Chapter 6
High-Pressure Technologies in Dairy Processing: Quality Maintenance and Increase in Consumption
Bruno R. de Castro Leite, Jr.*
Abstract
Emerging technologies, such as high isostatic pressure and dynamic high pressure, have been widely studied in food processing. These technologies can be applied to several food products and ingredients in order to improve quality and increase the acceptance of processed foods. The main advantage is the replacement of thermal process by high-pressure process, aimed at the inactivation of microorganisms at room temperature. With this technology it is possible to replace the sensory changes caused by high temperature–produced foods with the characteristics of close-to-fresh foods, besides changing the structure and constituents. These changes have been studied in various foods, including milk and dairy products. The results show that depending on the conditions used with each technology, both processes can improve the consistency and increase water retention and emulsion stability in dairy products. The purpose of this chapter is to compare the evolution of these technologies in milk processing and discuss their application in improving the quality and acceptance of these products.
Keywords
casein micelle
dynamic high pressure
high isostatic pressure
high-pressure homogenization
high-pressure processing
milk products
whey protein
1. Introduction
Currently, two emerging technologies are used for food processing using high pressure: high isostatic pressure (HIP) (also called high-pressure processing) and dynamic high pressure (DHP) (also called high-pressure homogenization). Although both use high-pressure conditions, the principles are different, causing different effects on milk constituents. The differentiation of these two technological processes is often misunderstood. This chapter discusses the differences between HIP and DHP on milk constituents, as well as the effects of these changes on the acceptance of dairy products, providing encouragement for research and partnerships with researchers from related areas. Table 6.1 shows the main differences in process conditions of high-pressure technologies.
Table 6.1
| Parameter | HIP | DHP |
|---|---|---|
| Type of food | Liquid/semisolid/solid | Liquid |
| Operation flow | Batch/semicontinuous | Continuous |
| Physical forces | Compression and decompression | Compression, cavitation, turbulence, and impact |
| Pressure range | Up to 1000 MPa | Up to 350 MPa |
| Residence time under pressure | Unlimited (controlled by the operator, depending on the goal) | Very fast (few seconds—variable not controlled) |
| Processing temperature | Freezing, low or mild temperature | Low or mild temperature (not frozen) |
| Heating during pressurization | 3–10°C per 100 MPa (adiabatic heating) | 15–25°C per 100 MPa (energy conservation) |
| Capacity | Chambers up to 525 L a ; production up to 3.000 kg/h | Up to 5.000 L/h at 150 MPa b |
| Filling | Product packaged in flexible packaging before processing (most common) or product without packaging (less common) | Product packed after processing |
DHP, Dynamic high pressure; HIP, high isostatic pressure. Trujillo et al. (2002), Hayes et al. (2005), Diels and Michiels (2006), Huppertz et al. (2006), Dumay et al. (2013).
a Information extracted from Hiperbaric: high pressure processing.
b GEA Process Engineering Ltd.
The most common characteristic of these processes is the ability to process food at low temperatures. In this context, these technologies are used in place of or together with thermal processing aiming microbiological safety with minor damage to the sensory characteristics of the food, especially color and flavor, as well as decreasing nutrient losses and preserving bioactive compounds (Evert-Arriagada et al., 2013, 2014). Thus, these technologies have the potential to be exploited, enabling the development of new products.
Although HIP has been widely applied in vegetable and meat processing, its use in the dairy industry is still restricted. In contrast, DHP is often used in the pharmaceutical and cosmetics industries, with a smaller application in the food industry, despite the promising results in research and pilot plants. An important reason for the delay to implement these technologies in the industry, especially to replace pasteurization, is the low processing equipment capacity. However, there is an increased demand in the development of new equipment with higher production capacity, leading to industrial application of high-pressure technologies.
2. High Isostatic Pressure
The HIP, also known as high hydrostatic pressure or high-pressure processing, is an emerging process for food preservation, keeping the heat-sensitive compounds (Rendueles et al., 2011). However, this process can change food constituents, including milk (Trujillo et al., 2002), allowing the development of new products/ingredients.
2.1. Principle and Operation
The HIP process has pressure, temperature, and holding time as processing variables. The choice of these variables is a function of the desired goal for each product. Usually, HIP is implemented by subjecting the food (liquid or solid) sealed in flexible packages to a pressure up to 1000 MPa (10,000 bar) for a specific time under freezing or extremely high temperatures.
The process promotes a series of changes in cell membranes and enzymatic mechanisms of microorganisms (Rendueles et al., 2011). Concerning the food constituents, HIP can break noncovalent bonds, such as ionic bonds and hydrophobic interactions, while covalent bonds are not affected. Thus, although large biomolecules, such as proteins and polysaccharides, can be affected by changes in their structures, small molecules (functional compounds and vitamins, and flavor and color components) are not affected by HIP, keeping unchanged after processing (Chakraborty et al., 2014).
Moreover, the pressurization process, following the principle of Le Chatelier, induces a reduction in molecular volume (Tomasula et al., 2014), accelerating exponentially the occurrence of pressure-favored reactions. Thus, the reaction rates catalyzed by proteolytic enzymes, such as proteolysis, can be accelerated by HIP (Delgado et al., 2012).
Fig. 6.1 illustrates the HIP process. During the indirect pressurization by a low-compressibility fluid (e.g., water or propylene in processes under freezing temperatures), food instantly receives the same intensity of pressure, regardless of the size and geometry. Thus, there is a pressure gradient, that is, there is no lower heating point or cold spot, as in the case of thermal processes. In addition, pressurization is accompanied by adiabatic compression heating. The adiabatic heating rate is specific to each chemical compound (e.g., foods with high water content increased 3–5°C per 100 MPa, while foods with a high fat content increased 6–10°C per 100 MPa), being dependent on pressure and temperature (Patazca et al., 2007). In addition, the adiabatic heating is completely reversed upon pressure release.
Figure 6.1 Scheme of Operation for the High Isostatic Pressure Device.
3. Dynamic High Pressure
The DHP or high-pressure homogenization, also called ultrahigh-pressure homogenization, is a nonthermal physical process introduced in food processing in the 1980s to improve the efficiency of homogenization of dairy emulsions (Diels and Michiels, 2006). This technology has a similar operation principle of the conventional homogenizers, but using pressures in the order of 10–15 times higher than those normally applied (up to 350 MPa) (Diels and Michiels, 2006). In addition, several authors have found that the process is capable of promoting the inactivation of microorganisms, and changing food constituents (Augusto et al., 2012; Baier et al., 2015; Bravo et al., 2015; Dumay et al., 2013; Franchi et al., 2011a,b). Despite that this technology has been widely used in chemical, pharmaceutical, and biochemical industries, it is rarely applied the food industry, probably due to the low production flow. However, the industrial interest has led to the development of new equipment with higher capacities, allowing the industrial application of this technology.
3.1. Principle and Operation
This process is described only for the application in fluid foods. In the apparatus, fluid is forced to pass through a homogenizing valve at high pressures. The passage through the narrow valve aperture (in the order of micrometers) and the sudden decompression of fluid generate an increase in both speed (between 150 and 300 ms−1; Dumay et al., 2013) and temperature (about 15 at 25°C per 100 MPa; Diels and Michiels, 2006), caused by heavy friction in the region of the homogenization valve, which is dependent on the food matrix, total solids concentration, and other factors (Dumay et al., 2013; Hayes and Kelly, 2003a). The operating pressure is controlled by the width of the homogenization valve that restricts the product’s flow (Diels and Michiels, 2006; Pinho et al., 2011). Fig. 6.2 shows a schematic illustration of the DHP equipment.
Figure 6.2 Operating Diagram for the Dynamic High Pressure Apparatus.
4. Effect HIP and DHP on Milk Constituents
The effects of HIP and DHP had a primary focus on the inactivation of microorganisms (Dumay et al., 2013; Franchi et al., 2011b; Poliseli-Scopel et al., 2014; Silva, 2015; Tribst et al., 2008). However, several authors have reported that high pressure also affects milk constituents (Baier et al., 2015; Bravo et al., 2015; Dumay et al., 2013; Rodríguez-Alcalá et al., 2015; Sørensen et al., 2014; 2015; Zamora et al., 2012). Strategically, these changes in milk constituents help to improve the sensory and technological characteristics of dairy products.
Changes in milk constituents are distinct due to the different effects of both technologies. Thus, each technology is used according to the product of interest. These differences are highlighted in Table 6.2.
Table 6.2
| HIP | DHP | |
|---|---|---|
| Fat | No changes in fat globule in bovine milk (Huppertz et al., 2003); increased number of small globules in sheep milk (Gervilla et al., 2001) | Reduction of size of fat globules (Ciron et al., 2010; Oliveira et al., 2014) |
| Increased creaming (<250 MPa favors the interaction of lipoproteins; Huppertz et al., 2003) or reduced creaming (>400 MPa, inactivates agglutinin (Huppertz et al., 2003) | Increased lipolysis in raw milk (Datta et al., 2005; Pereda et al., 2008a; Serra et al., 2008a) | |
| No formation of free fatty acids in sheep milk (Gervilla et al. 2001) | Better emulsification and stability (Hayes and Kelly, 2003b) | |
| No emulsifying effect (Huppertz et al., 2003) | No changes in the structure of the triglyceride (Rodríguez-Alcalá et al., 2009) | |
| Protein (casein) | Fragmentation of the micelle (50% reduction; pressure >400 MPa; Huppertz et al., 2006; López-Fandiño, 2006) | Fragmentation of the micelle (∼30% reduction; Roach and Harte, 2008) |
| Solubilization of CCP (Huppertz et al., 2006; Huppertz and De Kruif, 2006) | Increasing the size of the micelle ∼45% (over 300 MPa; Roach and Harte, 2008) | |
| Reduction of hydrophobic interactions (Huppertz et al., 2006) | Solubilization of CCP (Zamora et al., 2007) | |
| Solubilization of casein fractions (in order: β-casein>κ-casein>αs1-casein>αs2-casein; López-Fandiño et al., 1998) | Reduction of hydrophobic interactions (Zamora et al., 2007) | |
| Whey protein | Denaturation of β-lactoglobulin (β-Lg) at 100 MPa and α-lactalbumin (α-La) at 400 MPa (Huppertz et al., 2004c) | No denaturation of β-Lg (little formation of disulfide bonds; Sørensen et al., 2014) |
| Immunoglobulins (IgG, IgM, and IgA) more resistant to pressure than the thermal process (Contador et al., 2013; Sousa et al., 2014) | α-Lg resistant to pressure (Sørensen et al., 2014) | |
| Reduction of protein size (>200 MPa; Bouaouina et al., 2006) | ||
| Sensitivity to denaturation: Lactoferrin<β-Lg<immunoglobulin<BSA<α-La (Patel et al., 2006) | Increase in solubility of whey proteins (Dissanayake and Vasilejvic, 2009) | |
| Enzymes | Higher resistance of alkaline phosphatase (800 MPa inactivation for 8 min; Rademacher et al., 1998) | Alkaline phosphatase: activation from 100 to 150 MPa and inactivation above 175 MPa (Picart et al., 2006) |
| Plasmin resistant at 400 MPa/30 min at 25°C. 87% inactivation of plasmin at 400 MPa/15 min at 60°C; Garía-Risco et al., 2000; Huppertz et al., 2004b) | Plasmin resistant up to 200 MPa (Iucci et al., 2008) | |
| Lactoperoxidase very stable (50% reduction after 800 MPa/4 h at 60°C; Rademacher et al., 1998) | Lactoperoxidase increased activity at 75 MPa (Vannini et al., 2004) | |
| Lysozyme very resistant (Viazis et al., 2007) | Lysozyme activity increased at 75 MPa (Vannini et al., 2004) | |
| Lipase resistance up to 400 MPa at 3°C (Pandey and Ramaswamy, 2004) | Lipase activated at 200 MPa at <58°C of outlet temperature or inactivated at 200 MPa at outlet temperature >71°C (Datta et al., 2005) | |
| Minerals | Solubilization of colloidal calcium phosphate (63% at 350 MPa; Kielczewska et al., 2009) | Solubilization of colloidal calcium phosphate (8%–30% from 150 to 300 MPa; Serra et al., 2008b) |
CCP, Colloidal calcium phosphate; DHP, dynamic high pressure; HIP, high isostatic pressure.
4.1. Fat
4.1.1. Changes in milk fat by HIP
HIP does not change the bovine milk fat globule size (100–600 MPa for up to 60 min at 20°C) (Huppertz et al., 2003), however, Gervilla et al. (2001) found a greater number of smaller particles in sheep milk after processes at 200 or 300 MPa at 25 or 50°C, which may be related to the methodology, process conditions, or type of milk (Huppertz et al., 2003). In addition, no formation of free fatty acids was observed in sheep milk (Gervilla et al., 2001), which is interesting to prevent off-flavor by lipolytic enzymes (Trujillo et al., 2002). However, creaming of fat globules can increase at pressures lower than 250 MPa or decrease at pressures higher than 400 MPa (Huppertz et al., 2003). Similar results were observed in sheep milk (reduction in creaming in processes at 500 MPa at 25 and 50°C; Gervilla et al., 2001). The increase in creaming can be due to interactions between the fat globules and milk proteins (Huppertz et al., 2003), while lower creaming is probably due to inactivation of agglutinins (Huppertz et al., 2003) or an increase in the number of smaller particles (Gervilla et al., 2001). Thus, it appears that the HIP processing under optimized conditions can be used for reducing both creaming for processing of milk and milk beverages (Huppertz et al., 2003), or increasing creaming, facilitating cream separation prior to butter manufacturing (Trujillo et al., 2002).
4.1.2. Changes in milk fat by DHP
The effect of homogenization on milk fat has been extensively studied, mainly due to its wide application in dairy products. The DHP enhances dispersion and reduces the size of fat globules. The temperature of the fat matrix influences the reduction of globules, because the process is more effective when all fat is in liquid phase, with no formation of crystals at temperatures >40°C (Zamora et al., 2012).
Although the reduction of fat globules is a function of the level of pressure applied in the DHP process, larger reductions than those obtained by the conventional homogenization can be achieved using pressures between 50 and 300 MPa (Sandra and Dalgleish, 2005). Thus, reduction in size of the fat globules is more intense with increasing pressure (Hayes and Kelly, 2003b).
However, at homogenization pressures higher than 300 MPa, an opposite effect is observed, because greater reduction of fat globules modifies their electrical charge and enhances coalescence (Serra et al., 2007; Thiebaud et al., 2003). Coalescence is also favored by the absence of casein to adsorb new small globules. This phenomenon can be minimized by homogenization in two stages (Hayes and Kelly, 2003b) or the addition of emulsifiers (Thiebaud et al., 2003).
The characterization of fat composition of bovine, goat, and sheep milk demonstrated that homogenization up to 350 MPa did not alter the fatty acid profile of the samples or isomers of conjugated linoleic acids (Rodríguez-Alcalá et al., 2009), indicating that, despite the homogenization, was able to break down the fat globules, the process does not alter the structure of triglycerides.
When raw milk is subjected to DHP or conventional homogenization, the rupture of milk fat globule membrane increases the performance of native milk lipase, accelerating oxidation processes (Pereda et al., 2008a; Serra et al., 2008a). However, the induction of lipolysis in raw milk by the DHP can be prevented by using temperature conditions sufficient to inactivate lipase (inactivated at 200 MPa/40°C or 300 MPa/30°C; Serra et al., 2008a).
4.2. Protein
4.2.1. Changes in milk protein by HIP
HIP process can cause changes in the milk proteins. Depending on the processing conditions, casein micelles can be blown away, not affected or aggregated, while whey proteins can also be denatured or not affected. These can alter the functional properties of proteins, improving the sensory characteristics of milk and milk products processed by HIP.
4.2.1.1. Casein
In general, the processes carried out between 100 and 200 MPa for 30 min at 20°C promote little or no change in the casein micelle, while an increase in the average size of the micelles is observed (∼25%) in processes carried out at ∼250 MPa for times greater than 15 min, due to casein aggregation. In processes conducted above 400 MPa, a reduction in the average size of up to 50% is observed, regardless of time and temperature (Bravo et al., 2015; López-Fandiño, 2006). This phenomenon occurs due to breakage of the hydrophobic interactions and partial solubilization of colloidal calcium phosphate (CCP), leading to solubilization of casein fractions (Huppertz et al., 2006; Huppertz and De Kruif, 2006). However, fragmentation of casein can be reversed after 24 h or after heating (80–85°C) (Harte et al., 2003; Huppertz et al., 2004e), but the presence of denatured β-Lg (β-Lg-κ-CN interaction) prevents casein aggregation (Johnston et al., 2002).
In structural terms, HIP can promote drastic changes in quaternary (at pressures higher than 150 MPa) and tertiary structures (at pressures higher than 200 MPa) of the globular protein, despite providing a slight or no effect on the secondary structure, due to the stability of hydrogen bonds (López-Fandiño, 2006). Thus, depending on the composition and conformation of the different caseins, the order of solubilization was determined in HIP procedures above 400 MPa, as follows: β-casein>κ-casein>αs1-casein>αs2-casein (López-Fandiño et al., 1998). Although the order has been due to the amount of serine phosphate residues, it may also be related to its hydrophobicity.
4.2.1.2. Whey proteins
Whey proteins can undergo reversible or irreversible denaturation, unfolding with their molecular structures under specific pressure conditions. The major whey proteins, β-lactoglobulin (β-Lg) and α-lactalbumin (α-La) present different resistances to pressure. Irreversible denaturation of β-Lg (by formation of the β-Lg-κ-casein complex by disulfide bonds) begins at 100 MPa, while denaturation of α-La starts at pressures higher than 400 MPa (Huppertz et al., 2004c). The intensity of denaturation is directly related to increased pressure and temperature, and a reaction time is needed during pressurization for irreversible denaturation (Bravo et al., 2015). Furthermore, the highest amount of intramolecular disulfide bonds and the absence of free sulfhydryl groups, confer greater pressure resistance to α-La (López-Fandiño et al., 1996).
Thus, the sensitivity of whey proteins to denaturation by pressure follows the order: lactoferrin>β-Lg>immunoglobulin>BSA>α-La (Patel et al., 2006). Immunoglobulins (IgG, IgM, and IgA) are bioactive compounds that are very heat-sensitive, but pressure-resistant (400 MPa for 6 min), while IgG is able to support up to 600 MPa for 3 min (Contador et al., 2013; Sousa et al., 2014).
4.2.2. Changes in milk proteins by DHP
Several authors have studied the effect of DHP on different types of proteins, and found that the process was able to change the conformation and functionality of some proteins (Dong et al., 2011; Luo et al., 2010; Yuan et al., 2012), but without changing other proteins (Bouaouina et al., 2006). The different effects are related to the type of protein and processing conditions.
The DHP is capable of providing enough energy to alter the tertiary and quaternary structure of most globular proteins (Luo et al., 2010). This phenomenon can cause disruption of protein, reducing the molecular weight and, consequently, increasing the area of exposure, with higher reducing power, and elimination of hydroxyl radicals, which are the most active potential groups (Dong et al., 2011). In milk, the DHP promotes different effects on caseins and whey proteins with consequent changes in the technological functionalities, aimed at increasing the acceptance of various dairy products.
4.2.2.1. Casein
One of the main effects observed in casein subjected to DHP is the change in micelle size. When pressures up to 250 MPa are used, a reduction of ∼30% in the micelle size is observed (Hayes and Kelly, 2003a; Roach and Harte, 2008), followed by solubilization of CCP, and reduction of hydrophobic interactions (Zamora et al., 2007). Sandra and Dalgleish (2005) studied reconstituted skimmed milk powder subjected to pressures up to 186 MPa up to six runs, and found that the size of the casein micelle decreased with increasing pressure and increasing the number of passages. On the other hand, a slight increase in the average size of casein was observed after DHP at 300 or 350 MPa (Roach and Harte, 2008). The increase in micelle size is associated with denaturation of β-Lg and/or aggregation of casein micelles. Aggregation can occur due to removal of κ-casein hairs, reducing the electrostatic repulsion and favoring the formation of casein clusters (Roach and Harte, 2008).
4.2.2.2. Whey proteins
Some authors have found no denaturation of whey protein processed by DHP (Dissanayake and Vasilejvic, 2009), while others reported some denaturation (Datta et al., 2005; Hayes et al., 2005). The apparent discrepancy between the results may be due to the levels of pressures applied and inlet temperatures used.
The most interesting and potential effect of DHP on whey protein is related to the changes in its functional properties. Even without protein denaturation, significant changes in functionality are observed, such as increased solubility and improved thermal stability (Dissanayake and Vasilejvic, 2009). In addition, the increased exposure of hydrophobic groups on the surface of the molecules by DHP can favor overrun and foam stability (Dissanayake and Vasilejvic, 2009).
4.3. Enzymes
The high-pressure technologies have the ability to activate, inactivate, or not change the activity of the enzymes present in milk. This is interesting from a technological point of view, as these processes can activate or inactivate proteolytic and lipolytic enzymes, thus controlling the manufacturing process of dairy products, including ripened cheeses. However, these results depend on the technology used and the process conditions applied. These differences are discussed in the next sections.
4.3.1. Changes in enzymes by HIP
Some studies have shown that the HIP process is capable of promoting enzyme activation (Leite Júnior et al., 2016a) or stabilization (Eisenmenger and Reyes-De-Corcuera, 2009), by applying low pressure (up to 400 MPa), and moderate temperatures. For each enzyme, there is a pressure limit to be applied, because a loss of activity is observed from this limit (Leite Júnior et al., 2016b) due to denaturation (Eisenmenger and Reyes-De-Corcuera, 2009).
In general, milk enzymes are more resistant to the HIP process when compared with the thermal process, such as high stability of lactoperoxidase (maintaining 50% of its activity after processes at 800 MPa for 4 h at 25 to 60°C; Rademacher et al., 1998) and lysozyme (400 MPa for 30 min; Viazis et al., 2007). These results are interesting for production of dairy products processed by HIP due to maintenance of the antimicrobial activity of these heat-sensitive enzymes. However, the individual effect on each enzyme is variable, for example, alkaline phosphatase is very pressure resistant (inactivation at 800 MPa for 8 min; Rademacher et al., 1998), while acid phosphatase is easily inactivated (inactivated at pressures higher than 200 MPa; Balci et al., 2002).
Lipases can be used in cheese ripening when lipolysis is desirable. In this sense, milk subjected to 350 and 400 MPa up to 100 min presented an increase up to 140% in the activity of these enzymes (Pandey and Ramaswamy, 2004). On the other hand, plasmin can have its activity reduced to 75% or 87% in milk and milk derivatives subjected to 600 MPa/30 min/20°C (Huppertz et al., 2004b) or 400 MPa/15 min/60°C (Garía-Risco et al., 2000), respectively.
4.3.2. Changes in enzymes by DHP
Studies have shown that DHP can affect the activity and stability of enzymes and other macromolecules. Most of DHP application studies on enzymes were performed in order to inactivate undesirable enzymes in processed foods (Calligaris et al., 2012; Velázquez-Estrada et al., 2012). Some studies have also evaluated the effect of DHP on enzymes with antimicrobial function, such as lysozyme (Tribst et al., 2008), lactoperoxidase (Iucci et al., 2007; Vannini et al., 2004) and lactoferrin (Iucci et al., 2007). The results showed increased antimicrobial activity of lysozyme and lactoperoxidase at 75 MPa (Vannini et al., 2004) or 100 MPa (Iucci et al., 2007).
Other studies have evaluated the activity of native enzymes, such as plasmin, lipase, and alkaline phosphatase (Datta et al., 2005; Hayes et al., 2005; Iucci et al., 2008; Lanciotti et al., 2004; Picart et al., 2006; Vannini et al., 2008). Concerning plasmin, no reduction in activity was observed in the processes carried out up to 200 MPa (Iucci et al., 2008). For lipase, an increase of 140% was observed at 200 MPa and inlet temperature of 10°C, with inactivation at 200 MPa in outlet temperature higher than 71°C (Datta et al., 2005). For alkaline phosphatase, DHP processes using inlet temperature of 24°C were able to activate the enzyme after processing at 100 or 150 MPa, with no changes at 175 MPa, and 94% inactivation at 300 MPa (Picart et al., 2006). At 200 MPa, ranging the inlet temperature from 10 to 50°C, no reduction of enzyme activity was observed from 10 to 15°C, with enzyme inactivation at temperatures lower than 45°C; however, processes using inlet temperatures higher than 45°C resulted in the inactivation of this enzyme (Datta et al., 2005), and the outlet temperature (>75°C) was the determining factor for inactivation (Datta et al., 2005).
In addition, some authors evaluated cheeses made from milk processed by DHP at 100 MPa and reported an increase in activity of proteolytic and lipolytic enzymes present in milk or produced by microorganisms (Hayes and Kelly, 2003b; Lanciotti et al., 2004; Pinho et al., 2011; Vannini et al., 2008), thus accelerating cheese ripening by improving flavor, texture (Vannini et al., 2008), color, and aroma (Lanciotti et al., 2006).
4.4. Minerals
4.4.1. Changes in minerals by HIP and DHP
The greatest effect of HIP on milk minerals is the solubilization of CCP (López-Fandiño, 2006). According to Kielczewska et al. (2009), both calcium and phosphorus significantly increase its solubility at 150–350 MPa (an increase of 42% and 63%, respectively). In contrast, the DHP also solubilized calcium and phosphorus due to fragmentation of casein micelles (Serra et al., 2008b), although CCP solubilization is less intense than that observed in the HIP process. According to Zamora et al. (2007), a maximum solubilization of 8% of calcium was observed at 130 MPa, while Serra et al. (2008b) found maximum solubilization of ∼30% at 300 MPa. However, more studies under similar conditions are required.
5. Industrial Applications
Dairy products processed by HIP and DHP have great advantages when compared with conventional processes. Table 6.3 highlights the major changes in the dairy products that contribute to improving the marketing of these products.
Table 6.3
| Product | HIP | DHP |
|---|---|---|
| Milk | Can replace pasteurization and sterilization processes (Vazquez-Landaverde et al., 2006) | Can replace pasteurization processes (Pedras et al., 2012) or used in combination with thermal process for sterilization (Amador Espejo et al., 2014a) |
| Skimmed milk appears semi transparent due to casein fragmentation (>400 MPa; Devi et al., 2015) | No changes in milk appearance (Hernández and Harte, 2008) | |
| Absence of undesirable volatile compounds generated in the thermal process (Trujillo et al., 2002) | Absence of undesirable volatile compounds generated in the thermal process (Amador-Espejo et al., 2014b) | |
| No significant reduction of vitamins, amino acids, simple sugars and flavor compounds (Trujillo et al., 2002) | High stability of the fat emulsion, preventing phase separation (Zamora et al., 2012) | |
| Processed milk for cheese manufacture | Moderate pressures (<300 MPa) accelerates coagulation (casein fragmentation; López-Fandiño et al., 1996; Ohmiya et al., 2014) | Acceleration or no effects on coagulation (with no denaturation of β-Lg; Hayes and Kelly, 2003b; Sandra and Dalgleish, 2007; Zamora et al., 2007) |
| Higher pressures (>400 MPa) increase coagulation time and cheese yield (better retention capacity due to denaturation of β-Lg; Huppertz et al., 2004a,c, 2005) | Increase in lipolysis during ripening (200 MPa, <58°C) or no effects (200 MPa, >71°C; Datta et al., 2005; Juan et al., 2015) | |
| Fresh cheese is more soft, less brittle and more rigid (Molina et al., 2000) | Can accelerate cheese ripening (Juan et al., 2016; Lanciotti et al., 2004; Vannini et al., 2008) | |
| Cheese manufacture | Reduction of contamination and extension of shelf life (>400 MPa; Evert-Arriagada et al., 2014; O’Reilly et al., 2000) | It cannot be used in cheese (only fluids) |
| Accelerating or delaying the ripening process depending on the conditions and microbial cultures (Costabel et al., 2016; Delgado et al., 2012) | ||
| Fresh cheese more compact and elastic (Sandra et al., 2004) | ||
| Yogurt | Increased consistency (Harte et al., 2002), mainly in set yogurt | Increased consistency, mainly in stirred yogurt (Serra et al., 2007) |
| Reduction of spoilage microorganisms (Penna et al., 2007; Shah et al., 2008) | Reduction of post acidification (Patrignani et al., 2007; Serra et al., 2009a) | |
| Increased water retention capacity | Increased water retention capacity (Oliveira et al., 2014) | |
| Extension of shelf life (Penna et al., 2007; Shah et al., 2008) | ||
| Ice cream | Improved foaming stability of whey protein (Liu et al., 2005) | Improved foaming capacity of whey protein (Bouaouina et al., 2006; Dissanayake and Vasilejvic, 2009) |
| Better interaction with aromas (Kühn et al., 2006; Liu et al., 2005) | Enables to produce low-fat ice creams with texture similar to full-fat ice creams (Innocente et al., 2009) | |
| Smooth texture (controlling small crystals formation; Eberhard et al., 1999; Huppertz et al., 2011) | ||
| Butter | Extension of shelf life (Dumay et al., 1996) | |
| Improving aggregation of fat and consistency (Dumay et al., 1996) |
DHP, Dynamic high pressure; HIP, high isostatic pressure.
Various studies and patents have shown potential applications of HIP in the production of dairy products, including clarification and stabilization of protein gels; lower proteolysis in fresh cheeses to maintain the functional and sensory properties; extension of shelf life of fresh cheeses; increased resistance of probiotic cultures; maintenance of thermosensitive bioactive compounds (such as lactoferrin and immunoglobulins); accelerated proteolysis in cheese or inhibition of proteolysis in aged cheeses (Bravo et al., 2015; Calzada et al., 2014a,b; Carroll et al., 2004, 2008; Costabel et al., 2016; Evert-Arriagada et al., 2013, 2014; López-Fandiño, 2006; Trujillo et al., 2002; Voigt et al., 2011; Yang et al., 2014).
Concerning the DHP, despite its low pressure capacity for equipment with high flow rates (pharmaceutical industry as main commercial focus) it presents as main advantages: emulsion stability, extension of shelf life and maintenance of sensory characteristics in milk; increased yield, improved flavor and texture, and acceleration of cheese ripening; increased consistency in yogurt made from DHP-processed milk; extraction of intracellular enzymes and development of high added value products (Ciron et al., 2011; Datta et al., 2005; Hayes and Kelly, 2003b; Hernández and Harte, 2008; Juan et al., 2015; 2016; Lanciotti et al., 2006; Oliveira et al., 2014; Pedras et al., 2012; Pereda et al., 2008b; 2009; Vannini et al., 2004; 2008; Zamora et al., 2007; 2011). Thus, the reduction of equipment costs with increased production capacity and specific knowledge for each product can lead to improvements of these technologies in dairy industries, so that dairy products processed by DHP will be placed on the market in the coming years. The advantages of high-pressure processing in some dairy products are detailed in the next sections.
5.1. Milk
5.1.1. Effect of HIP on milk for direct consumption
The HIP process can be used as a preservation method, reducing the microbial load of milk with the possibility of processing under low temperatures, with less production of volatile compounds, which negatively interfere with milk flavor, as observed in conventional thermal processes (Garrido et al., 2015; Vazquez-Landaverde et al., 2006). Furthermore, no significant reduction of vitamins, amino acids, fatty acids, simple sugars, and flavor compounds are observed (Martínez-Monteagudo and Saldaña, 2014; Trujillo et al., 2002).
To reach pasteurization conditions, processes at 400–600 MPa for 3–15 min at 20°C produced milk with shelf life similar to thermal pasteurization of milk (Rademacher and Kessler, 1997). For sterilization, high temperatures (60–90°C) should be combined with high pressure (>600 MPa) to reach high temperatures (90–120°C) through adiabatic heat, sufficient to inactivate spores. In addition, lower pressure conditions (<400 MPa) can also be used to encourage spore germination with subsequent inactivation of vegetative cells (Black et al., 2007; Van Opstal et al., 2004). Thus, HIP can be used as an alternative to thermal processing to produce stable milk, reducing the undesirable taste produced by the thermal process.
However, this technology provides a limiting factor for the processing of skimmed milk, once semitransparent milk is obtained at pressures higher than 400 MPa, which is maintained for several days under refrigeration conditions (Devi et al., 2015). This phenomenon is mainly caused by the fragmentation of casein. However, negative effects are not observed in milk derivatives, thus milk can be used for the manufacture yogurts and cheeses, for example (Reps et al., 2009), due to casein aggregation during the manufacturing process (acid or enzymatic gel).
5.1.2. Effect of DHP on milk for direct consumption
Studies have shown that DHP (300 MPa) may be used to replace thermal pasteurization, maintaining milk stable under refrigeration for 1–2 weeks. However, pressures less than 200 MPa are inefficient to guarantee the absence of pathogens in milk (Vannini et al., 2004), and pressure of 130 MPa can inactivate only 0.3, 1.94, and 1.4 decimal reduction times of Escherichia coli 555, Staphylococcus aureus ST1, and Salmonella enteritidis E4, respectively (Vannini et al., 2004). In general, high pressures and inlet temperature increases the effectiveness of DHP process, but it is difficult to produce sterilized milk by this technology. However, the DHP process carried out at 300 MPa with an inlet temperature at 85°C promoted a complete inactivation of the several inoculated spores (Amador Espejo et al., 2014a) and these authors suggested that this process can produce commercially sterile milk. Further details on the process conditions and mechanism of inactivation of microorganisms in milk using DHP was published by Pedras et al. (2012).
The DHP is an excellent alternative to prevent phase separation due to the rupture of the fat globule and high protein adsorption, favoring protein–fat interactions (Ciron et al., 2011; Oliveira et al., 2014; Zamora et al., 2012). Another advantage of the DHP is not changing milk color (Hernández and Harte, 2008) and producing undesirable aromatic compounds. Pereda et al. (2008b) investigated DHP processed milk (200 MPa at 30 or 40°C), and reported lower formation of volatile compounds and oxidized off-flavors during heating, reduced formation of compounds during the Maillard reaction, and lower denaturation of β-Lg, with no lactose isomerization, when compared with commercial pasteurized milk. Furthermore, the DHP contributed to the maintenance of essential amino acids (Pereda et al., 2009) and milk vitamins (Amador-Espejo et al., 2015).
5.2. Cheese
5.2.1. Effect of HIP on cheese manufacture
HIP can be used in cheese manufacturing in two ways. The first is using HIP processed milk for cheese manufacture, which can lead to an increase in gel formation rate, higher yield, and a decrease in the initial microbial load. Another possibility is to subject cheese to HIP processing in specific storage periods to decrease postcontamination, thus increasing the shelf life of the product; to accelerate ripening due to enzyme activation, reducing storage costs reduction of the postripening due to enzyme inactivation to maintain the cheese quality. These two processing conditions are discussed in more detail in the next sections.
5.2.1.1. HIP–processed milk for cheese manufacture
The HIP processing in milk affects the coagulation time (time is reduced in milk processed at 300 MPa) and the final consistency of the gel (López-Fandiño et al., 1996). This reduction is due to the smaller size of the casein micelle that favors the increase in surface area, improving the performance of the rennet and accelerating the coagulation process. At pressures above 400 MPa, an increase in clotting time is observed, probably due to denaturation of β-Lg and its subsequent complexation with the casein micelle, preventing the enzyme to access κ-casein.
However, the β-Lg-κ-casein complex caused by HIP increases curd yield (Huppertz et al., 2004a,c, 2005), due to both the increased water absorption capacity of proteins, and higher incorporation of denatured β-Lg in curd, evidenced by the lower protein levels in whey (Huppertz et al., 2006; Roach and Harte, 2008; Zamora et al., 2007). Huppertz et al. (2004a) found an increase in cheese yield of up to 25% from milk subjected to 600 and 800 MPa, with no increase at pressures below 250 MPa.
The HIP process in milk can also improve the acceptance of fresh cheese by changes in its sensory attributes. In this context, low-fat cheeses made from milk subjected to 400 MPa for 15 min at 22°C, combined with pasteurization (65°C for 30 min), resulted in better consumer acceptance as compared to cheese made with pasteurized milk (Molina et al., 2000). Processed cheese made with HIP-processed milk exhibited better acceptance scores, because of a softer, less brittle and more rigid texture, and more pronounced flavor, probably due to changes in protein (Molina et al., 2000). Thus, the HIP is promising technology for cheese manufacture, with improved yields and better sensory qualities (Alonso et al., 2012; Sandra et al., 2004).
5.2.1.2. Cheese processed by HIP
HIP can also be used to process cheeses after manufacture and, therefore, reduce postprocessing contamination, thus extending the shelf life of the product (Evert-Arriagada et al., 2014; Ozturk et al., 2015). Several studies have found a reduction of 5–6 log cycles of mesophilic microorganisms, and complete inactivation of E. coli inoculated into goat cheese processed at 500 MPa for up to 15 min (Capellas et al., 1996); reduction of 7.6 to 3 log cycles of E. coli, Penicillium roqueforti, and S. aureus, respectively, inoculated into cheddar cheese subjected to 400 MPa for 20 min and 20°C (O’Reilly et al., 2000), and no mold growth and yeasts for up to 8 weeks in the processes carried out above 400 MPa (Daryaei et al., 2008). Furthermore, the process at 500 MPa/5 min/16°C increased the shelf life of fresh cheeses from 8 to 19–21 days (Evert-Arriagada et al., 2014). Thus, the use of pressures above 400 MPa in a relatively short time at room temperature can be an effective alternative for extending the shelf life of the product without compromising its quality.
Besides the microbiological inactivation, the HIP process can promote the acceleration of ripening due to increased proteolysis (Delgado et al., 2012) and modification of the protein network. As examples, there is the acceleration of the ripening period in cheddar cheese by the application of moderate pressures (345 MPa for 3 min) into the cheese curd, which facilitates cheddarization, resulting in similar textures to ripened cheddar cheese not subjected to the HIP process (Serrano et al., 2004). In addition, faster development of texture was observed in mozzarella cheeses subjected to 200 MPa for 60 min at 20°C (Johnston and Darcy, 2000). In hard cheeses, such as Argentine Reggianito, HIP processes at 400 MPa for 5–10 min at 20°C after 1 day of cheese manufacture led to an increase in proteolysis rate, accelerating the cheese-ripening process (Costabel et al., 2016). Thus, the HIP process at pressures lower than 400 MPa can be useful for cheese manufacture aimed to accelerate ripening. However, depending on the conditions applied, such as higher pressures, the delay in cheese ripening can be observed (O’Reilly et al., 2000). Such differences are mainly due to the increase or decrease of the enzyme activity responsible for proteolysis, such as rennet or plasmin produced by microorganisms (O’Reilly et al., 2001).
Alternatively, HPI can be applied to the cheese after ripening period. This procedure has the advantage of not affecting the ripening process, providing flavor and aroma characteristics similar to the conventional product. However, after ripening, the HIP processing can maintain the desirable sensory characteristics of cheeses during the shelf life, due to inactivation of enzymes and microorganisms, thus reducing the biochemical changes (Calzada et al., 2013a,b, 2014a,b; Voigt et al., 2010). As an example, blue-veined cheese processed at 400 or 600 MPa for 10 min at 20°C after 42 days at 4°C presented a reduction of proteolytic activity and deceleration of proteolysis, extending its shelf life (Voigt et al., 2010). Similarly, processes at 400 or 600 MPa after 14 or 21 days prevented Brie overripening (Calzada et al., 2014a) and the same strategy was used effectively to reduce proteolysis and avoid overripening in cheese produced from raw sheep milk, after 21 or 35 days (processes at 400 and 600 MPa for 5 min at 14°C; Calzada et al., 2014b). Our research group investigated Morbier cheese subjected to HIP process at 600 MPa for 30 min at 25°C, and stored for 30 days at 8°C, and found the extension of shelf life of the product, increasing time to market by 3 months (unpublished results). Thus, it is worth emphasizing the great potential of HIP processing for cheese making.
5.2.2. Effect of DHP on cheese manufacture
5.2.2.1. DHP–processed milk for cheese manufacture
DHP has been reported as capable of accelerating (processes 200 and 300 MPa; Zamora et al., 2007) or have no effect (Hayes and Kelly, 2003b) on milk coagulation time in the cheese-manufacturing process. The clotting time is reduced due to lower aggregation of casein micelle, which facilitates the increase in the surface area and decrease in steric hindrance and electrostatic repulsion between κ-casein (Sandra and Dalgleish, 2007). Another effect also observed by DHP is the adsorption of casein micelles at fat globules, despite that some authors have reported that this interaction does not affect the performance of rennet (Zamora et al., 2007).
Zamora et al. (2011) obtained higher curd yield after the application of DHP at 300 MPa in raw milk due to an increase in both moisture content (18% increase) and total solids (11% increase). Other authors have also reported an increase in the yield of fresh cheese (Lanciotti et al., 2006; Vannini et al., 2008; Zamora et al., 2007) and ripened cheese (Juan et al., 2016). The increased yield by DHP is associated with the higher water retention capacity of cheese curd, and protein/fat interactions (Vannini et al., 2008; Zamora et al., 2007).
During DHP, there is a disruption of milk fat globule membrane, exposing triglycerides to the action of endogenous lipase (Juan et al., 2015). Therefore, if endogenous lipase is not inactivated, cheese can exhibit high lipolysis during ripening (Lanciotti et al., 2004; Vannini et al., 2008), especially at the process conditions <200 MPa and <58°C that can activate up to 140% in endogenous lipase (Datta et al., 2005). On the other hand, if the process conditions are capable of inactivating the endogenous lipase (>200 MPa and >71°C; Datta et al., 2005) the hydrolysis profile is similar to that observed in cheese produced with pasteurized and nonhomogenized milk (72°C for 15 s) (Juan et al., 2015).
With respect to proteolysis, DHP breaks casein micelle, increasing the surface area making the protein more susceptible to hydrolysis. Thus, there is an increase in the hydrolysis of internal fractions (αs2- and β-casein), with release of hydrophobic and hydrophilic peptides. However, the overall profile of free amino acids is not changed significantly when compared to cheese made from pasteurized milk (Juan et al., 2016).
The changes on lipolysis and proteolysis depend on DHP processing conditions, which can alter the formation of volatile compounds during ripening. Vannini et al. (2008) reported higher levels of butanoic, capric, caproic, and caprilic acids, and acetic acid and acetoin in pecorino cheese made with sheep’s milk processed at 100 MPa. In sensory evaluation, the aromatic compounds of the cheese conferred higher scores to piquant flavor and lack of bitter aftertaste. No differences were observed in the sensory evaluation of caciotta cheese made with bovine milk (100 MPa), when compared to traditional cheese (Lanciotti et al., 2006). It is worth noting that the flavor and aroma of cheese is influenced by the culture used in the cheese manufacture, and DHP can accelerate or delay the development of specific species (Juan et al., 2016). However, the DHP has the limitation of processing only fluids, thus it is not possible to subject cheese to DHP processing.
5.3. Yogurt
Traditionally, for yogurt production, milk is heated to high temperatures (85–95°C for 3–10 min) to denature whey proteins, especially β-Lg, leading to interactions between β-Lg and κ-casein by disulfide bonds. This structure limits the approximation of casein micelles in the isoelectric point (pH 4.6), increasing consistency, reducing syneresis, and increasing water retention capacity. However, the HIP and DHP technologies may modify yogurt microstructure, improving the sensory characteristics when compared with the traditional process. Fig. 6.3 summarizes the main changes caused by the HIP and DHP processes in the manufacture of set yogurt and stirred yogurt. In general, HIP is most suitable to increase the consistency of set yogurt, while the DHP is more effective for increasing the consistency of stirred yogurt.
Figure 6.3 Rheological behavior of set yogurt (A) and stirred yogurt (B). Black bars indicate the HIP process (600 MPa for 15 min at 50°C) and the gray bars indicate the DHP process (150 MPa at 50°C). (1) Oliveira et al. (2014), (2) Ciron et al. (2010), (3) Zamora et al. (2012), (4) Ciron et al. (2012), (5) Ciron et al. (2011), (6) Serra et al. (2009a), (7) Harte et al. (2002), (8) Penna et al. (2007), (9) López-Fandiño (2006).
5.3.1. Effect of HIP on yogurt manufacture
The use of HIP processed milk for yogurt manufacture has several advantages, including increased consistency, lower syneresis, and extension of shelf life due to selective inactivation of spoilage microorganisms and maintenance of starter bacteria (Penna et al., 2007). In this context, patents have been developed to increase the shelf life of probiotic yogurt, by inactivating spoilage microorganisms, such as coliform bacteria, fungi, and yeasts while maintaining the viability of probiotic bacteria resistant to pressure (Carroll et al., 2004, 2008). Other studies used HIP in yogurt to inactivate starter cultures (Lactobacillus delbrueckii sp. bulgaricus and Streptococcus salivarius spp. thermophilus), aimed to increase the shelf life of the product. After processing at 300–700 MPa for 15 min, both L. delbrueckii spp. bulgaricus and S. salivarius sp. thermophilus were completely inactivated; thus, it was possible to reduce the postacidification and increase the time of market of the product (Reps et al., 2009). However, it is important to check the laws of the country, because in some regions the product must contain minimum amounts of viable starter cultures throughout the marketing period.
The HIP process can also be used to increase yogurt consistency (Harte et al., 2002), with greater intensity in set yogurt (Fig. 6.3). This is achieved due to (1) fragmentation of casein micelle, (2) partial solubilization of CCP, and (3) β-Lg denaturation caused by high pressures for longer times. Changes in casein lead to an increase in protein interactions, forming a more cohesive structure. De Ancos et al. (2000) have reported that the greater consistency is perceived by consumers. HIP can also reduce yogurt syneresis (Harte et al., 2003), and yogurt firmness increases with increasing pressure and process time.
5.3.2. Effect of DHP on yogurt manufacture
The DHP process in milk for yogurt production also contributes to increasing consistency, reducing syneresis (Serra et al., 2007), postacidification, and development of dairy cultures (Serra et al., 2007). Serra et al. (2007) observed that milk processed at 200 and 300 MPa showed higher gel strength and reduced syneresis when compared to milk fortified with 3% milk powder. The improved consistency of yogurt is due to changes in protein and fat. In protein, in particular casein, there is fragmentation of the micelle and solubilization of CCP (with no β-Lg denaturation). DHP results in an intense size reduction of milk fat globules and increases in the surface area, favoring the adsorption of casein micelles at fat globules, which promotes the increase in gel consistency (Figure 6.3A). In this sense, the DHP contributes to the consistency of stirred yogurt (Figure 6.3B), because the fat crystal’s network (5°C) limits the reorganization of the proteins during the breaking of the gel. In set yogurt, consistency is not as favored by DHP, mainly because the process is not capable of denaturing β-Lg (Serra et al. 2009a). However, Oliveira et al. (2014) found that the combination of thermal process (90°C/5 min) and DHP (150 MPa at 50°C) can increase the consistency. Thus, it is possible to associate the heat denaturation of β-Lg and fragmentation of the micelle and CCP solubilization caused by the DHP. The changes in yogurt consistency were recognized by consumers in sensory tests (Ciron et al., 2011), and the yogurt samples were characterized for the attributes viscosity, creaminess, and texture (Ciron et al., 2011).
However, the disruption of the globules may favor lipolysis, especially if the enzymes were not inactivated by the process conditions (e.g., <200 MPa at <30°C cannot inactivate the endogenous lipase; Serra et al., 2008a). In contrast, proteolysis in yogurt made with milk processed at 300 MPa did not differ from conventional industrial process, without impact on the sensory characteristics (Serra et al., 2009b).
Regarding the fermentation rate, the DHP does not affect the fermentation of yogurt cultures, due to the very rapid metabolism of these organisms (S. thermophilus and L. delbrueckii ssp. bulgaricus), being able to reduce pH to 4.6 in less than 6 h (Oliveira et al., 2014; Serra et al., 2007). However, during storage, DHP can reduce yogurt postacidification, because it favors the development of S. thermophilus rather than L. delbrueckii ssp. bulgaricus, which is mainly responsible for yogurt postacidification during storage (Patrignani et al., 2007; Serra et al., 2009a,b).
5.4. Ice Cream and Butter
5.4.1. Effect of HIP on ice cream and butter manufacture
The application of HIP in cream is able to induce the formation of crystals during pressurization, mainly the peripheral fat globules (between 300 and 500 MPa). Whipping properties improved when cream was processed at pressures up to 600 MPa for up to 2 min (Eberhard et al., 1999), probably due to better fat crystallization. However, in more severe process conditions, whey denaturation (β-Lg) is observed, reducing the stability of whipped cream. The HIP process can also modify the solid–liquid phase diagram of water, reducing the freezing point of water to −22°C at 201.5 MPa (Kalichevsky et al., 1995). Thus, it is possible to induce the formation of small crystals by pressurizing the product at freezing temperatures, which pass to the liquid state during pressurization, followed by formation of small crystals after rapid depressurization. Moreover, HIP (300 MPa for 15 min) improves whey protein functionality and foam stability in low-fat products and increases protein-binding sites with flavor molecules (Kühn et al., 2006). Thus, HIP contributes to the formation of the smooth texture in ice cream and other frozen products, improving aroma and foam stability (Huppertz et al., 2011).
Another viable application of HIP is the production of pasteurized or sterilized cream. Dumay et al. (1996) found that cream (35% fat) processed at 450 MPa for 30 min at 25°C did not change the size of fat globules, and was stable for 8 days at 4°C. However, in sterilization processes requiring higher pressures and temperatures (>40°C), emulsion destabilization can occur, leading to aggregation of fat globules.
5.4.2. Effect of DHP on ice-cream manufacture
The application of DHP for ice-cream manufacture produces good results, however, research on the subject is still scarce. Hayes et al. (2003) evaluated ice-cream mixtures (3%–8% fat) subjected to DHP at 100 or 200 MPa, and found that the texture of ice cream produced with the mixture with 5% fat was similar to the conventional mixture containing 8% fat, suggesting that DHP may be a promising technology to improve the texture of low-fat ice creams. Furthermore, DHP changes the functionality of whey protein, and increases overrun and foam stability (Dissanayake and Vasilejvic, 2009), probably due to increased exposure of hydrophobic groups on the surface molecules.
6. Prospects and Acceptance of Processed Products Through High Pressure Processing Technologies
An interview in the US showed that consumers do not know HIP technology (Hicks et al., 2009). However, it is known by health-care professionals that technological innovations, including high-pressure processing, are related to prolonging products shelf life and health promotion (Delgado-Gutierrez and Bruhn, 2008; Ronteltap et al., 2007).
Hicks et al. (2009) found that after a brief explanation about HIP technology, 40% of consumers were willing to pay more for seafood processed by high pressure (between $0.25 and $0.50), and only 15% of respondents would not pay more. Of the remaining respondents, 45% were not sure if they would pay more, but were willing to learn more about the technology. The survey also pointed to the Internet, TV/radio, and magazines/newspapers as the most important means of communication to disseminate new technologies. In a survey conducted in France and England in 2003, consumers reported that they would buy products processed by high pressure, especially if the product conferred health benefits, but would not pay more for that product (Butz et al., 2003). In addition, Delgado-Gutierrez and Bruhn (2008) showed that consumers were interested in information on the safety and freshness of food, as provided by high-pressure processes.
Based on literature, the results indicate that consumers are receptive to consuming products processed by high pressure, unlike that for irradiated products. However, some companies have chosen to not state on a product label that it was subjected to high-pressure process to avoid bias/distrust of poorly informed consumers, leading to a reduction of sales. In fact, the advantages of high-pressure processing, especially for extending the product shelf life without additives and preservatives, make these products desirable, even without other high-pressure claims.
7. Conclusion
The benefits of the HIP and DHP processes as compared with thermal processes is the fact that there is no heating step which reduces the changes in flavor (i.e. cooked flavor) when compared to thermally processed Milk.
The main advantages to the consumption of dairy products processed by high-pressure technology are reducing the use of additives and improving the sensory characteristics of products. In HIP, packaged products can be processed while minimizing postcontamination and extending their shelf life. Furthermore, high-pressure technology can contribute to the development of new goods/ingredients, promote consistency of set yogurt, contribute to cheese ripening and flavor characterization, among others. Although the DHP process is less effective on reducing the microbial load, it can improve emulsion formation and stability, providing greater fat–protein interactions, thus favoring consistency of stirred yogurt and ice cream, as well as increasing the yield in cheese making. The protein–fat interactions can reduce the amount of fat in dairy products (yogurt and ice cream), besides maintaining the organoleptic characteristics of the product similar to full-fat products.
However, it is worth mentioning that the HIP and DHP processes are quite different, which result in different changes in milk constituents, thus affecting the sensory characteristics of dairy products. Further studies on the effects of these technologies on milk constituents are needed to assess the final quality of these products.