiotic food items.

Probiotic strain	Inoculation concentration	Cells homogenized	Food item	Treatment	Effect on activity/Results	Reference
L. paracasei A13; L. acidophilus DRU	8 log CFU/mL	Yes.	Butter milk	Pressure: 50MPa; inlet temperature: 20°C; increase rate of temperature 3°C/10MPa	Strains viability of 7.6 log CFU/mL at pH (7, 4.6) throughout refrigerated storage period (30 days)	Tabanelli et al. (2015)
Lb. paracasei A13	7 log CFU/mL	Yes.	Caciotta cheese	50MPa; Inlet temperature: 20°C; improved rate of temperature was 2.5°C −10 MPa/s	Increase in Lb. paracasei gastric resilence in cheese and viability 5 log CFU/g after 14 days of storage.	Burns et al.^[Citation58]
Lb. rhamnosus BFE5264	8 log CFU/mL	No	Milk	60MPa	More than a 60-day period of storage, viability was retained as 6.0 log10 CFU/g in milk.	Patrignani et al.^[Citation26]
Lb. casei and Lb. acidophilus	6 log CFU/mL	No	Crescenza cheese	100 MPa	1% increase in cheese yield; viability maintained as 8 log CFU/g after 12 days of refrigerated storage	Burns et al.^[Citation81]
Lactobacillus salivarius	9 log CFU/mL	No	Mandarin juice	0, 20 and 100 MPa; 0, 100, 300 g/Kg of trehalose	With a pressure of 20 MPa and 100 g/kg of trehalose, 106 (CFU)/mL were generated in mandarin juice after a 10-day prolonged storage	Betoret et al. (2017)
Lactobacillus acidophilus	10^8 and 10^9CFU/ml	No	Yoghurt	220 and 660 MPa	Yoghurt showed survivability rate of 6 × 10^7CFU/mL during 14 days of storage	Roostazadeh et al. (2016)
Lactobacillus paracasei BFE 5264	6 log CFU/mL	No	Milk	20–100 MPa; inlet temperature: 2–4°C; the elevated rate of temperature: 3°C/10 MPa	The cell counts of the strain Lb. paracasei after HPH treatment varied from 8.5 to 9.0 log CFU/g.	Patrignani et al.^[Citation71]
L. salivarius spp. Salivarius	8.44 log CFU/mL	Yes	Clementine juice	25, 50, 100 and 150 MPa; 10 or 20% trehalose	Total phenol, flavonoid content and antioxidant activity were improved when 10% of trehalose was added.	Barrera et al.^[Citation72]
S. thermophilus Sty1 and Lactobacillus delbrueckii subsp. Bulgaricus Lby1	ND	No	Milk	60 MPa; inlet temperature 5°C	After 35 days of refrigerated storage, the viability remained as 7 log CFU/g	Patrignani et al.^[Citation82]

Fruit juices

It represents a fantastic strategy on employing HPH to limit microbial load and retaining the standard quality of the perishable product, still as moving the physical features, including viscosity. Tahiri et al.^[83] and Lacroix et al.^[84] centered their analysis on fruit juice, examining the potential of HPH technology to inactivate harmful and spoilage bacteria. They found out the result of HPH alone or along with pre-warming on pectin methyl esterase (PME) activity, which is assumed to cause the loss of opalescence of orange juice during storage.^[84] Results revealed that, upon a multi-cycle treatment (5 cycles) of HPH (Emulsiflex C5) at 200 MPa and 25°C, Lactobacillus plantarum diminished by 2.3 log units, Leuconostoc mesenteroides by 6 log units, 2.5 log units for Saccharomyces cerevisiae, 4 log units for Penicillium ssp., and 6 log units for Escherichia coli (5 log units for three cycles of HPH).^[83] Five cycles of HPH treatment lowered the activity of pectin methylesterase in fruit juice at 170 MPa (Emulsiflex C50). HPH-treated juices, on the other hand, were much more stable, owing to changes in their pectin structure, which reduced the substrate available to PME, as well as a reduction in pulp particle size. Mechanisms of microbial inactivation by HPH processing are the outcomes of several phenomena viz. cavitation, shear stress, turbulence, and impingement, which emerge during the food treatment.^[26] The process has also been proven to inactivate or modulate the activity of enzymes that lead to the phase separation in fruit and vegetable juices, to preserve the initial juice color, flavor, and aromas and to retain the nutritional and functional characteristics of the matrices.^[85] Furthermore, when it comes to sterilization, HPH contributes in the preservation of the freshness of fluids and texture^[84] (Table 3). HPH also has a considerable impact on the rheological characteristics of juice.^[90] HPH reduced the suspended particle size and dispersion (which became narrower) in tomato juice, resulting in enhanced particle and suspended particle interaction. As a result, the HPH technique increases the consistency, thixotropy, viscosity and elastic properties of the product.^[91] As a result, despite the benefits of avoiding juice deposition, the HPH method can also be utilized to minimize the utilization of hydrocolloids for a more uniform juice.^[92] A study looked into how pomegranate juice’s microbiological, nutritional, and organoleptic qualities were altered by high-pressure homogenization (HPH). HPH at 100 and 150 MPa were compared to thermal pasteurization at 55, 65, and 75°C for 15s, as well as combined treatments, on juices. Both treatments exhibited a minor impact on the physicochemical parameters of pomegranate juices, including color, pH, acidity, and total soluble solids. Using HPH at 150 MPa followed by heat treatment at 65°C, a considerable microbiological inactivation for the juices containing Escherichia coli and yeast was accomplished during 28 days of shelf life. Electronic tongue and nose examination of treated HPH samples indicated flavor attributes that were identical to those of fresh juice.^[93] Several authors have also verified the efficacy of this treatment on several matrices such as vegetable milks,^[49] vegetable and fruit juices (Briñez et al., 2006),^[94] milk (Lanciotti et al., 2004a), milk-based products,^[77] and liquid whole egg (Velazquez-Estrada et al., 2008), suggesting that the combination of HPH with further hurdles viz. low storage temperature and low pH prolongs the shelf life of foods.^[95]

Table 3. Effect of HPH on fruits.

Fruit juice	Pre-processing conditions	Treatment	HPH units	Interpretations	References
Annurca apple	To prevent browning, 4 sections of one apple were soaked in a chemical bath containing 0.2% wt. ascorbic acid and 1% wt. citric acid. blanched and sieved (1 mm screen) to eliminate fibrous material; combined with water (50:50) and sugar to a final concentration of 15 g/L; 20 minutes of centrifugation at 9000 rpm	150–300 MPa; temp = 4 and 37°C	Stansted Fluid Power Ltd.	Extended shelf life; microbial stability; samples held at 37°C showed physical destabilization, color changes, and pH changes, reducing shelf life and necessitating refrigeration to retain organoleptic and nutritional attributes.	Donsì et al.^[Citation34]
Cashew apple	Cashew apple pulp thawed overnight and diluted to 10°Brix with deionized water; final pH was 5.0	Up to 150 MPa; inlet temp-25°C	Panda Plus, GEA Niro Soavi, Italy	Mean particle size reduced with elevated pressure resulted in rheological changes like increase in flow behavior index, and decreases in yield stress, consistency coefficient, ζ-potential and product thixotropy	Leite et al.^[Citation86]
Concentrated orange	thawed at 5°C overnight; conditioned at 25°C before processing; stored at −18°C	150 MPa	Panda Plus, GEA Niro Soavi, Italy	Reduced consistency index, Mean particle size decreased; thixotropy and improved its flow behavior index; no impact on color and storage time.	Leite et al.^[Citation86]
Orange	The sample was sterilized in an autoclave at 121°C for 15 minutes before being processed at 8°C.	100, 150, 200, 250, 300 MPa; Inlet temp-10 degree celsius	Stansted Fluid Power Ltd (UK), model nG7400H:350	Initial loads of 1.2 107 CFU/mL of Lactobacillus plantarum and 2.9 105 CFU/mL of Saccharomyces cerevisiae in the sample were entirely destroyed by pressures greater than 250 MPa.	Campos and Cristianini (2007)
Banana	Banana puree was defrost overnight at 10 degrees Celsius; combined with drinking water (1:1 w/w) at 4 degrees Celsius and pH 4.8; and kept at 4 degrees Celsius till HPH.	150–400 MPa	GEA Niro Soavi S.p.a., Parma, Italy and NS1001L-PANDA 2K GEA Niro Soavi S.p.a., Parma, Italy	At 4 degrees Celsius, pressures greater than 200 MPa were required to achieve a 4 log unit reduction in total mesophilic bacteria and pectate lyase inactivation.	Calligaris et al.^[Citation87]
Organic Kiwi	Kiwi were sorted by homogeneous size, with a diameter of 40 mm, a length of 80 mm, and a refractometric index of 13 1 °Brix; juice was extracted using a lab extractor (Russell Hobbs, 27700–56) and divided into three 5-L batches, after removing the seeds, and subjected to different UHPH treatments at 0.1 MPa.	200MP a, 2–3 cycles at temperature-5, 15,and 25°C	PANDA high pressure homogenizer (GEA, Parma, Italy)	The use of 200 MPa for three cycles resulted in a kiwifruit juice that was stable for more than 40 days in chilled conditions; naturally occurring yeasts (2.4 log CFU/mL) were reduced to 1 log CFU/mL. Between 27 and 32 days at 5°C, the control juice met the microbiological spoilage criterion of 6 log CFU/mL.	Patrignani et al.^[Citation88]
Tomato	Diluting a commercial 30 °Brix pulp in distilled water yielded 4.9 °Brix tomato juice.	100MPa	Panda Plus, GEA Niro Soavi, Italy	The tomato juice’s particle size distribution (PSD), serum cloudiness (turbidity), pulp sedimentation behavior, color, and microstructure were altered.	Kubo et al.^[Citation89]
Pomegranate	ND	150 MPa and thermal temp = 65°C for 15s	SPV flow, Soeborg, Denmark	3 log CFU/mL reduction of microbial load	Benjamin and Gamrasni.^[Citation93]

Wine

The first attempt to use HPH for must and wine production was made in the 1990s. The extraction of phenolic constituents and color, and the deactivation of uncontrolled microbes in grape, juice, and wine, has long been known to be affected by high hydrostatic pressure.^[8,10,20] When HPH was used to stabilize must, it proved to be a successful method for increasing the prevalence of industrial non-Saccharomyces yeast strains. Inoculation with S. cerevisiae was carried out using these microorganisms in a stepwise manner. S. cerevisiae, a unique strategy to decrease wild microbe competition, regulating wine alcoholic fermentation, and permitting the reduction of sulfur dioxide addition, paved the way for organic winemaking and SO₂-free wines.^[10,96] HPH changes yeast cell fatty acid content by raising the proportion of un saturated fatty acids in comparison to saturated fatty acids (SFA), according to Serrazanetti et al.,^[80] Since the significance of USFA in yeast metabolism is well understood, this finding could lead to new approaches to yeast nutrition and pre-fermentative activities.^[80] Total yeasts (2.9 × 10⁵CFU/mL) were entirely killed from red wine in 30 minutes and 10 minutes at 300 MPa and 350 MPa, respectively; LAB (2.9 × 10⁵ CFU/mL) were eradicated in 5 minutes at the latter pressure range.^[97] Puig et al.^[98] examined the impact of HPH on native fauna in Trepat and Parellada musts, finding that HPH procedure at 200 MPa was able to effectively destroy LAB (5 and 3 log units decline in Trepat and Parellada musts, respectively), with only a small residual total bacterial count other than LAB detected in both musts. As a result, microorganisms can be completely inactivated at pressures more than 250 MPa. Patrignani et al.^[94] were the first to report on the possibility of using HPH for yeast autolysis. For sparkling wine refermentation, HPH treatment at 90 MPa was given to several yeast isolates such as S. Bayanus and S. cerevisiae before they were used for the manufacture of tirage solutions. At 25°C, all strains were given a final pressure of about 6 bars; the treatment had little effect on yeast viability or refermentation behavior, but SEM demonstrated that HPH hastened oxidative degradation over a 40-day aging period. As a result, the researchers hypothesized that HPH could trigger the autolytic enzyme pool thereby, causing enzymatic spoilage in food items.^[94]

Development of nano-sized food additives

Proteins are widely utilized as the major stabilizer in food emulsions to achieve stability. Low-molecular-weight emulsifiers and proteins decrease coalescence by lowering the surface tension between the emulsified interfaces and a complex molecular layer around the suspended particles^[99]Perrier Cornet et al., 2005). HPH treatments can cause molecular modifications within the compounds with gelling and advantageous qualities, as established by Corrading and Wicker (2001), for pectin and Flory et al. (2002), for methylcellulose. HPH processing at 300 MPa increased the desired properties of whey proteins by dissociating bulky proteins without affecting protein stability, leading in improved frothing and stabilizing capacities.^[100,147] For beverages and various types of foods during storage, nano emulsification and nano dispersion by HPH were applied to improve the stability and avoid coalescence of additives, as well as for ß-carotene nano dispersions as an active ingredient in food formulations.^[101] HPH treatment has been demonstrated to improve the solubility of dry whey product and spice microemulsions, increase their dispersibility, permeability, and flavoring ability, and alter spice compatibility with food.^[102] HPH treatment enhances the formation of collagen micro and nanofibers while also boosting the film’s performance, increasing the application of collagen materials in biodegradable/edible packaging in industry.^[103]

HPH may be applied in the manufacture of nano emulsion systems comprising ß-carotene enhance O/W emulsions stabilized by Tween 20 and decaglycerol monolaurate, as well as biopolymers (WPI and modified starch).^[104] Another investigation by Ribeiro et al. (2006) indicated that cooperating in an o/w emulsion boosted carotenoids bioavailability, thereby boosting their health-promoting characteristics. Furthermore, Mao et al. (2010) used HPH in tandem with the homogenization/solvent displacement technique to develop a nanoemulsion containing carotenoids. HPH was utilized by McClements et al. (2012) to generate a variety of 5 wt percent o/w emulsions stabilized by modified starch and with various lipid-phase compositions (orange oil: maize oil).

Encapsulation of bioactive compounds

High Pressure homogenization method could be employed to enhance the nutritional qualities of meals by encapsulating bioactive components in the food systems (Table 4). It is feasible to improve food functionality by boosting stability, conservation, and regulated delivery to specific areas.^[65,105] HPH creates powerful disruptive forces that split particles into manageable sizes, making it easier to encapsulate specific components in a suitable medium. The efficiency of the process, as well as the bio accessibility of the bioactive chemical, might be influenced by mechanical stress, related heating, and emulsifier interactions.^[1] For encapsulating roasted coffee oil/poly L-lactic acid (PLLA)/poly hydroxybutyrate-co-hydroxy valerate (PHBV) ultrasonic and high-pressure homogenization (HPH) emulsification procedures were utilized. For PLLA systems, the maximum oil recovery was reached by sonification while HPH emulsification is the most important oil recovery method for PHBV systems.^[106,107] Utilizing a high-pressure homogenizer, the process of emulsification involves two steps: (i) creating a coarse emulsion using a high-shear mixer, and (ii) passing the coarse emulsion through a narrow vent at a high speed and pressure to produce smaller droplets. The emulsions’ zeta potential, polydispersity index (PDI), zeta potential, bioactive retention, and turbidity are significantly influenced by high-pressure homogenization (HPH). It can create small-sized lycopene nanodispersions for use in beverage products that have a narrow PDI and good stability.^[108] In order to enhance the encapsulation procedure and the properties of the finished product, a number of possible applications have also been integrated into the emulsification method.^[109] For example, emulsion-ionic gelation, emulsion-interfacial protein crosslinking, emulsion-solvent evaporation, and emulsion-diffusion have all been investigated for beta-carotene with improved thermal and storage stability and enhanced intestine-specific delivery,^[110] Castor oil has an encapsulation effectiveness of 72–91% and an emulsion size of 159–220 nm, whereas, beta-carotene has a nano-emulsion diameter ranging from 9 to 280 nm and good physical stability and a smaller emulsion size of 159–220 nm (Park & Yang, 2013). Furthermore, the use of HPH showed an inverse effect on the Peclet number, increased diffusivity over advection effects on the submicron particles in spray drying of Quercus resinosa infusions. The particles also showed high inhibition of deoxy-D-ribose oxidation at very low concentrations.^[155]

Table 4. Encapsulation treatment in food items for different polymers.

Food item	Compound Encapsulated	Treatment	Encapsulation yield	Size of microcapsules	Polymers used	Results	Reference
Mandarin juice	L. salivarius	70 MPa	ND	0.5–1500 µm	Sodium alginate, tween 80, sunflower oil	When the juice was held for 7 to 10 days, microorganism encapsulation reduced the percentage of degradation from 8–9% to 0–2%.	Calabuig-Jiménez et al.^[Citation168]
ND	L. salivarius	68 MPa	86.43%	127 µm	Sodium alginate and vegetable oil	Viability remained as 9.24 log CFU/mL after encapsulation	Ding and Shah (2009)
Milk	L. paracasei A13 and L. salivarius CET 4063	50 MPa	87, 83%	<100 µm	Sodium alginate and vegetable oil	Over the course of two months of refrigerated storage, the survivability of the isolates in the products was monitored. A decrease of hyperacidity phenomena; improved functionality and enhanced sensory properties	Patrignani et al. (2017)
Apple discs; mandarin juice	L. salivarius spp. Salivarius	70 MPa	ND	ND	Sodium alginate, tween 80, sunflower oil	The study found that capsules could protect L. salivarius spp. salivarius against degrading reactions after 14 days of storage.	Ester et al. (2019)

Conclusions and future perspectives

HPH is an emerging technology with potential applications in various areas of food industry. Its wide applications include pasteurization, sterilization, stabilization of emulsions and suspensions, modification in the structure of whole matrices and specific biopolymers produce functional foods and novel ingredients. Although in the beginning, the application of HPH was aimed at more efficient homogenizing and increasing the stability of emulsions such as milk, the recent advances in the valve design have allowed for an increase in working pressure extending the scope of possible applications. More studies involving the applications in food industry are however, needed, as HPH can help to develop food products with quality close to that of the fresh food products. Some recent studies show its wide applications in food industry. This includes its application in extraction of bioactive components from agri-food wastes. Besides, it could be used to encapsulate and improve the bioavailability of bioactive components. Furthermore, progress has been made in the application of HPH to reduce the microbial load and modulate the activity of some enzymes. Owing to its noticeable effects, HPH is a preferred alternative to heat treatment for functional supplements containing heat sensitive components. This technology is believed to have the potential to eventually replace the existing heat treatment techniques employed for pasteurization and sterilization. This shall not only help to preserve the food product but also to generate various stable emulsion systems. Ameer,^[111] Bernat,^[112] Bevilacqua,^[113] Bevilacqua,^[114] Brinez,^[115] Burns,^[116] Capela,^[117] Codina-Torrella,^[118] Cogan,^[81] Cook,^[119] Corredig,^[120] Datta,^[121] Desrumaux,^[122] Diagram,^[123] Donsi,^[124] Dos Santos Aguilar,^[125] EI-Shibiny,^[126] Espitia,^[127] Ferragut,^[128] Fiocchi,^[129] Floury,^[130] Hansen,^[131] Hashemi,^[132] Hashemi,^[133] Hettiarachchi,^[52] Islam,^[134] Jiang,^[135] Jiang,^[136] Keshavarz-Moore,^[137] Lanciotti,^[138] Lee,^[139] Leite,^[140] Liu,^[141] Majeed,^[142] Martinez-Monteagudo,^[143] Middelberg,^[144] Panozzo,^[145] Paquin,^[146] Paquin,^[147] Park,^[148] Patrignani,^[82] Patrignani,^[149] Patrignani,^[150] Perrier-Cornet,^[151] Rademacher,^[152] Ranadheera,^[153] Ranadheera,^[154] Rocha-Guzman,^[155] Roobab,^[156] Sandra,^[157] Santos,^[158] Sarao,^[159] Sarkar,^[160] Senorans^[161,162]Shah,^[163] Siddiqi,^[164] Tan,^[165] Trujillo,^[166] Yipeng^[167]

Author contributions

Tanu Malik: Conceptualization, Supervision, Project Administration, Funding acquisition; Ruchi Sharma: Investigation, Formal Analysis, Methodology, Writing – Original Draft, Conceptualization, Writing – Review & Editing; Omar Bashir: Finalizing the Draft, Methodology, Results and Discussion; Kashif Ameer: Writing – Review & Editing, Data Interpreting, Results and Discussion; Finalizing the Draft; Tawheed Amin: Writing – Review & Editing, Finalizing the Draft; Sobiya Manzoor: Introduction and Methodology; Isam A. Mohamed Ahmed: Writing – Review & Editing, Finalizing the Draft

Acknowledgments

There was no funding received from any organization to complete this research.

Data availability statement

No such data set is available.

Disclosure statement

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