high hydrostatic processing pressure in cheese

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High Hydrostatic Pressure Processing of CheeseYamile Martnez-Rodrguez, Carlos Acosta-Muniz, Guadalupe I. Olivas, Jose Guerrero-Beltran, Dolores Rodrigo-Aliaga, andDavid R. Sepulveda

Abstract: High hydrostatic pressure (HHP) is a cutting-edge processing technology attracting research and industrial

interest in the food sector due to its potential to produce microbiologically safe products, modify the functional properties

of proteins and polysaccharides, and alter biochemical reactions without significantly affecting the nutritional and sensory

properties of food. Currently, there are only a limited number of pressure-treated cheese products available in the market.

Nevertheless, results from numerous research studies on various cheese varieties seem promising, especially since HHP

technology is today more cost-effective than in the past. Considering the progress made in the application of HHP on

cheese during the past 15 years, this paper reviews the direct application of HHP treatments to cheese and the effects it

has on its microbiology and ripening process, as well as on quality parameters such as physicochemical, rheological, and

sensory properties. Detailed information of published studies is presented with the aim of providing a clear picture of theuse of this technology on cheese processing. Areas of research in need of more attention are also identified.

IntroductionConsumer demand for more natural, preservative-free, tastier,

and more wholesome foods has led to the search of improved foodprocessing technologies. Many research studies over the years have

shown that high hydrostatic pressure (HHP) technology is capa-ble of producing microbiologically safe products, with additional

advantages for consumers and food processors over thermal pro-

cessing. Unlike thermal pasteurization, HHP can maintain keyquality attributes such as food freshness, nutritional value, andsensory properties because it only affects noncovalent bonds, thus

amino acids, vitamins, flavor molecules, and other low-molecular-weight compounds remain unaffected. Furthermore, HHP can

lower production costs due to energy savings (Toepfl and others2006; Pereira and Vicente 2010), reduced processing times (Ser-

rano and others 2004), and fewer handling steps (Serrano andothers 2005), and modify the functional properties of proteins and

polysaccharides, which could lead to the development of novelor improved products. The industrial use of HHP in different

food sectors around the world has risen from 1 in 1990 to 130 in2009, making acquisition costs more accessible as demand increases

(Purroy 2009).

Based on the isostatic principle, pressure applied in HHP treat-ments is instantaneously and uniformly transmitted throughout thefood, regardless of size, shape, and composition. In cheese man-

MS 20120087 Submitted 1/16/2012, Accepted 3/18/2012. Authors Mart nez-

Rodr guez, Acosta-Muniz, Olivas, and Sepulveda are with Centro de Investigaci onen Alimentaci on y Desarrollo A.C., Unidad Cuauht emoc, Av. Rio Conchos S/N,Parque Industrial. C. P. 31570, Apar tado Postal 781, Cd. Cuauht emoc, Chihuahua,M exico. Author Guerrero-Beltr an is with Univ. de las Americas Puebla, Sta. Cata-rina M artir, Cholula, Puebla, C.P. 72810, M exico. Author Rodrigo-Aliaga is withInstituto de Agroqumica y Tecnologa de Alimentos, CSIC, Apartado Postal 73,46100 Burjassot, Valencia, Espana. Direct inquiries to author Sep ulveda (E-mail:

[email protected]).

ufacturing, the application of HHP initially focused on pressure-treating milk and making cheese therefrom, resulting in microor-ganism inactivation, reduced rennet coagulation time, and in-

creased cheese yield, which many research groups have reviewed(Trujillo and others 2000a, 2002; OReilly and others 2001;

Huppertz and others 2002; Lopez-Fandino 2006; San Martn-Gonzalez and others 2006). However, more recently, researchers

have applied HHP directly to the pressed curd and/or ripenedcheese, and studies have centered on 2 main areas: cheese preser-

vation and modification of the ripening process. Pressures appliedfrom 200 to 800 MPa have shown the ability to inactivate lactic

acid bacteria (LAB) and pathogenic and spoilage microorganismspresent in cheese, whereas a combination of low-pressure treat-

ments followed by high pressure treatments has been employedwith some degree of success for the inactivation of bacterial spores

in cheese. The effect of HHP on the ripening process has pro-duced varied results in different cheese varieties studied and in their

physicochemical and sensory characteristics, resulting sometimesin ripening acceleration and with some others in deceleration.

This review takes into account all the studies that have been con-ducted in the past decade dealing with HHP processing of pressed

curds and/or cheese, as well as pertinent results and integrates andcritically discusses the most relevant aspects regarding this topic.

High Hydrostatic Pressure Inactivation ofMicroorganisms in Cheese

Food scientists have employed HHP technology in cheese pro-cessing to inactivate toxigenic and infectious pathogens such as Es-cherichia coli, Staphylococcus aureus, Listeria monocytogenes, Aeromonas

hydrophila, Salmonella enterica, and Yersinia enterocolitica, as well

as spoilage microorganisms such as Staphylococcus carnosus, En-terococcus spp., coliforms, yeasts, and molds, and also microbial

spores from Bacillus subtilis, Bacillus cereus, and Penicillium roqueforti(Table 1). Results have revealed that HHP treatments cause

c 2012 Institute of Food Technologists

doi: 10.1111/j.1541-4337.2012.00192.x Vol. 11, 2012 r ComprehensiveReviewsinFoodScienceandFoodSafety 399


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High hydrostatic pressure processing of cheese . . .

structural and functional alterations in vegetative cells and sporesleading to cell injury or death. These include cell membrane dis-

ruption or increased permeability, ribosomal destruction, collapseof intracellular vacuoles, denaturation of membrane-bound pro-

teins, damage to the proton efflux system, inactivation of keyenzymes, including those involved in DNA replication and tran-

scription, release of dipicolinic acid and small acid-soluble sporeproteins, and hydrolysis of spore core and cortex (Black and others

2011). The factors that influence microbial inactivation by HHP

treatments can be classified into 3 groups: microbial characteris-tics, process conditions, and product parameters (Manas and Pagan2005). Several authors have used a combination of HHP treatments

with other preservation technologies such as antimicrobial agentsto enhance the inactivation rate.

Effect of High Hydrostatic Pressure on VegetativeForms of Microorganisms in CheeseMicrobial characteristics

Yeasts and molds are the microorganisms most sensitive to HHP

treatments. Yeasts are not commonly associated with food-bornedisease but are important in spoilage (Patterson 2005). Daryaei and

others (2008) reported that pressure treatments 300 MPa applied

for 5 min to fresh lactic curd cheese were capable of effectivelycontrolling the outgrowth of yeasts, therefore, extending productshelf-life from 3 to 68 wk. Generally, Gram-positive bacteria are

more pressure-resistant than Gram-negative bacteria. However,there are notable exceptions to the previous statement. For exam-

ple, Shao and others (2007) inoculated raw milk Cheddar cheesewith E. coli O157:H7 and L. monocytogenes Scott A and found

E. coli to be more baroresistant, with decimal reduction values(D-values) at 300 MPa and 25 C of 14.5 and 3.6 min, respec-

tively. It has been suggested that the lack of teichoic acid in thecell wall of Gram-negative bacteria makes them more susceptible

to HHP treatments than Gram-positive bacteria (Datta and Deeth2002).

Several research studies have indicated variations in resistance toHHP among bacterial strains. Strains isolated from foods are gen-

erally more pressure-resistant than strains from culture collections(Cheftel 1995). De Lamo-Castellv and others (2005) observed

that Y. enterocolitica CECT 4055 (setotype O:3) was more baro-tolerant than 2 other human pathogenic strains (CECT 559 and

CECT 4054) of Y. enterocolitica in washed-curd cheese treated at300 MPa. OReilly and others (2000a) showed that food isolatesof S. aureus were more pressure-resistant than S. aureus ATCC

6538, but E. coli K-12 was more pressure-resistant than food iso-lates, with values varying by approximately 2 log cfu/g for both

bacterial species in Cheddar cheese slurry pressure-treated at 400MPa for 20 min. Lopez-Pedemonte and others (2007a) assessed

the inactivation of L. monocytogenes NCTC 11994 and Scott A

in washed-curd cheese at 400 and 500 MPa for 10 min, and re-ported strain NCTC 11994 to be more sensitive to HHP. OReillyand others (2002a) added 4 Lactococcus lactis strains (303, 223, 227,

AM2) in pasteurized milk to make miniature cheese and foundthat at 400 MPa for 20 min, L. lactis 227 was the most pressure-

tolerant with a 2.8 log cycle reduction, while L. lactis AM2 wasthe most pressure-sensitive with a 5.2 log cycle reduction.

Microbial resistance to HHP depends not only on the intrinsicresistance of the microorganisms but also on their physiological

state (Manas and Pagan 2005). OReilly and others (2000a) ob-served that cells of S. aureus ATCC 6538 and E. coli K-12 in the

exponential phase of growth were more sensitive to HHP treat-ments in Cheddar cheese slurry than cells in the stationary phase.

Previous research had associated this behavior to the synthesis ofnew proteins when bacteria enter the stationary phase, protecting

cells against adverse conditions (Patterson and others 2006).

Process conditionsLike any other food preservation technology, in HHP process-

ing, increasing the intensity of treatments or extending their length

of exposure will lead to an increased microbial inactivation rate.Nevertheless, there is a minimum critical pressure below which

microbial inactivation by pressure will not occur irrespective ofprocess time.

Ding and others (2001) observed that higher pressure condi-tions (345 and 550 MPa) and longer exposure times (10 and 30

min) achieved a greater reduction in numbers of undesirable bac-teria in the natural microflora of Swiss cheese slurries (coliforms,

presumptive coagulase-positive Staphylococcus, yeasts, and molds)and in starter LAB added to milk for acid production and fla-

vor development. Fonberg-Broczek and others (2005) found that

A. hydrophila strains (Panstwowy Instytut Weterynaryjny N.98,

Panstwowy Inspekcja Sanitarna N. 98, Inspekcja Sanitarna N. 95)in samples of Gouda cheese treated at 100 MPa and 50 C had a

D-value of 32.05 min, while at 200 MPa the D-value fell to 12.97

min, and to 2.43 min when subjected to 300 MPa. More recently,in raw milk Cheddar cheese, an increase in pressure intensity from250 to 350 MPa applied at 25 C resulted in a decrease of D-values

from 23.5 to 1.4 min forL. monocytogenes Scott A (Shao and others2007).

Lopez-Pedemonte and others (2007b) studied the efficacy ofHHP treatments on the inactivation of S. aureus CECT4013 and

ATCC13565 in washed-curd cheese and the presence of staphylo-coccus enterotoxin (SE) A (artificially inoculated) only in cheese

containing ATCC13565. Inactivation ofS. aureus increased as pres-sure increased from 300 to 500 MPa. However, all cheese samples

still contained SE, but it was not clear if it retained its toxic activityor not. No other research group has addressed the impact of HHP

on bacterial toxins in cheese. SEs are relatively heat-resistant, withD-values at 121 C for SE A, B, and C ranging from 8.3 to 34 min

(Tibana and others 1987). Margosch and others (2005) studied theeffect of HHP and heat on several bacterial toxins in buffer and

reported that pressurization (0.1 to 800 MPa for 30 to 120 min) ofSE A-E at 5 and 20 C caused no observable effect. A combined

heat (80 C) and pressure (0.1 to 800 MPa) treatment led to adecrease in the immunoreactivity to 20% of its maximum. Thehigh barotolerance of SEs is clear from the information provided

by this study.Temperature including adiabatic heating in HHP processing can

have a significant effect on microbial survival. Adiabatic heating isapproximately 3 C for every 100 MPa, depending on the food

composition (Farkas and Hoover 2000). A greater antimicrobial

impact can be achieved with moderate pressure treatments andshorter pressure holding times when combining high tempera-tures with HHP treatments. However, the use of high temperatures

could lead to undesirable effects in certain cheese quality param-eters. Capellas and others (2000) noticed that S. carnosus 4491

CECT counts in Mato cheese could not be greatly decreased withpressure treatments at 500 MPa for 30 min at 10 or 25 C, whereas

treatments at 50 C for 5 min achieved a 7 log cycle reduction.However, treatments at 50 C caused high whey losses and unac-

ceptable textural characteristics. Shao and others (2007) evaluatedthe effect of HHP treatments at 350 MPa for 5 min at 10 to

50 C on E. coli K-12 inactivation in raw milk Cheddar cheese.They also determined pressure destruction kinetics at 200 to

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300 MPa at 25 C. The authors reported that inactivation of E.coli became more significant as the temperature applied in HHP

treatments increased above 40 C. The D-value at 300 MPa was of4.4 min. OReilly and others (2000a) also observed that reduction

in total viable numbers of E. coli K-12 in Cheddar cheese slurryincreased in parallel with the increase of temperature in pressure

treatments above 300 MPa. However, the D-value at 300 MPaevaluated at 20 C widely differed from that indicated by Shao

and others, being 22 min. Differences between studies could be

related to the temperatures used in the experiments, which were5 C higher in Cheddar cheese than in slurry. Another plausibleexplanation may lie in the cheese matrix, with E. colimore sensi-

tive to pressure in cheese than in slurry as a result of acid injury tothe bacteria during fermentation (OReilly and others 2000a).

Product parametersCheese is a food consisting of proteins, fats, carbohydrates, salts,

and minerals. Research studies have indicated that such compo-nents can influence microbial susceptibility to HHP inactivation,

acting as protective colloids to bacterial cells by maintaining themembrane in a more fluid state during pressure treatments, thus

enhancing their resistance to pressure (Molina-Hoppner and oth-

ers 2004). Carbohydrates are generally more protective than salts(Smelt 1998). Water activity and pH also play important roles. Inlow aw environments, enhanced survival of microorganisms oc-

curs due to cell shrinkage, which causes thickening of the cellmembrane, thus reducing its permeability (Goh and others 2007).

Nevertheless, microorganisms injured by pressure are generallymore sensitive to low water activity (Smelt 1998). Bacteria are

sensitive to low pH and more sensitive to suboptimal pH afterpressure treatments, therefore, low pH will not only enhance in-

activation during HHP treatments, but also inhibit outgrowth ofinjured cells (Smelt 1998).

Morales and others (2006) evaluated the effect of cheese a wand carbohydrate content on the barotolerance of L. monocyto-

genes Scott A. As expected, the higher the aw of the cheese, thehigher the inactivation rate, being 3.8 log cycle reductions at 400

MPa for 3 min in Hispanico cheese (aw value of 0.983) and 1 logcycle reduction in Mahon cheese (aw of 0.922) at 400 MPa for

18 min. Addition of lactose at a concentration of 5 mg/g to an85:15 mixture of Mahon cheese:distilled water did not influence

L. monocytogenes barotolerance. On the other hand, galactose atthe same concentration had a protective effect during HHP treat-ments and glucose favored L. monocytogenes Scott A survival during

refrigerated storage of pressurized samples.De Lamo-Castellv and others (2006) reported that no viable

cells of E. coli O59:H21 and O157:H7 were found in pressure-treated (500 MPa) washed-curd cheese manufactured with and

without starter culture when analyzed immediately after treat-

ments. However, in cheese made with starter (pH 4.78), no cell-injury recovery was observed after 15 d of storage at 8 C, whereasin cheese made without starter (pH 6.46) injured cells of both

serotypes recovered reaching counts of up to 6 log cfu/g at theend of the storage period. In a later study, the same research group

evaluated the effect of similar HHP treatment conditions on otherpathogenic bacteria. HHP treatments at 300 and 400 MPa ap-

plied to cheese made with starter culture (pH about 4.82) causedcomplete inactivation of S. Enteritidis CECT 4300 and S. Ty-phimurium CECT 443 with no recovery following 15 d of storage at12 C (De Lamo-Castellv and others 2007). In cheese made with-

out starter culture (pH about 6.53) injured cells of both serotypesrecovered reaching counts over 3 log cfu/g after 15 d of storage.

Carminati and others (2004) determined the inactivation ef-fectiveness of HHP treatments applied for 1 to 15 min at 30 C

and 400 to 700 MPa on the inactivation of 7 hemolytic strains(isolated from the surface of Gorgonzola cheese) belonging to

serotype 1/2a ofL. monocytogenes in Gorgonzola cheese rind. Theauthors reported a strong resistance of the microorganism to pres-

sures up to 500 MPa, requiring treatments of 700 MPa for 15min to reduce L. monocytogenes at least 5 log cycles. In contrast,

Gallot-Lavallee (1998) registered 5.6 log cycle reductions of L.

monocytogenes F13 in 14-d-old Sainte Maure de Touraine cheeseapplying HHP treatments of 450 MPa for 10 min or 500 MPafor 5 min at 11 C. Differences in pH, aw, and the strains studied

could account for the discrepancies encountered in the sensitivityto HHP treatments of the microorganism in both studies. The

lower pH of Sainte Maure de Touraine cheese (4.7), compared tothe Gorgonzola cheese rind (7.0), and its higher aw may favor a

greater bacterial inactivation rate.

HHP in combination with other preservation technologiesSeveral authors have reported a synergistic effect between pres-

sure and antimicrobial compounds like bacteriocins of LAB.

Rodrguez and others (2005) investigated E. coli O157:H7 in-

activation in raw milk cheese made with bacteriocin-producingLAB and HHP-treated on day 2 and 50 at 300 and 500 MPa.The authors observed a synergistic effect after 3 d of ripening that

persisted in 60-d-old cheese. Application of the combined treat-ment at day 50 was more effective than when applied on day 2,

resulting in complete inactivation of E. coli in 60-d-old pressure-treated cheese (300 MPa) made with nisin A-producing L. lactissubsp. lactis TAB 50, L. lactis subsp. lactis biovar diacetylactis TAB57 producing noncharacterized bacteriocin TAB 57, enterocin

I-producing E. faecalis TAB 52, and enterocin AS-48-producing

E. faecalis INIA 4. The authors attributed the higher inactivation

rate of HHP treatments applied at 50 d postmanufacture to dif-ferences in the physiological status of cells and to more favorable

conditions (substrate availability) for injured cells to recover at thebeginning stages of manufacturing rather than at more advanced

stages. They hypothesized that synergism occurred due to sub-lethal injury of the outer membrane of Gram-negative cells or

changes in membrane fluidity caused by HHP treatments, facil-itating the access of bacteriocins through the cytoplasmic mem-

brane. Arques and others (2005a,b) reported similar results whencombining bacteriocin-producing LAB and HHP treatments on

S. aureus CECT 976 and L. monocytogenes Scott A survival in raw

milk cheese. One day after pressure treatments, counts of S. au-reus in control cheese were 6.46 log cfu/g. Bacteriocin-producing

LAB lowered counts in cheese by up to 0.46 log cfu/g, whileHHP treatments at 300 MPa caused a reduction of 0.45 log cfu/g

and 2.43 log cfu/g at 500 MPa. Cheese made with bacteriocin-

producing LAB treated at 300 MPa lowered S. aureus counts onday 3 by up to 1.02 log cfu/g and by up to 4.00 log cfu/g at500 MPa. ForL. monocytogenes, control cheese had 7.03 log cfu/g,

while cheese with bacteriocin-producing LAB had a population of6.41 log cfu/g. Treatments at 300 MPa lowered counts to 6.13 log

cfu/g and the combined effect of both treatments lowered countsto 3.83 log cfu/g.

In summary, HHP can increase the shelf-life and improve thesafety of many cheese varieties. Recently, there have been many

disease outbreaks associated with raw or pasteurized cheese con-sumption all around the world (Table 2), which could be prevented

with the use of HHP alone or in combination with other preser-vation technologies. The barotolerance of spoilage and pathogenic

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Table 2Recent outbreaks associated with cheese contaminated with pathogenic bacteria.

Year Country Cheese variety Pathogen Reference

1995 France, G ermany, a nd I taly Soft a nd s emi soft c heese L. monocytogenes Loncarevic and others 19951997 USA Raw milk cheese S. Typhimurium DT104 Villar andothers 19992001 Italy,Germany, Austria, andFrance Soft and hard cheese L. monocytogenes Rudolf and Scherer 20012001 France Cantal cheese S. enterica Haeghebaert and others 20032002 Canada Unpasteurized Gouda cheese E. coliO157:H7 AICF 20032006 France Raw milk cheese S. enterica Domnguez and others 20092007 USA Raw milk fresh cheese S. Typhimurium CDC 20072010 USA Cold pack cheese food L. monocytogenes FDA2010

2010 USA Queso fresco, panela, requeson L. monocytogenes FDA20102010 USA Gorgonzola cheese E. coliO157:H7 FDA 20102010 USA Gouda and other cheese E. coliO157:H7 CDC 2010

L. monocytogenes2010 Canada Grated cheese L. monocytogenes CFIA 20112011 USA Queso fresco S. aureus FDA20112011 USA Blue cheese L. monocytogenes FSN 20112011 USA Cheddar cheese spread Salmonella spp. Marler 20112012 Australia Country cheese E. coliO157:H7 Food Standards 2012

L. monocytogenes

bacteria in cheese follow the order: S. aureus > L. monocytogenes> E. coli> A. hydrophila > Y. enterocolitica > S. enterica > yeasts,and molds. HHP treatments can achieve complete inactivation of

microorganisms in some cases. However, upon prolonged storage

injured cells may recover. Therefore, it is necessary to conductshelf-life studies over a period of time to ensure microbial safety.Generally speaking, HHP treatments will cause a higher microbial

inactivation rate in cheese with higher aw and lower pH value. Ad-ditionally, the effectiveness of pressure treatments is greater when

applied at more advanced stages of ripening, which also guaran-tees safety in cheese contaminated postpasteurization. In certain

cheese varieties, for example, fresh cheese, the use of high tem-peratures (above 40 C) in HHP treatments could result in highwhey losses and unacceptable textural characteristics. The com-

bined effect between HHP treatments and bacteriocin-producing

LAB is synergistic, enhancing the rate of microbial inactivationas compared to HHP treatments alone. An area of research thatneeds more attention is the effect of HHP on the inactivation of

bacterial toxins. The pH of the system affects the susceptibilityof enterotoxins to thermal inactivation (Erikson 2003). Hence,

strategies such as low pH values combined with HHP treatmentsshould be investigated.

Effect of High Hydrostatic Pressure on MicrobialSpores in Cheese

HHP treatment at 400 MPa applied to cheese at room tem-

perature can easily inactivate yeast and mold spores. In Cheddarcheese slurry, OReilly and others (2000a) reported 6 log cycle

reductions of P. roqueforti spores at 400 MPa for 20 min at 20 C,which did not recover following 72 h of incubation at 8 C. On

the other hand, bacterial spores can survive temperatures over 100C and pressures exceeding 1000 MPa (Smelt and others 2002).Factors such as the low spore core water content, a thick pepti-doglycan layer, low permeability of the inner spore membrane to

hydrophilic molecules, and high levels of minerals and dipicolinicacid account for their high resistance (Knorr and others 2011).

The mechanism of bacterial spore inactivation by HHP involvesspore sensitization, at 1st by low-pressure treatments resulting in

the activation of nutrient germinant receptors, followed by highpressure treatments to inactivate the resultant germinated spores

(Black and others 2007). During inactivation, events such as therelease of dipicolinic acid and small acid-soluble spore proteins,

the hydrolysis of core and cortex, and the decrease of intracellularpH occur (Rendueles and others 2011).

Germination treatments of 60 MPa at 25 C for 210 min, fol-

lowed by inactivation treatments of 500 MPa at 25 C for 15 min,caused a lethality of 2.7 log cycles ofB. subtilis 4491 CECT spores

in Mato cheese that started with an initial concentration of around

5 log cfu/mL in pasteurized milk prior to cheese making (Capellasand others 2000). The same combination of treatments applied at40 C caused a 4.9 log cycle reduction. Under similar conditions

(60 MPa during 210 min at 30 C, followed by 500 MPa for 5 minat 30 C), Lopez and others (2003) reported a 2 log cycle reduction

of B. cereus ATCC 9139 spores (initial count of 6 log cfu/g) after15 d of HHP treatments in washed-curd cheese. Additionally, the

same research group assessed the effect of pressure combined withthe addition of nisin or lysozyme to cheese (Lopez-Pedemonteand others 2003). The highest inactivation rate achieved was 2.4

log cycle reductions at a germination cycle of 60 MPa at 30 C

for 210 min, followed by a destruction cycle of 400 MPa at 30 Cfor 15 min with the presence of nisin (1.56 mg/L of milk).

It is clear from the few studies presented in this section that this

area of research needs attention in order to gain a better under-standing of what factors could help enhance the inactivation of

microbial spores in cheese. Black and others (2011) stated that theproblems with the use of cycle treatments are super-dormancy and

inability to achieve 100% germination, which leads to low inacti-vation rates. The use of high temperatures (above 40 C) in HHP

treatments leads to higher spore inactivation rates as demonstratedby Capellas and others (2000). However, as previously mentioned,

it may cause negative impacts on other cheese quality attributes.To avoid the use of high temperatures, the combination of 1 or

more hurdles with HHP such as bacteriocin-producing LAB orlow pH values should be assessed.

Effect of High Hydrostatic Pressure on CheeseRipening and Related Agents

Cheese ripening is a slow and expensive process due to high

storage costs. Therefore, an efficient way to reduce aging timewithout significantly affecting other quality attributes would pro-

vide significant savings to cheese manufacturers (El Soda and Awad2011). Proteolysis, lipolysis, and glycolysis along with secondary

reactions of the products formed are the biochemical events in-volved in ripening, catalyzed by enzymes derived from milk, co-

agulant, starter LAB, nonstarter LAB, adjunct secondary cultures,and secondary flora. Numerous research groups have assessed the

application of HHP treatments to accelerate the ripening of cheese.The conditions evaluated can be grouped into: high pressure held



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for short times (300 to 600 MPa for 5 to 20 min), low to moderatepressure retained for long periods of time (50 to 200 MPa for up

to 82 h), and combination of shock high pressure treatments fol-lowed by low to moderate pressure treatments (Table 3). Results

have revealed that HHP treatments are able to accelerate cheeseripening by causing alterations in enzyme structure, conforma-

tional changes in the casein matrix making it more susceptibleto the action of proteases, and/or bacterial lysis enhancing the

release of microbial enzymes that promote biochemical reactions

(Messens and others 1998; OReilly and others 2000b, 2003; Saldoand others 2000, 2002a; Garde and others 2007; Voigt and others2010). In addition, HHP treatments increase pH (0.1 to 0.7 units)

and modify water distribution of certain cheese varieties, leadingto enhanced conditions for enzymatic activity (Saldo and others

2002b).

Influence of High Hydrostatic Pressure on ProteolyticEnzymes in Cheese

Primary proteolysis results mainly from the action of plasmin,

chymosin, and to a lesser extent by pepsin, which are respon-sible for the initial hydrolysis of caseins in milk. Plasmin is the

main indigenous proteinase in milk responsible for hydrolyzing

s2- and -caseins at the same rate and s1-casein at a slowerrate (Nielsen 2002). It is stable to pressures of up to 800 MPa incheese, depending on the temperature employed. For example,

the application of 800 MPa for 60 min at 8 C did not inactivateplasmin in 14-d-old Cheddar cheese, while at 20 C its activity

was reduced by 15% compared to controls, and at 30 C up to 50%(Huppertz and others 2004). On the other hand, chymosin is the

major proteinase in traditional animal rennet whose role in cheesemaking is to hydrolyze the Phe105-Met106 bond of-casein during

the coagulation of milk (McSweeney and Sousa 2000). Chymosinis much less barotolerant in cheese than plasmin, being stable to

HHP treatments from 50 to 400 MPa when held between 10and 100 min at temperatures from 2 to 30 C (Messens and oth-

ers 1999; Trujillo and others 2000b; OReilly and others 2002a;Huppertz and others 2004; Rynne and others 2008), although

Saldo and others (2002a) reported that residual coagulant activitywas reduced to about half the value of control cheese after HHP

treatments of 400 MPa for 5 min at 14 C applied to Garrotxacheese on the 1st day of ripening. Juan and others (2007a) observed

a similar result in treatments of 400 MPa applied for 10 min at12 C postmanufacture on semi-hard ewes milk cheese. Chy-mosin activity reduced by 62% compared to control cheese at day

15 of ripening.Other proteinases such as cell envelope proteinase from starter

LAB participate in primary proteolysis by hydrolyzing theintermediate-sized and short peptides produced from the caseins

by the action of chymosin or plasmin (Upadhyay and others 2004).

However, information on the effect of HHP treatments when ap-plied directly to cheese on these enzymes is scarce. Furthermore,there are no published studies on the effect of pressure on the

activity of proteolytic enzymes of adjunct secondary cultures (forexample, Penicillium roqueforti and Penicillium camemberti), which

have an important role in smear and mold-ripened cheese.Secondary proteolysis results mainly from the action of starter

peptidases, which degrade peptides and produce free amino acids(FAA). Most of these enzymes require autolysis of starter bacteria

to be released into the cheese matrix, since they are intracellularenzymes. Results from different studies have shown that pressure-

induced lysis is strain dependent and that HHP treatments canincrease the autolysis of starter culture cells and affect aminopep-

tidase activity in cheese (Malone and others 2002; Juan and others2007a). Juan and others (2008) reported autolysis of starter bac-

teria (L. lactis ssp. lactis and L. lactis ssp. cremoris) to be higher inewes milk cheese when pressure treated at 300 MPa for 10 min at

12 C on day 1 of ripening than on day 15, compared to controlsas determined by lactate dehydrogenase activity, yielding values of

0.39, 0.30, and 0.27 U/g, respectively. These results are consis-tent with those of Malone and others (2002), who observed that

L. lactis ssp. cremoris MG1363 cell suspensions lysed more rapidly

when treated at 300 MPa than those treated between 100 to 200and 600 to 800 MPa for 5 min. In contrast, cell lysis of L. lac-

tis strains 303, 223, 227, and AM2 did not occur in Cheddar

cheese when subjected to HHP in the range of 100 to 400 MPa at25 C for 20 min (OReilly and others 2002a). Also, lactate dehy-

drogenase activity in brined sheep cheese pressure-treated on day15 of ripening at 200 or 500 MPa for 15 min at 20 C was not

statistically different from the control cheese throughout 90 d ofripening (Moschopoulou and others 2010).

Aminopeptidase activity increased in ewes milk cheese whenHHP treated from 200 to 500 MPa and held for 10 min at 12 C,

as cheese aged, and was higher in cheese pressure-treated on day1 of ripening than that treated on day 15 (Juan and others 2007a).

After 60 d of ripening, cheese pressure-treated at 300 MPa onday 1 had the highest activity (8.03 nmol of Leu-p-NA/g per

h) and cheese treated at 500 MPa on day 15, the lowest (2.19nmol of Leu-p-NA/g per h). On the other hand, in 15-d-old

brined sheep cheese, aminopeptidase activity was not significantlyaffected by HHP treatments of 200 or 500 MPa for 15 min at

20 C (Moschopoulou and others 2010).

Influence of High Hydrostatic Pressure on CheeseProteolysis

Pioneering research in cheese ripening acceleration by HHP

treatments began with work performed by Yokoyama and oth-ers (1993) who significantly reduced ripening times of Japanese

Cheddar and Parmesan-type cheese without affecting sensory at-tributes. In the case of Cheddar cheese, a 3-d-old cheese made

with 10 times more starter culture than usual had similar FAAlevels compared to a 6-mo-old commercial Cheddar cheese af-

ter undergoing HHP treatments from 5 to 200 MPa for 72 h at25 C. FAA levels were 16.2, 20.3, 26.5, and 25.3 mg/g after

HHP treatments at 5, 15, 50, and 200 MPa, respectively, while incontrol cheese the FAA level was 21.3 mg/g. Taste was consid-erably superior for the Cheddar cheese HHP-treated at 50 MPa

and commercial control cheese. For the Parmesan-type cheese,the authors treated cheese curd with added italase and lipase at 50

MPa for 72 h at 25 C and claimed that the resultant cheese alsohad considerably superior taste just like the controls. FAA levels

were 76.7 mg/g for treated cheese and 88.7 mg/g for commercial

control cheese. Since the findings of Yokoyama and others manyother research groups have attempted to reproduce their results onCheddar and other cheese varieties.

OReilly and others (2000b) investigated HHP treatments ap-plied at 50 MPa for 72 h at 25 C on day 2, 7, 14, 21, and 28 of age

on commercial Irish Cheddar cheese ripening. Results showed asignificant decrease in the levels of s1-casein and accumulation

of s1-I-casein in cheese during HHP treatments. Pressures ap-plied on day 2, 7, and 14 increased pH 4.6 SN/TN by as much

as 2-fold compared to controls, while those applied at more ad-vanced stages of ripening caused no significant differences. The

authors found increased levels of FAA by 1.4-(Met) to 3.9-fold(Gly, Leu, and Phe) when applying HHP treatments on day 2 of



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ripening. A few years later, the same research group studied theacceleration of Cheddar cheese ripening at more intense pressure

conditions (70 to 400 MPa for 3.5 to 81.5 h at 25 C) (OReillyand others 2003). HHP treatments of 100 MPa held for 70 h

resulted in increased degradation ofs1-casein and maximum ac-cumulation ofs1-I-casein, while treatments performed between

350 and 400 MPa resulted in reduced accumulation. Treatmentsbelow 150 MPa caused the greatest increases in levels of pH 4.6

SN/TN in cheese. Production of total FAA decreased as pressure

increased from 100 to 400 MPa. Conversely, increasing process-ing time up to 60 h, raised total FAA levels. Overall, data fromthese research studies on Cheddar cheese ripening clearly demon-

strate that HHP treatments enhanced proteolysis. However, resultswere not as significant as those obtained by Yokoyama and oth-

ers (1993). OReilly and co-workers attributed differences to thetype (more proteolytic) and quantity of starter culture used in the

manufacturing process of Japanese Cheddar cheese. Other relevantfindings from these studies were that while HHP enhanced prote-

olysis, it did not lead to altered pathways of proteolysis, thus flavorand texture development is very similar in HHP-treated Cheddar

cheese and in traditional commercial Cheddar cheese.On the other hand, Wick and others (2004) subjected 1- and

4-mo-old commercial cheese to pressures ranging from 200 to800 MPa for 5 min at 25 C and reported that HHP treatments

400 MPa could be useful in arresting ripening. FAA levels in1-mo-old cheese treated at pressures of 400, 500, and 800 MPa

were approximately 0.09, 0.06, and 0.04 mmol/g after 160 daysafter the pressure treatments, respectively, while those treated at

lower pressures (200 and 300 MPa) had the same FAA contentas the controls (0.16 mmol/g). Pressure treatments (500 to 800MPa) applied to 4-mo-old cheese resulted in significantly lower

FAA content than control cheese beyond 56 d of storage. Similarly,Rynne and others (2008) suggested that HHP conditions of 400

MPa for 10 min at room temperature applied to 1-d-old full-fatCheddar cheese may be useful to arrest or slow down ripening.

These studies along with those performed by OReilly and othersindicate that low to moderate HHP treatment conditions (50 to

150 MPa) applied to young Cheddar cheese are effective at ac-celerating proteolysis, whereas higher HHP treatment conditions

(400 MPa) may help cheese manufacturers arrest the ripeningprocess at a desired stage, thus maintaining optimum commercial

attributes for a longer period of time.Accelerated proteolysis due to HHP treatment has also been

achieved in other cheese varieties such as smear and mold-ripenedcheese, Garrotxa, and ewes milk cheese, but not in Gouda, Edam,

or mozzarella cheese.The application of 50 MPa for 8 h at 20 C to Pere Joseph and

Paillardin cheese accelerated proteolysis near the rind (Messensand others 2000, 2001). The authors noted increased pH in HHP-

treated cheese, which probably resulted in a higher amount and/oractivity of proteolytic enzymes of Brevibacterium linens and Peni-cillium camemberti, and in higher activity of peptidases of starterculture. They also observed higher levels of 12% TCA-SN/TN

and FAAs near the center of HHP-treated cheese, probably as aresult of diffusion toward the center of small peptides and amino

acids formed at the rind. In addition to the pH effect, Messens andothers attributed the enhancement of proteolysis to a weakening

of hydrophobic interactions, which might have led to an increasedexposure of susceptible bonds that are cleavable by proteolytic

enzymes. Similarly, in Camembert cheese exposed to HHP treat-ments from 0.1 to 500 MPa for 4 h at 5 C after 5 or 10 d

of ripening Kolakowski and others (1998) observed the most in-

tense proteolysis at pressures of 50 MPa for 10-d-old cheese. In42-d-old Irish blue-veined cheese, HHP treatments at 400 and

600 MPa for 20 min at 20 C accelerated primary and secondaryproteolysis as a result of enzyme activation or changes in protein

conformation (Voigt and others 2010). Two-dimensional SDS-PAGE gel electrophoresis indicated accelerated breakdown of-

and s2-casein at 400 and 600 MPa. Levels of phosphotungsticacid (PTA) SN/TN after 14 and 28 d of pressure treatments were

8.65% and 10.79%, respectively, while those of control cheese were

4.56% and 9.04%. Contradictory results were found by Messensand others (1999) and Kolakowski and others (1998) who didnot observe any significant differences in proteolysis rates between

pressure-treated Gouda cheese and control cheese after applyingHHP treatments between 50 and 500 MPa held for 20 to 100

min at 14 C as determined by pH 4.6 soluble nitrogen (SN),PTA SN, FAA content, and SDS-PAGE profiles, despite finding

higher pH values in pressure-treated cheese. Moreover, Messensand others (1999) also tested the same HHP treatment conditions

employed by Yokoyama and others (1993) to accelerate Ched-dar cheese ripening and reported no acceleration of Gouda cheese

ripening. Differences encountered in these studies could be relatedto the proteolytic activity of peptidases from secondary cultures

and to the levels and activity of residual rennet in each cheese va-riety. Proteolysis is more pronounced in mold- and smear-ripened

cheese than in bacterially ripened cheese since not only proteinasesand peptidases from starter bacteria, plasmin, and rennet partic-

ipate, but also exo- and endopeptidases from secondary cultures(Voigt and others 2010). Unfortunately, as previously stated, the

effect of HHP treatments applied directly to cheese on the ac-tivity of proteolytic enzymes of adjunct secondary cultures is notwell known. Concerning residual rennet activity, levels range from

15% in Gouda cheese to about 50% in Camembert cheese, typi-cally being higher in Camembert, followed by Cheddar and lower

in Gouda cheese (Bansal and others 2007, 2009). Hence, low-intensity HHP treatments may enhance chymosin activity to a

greater extent in certain cheese varieties in comparison with oth-ers depending on natural residual activity level.

More recently, Wachowska (2010) applied HHP treatments at50 and 100 MPa for 0.5 h at 18 C to extracts of frozen Edam

cheese after 1, 4, 6, and 8 wk of ripening in order to, 1st, inducelysis of starter culture cells and, second, enhance enzyme activity.

Results showed no significant differences in the proteolytic activ-ity of enzymes from controls and frozen pressurized cheese. These

results were similar to those reported by Iwanczak and Wisniewska(2005) in which Edam cheese subjected to pressurization at 200

and 400 MPa for 30 min at room temperature directly after salting,and after 4, 6, and 8 wk of ripening, did not differ in proteolysis

indexes from controls as measured by levels of nonprotein nitro-gen, amino acid nitrogen, and pH 4.6 SN. In Garrotxa cheese

pressurized at 50 MPa for 72 h at 14 C 1 d after salting, levelsof proteolysis were only slightly different from those in control

cheese, with differences being less apparent after 28 d of r ipening(Saldo and others 2002a). However, treatments at 400 MPa for 5

min enhanced the production of FAAs, reaching twice the valuefound in control cheese after 28 d. An increase in peptidase activity

(produced by cell lysis) favored by high moisture content and pH(33.6%, 5.0 in controls and 39.7%, 5.4 in pressure-treated cheese)

caused the acceleration of secondary proteolysis. The combinationof these last 2 conditions (shock high pressure treatment at 400

MPa for 5 min at 14 C, followed by a low-pressure treatmentof 50 MPa for 72 h), reduced the ripening period of Garrotxa

from 28 to 14 d as determined by noncasein nitrogen, nonprotein



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nitrogen, and FAA levels (Saldo and others 2000). According tothe authors, the treatment at 400 MPa caused a release of micro-

bial enzymes into the cheese matrix, and the 50 MPa treatmentenhanced enzyme activity. To a certain extent, the use of different

starter cultures in Edam cheese and Garrotxa cheese could haveled to the different outcomes observed during secondary prote-

olysis in these cheese varieties after pressure treatments. Starterbacteria in Garrotxa cheese are lysed after an HHP treatment of

400 MPa, causing a release of peptidases that accelerate secondary

proteolysis, whereas in Edam cheese, this effect does not occur.With regard to primary proteolysis, Saldo and others (2000) no-ticed an increase in the proteolytic activity of rennet during HHP

treatments, whereas Iwanczak and Wisniewska (2005) reportedno significant differences in the proteolytic activity of enzymes in

pressurized cheese and control, based on analysis of the contentof 12% trichloroacetic acid (TCA)-soluble nonprotein nitrogen

compounds and 2% TCA-soluble compounds.In mozzarella cheese, HHP treatments have not resulted in ac-

celerated proteolysis under the conditions tested. Sheehan andothers (2005) applied 400 MPa for 5 min at 21 C to 1-d-old

reduced-fat mozzarella cheese (10.7% fat) and reported no signif-icant effect of HHP treatments on mean levels of pH 4.6 SN or

PTA SN over 35 d of ripening. In a similar manner, OReillyand others (2002b) reported no significant differences in proteol-

ysis indexes in pressure-treated (400 MPa for 20 min at 25 C)low-moisture mozzarella cheese compared to controls at different

stages of ripening (every 5 d starting from day 1 up to day 25).There was no effect on the extent of casein degradation, pH 4.6

SN/TN, and total levels of FAA. These results coincide with thoseof Johnston and Darcy (2000) on immature mozzarella cheese, inwhich proteolysis as indicated by water soluble nitrogen, was un-

affected by HHP treatments. Chymosin inactivation in mozzarellacheese, due to the utilization of high cooking temperatures during

manufacture, could, to a certain extent, explain the results fromthe previously described studies. Past research has demonstrated

that among different cheese varieties, evaluated for the extent ofresidual coagulant activity, low-moisture part-skim mozzarella and

mozzarella di bufala Campana have the lowest values (Bansal andothers 2009).

Juan and others (2007a) evaluated changes in proteolysis ofewes milk cheese after HHP treatments from 200 to 500 MPa for

10 min at 12 C applied on the 1st and 15th d of ripening. At60 d of ripening, pressures of 300 and 400 MPa applied on day

1 and pressures of 200 to 500 MPa applied on day 15 enhancedprimary proteolysis, as determined by casein degradation, as a

consequence of the barostability of plasmin combined with con-formational changes in the casein structure. HHP treatments of

500 MPa on day 1 produced the highest level of intact s1-caseinand para--casein as a result of chymosin inactivation. The authors

observed increased peptidolytic activity and the highest amountof FAA in cheese after treatment of 300 MPa applied on day 1,

which favored the lysis of starter bacteria, enhancing the releaseof intracellular aminopeptidases into the cheese matrix. Avila and

others (2006) reported similar results in Hispanico cheese manu-factured with a mixture of cows and ewes milk. HHP treatments

at 400 MPa for 5 min at 10 C applied after 15 days of ripeningaccelerated the hydrolysis of casein and increased total FAA con-

tent. Also, Garde and others (2007) assessed the effect of HHPtreatments at 300 or 400 MPa for 10 min at 10 C applied on

days 2 or 50 of ripening on the proteolysis of La Serena cheesemade from raw sheep milk. Proteolysis, as determined by the o-

phthaldialdehyde test, was highest in cheese treated at 400 MPa onday 2 after 60 days of r ipening. Levels of Ile, Ser, Pro, Met, and Thr

more than doubled compared with control cheese. In this study,higher aminopeptidase activity on Lys-p-NA favored by higher

pH values and conformational changes in peptide structures werein part responsible for enhanced proteolysis. In contrast, the re-

sults reported by Juan and others (2007a) show that cheese treatedat 300 or 400 MPa on day 2 exhibited lower casein degradation

than controls after 60 d of ripening. Possible differences in the

outcomes between studies could be related to the use of rennetsfrom different origin. Juan and others (2007a) used calf rennet,which contains chymosin and to a lesser extent pepsin, whereas

Garde and others (2007) used Cynara cardunculus aqueous extractsthat contain cardosin A and B, which could be affected more than

chymosin and pepsin by HHP treatments. The effect of pressureon proteinases from this type of rennet has not been studied.

To summarize, the application of HHP treatments acceleratesor arrests proteolysis in cheese depending on cheese variety and

on the intensity of treatments. Up to now, the most effective com-bination of treatments employed to accelerate (Cheddar) cheese

proteolysis without negatively affecting its sensory properties hasbeen to add an abnormally large quantity of starter culture (up

to 10 times) followed by low-pressure treatment (Yokoyama andothers 1993). Research focused on evaluating the direct applica-

tion of HHP treatments to cheese and the effects it causes onenzymes from starter and secondary adjunct cultures are not avail-

able and could help optimize treatment conditions to accelerateor decelerate cheese ripening. For commercial purposes, it would

be interesting to compare the results in proteolysis accelerationemploying current methods individually (elevated ripening tem-peratures, modified starters, and so on) and those obtained by

HHP (OReilly and others 2001).

Influence of High Hydrostatic Pressure on CheeseLipolysis and Glycolysis

Limited information is available on the impact of HHP treat-ments on cheese lipolysis and glycolysis (Table 3). Lipolysis is the

major biochemical event in blue and Italian cheese varieties, car-ried out by esterases and lipases that catalyze the hydrolysis of the

ester bond in milk triglycerides, yielding free fatty acids and glyc-erol and mono- and diglycerides (Avila and others 2007). Pressure

treatments 400 MPa applied to Garrotxa, blue-veined, ewesmilk, and Hispanico cheeses have resulted in decelerated lipolysis,

with a reduction of LAB counts or inactivation of enzymes as themain factors causing this effect.

HHP treatments applied to Garrotxa cheese at 400 MPa for5 min at 14 C postmanufacture decelerated lipolysis, resulting in

cheese with lower amounts of free fatty acid (FFA) (C 4:0, C6:0,and C8:0) compared to controls (Saldo and others 2003). Factors

considered having influenced results were reduction of lactococcicounts (3 log units) or inactivation of lipolytic enzymes from sec-

ondary microbiota in cheese caused by HHP treatments. Voigt andothers (2010) reported similar observations at more intense HHP

treatment conditions in a 42-d-old blue-veined cheese. Levels ofFFAs decreased to a greater extent in HHP-treated cheese than

in control cheese over 28 d of storage. According to the au-thors, this observation could reflect reduced lipolytic activity of P.roqueforti, consistent with the 3.42 log cycle reduction caused bytreatment of 600 MPa for 10 min at 20 C compared to control

cheese which experienced a 2.68 log cycle reduction during thesame time period. In ewes milk cheese pressure-treated at 400 to



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500 MPa on day 15 of ripening for 10 min at 12 C, Juan andothers (2007b) reported the lowest concentration of total FFAs

compared to controls at 60 d of evaluation. They attributed thisresult to reduced water availability for the enzyme at this stage

of ripening or to lipid-protein interactions, which could haveprotected lipid hydrolysis by enzyme action. On the other hand,

cheese pressure-treated on day 1 of ripening at 300 MPa exhibitedthe highest levels of C8:0, C10:0, C14:0, and C18:1 FFAs after 60 d

of ripening presumably as a result of faster release of intracellular

enzymes into the cheese induced by pressure treatments.Avila and others (2007) investigated the effect of HHP treat-

ments applied after 15 d of ripening at 400 MPa for 5 min at 10 C,

separately or combined with addition of bacteriocin-producingLAB, on the release of intracellular esterases and cheese lipolysis

in Hispanico cheese. On day 15, the esterase activity value foundin pressure-treated cheese was similar to that of controls (0.49 and

0.52 pmol of-naphthol released/min/g of cheese, respectively),with no significant differences after 50 d of ripening (0.99 and

1.08 pmol of-naphthol released/min/g of cheese, respectively),indicating a notable barotolerance of the enzyme. However, total

FFAs (C4:0-C18:2) were lower in treated cheese (579.90 mg/kgof cheese) than in control cheese (612.47 mg/kg of cheese) after

50 d as a result of LAB inactivation. Combined treatments, includ-ing addition of bacteriocin-producing LAB and cheese pressuriza-

tion, produced the highest value of esterase activity after 50 d ofripening in comparison to other treatments, with 1.38 pmol of-naphthol released/min/g of cheese due to lysis of LAB cells, fol-lowed by the release of esterases into the cheese matrix. In general,

HHP-treated cheese with bacteriocin-producing LAB showed thesame pattern of lipolysis (release of FFAs) than controls. In full-fatCheddar cheese, treated postmanufacture at 400 MPa for 10 min

at room temperature, lipolysis was not significantly different fromcontrols over 180 d of ripening (Rynne and others 2008). Total

FFA levels in the treated cheese were numerically higher thanthose in the control cheese up to 42 d, but were lower thereafter,

with approximately 1100 mg/kg of cheese in treated cheese at 180d of ripening and 1200 mg/kg of cheese in control cheese.

The metabolism of residual lactose, lactate, and citrate (glycol-ysis) is essential in the early stage of ripening in all cheese varieties

(McSweeney 2004), but is the least studied in regard to HHP treat-ments. Only 1 research group has evaluated changes in glycolysis

in cheese after HHP treatments. Employing the same conditionspreviously described in the study of lipolysis, Rynne and others

(2008) observed the mean concentration of total lactate in HHP-treated cheese to be significantly lower compared to controls after

180 d of ripening, with 1.1 g/100 g of cheese in treated cheese and1.4 g/100 g in control cheese. The authors attributed the result

to the inactivation of starter bacteria as a consequence of HHPtreatments. The mean concentration of D(-)- and L(+)-lactate also

decreased significantly with the pressure treatment.

Effect of High Hydrostatic Pressure onPhysicochemical, Rheological, and SensoryProperties of Cheese

The physicochemical and sensory properties of cheese are themost valued. Almost all varieties have special characteristics that

make them different in commercial terms. Therefore, ensuring thatthe processing technologies applied to them do not affect these

identity attributes in a negative fashion is of utmost importance.Table 4 summarizes the results from studies conducted on cheese

in regard to the impact HHP treatments have on physicochemical,rheological, and sensory properties.

Influence on Physicochemical PropertiesHHP treatments do not change total solid, ash, fat, protein,

moisture, and nutrient contents in cheese (Capellas and others

2001; Sandra and others 2004; Serrano and others 2004; Sheehanand others 2005; Rynne and others 2008; Moschopoulou and

others 2010; Koca and others 2011). On the other hand, pressuretreatments modify the pH to an extent that depends on treatment

conditions and cheese age. Research studies have shown a higherpH value of pressure-treated cheese compared to controls in vari-

eties such as Camembert (Kolakowski and others 1998), Cheddar(Rynne and others 2008), ewes milk cheese (Juan and others

2007a, 2008), fresh cheese (Sandra and others 2004; Okpala andothers 2010), Edam (Iwanczak and Wisniewska 2005), Garrotxa

(Saldo and others 2000, 2002a), Gouda (Kolakowski and oth-ers 1998; Messens and others 1998, 1999), Manchego (Pavia and

others 2000), mozzarella (Johnston and Darcy 2000), La Serena(Arques and others 2006, Garde and others 2007), Pere Joseph

(Messens and others 2000), and Paillardin (Messens and others2001). This result is more pronounced at higher pressure levels,

longer exposure times, and when applying treatments at an earlystage of ripening, due to the release of colloidal calcium phosphate

into the aqueous phase of cheese, LAB inactivation, or reduced

ability of LAB to produce acid even when there is no apparent lossof cell viability as a result of damage to the glycolytic enzymes.

However, pH differences between treated and nontreated samplesbecome less significant during the r ipening process.

HHP treatments also alter water and salt distribution in thecheese matrix. Messens and others (1999) observed a reduction in

water loss during brining of Gouda cheese at pressures from 300to 500 MPa. Explanations offered for this phenomenon were the

conversion of free water into protein-bound water and a reducedcompliance of the cheese matrix during pressure brining. Saldo

and others (2001) made similar observations on Garrotxa cheesetreated at 50 MPa for 72 h at 25 C. Results showed that treated

samples and controls had the same moisture contents, but water

retention was different. HHP-treated cheese had 12.7% free wa-ter and 27.6% bound water, whereas control cheese had 18.9%free water and 21.4% bound water. They also observed that so-

lute diffusion improved by pressure treatments as enhanced saltdistribution occurred in treated cheese. Likewise, Juan and others

(2008) observed better salt diffusion in ewes milk cheese pressure-treated at 300 MPa for 10 min at 12 C on day 1 or 15 of ripening.

HHP-treated cheese showed higher levels of salt-in-moisture con-tent in the medium and interior sectors than control cheese at 15

and 60 d of ripening, respectively. In contrast, HHP treatmentsfrom 50 to 500 MPa applied to Gouda cheese and Manchego

cheese during brining did not significantly affect salt uptake or saltdiffusion (Messens and others 1999; Pavia and others 2000). Saldo

and others (2001) stated that the preliminary step of salt intake by

capillarity seems necessary to allow the increase in solute mobilityobserved in cheese samples subjected to HHP.

Color is another parameter significantly affected when apply-

ing HHP to cheese, and the factors that influence this attributethe most are treatment temperature, pressure intensity, and hold-

ing time. Total color difference values of 1-d-old Mato cheesetreated at 500 MPa for 5, 15, and 30 min at 10 C were higher

than those of cheese treated at 25 C and in 5 min cycles, mainlydue to L value changes which were lower compared to con-

trols (Capellas and others 2001). The b value was the index thatchanged the most in all treatments, increasing as pressure holdingtime increased. The authors related increase in lightness and yel-

lowness of the cheese surface to microstructural changes. Control



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cheese displayed longitudinal concavities on the surface, whereaspressure-treated cheese had a more uniform and smoother surface.

Trained panelists also perceived HHP-treated queso fresco cheese(400 MPa for 20 min at 20 C) to be more yellow than controls

when evaluated 1 d after pressurization (Sandra and others 2004).However, cheese evaluated 8 d after pressure treatments displayed

no significant differences in comparison with controls.Saldo and others (2002c) evaluated color changes in HHP-

treated Garrotxa cheese at 400 MPa for 5 min at 14 C 3 d

postpressurization, during ripening, and 60 d after pressure treat-ment. L-values were significantly lower in pressure-treated cheesefrom day 3 to 30, after which they became similar to the val-

ues observed in control cheese, whereas a- and b-parameters werehigher throughout the evaluation period with treated cheese hav-

ing a more yellow-orange color. Saldo and others did not assesschanges in the microstructure of cheese at the treatment con-

ditions employed, but stated that changes in cheese color afterHHP treatments could be related to differences in microstructure

between treated and untreated cheese. More recently, Koca andothers (2011) pressure-treated Turkish brined white cheese in the

range of 50 to 400 MPa held for 5 and 15 min at 22 C and didnot observe any effect on the L value. However, higher pressure

levels and longer pressure-holding times resulted in significantlylowera values and higher b values, making treated cheese more

greenish and yellowish. Cheese treated at 50 and 100 MPa hada sponge-like structure with fat globules of different sizes and

also large mechanical holes in the protein matrix, similar to un-pressurized cheese, while those treated at 200 and 400 MPa had

denser and more continuous casein structures. Rynne and oth-ers (2008) made similar observations on 1-d-old full-fat Cheddarcheese treated at 400 MPa for 10 min at room temperature. Color

analysis of HHP-treated cheese indicated that L-values remainedconstant, a-values decreased, and b-values increased in compari-

son with controls, resulting in cheese being more green and yellowthroughout the evaluation period of 6 mo.

Influence on Rheological PropertiesThe rheological properties of cheese are important to manu-

facturers since they influence texture, eating quality, and phys-

ical behavior, which depend on composition, microstructure,macrostructure, and physicochemical state of components (Guinee

2011). Serrano and co-workers have described one of the most sig-nificant findings of the impact of HHP on cheese rheology. Mod-erate pressure treatments (345 and 483 MPa) applied to unripened

milled or stirred-curd Cheddar cheese for up to 7 min modified itsmicrostructure and textural properties, which resulted in acceler-

ated shredability (Serrano and others 2004, 2005). Results showedsimilar visual and tactile sensory properties for 27-d-old shred-

ded control cheese and 1-d-old pressure-treated shredded cheese.

Furthermore, HHP treatments reduced the amount of crumbles,increased mean shred particle length, improved length unifor-mity, and enhanced surface smoothness in shreds produced from

unripened cheese. The authors stated that their results could re-duce manufacturing costs to cheese processors that shred Cheddar

cheese as a means of adding value to their product, by at least US$30/1000 kg, when shredding immediately after block-cooling,

and suggested that their results could be applicable to other cheesevarieties.

In a study conducted on a low-moisture mozzarella cheese,HHP treatments (400 MPa for 20 min) also accelerated age-related

changes in microstructure, protein hydration, and cooking char-acteristics, which reduced the time required to attain a satisfactory

cooking performance (OReilly and others 2002b). HHP-treatedcheese showed an increase in fluidity, flowability, stretchability,

and reduced melting time on heating at 280 C due to an en-hanced development of age-related swelling of the paracasein ma-

trix and increased protein hydration. In contrast, Sheehan andothers (2005) reported no significant effect on rheological prop-

erties of reduced-fat mozzarella cheese after an HHP treatmentof 400 MPa for 5 min. They attributed the differences between

their study and that of OReilly and others to the higher protein

and lower fat levels in their cheese, moment of application, andpressure holding times. Rynne and others (2008) evaluated sim-ilar conditions to those tested in low-moisture mozzarella cheese

on Cheddar cheese. They reported that HHP treatments at 400MPa applied for 10 min at room temperature 1-d postmanu-

facture did not significantly affect the mean values for firmness,but increased fracture strain and fracture stress values throughout

180 d of ripening. Pressure negatively affected viscoelastic andcooking properties. Treated cheese had lower fluidity and flowabil-

ity than control cheese. Although stretchability increased up to 21d,it did soto a lesser extent thancontrolcheese (24.5 cm at day 1 to

30 cm at day 21 compared to 13.7 cm at day 1 to 66.3 cm at day21). According to the authors, differences in both studies could

be related to insufficient hydration of the paracasein matrix in theHHP-treated Cheddar cheese at the conditions evaluated.

Juan and others (2007c) studied the effect of pressure treamentsfrom 200 to 500 MPa for 10 min at 12 C, applied on day 1

or 15 after manufacture, on ewes milk cheese rheological andtextural characteristics. Cheese treated on day 15 was similar to

control cheese. Moderate pressures (200 to 300 MPa) enhancedfirmness and cheese treated at higher pressures (500 MPa) showedthe highest deformability and the lowest fracturability and rigidity.

Juan and others related their results to higher water retention ca-pacity, higher pH value, and a more homogeneous microstructure

in HHP-treated cheese, which contributed to higher dispositionto deformation and to a reduction of possible areas of fracture.

Trained panelists evaluated textural properties of cheese at 30 and60 d of ripening and found cheese treated at 500 MPa to be less

crumbly and to be the most elastic cheese among all the cheesessubjected to different HHP conditions. Other research studies have

reported similar observations in other cheese varieties at high-pressure conditions. Low-pressure treatments (50 MPa for 72 h at

25 C) applied to Garrotxa cheese made it more fluid and less elas-tic than controls (Saldo and others 2001). Hardness and shortness

remained higher in control cheese, indicating a softening of cheesedue to a weakening of the casein matrix. Higher pressure treat-

ments (400 MPa for 5 min at 14 C) resulted in cheese being lesscrumbly and more elastic than controls (Saldo and others 2000).

In queso fresco cheese, controls and HHP-treated cheese (400MPa for 20 min at 20 C) were not significantly different in most

textural attributes evaluated (Sandra and others 2004). The mostnotable difference found in this study was that pressure-treated

cheese was less crumbly than controls. Texture profile analysis in-dicated that firmness, gumminess, and chewiness were higher in

treated cheese than in control cheese 1 d after pressure treatments,but significantly lower after 8 d.

Messens and others (2000) determined the rheological prop-erties of HHP-treated Gouda cheese (50, 225, and 400 MPa for

1 h at 14 C applied 3 d after brining) immediately after pressurerelease (day 0), and after 21 and 42 d of ripening. At day 0, the vis-

coelastic properties of cheese treated at 225 and 400 MPa differedsignificantly from those of untreated cheese. HHP-treated cheese

was less rigid and solid-like, more viscous, and had less resistance



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to flow. According to the authors, these rheological changes weredue to the weakening of hydrophobic interactions and not to

changes in the pH, water content, or proteolysis level. At day 42,there were no significant differences in the rheological properties

between treated and untreated cheese. Wick and others (2004)assessed the effects of HHP treatments ranging from 200 to 800

MPa for 5 min at 25 C on the rheological properties of 1- and4-mo-old Cheddar cheese. Pressures up to 300 MPa applied to 1-

mo-old cheese had no significant effect on fracture stress, fracture

strain, fracture work, and Youngs modulus. In a similar manner,extremely high pressure (800 MPa) resulted in cheese with similarfracture stress and Youngs modulus across 160 d of storage than

controls. HHP treatments applied to 4-mo-old cheese had no sig-nificant effect on rheological properties, except for fracture work,

which increased in HHP-treated cheese. Garde and others (2007)reported that fracturability, hardness, and elasticity were higher

throughout ripening in La Serena cheese, pressure-treated at 300or 400 MPa for 10 min at 10 C on day 2 of ripening, than in

control cheese and in cheese pressure-treated on day 50. Resultsshowed a strong correlation between residual s1- and -caseins

and cheese hardness. HHP treatments on day 2 had a negativeeffect on texture preference when evaluated by trained panelists.

Influence on Sensory PropertiesOne of the most frequently cited benefits of employing HHP

in food processing over traditional methods, such as heating, isensuring microbiological safety while still retaining the sensory

quality characteristics of fresh food products. In cheese, this is trueif treatment conditions are not too intense and not applied in

the early stages of ripening. This behavior is mainly due to thehigher inactivation rates observed in HHP treatments applied on

immature cheese, which hinders the formation of certain volatilecompounds and lowers enzymatic activity. Ding and others (2001)

found more intense pressure treatments (550 MPa compared to345 MPa) held for longer periods of time (30 min compared to 10

min) to cause a greater reduction in microorganism counts withless outgrowth during ripening, which resulted in Swiss cheese

slurries with less aroma development. Delgado and others (2011)observed that lower pressure treatments (400 MPa compared to

600 MPa) applied at more advanced stages of ripening (50 d com-pared to 30 or 1 d) produced less intense changes in the volatile

profile of treated raw milk goat cheese compared to controls. HHPtreatments applied on day 1 decreased the amount of most volatilecompounds due to LAB inactivation, but enhanced the formation

of ketones, hydrocarbons, and -decalactone.Arques and others (2007) evaluated volatile compounds, odor,

and aroma of La Serena cheese HHP-treated at 300 or 400 MPafor 10 min at 10 C on day 2 or 50 after manufacture. HHP treat-

ments applied on day 50 did not influence either the volatile com-

pound profile or the sensory characteristics of 60-d-old cheese.On the other hand, pressure treatments on day 2 enhanced theformation of branched-chain aldehydes and 2-alcohols except 2-

butanol, but retarded the formation of n-aldehydes, 2-methyl ke-tones, dihydroxy-ketones, n-alcohols, unsaturated alcohols, ethyl

esters, propyl esters, and branched-chain esters. Differences in thelevels of some volatile compounds between treated and untreated

cheeses disappeared during ripening. The odor quality and inten-sity of 60-d-old cheese were not significantly affected by HHP

treatments on day 2, but aroma quality and intensity of cheesetreated at 400 MPa resulted in significantly lower sensory scores

than obtained for the control cheese. Scores for families of odorand aroma descriptors (lactic, vegetable, floral, toasted, and ani-

mal) were not significantly affected by any of the HHP treatmentsapplied on day 2 or 50.

Juan and others (2007d) investigated the effect of pressure condi-tions between 200 and 500 MPa applied on day 1 or 15 of ripening

for 10 min at 12 C on the volatile profile of cheese made fromewes milk. Cheese pressurized after 15 d of ripening and that

treated on day 1 at 200 MPa were similar to controls. Higher pres-sure treatments applied on day 1 altered microbial populations and

enzyme activities, enhancing or limiting the formation of volatile

compounds. Cheese pressure-treated at 300 MPa showed higherlevels of FFAs, ethanol, ethyl esters, and branched-chain aldehydes,whereas cheese treated at 500 MPa showed the highest amounts

of 2,3-butanedione, pyruvaldehyde, and methyl ketones and thelowest amount of alcohols.

Avila and others (2006) investigated the effect on volatile com-pounds, odor, and aroma of 15-d-old Hispanico cheese HHP-

treated at 400 MPa for 5 min at 10 C made with and with-out bacteriocin-producing LAB culture. Treated cheese showed

higher levels of hexanal, 3-hydroxy-2-pentanone, 2-hydroxy-3-pentanone, and hexane and lower levels of ethanal, ethanol,

1-propanol, ethyl acetate, ethyl butanoate, ethyl hexanoate, 2-pentanone, and butanoic acid in comparison with untreated

cheese. HHP-treated cheese received higher milky odor de-scriptor scores and lower scores for odor quality and intensity,

as well as, for buttery, yogurt-like, and caramel odor de-scriptors. Addition of the bacteriocin-producing LAB culture, en-

hanced the formation of 3 aldehydes, 3 alcohols, 3 ethyl esters,and 3 ketones, but decreased levels of 7 ketones and butanoic acid.

Cheese made with bacteriocin-producing LAB received higherscores for aroma intensity and for yogurt-like and cheesyaroma descriptors.

Alonso and others (2011) pressure-treated curds made fromsheep milk immediately after manufacture at 400 and 500 MPa

for 10 min at 8 C and froze them for 4 mo. After thawing,the authors mixed treated curds (20%) with fresh cow milk curd

(80%) for the manufacture of Hispanico cheese. Cheese obtained

with curds treated at 400 MPa showed the highest concentrations

of short-chain and long-chain FFAs, 2-propanol, 2-butanol, 2-pentanol, and ethyl hexanoate after 30 and 60 d of manufacture,

while those treated at 500 MPa had the lowest concentrations ofall compounds identified, except for 2,3-butanedione on day 60.

All treatments (including controls) caused similar counts of to-tal viable bacteria, mesophilic LAB, and thermophilic LAB, but

cheese treated at 400 MPa had higher enzyme activity comparedto controls as a result of cell lysis. The authors also stated that wild

strains of LAB surviving HHP could be responsible for differencesin the profile of cheese volatiles.

The changes induced by HHP treatments described in the lit-erature in regard with the physicochemical, rheological, and sen-

sory properties of cheese are not necessarily negative and in somecases are even beneficial, economically speaking. Even though

changes in these attributes can be observed when HHP treatmentsare applied in the early stages of ripening, they are minimized

or even disappear during ripening. However, novel or distinctivecheese textures, aromas, tastes, and appearances can be obtained

depending on treatment conditions which could be appealing toconsumers.

Commercial Applications and Opportunities for HHPProcessing of Cheese

The decision to implement HHP processing as a commer-cial preservation or ripening acceleration method requires careful



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S. aureus >

L. monocytogenes >

E. coli >

A. hydrophila >

Y. enterocolitica >

S. enterica >

yeasts and molds

Treatment conditionsPressure / Time / Temperature

Microorganisms Enzymes

Plasmin >

Pepsin >

Chymosin

Impact in cheese

Figure 1Schematic representation of the effect of HHP on microorganisms and enzymes in cheese.

planning based on technical and business plans (Farkas 2011). At

the present moment, there are some cheeses and cheese-relatedproducts processed with HHP technology available in the Euro-

pean market. These include sandwich fillings (based on cheesemixed with other ingredients), cream cheese, Cheddar cheese

snacks, and cheese jerky which are pathogen-free, have increased

shelf-life, and are being marketed as clean label products (Hiper-baric 2011). An advantage of HHP processing is the possibilityof reducing or eliminating additives and preservatives from food

products. Rodilla is a company located in Spain that reducedproduction costs and increased refrigerated shelf-life of their sand-

wich fillings from 46 to 21 d by pressurizing at 500 MPa forseveral minutes without changing texture and flavor character-

istics (Tonello 2011). According to Purroy (2009), the costs ofHHP processing are related to equipment capacity, pressure in-

tensity, pressure holding time, and to the costs of labor, power,and maintenance. The initial investment on HHP equipment canrange from US $650,000 up to US $2,600,000 depending upon

equipment capacity (55 to 425 L). Small and medium sized com-panies that cannot afford HHP equipments or do not have suf-

ficient floor space can outsource contract service providers likeHHP Food Services in California, APC in Wisconsin, Deli 24 in

Buckinghamshire, GL Foods in Texas, Millard in Nebraska, SafePac in Pennsylvania, and Universal Cold Storage in Nebraska.

The HHP treatment cost per kilogram of food will depend onthe operating pressure intensity and pressure holding time. Present

HHP processing costs at fixed processing times are approximatelyUS $0.096/kg when treated at 300 MPa, US $0.112/kg at 400

MPa, US $0.129/kg at 500 MPa, and US $0.145/kg at 600 MPa.The cost of wear parts are US $0.015/kg, US $0.026/kg, US

$0.034/kg, and US $0.05/kg for the stated pressure conditions,respectively. With regard to processing times, 5 min holding time

at a constant pressure would imply costs of US $0.159/kg, while

10 min would cost US $0.21/kg, 15 min US $0.263/kg, and 20min US $0.316/kg.

Several research studies have shown that pressure treatments at500 to 600 MPa applied to cheese for 5 to 20 min are sufficient

to achieve over 5 log cycle reductions of S. aureus, L. monocyto-

genes, and E. coliwhen applied soon after manufacture or at moreadvanced stages of ripening. Less severe pressure conditions (345MPa for 3 min) are needed to accelerate Cheddar cheese shred-

dability. Typical operating conditions for seafood, juice, and readyto eat products are 300, 450, and 590 MPa applied for 1, 1, and 3

min, respectively (Purroy 2009). Overall, depending on operatingparameters and on the scale of operation, the cost of HHP pro-cessing is around US $0.05 to 0.5/kg of food (Rastogi and others

2007). Undoubtedly, the costs of implementing HHP could seem

very high compared to traditional processing technologies. How-ever, product recalls can cost company large amounts of moneyand permanently damage their brand. The human cost associ-

ated can be even more severe. In addition, reducing processingtimes through cheese ripening acceleration can have significant

impacts on production costs. Most types of soft cheese, includingunpasteurized soft cheeses which have recently been implicated

in disease outbreaks such as panela, requeson (ricotta), and frescoare good candidates for HHP processing due to their high wa-

ter activity. Cheese varieties with low pH values (pH about 4.75)could also benefit from HHP pasteurization as confirmed by De

Lamo-Castellv and others (2006, 2007).

Final RemarksThe application of any new food processing technology presents

significant challenges to food technologists and scientists. HHP

processing of cheese can ensure microbial safety and extend



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product shelf-life. However, depending on the intensity of treat-ment conditions and moment of application, physicochemical,

rheological, and sensory properties may be altered. Therefore, agood balance must be attained between ensuring microbial safety

and maintaining traditional cheese quality attributes. Althoughimmature cheese is more sensitive to changes induced by pressure

treatments, most of the observed changes are reversible and HHP-induced differences become less significant compared to nonpres-

surized cheese during ripening. With regard to cheese ripening,

application of HHP has mainly focused on ripening accelerationto reduce production costs. Noteworthy accomplishments havebeen the reduction in r ipening time from 6 mo to 3 d of Cheddar

cheese without negatively affecting sensory attributes (which toour knowledge has not been further investigated and evaluated on

a commercial scale), the acceleration of Cheddar cheese shred-ability, which could reduce manufacturing costs by at least US

$30/1000 kg, and the reduction in time required to attain satisfac-tory cooking properties of mozzarella cheese. Current trends are

to apply HHP treatments at a desired stage in order to deceleratethe ripening process and, therefore, extend optimal commercial

quality by controlling enzyme and bacterial participation. Gen-eral conclusions from this review can be schematically seen in

Figure 1.

Nomenclature

HHP = high hydrostatic pressureLAB = lactic acid bacteria

D-value = decimal reduction valueLeu--NA = leucine-p-nitroanilide

FAA = free amino acidFFA = free fatty acid

TCA = trichloroacetic acidPTA = phosphotungstic acid

SN = soluble nitrogenTN = total nitrogen

SDS-PAGE = sodium dodecyl sulfate polyacrylamide gel elec-trophoresis

AcknowledgmentsAuthor Y. Martnez-Rodrguez acknowledges support from

CONACYT (Mexico) via a Ph.D. fellowship (ref. 179692). Theauthors thank Marvin Martnez for his valuable comments on the

manuscript.

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