Pressure Shift Freezing Research Articles

Pressure shift freezing as potential alternative for generation of decellularized scaffolds.

Background. Protocols using chemical reagents for scaffold decellularization can cause changes in the properties of the matrix, depending on the type of tissue and the chemical reagent. Technologies using physical techniques may be possible alternatives for the production grafts with potential superior matrix characteristics. Material and Methods. We tested four different technologies for scaffold decellularization. Group 1: high hydrostatic pressure (HHP), 1 GPa; Group 2: pressure shift freezing (PSF); Group 3: pulsed electric fields (PEF); Group 4: control group: detergent (SDS). The degree of decellularization was assessed by histological analysis and the measurement of residual DNA. Results. Tissue treated with PSF showed a decellularization with a penetration depth (PD) of 1.5 mm and residual DNA content of 24% ± 3%. HHD treatment caused a PD of 0.2 mm with a residual DNA content of 28% ± .4%. PD in PEF was 0.5 mm, and the residual DNA content was 49% ± 7%. In the SDS group, PD was found to be 5 mm, and the DNA content was determined at 5% ± 2%. Conclusion. PSF showed promising results as a possible technique for scaffold decellularization. The penetration depth of PSF has to be optimized, and the mechanical as well as the biological characteristics of decellularized grafts have to be evaluated.

Effects of High Pressure–Low Temperature treatment on freezing behavior, sensorial properties and air cell distribution in sugar rich dairy based frozen food foam and emulsions

Abstract The basic principles of High Pressure Low Temperature treatment (HPLT) of foods have been extensively explored in several studies over the last decade. Research activities in this field mostly focused on the inactivation of microorganisms, textural damage in plant and animal tissue and mechanisms behind nucleation and ice formation. Of central concern in the present study is the effect of High Pressure Low Temperature treatment on the properties of dairy based, emulsified frozen food foam and the equivalent non aerated liquid system. Special emphasis was put on the freezing behavior under pressure, sensorial properties, the air cell distribution and ice crystal size and distribution. A phase diagram was modeled on the base of atmospheric pressure DSC data and freezing and melting points determined at atmospheric and high pressure conditions. High Pressure Shift Freezing (HPSF) from metastable liquid state at max. pressure of 360 MPa and − 25 °C and pressure induced solid–solid phase transition (ice I–ice III–ice I) were applied. Liquid non aerated emulsion was HPLT treated in the presence of air to investigate the potential of aeration upon pressure release due to expansion of supercritical and dissolved gas. The latter treatment did not result in the formation of air cells in the partially frozen matrix. In HPLT experiments that started with liquid foam, the volume fraction of the incorporated air after treatment was about 78% of the reference value before treatment and the average ice crystal size was reduced from 40 μm to 34 μm. When frozen foam was HPLT treated, ice I to ice III phase transition occurred and a massive volume reduction of the gas fraction was observed. All samples showed an increase in smoothness and mouth coating in technical tasting after HPLT treatments. Industrial relevance High Pressure Low Temperature processes (HPLT) offer a wider range of different effects that can be induced by different treatments. In the past, scientific work in this field was predominantly focused on the inactivation of microorganisms, textural damage in plant and animal tissue and mechanisms behind nucleation and ice formation. Of central concern in the present study is the effect of High Pressure Low Temperature treatment on the properties of dairy based, emulsified frozen food foam and the equivalent non aerated liquid system. Special emphasis was put on the freezing behavior under pressure, sensorial properties, the air cell distribution and ice crystal size and distribution. In cooperation with a leading ice cream manufacturer potential benefits of HPLT processing of dairy based foam products, that may give rise for further scientific work in this field, were identified and described.

The particle image velocimetry method in the study of the dynamics of phase transitions induced by high pressures in triolein and oleic acid

Particle image velocimetry (PIV) is an optical measurement method capable of providing visualisation of velocity field of particle flow in fluids. After analysis of data acquired in the form of an image sequence, it is possible to retrieve information about flow parameters as mean values of velocity, vorticity, shear and normal strain. This paper presents the results of high pressure experiments using this method applied to triolein and oleic acid samples in their phase transition region. A high pressure optical chamber, He–Ne laser and light-sheet optics together with a digital camera and image acquisition computer allow us to study the motion of particles in high pressure conditions. The set-up was similar to that presented in Özmutlu et al. [Momentum and energy transfer during phase change of water under high hydrostatic pressure, Innov. Food Sci. Emerg. Technol. 7(3) (2006), pp. 161–168] and Kulisiewicz et al. [Visualization of pressure-shift freezing and thawing of concentrated aqueous sucrose solutions, High Press. Res. 27(2) (2007), pp. 291–297]. The analysis of phase transition dynamics in triolein and oleic acid is an extension to the work presented in Tefelski et al. [The investigation of the dynamics of the phase transformation in triolein and oleic acid under pressure, J. Phys.: Conf. Ser. 121(142004) (2008), pp. 1–6]. Oleic acid is a monounsaturated fatty acid and has a bent rod shape. Triolein is a triglyceride and has a “chair”-like shape. It is the base particle of many vegetable oils, especially olive oil. Triolein consists of three chains of oleic acid bound by a glycerol part. Information obtained by the study of phase transitions dynamics is important for food science and food technology processes which involve high pressure treatment. The PIV method shows differences in the solidification process of both substances in time, the existence of inhomogeneities (layers of different densities in the observed flow) and allows us to calculate the parameters of flow using the PIVview2C software from PIVTEC GmbH.

Quality changes during the frozen storage of sea bass (Dicentrarchus labrax) muscle after pressure shift freezing and pressure assisted thawing

Abstract Quality of frozen sea bass muscle stored (1, 3 and 5 months) at two levels of temperature (−15 and −25 °C) after a pressure shift freezing process (200 MPa) — PSF — and/or a pressure assisted thawing process (200 MPa) — PAT — was evaluated in comparison with samples frozen and thawed using conventional methods (air-blast AF and AT, respectively). Frozen storage of high-pressure treated samples did not significantly affect initial quality of frozen muscle. Thus, parameters related to protein denaturation and extractability, water holding capacity and color presented similar values than those obtained for not stored samples. In addition, the improvement of the microstructure achieved by PSF application remains unchanged during frozen storage. On the other hand, conventional treated samples experienced significant changes during frozen storage, such as protein denaturation, and water holding capacity and color modifications. Storage temperatures did not have influence in the quality of PSF and PAT samples, but it showed some effects in AF muscle. Industrial relevance: This work demonstrates the potential application and benefits of high pressure (HP) in the freezing and thawing of fish meat in comparison to conventional methods, due to an improvement on the cellular integrity of the tissue. Although some negative effects are produced during processing with HP, no additional modifications occur during the frozen storage. The studied methodologies seemed to be very suitable for fish freezing and thawing, especially for products which will be frozen stored and/or cooked.

High pressure inactivation of Pseudomonas in black truffle – comparison with Pseudomonas fluorescens in tryptone soya broth

Pseudomonas is one of the most common genera in black Perigord truffle. Its inactivation by high pressure (100–500 MPa/10 min) applied on truffles at sub-zero or low temperatures was studied and compared with those of Pseudomonas fluorescens in tryptone soya broth. Pressurization of truffles at 300 MPa/4 °C reduced the bacterial count of Pseudomonas by 5.3 log cycles. Higher pressures of 400 or 500 MPa, at 4 °C or 20 °C, allowed us to slightly increase the level of destruction to the value of ca. 6.5 log cycles but did not permit us to completely inactivate Pseudomonas. The results showed a residual charge of about 10 CFU/g. Pressure-shift freezing of truffles, which consists in applying a pressure of 200 MPa/−18 °C for 10 min and then quickly releasing this pressure to induce freezing, reduced the population of Pseudomonas by 3.3 log cycles. The level of inactivation was higher than those obtained with conventional freezing. Endogenous Pseudomonas in truffle was shown to be more resistant to high pressure treatments than P. fluorescens used for inoculation of broths.

초고압 동결 및 해동방법이 돈육의 물리적 특성에 미치는 효과

본 실험은 초고압 동결 및 해동기법이 돈육의 이화학적 특성에 미치는 효과를 규명하고자 시도하였다. 동결 및 해동처리 과정에서 가압에 따른 pH 증가 및 단백질 변성에 따른 보수력의 저하로 관찰되었지만, 초고압 동결 기법을 이용함으로써 효과적으로 해동 및 가열감량을 최소화할 수 있었다. 반면에 초고압 해동기법은 느린 해동속도에 기인한 얼음 재결정화로 해동육의 수율 측면에 영향을 미칠것으로 판단되었다. 따라서 초고압 동결처리에 의한 빠른 동결 및 빠른 해동처리를 통하여 돈육의 물리적 특성 저하를 최소화할 수 있을 것으로 간주되었다. 반면에 250 MPa의 압력은 돈육의 색도에 부정적인 영향을 미치는 것으로 나타났다. This study was conducted to investigate the effect of various high pressure freezing and thawing treatments on the physical properties of pork. To compare the effects of the freezing and thawing process on meat quality, atmospheric freezing followed by running water thawing (AFRT), pressure shift freezing followed by running water thawing (SFRT), and pressure shift freezing and pressure assisted thawing (SFAT) were conducted at pressure of 250 MPa and cooling temperature of <TEX>$-22^{\circ}C$</TEX>. SAFT and SFRT showed a shorter phase transition time and total thawing time than AFRT. The pH value of treated samples increased significantly (p<0.05) compared to unfrozen meat. In addition, SFAT and SFRT showed a higher pHvalue than AFRT. Although the water holding capacity was significantly decreased (p<0.05) for SFAT and SFRT, SFRT reduced drip loss. In regards to color, SFAT and SFRT resulted in a significant increase in color parameters (p<0.05) relative to AFRT, while SFAT produced a higher L*-value. High pressure treatment significantly increased shear force (p<0.05) compared to AFRT, and, where SFRT showed the highest shear force. Therefore, these combined results indicated that the hydrostatic pressure treatment improved the functional properties of pork and increased the freezing and thawing rate.

Impact of Freezing Process on Salt Diffusivity of Seafood: Application to Salmon (Salmo salar) Using Conventional and Pressure Shift Freezing

The depression of the melting temperature of ice under pressure permits to obtain a rapid freezing of foods. The expected benefit lies in reduced water diffusion from the intra- toward the extracellular media, resulting in a reduced drip loss during thawing. Beside, the modification of the cellular structure induced by ice formation may affect the mass diffusivity of the flesh. In the present study, salmon was used as a model food. Slabs of salmon (1-cm thick) were frozen using blast air and pressure shift freezing at 200 MPa. The impact of the freezing process on the mass diffusivity of salt was evaluated using an aqueous solution (NaCl, 3% w/w). Results indicate that the effective mass diffusivity was slightly increased in comparison to non-frozen flesh when a rapid freezing process was used. This may be attributed to a change in the permeability of cell membranes caused by freezing and high pressure.

Simulation of high pressure freezing processes by enthalpy method

High pressure freezing processes such as pressure assisted freezing (PAF) and high pressure shift freezing (HPSF) are novel technologies that can be used to improve the quality of frozen foods. A one dimensional finite difference numerical model based on the enthalpy formulation was developed to simulate high pressure freezing of tylose, agar gel and potatoes. The Schwartzberg equation was used in the prediction of both the initial freezing point and the temperature evolution below freezing. Results showed that the model can satisfactorily describe the PAF and HPSF processes. When compared under similar heat transfer conditions, the phase transition times for HPSF were shorter than those at atmospheric pressure. The amount of ice instantaneously formed upon pressure release and the total freezing times were also determined by the developed model and were in reasonable agreement with the experimental data in the literature.

Effect of High Pressure Shift Freezing Process on Microbial Inactivation in Dairy Model Food System

This study was carried out to investigate the microbial inactivation in dairy model system by high pressure shift freezing (HPSF). The UHT milk and broths were inoculated with Escherichia coli ATCC 25922, Staphylococcus aureus KCCM 11335 and Listeria monocytogenes HTCC 19115, respectively. The samples were pressurized to 200 MPa under different holding time at -18ºC. Inactivation effects of both E. coli ATCC 25922 and L. monocytogenes HTCC 19115 were significantly shown by the increment of pressure holding time (p&lt;0.05) for not only in broth, but also UHT milk. The highest value of log reduction in NB media was observed as 6.1 after HPSF. However, inactivation effects of S. aureus KCCM 11335 were not significantly shown in tryptic soy broth (TSB) and UHT milk.

DSC Determination of Glass Transition Temperature on Sea Bass (Dicentrarchus labrax) Muscle: Effect of High-Pressure Processing

Differential scanning calorimetric determination of glass transition temperature in the freeze-concentrated matrix (\( T_{\text{g}}^{\text{'}} \)) of sea bass muscle was optimized. Conventional and modulated differential scanning calorimetry (DSC) techniques (using diverse cooling/heating rate and modulation parameters) and effect of an annealing step (−30, −20, or −15°C, 30min) were assayed. Transition was more evident using conventional DSC assays, cooling/heating rate: 10°C/min, annealing step at –20°C. A \( T_{\text{g}}^{\text{'}} \) value of –15.2 ± 0.3°C was observed for sea bass fresh muscle. This method was chosen for \( T_{\text{g}}^{\text{'}} \) determination on high-pressure (HP) treated and pressure shift freezing (PSF)—stored at –20°C—sea bass muscle. Thus, in both cases, transition at –15°C was less evident as a function of the pressure level applied, being very difficult to detect after treatment at 400 and 600MPa. It was observed that \(T_{\text{g}}^{\text{'}} \) values were shifted to slightly higher temperatures (around 1°C higher) after HP treatment at 400 and 600MPa. The present work constituted a first approach to the study on the effect of HP on the glass transition of a complex food matrix, giving useful information about stability of the frozen food.

Effect of air freezing, spray freezing, and pressure shift freezing on membrane integrity and viability of Lactobacillus rhamnosus GG

The objective of this work was to assess and compare the impact of three different freezing methods on the physiology of probiotic bacteria based on evaluation of vitality, membrane integrity and special metabolic properties. Lactobacillus rhamnosus GG (LGG) was used as a model strain and was analysed with the plate enumeration method and flowcytometric analyses (FCM) before and after treatment in phosphate buffer saline (PBS) and 20% (w/v) skim milk (RSM), respectively. To get insight into the induced changes in esterase activity and membrane integrity combined staining with carboxyfluorescein diacetate (cFDA) and propidium iodide (PI) was applied. Furthermore the ability of the cells to extract intracellular accumulated cF in presence of glucose was investigated as an indicator for ATP driven membrane transport processes. The freezing methods applied were static air freezing (AF) at −30 °C for 3 h, high pressure shift freezing (PSF) at −21 °C/210 MPa and spray freezing (SF) at −30 °C. Spray freezing was accomplished by spraying the bacteria suspension in a cold air stream using a two fluid atomizer. The atomizing gas was air. After each treatment all samples were stored at −20 °C for one day before they were analysed. Minimum losses in viability occurred when spray freezing LGG in presence of 20% (w/v) RSM whereas air freezing in PBS resulted in the lowest survival rates. For all treatments higher survival rates were achieved when 20% (w/v) RSM was used as protecting media. Comparing the results of live cell count with the FCM data gave evidence for a fraction of viable but not culturable cells. LGG cells frozen by PSF showed viability comparable to AF samples, but physiological characteristics of pressure treated bacteria.

Effects of Pressure‐Shift Freezing and Pressure‐Assisted Thawing on Sea Bass (Dicentrarchus labrax) Quality

Effects of pressure-shift freezing and/or pressure-assisted thawing on the quality of sea bass muscle were evaluated and compared with conventional (air-blast) frozen and thawed samples. Microstructural analysis showed a marked decrease of muscle cell damage for pressure-assisted frozen samples. According to differential scanning calorimetry (DSC), protein extractability, and SDS-PAGE results, high-pressure treatment (200 MPa) produced a partial denaturation with aggregation and insolubilization of the myosin, as well as alterations of the sarcoplasmic proteins. Only small differences between high-pressure processes (freezing or/and thawing) were registered. High-pressure-treated systems led to a decrease of water holding capacity but differences between high-pressure and conventional methods disappeared after cooking. Muscle color showed important alterations due to high-pressure treatments (increasing L* and b*).

Effect of different freezing processes on the microstructure of Atlantic salmon (Salmo salar) fillets

Abstract Salmon fillets were frozen either by pressure shift freezing (PSF, 200 MPa, − 18 °C or 100 MPa, − 10 °C) or by air-blast freezing (ABF, − 30 °C, 1 m/s or 4 m/s) or direct-contact freezing, and then stored at − 20 °C for 6 months. The influence of these treatments on the microstructure of Salmon fillets was studied. The equivalent diameter of the intracellular ice crystals were 14.69 ± 4.11, 5.52 ± 2.11, and 30.65 ± 6.31 μm for the samples subjected respectively to PSF at 100, 200 MPa and ABF (− 30 °C, 4 m/s) after 2 days of storage. Smaller and more regular intracellular ice crystals were observed in fillets frozen by PSF (200 MPa) compared with PSF (100 MPa), ABF and direct-contact frozen ones. Significant differences were observed between the size of the ice crystals obtained after conventional freezing process and PSF. Large and extracellular ice crystals were observed in fillets frozen by ABF (1 m/s) and direct-contact frozen. Minimal changes in the size of ice crystals were observed during a 3 months storage. Industrial relevance This paper compares different freezing methods and subsequent frozen storage with respect to their effect on microstructures of salmon fillets. Pressure shift freezing at 200 MPa was superior to conventional freezing regarding small and regular ice crystal formation. Interestingly, during frozen storage for up to 3 months the high quality product obtained via pressure freezing at 200 MPa could be retained. For longer storage periods lower pressures (100 MPa) seem sufficient to achieve stable ice crystals.

Visualization of pressure-shift freezing and thawing of concentrated aqueous sucrose solutions

A visualization of pressure-shift freezing of 0.7 w/w sucrose solutions was carried out at three temperatures 268, 253 and 235 K by release of pressure from 200 MPa to atmospheric value. Furthermore, pressure-shift freezing at 268 K and additionally pressure-shift thawing was carried out for a solution of 0.2 sucrose mass fraction. The solid phase observed at 268 K in the case of solution with 0.2 w/w sucrose fraction was ice I. The phase changes of 0.7 w/w sucrose solutions at 253 K and 235 K resulted in formation of spherical solids which are hypothesized to be eutectics, i.e. crystals with structure containing sucrose hydrates and water. The visual evaluation revealed differences in size and distribution of spherical crystals. The solids formed at 235 K were more numerous, more homogenously distributed and finally smaller than those observed at 253 K. It is explained by the higher supercooling of the solution in the former case, which provided higher driving force for nucleation and crystal growth.

Effects of Freezing and Thawing Processes on the Quality of Atlantic Salmon (Salmo salar) Fillets

High-pressure processing is finding a growing interest in the food industry. Among the advantages of this emerging process is the ability to favorably freeze and thaw food. This study aims at comparing the effect of different freezing and thawing processes on the quality of Atlantic salmon fillets. Atlantic salmon (Salmo salar) samples were frozen by Pressure-Shift Freezing (PSF, 200 MPa, -18 degrees C) and Air-Blast Freezing (ABF, -30 degrees C, 4 m/s). Samples were stored 1 mo at -20 degrees C and then subjected to different thawing treatments: Air-Blast Thawing (ABT, 4 degrees C, 4 m/s), Immersion Thawing (IMT, 20 degrees C), and Pressure-Assisted Thawing (PAT, 200 MPa, 20 degrees C). Changes in texture, color, and drip loss were investigated. The toughness of the PSF samples was higher than that of the ABF sample. The modification of color was more important during high-pressure process than during the conventional process. The PSF process reduced thawing drip compared with ABF. The presence of small ice crystals in the pressure-shift frozen sample is probably the major reason leading to the reduced drip volumes. The freezing process was generally much more influent on quality parameters than the thawing process. These results show the interaction between freezing and thawing processes on selected quality parameters.

Modelling industrial scale high-pressure-low-temperature processes

The existence of metastable phases of ice I and liquid in the domain of ice III permits the use of optimized paths for pressure shift freezing (PSF) and pressure induced thawing (PIT) processes, crossing the ice III domain, without actual crystallization of this ice polymorph. The use of higher pressures and lower temperatures before pressure release, in the case of PSF, and the use of higher pressures for PIT, increases the real temperature gradients of both processes, therefore reducing the total processing time. In this paper, a computational model has been developed to simulate heat transfer phenomena during the precooling (in PSF) and the heating (in PIT) steps of these optimized processes. The high-pressure-low-temperature (HPLT) processes are assumed to be conducted in a high-pressure tubular reactor designed to work in a semi-continuous mode on an industrial scale. Results showed that important vessel lengths (40–370 m) are needed when the sample velocity ranges from 1 to 6 m/min. These vessel lengths are feasible thanks to the modular structure of the suggested high-pressure system.

Synergy between high-pressure, temperature and ascorbic acid on the inactivation of Bacillus cereus

B. cereus strain (CECF 148) was used as a model system in the study of the behaviour of bacillus under high pressure, at temperatures over and below 0 °C and with ascorbic acid added to the culture. Three different assays were carried out in the present experiment. The first assay was performed to observe how B. cereus reacted to pressure shift freezing (PSF) treatment at different subzero temperatures (−8, −12, −20 and −17 °C) and pressures (120, 150, 210 and 350 MPa) in their vegetative form. In the second assay, we observed how different concentrations of ascorbic acid (1, 2, 5 and 20 mM) added to the growing brought decreased B. cereus on its vegetative form. Finally, we tried to inactivate the vegetative and spore form of B. cereus under pressure of 210 MPa at room (20 °C) (HP) and at subzero (−20 °C) (PSF) temperatures, in presence of ascorbic acid (20 mM), added to the growing culture (TSB). The results confirmed that pressures of 210 and 350 MPa at low temperatures (−20 and −17 °C) in the PSF treatment were not enough to inactivate bacillus and only about 10% of B. cereus at the assayed conditions (350 MPa at −17 °C) lost its growth capacity. The presence of ascorbic acid reduced the amount of B. cereus. The initial amount of B. cereus in the vegetative form was 108 to 109 cfu/mL. After HP (210 MPa at 20 °C) and PSF (210 MPa at −20 °C) treatments, the amount of B. cereus decreased by 4 and 2 logarithmic units, respectively. However, in both treatments, the presence of ascorbic acid (20 mM concentration) reduced the B. cereus growth capacity in about 5 logarithmic units. The presence of ascorbic acid in the spore form decreased the amount of B. cereus only by 2 logarithmic units, but without the antioxidant, the values remained close to control. The present research is a contribution to elicit the safety standards of food treated by high pressure.

Calorimetry and Pressure-shift Freezing of Different Food Products

Rapid depressurisation can create uniform, small and abundant ice nucleation during pressure-shift freezing (PSF) which can then protect the frozen food structure from cell damage. The amount of depressurisation-formed ice was evaluated using a high-pressure calorimeter for different food products (tylose, potato, salmon, pork and water). Experiments were conducted at an initial pressure of 62, 82, 112, 156, 180 and 196MPa, at temperatures set at −5, −7, −10, −15, −18 and −20°C, respectively (slightly above the phase diagram of water-ice I). Calorimetric thermograms recorded during PSF tests were used for computing the quantity of ice formed based on heat balance. A polynomial relationship was established for each product to compute the depressurisation-formed ice ratio as a function of the initial pressure applied. This model accurately predicted the maximum ice ratio for PSF at a given pressure (0.1 to 210MPa) or the minimum ice ratio for PSF at a given temperature (−22 to 0°C). Moisture content was the major factor affecting the sample-mass based (SMB) ice ratio with higher moisture yielding a higher SMB ice ratio. A general relationship between water-mass based (WMB) ice ratio ( R'ice-water) and initial pressure was found from the pooled data from all tested products: R'ice-water 0.114 P+0.00022 P2 (R2 0.94, n 47) which agreed well with relevant literature values for pure water.

Computer simulation of high pressure cooling of pork

A computer simulation was used to develop and evaluate two-dimensional axi-symmetrical of cooling of pork under high pressure (HP) processing conditions. The whole cooling process was divided into three stages of cooling: a preloading stage, a pressure build-up stage (compression) and a pressure hold stage (constant pressure), and the modeling domain covered the pressurization fluid, the sample holder and the pork sample. Modeling performance was evaluated by comparing the predicted and experimental temperatures at four locations: three within the pork sample and one for the high pressure fluid medium. Model generated images were used for visual observations of temperature distribution and movement of the pressure fluid, and transient temperature curves were generated for the four specified locations. Results indicated that the developed model well matched experimental results, especially for temperatures at the central area. The thermal conductivities of pork under pressure conditions: 100, 150 and 200 MPa were estimated by the model using error trials. The model provides a valuable tool for studying the pressure cooling behavior of test samples and for designing the pressure shift freezing process.

Assessment of cell damage in high-pressure-shift frozen broccoli: comparison with market samples

Pressure-shift freezing (PSF) is one of the most promising methods for obtaining high-quality frozen products. The aim of this work was to analyse the differences between broccoli that was frozen using two different PSF processes. In one of the processes, all the freezing was done inside the high-pressure vessel tempered at −20.5 °C. In the other process, the sample was taken out of the vessel after expansion, and freezing was completed using liquid N2. Colour, texture, electrical conductivity, microstructure and drip losses after centrifugation were analysed and a sensory test was performed. The results were compared with those for conventionally frozen broccoli purchased at the market. PSF broccoli presented less cell damage, lower drip losses and better texture than the market samples. The two different PSF processes assayed produced no significant differences in the final quality of the samples.