High-pressure Shift Freezing Research Articles

In-situ investigation of supercooling behaviour during high-pressure shift freezing of pure water and sucrose solution

Supercooling is a main controllable factor for the fundamental understanding the high-pressure shift freezing (HPSF). In the study, a self-developed device based on the diamond anvil cell (DAC) and confocal Raman microscopy was utilized to realize an in-situ investigation of supercooling behaviour during HPSF of the pure water and sucrose solution. The spectra were used to determine the freezing point which is shown as a spectral phase marker (SD). The hydrogen bond strengths of water and sucrose solution under supercooling states were estimated by peak position and peak area ratio of sub-peaks. The results showed that the OH stretching bands had redshift under supercooling states. Moreover, the addition of sucrose molecules could strengthen the hydrogen bonding strength of water molecules under supercooling states. Thus, the DAC combined with Raman spectroscopy could be considered a novel strategy for a deep understanding of the supercooling behaviour during HPSF.

Effects of high-pressure freezing and deep-frozen storage on cell structure and quality of cordyceps sinensis

Cordyceps sinensis (CS) is a kind of fungus with many biologically active components and it is better to preserve its freshness after harvesting. Therefore, the effect of high-pressure freezing and deep-frozen storage at −80 °C on the cell integrity and viability, quality-related attributes and microstructure of CS samples were investigated and compared with that of liquid nitrogen freezing (LNF), immersion freezing (IF) and normal frozen storage at −20 °C during 8 weeks of storage. LNF combined with deep-frozen storage exhibited the smallest damage to the cell integrity and viability, the most intact tissue and cellular structure, thereby minimizing quality loss. But the change rates showed high-pressure shift freezing (HPSF) combined with deep-frozen storage caused the slowest deterioration of the cell integrity, viability and quality-related attributes during the storage. Therefore, LNF combined with deep-frozen storage was the best way to freeze the CS samples, but HPSF combined with deep-frozen storage might be the better way for the long-term preservation of highly perishable fresh products with a cellular structure.

Frozen strawberry quality enhancement using high hydrostatic pressure and vacuum infusion with pectin methylesterase and calcium chloride solution

Fresh strawberry(Fragaria x ananassa) is a delicious fruit that is an excellent source of micronutrients and an array of beneficial phytochemicals. Emerging technologies like high pressure freezing and thawing have gained interest recently due to their ability to preserve the structure of the food during storage, albeit the possible shortcomings of degradation of texture and sensory quality. In this study, the effects of high hydrostatic pressure freezing and thawing on the physical quality attributes (texture, drip loss and Degree of Methylation(DM)) of strawberry were investigated. Strawberry samples were infused in a vacuum using pectin methyl esterase(PME) and CaCl2solutionat170 hPa pressure for 5 min at room temperature to improve textural integrity; infused with distilled water; and another group of samples further incubated at 40°C for 20 min. Fresh samples and non-pre treated samples were also studied. All the samples were subjected to high pressure freezing and thawing processes at 200 MPa and the effect of the processing conditions on texture were evaluated. The high pressure processed samples were compared with conventionally frozen and thawed samples.Pectin methyl esterase,CaCl2infusion and incubation gave a relative hardness of 1.5 pre treatment compared to water only infused at 0.5.TheCaCl2and PME-infused samples had a higher relative hardness after one day of storage at -18°C compared to non-pretreated and water-infused samples at 0.3 compared to 0.1,respectively. Pretreated, water-infused, and PME withCaCl2-infused samples showed no significant difference in hardness when measured immediately after conventional thawing and high pressure induced thawing HPIT but are the former are a third less hard compared to the latter upon storage after 3 hours and three months. Galacturonic acid per mg of Alcohol insoluble residues AIR sample for the fresh strawberrywas0.002±2.699E-05 and 0.002±1.070E-05molesfor the one-day vs.three months storage,respectively,for samples conventionally frozen and thawed in duplicate experiments.Therefore,a combination of high-pressure shift freezing (HPSF) with PME and CaCl2infusion improved the texture of the strawberry compared to those that were not pretreated,and gained weight by 15%. The PME and CaCl2-infused strawberry showed less degradation than the non-pretreated and water-infused during both long-and short-time frozen storage. Conventional freezing processes caused more degradation compared to HPSF. Degradation of 3 months conventional freezing was comparable to 1-day storage. For frozen storage, enzyme pretreatment combined with high pressure freezing can be used to enhance the quality of strawberry.

Design and Development of Preservative Free Herbal Dosage Forms

This review focuses on principles of product preservation, preservatives, and novel technologies for the future development of preservative free herbal products. The purpose of this study was to determine the amount of preservatives in pharmaceutical products as some recent studies reported serious side effects associated with the ingestion of these substances. The principles involved were asepsis and removal of microorganisms — both static and cidal effects. Some of the novel technologies of asepsis are high pressure processing, pulsed electric field treatment and non-thermal technologies including ultraviolet processing. All relevant literature databases were searched upto 2011. Majority of the human, animal, in vitro studies, and reviews were included. Preservative free dosage forms must be formulated for the reduction in side effects and hence a healthier mankind. Keywords: High pressure shift freezing, osmotic filtration, parabens, pasteurization, pulsed electric technique.

Mathematical Modeling of the Growth and Coarsening of Ice Particles in the Context of High Pressure Shift Freezing Processes

High pressure shift freezing (HPSF) has been proven more beneficial for ice crystal size and shape than traditional (at atmospheric pressure) freezing.1-3 A model for growth and coarsening of ice crystals inside a frozen food sample (either at atmospheric or high pressure) is developed, and some numerical experiments are given, with which the model is validated by using experimental data. To the best of our knowledge, this is the first model suited for freezing crystallization in the context of high pressure.

Generalized enthalpy model of a high-pressure shift freezing process

High-pressure freezing processes are a novel emerging technology in food processing, offering significant improvements to the quality of frozen foods. To be able to simulate plateau times and thermal history under different conditions, in this work, we present a generalized enthalpy model of the high-pressure shift freezing process. The model includes the effects of pressure on conservation of enthalpy and incorporates the freezing point depression of non-dilute food samples. In addition, the significant heat-transfer effects of convection in the pressurizing medium are accounted for by solving the two-dimensional Navier–Stokes equations. We run the model for several numerical tests where the food sample is agar gel, and find good agreement with experimental data from the literature.

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.

Experimental determination of the amount of ice instantaneously formed in high-pressure shift freezing

The main aim of this paper was to experimentally determine the amount of ice instantaneously formed after expansion during high-pressure shift freezing (HPSF). To do that, an easy, quick and cheap procedure was developed able to obtain accurate ice ratio estimations from temperature data of the sample after the pressure release. Very different pressure and temperature conditions, both near and far from the melting curve liquid–ice I, were chosen to produce different amounts of ice after expansion in HPSF experiments. Sucrose solutions of several concentrations (10%, 20%, 30% and 40% w/w) were also employed to study the influence of the water content of the sample. Good agreement was found between experimental estimations and theoretical predictions from the heat balance model for all the pressure and temperature conditions tested. The results showed that increasing pressure at a given temperature before expansion is an effective and fast way to increase the amount of ice produced.

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<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.

High-pressure shift freezing: recrystallization during storage

High-pressure shift freezing has been proposed as a method to produce frozen food with smaller ice crystal size and, consequently, with reduced tissular damage and higher overall quality. The fate of this initially improved crystal size distribution, decisive for the long-term value of this procedure, is unclear. The recrystallization behaviour of partially frozen aqueous solutions, as food models, is here compared with that of similar classically frozen samples. A microscopic observation cell has been specially designed for this purpose. The temporal evolution of high-pressure shift frozen ice crystals has been fitted to different mechanism models and is found to be similar within experimental error to that of classically frozen samples. However, differences in the shape evolution of crystals have been detected, which can be ascribed to small differences in the initial distribution. The implications of these observations for the long-term storage of frozen food are discussed.

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.

Use of pectinmethylesterase and calcium in osmotic dehydration and osmodehydrofreezing of strawberries

Strawberry samples of two varieties (Camarosa and Elsanta) were dehydrated using different osmotic solutions (60% glucose, fructose, sucrose and raftilose) and subsequently frozen by rapid and high-pressure shift freezing (HPSF). The effect of pectinmethylesterase (PME) and calcium (Ca++) added to the osmotic solutions on several compositional parameters and the textural/structural quality of dehydrated and osmodehydrofrozen-then-thawed samples was studied. Due to the presence of PME and Ca++ in the osmotic solutions, weight reduction upon dehydration was slightly decreased, which was correlated to a small positive effect on the net uptake of sugars and depression of the initial freezing point. Except for the Camarosa samples treated with sucrose, PME and Ca++ in osmotic sugar solutions positively affected the relative hardness of dehydrated fruits, which was ascribed to the effect of PME and Ca++ on the cell wall strength of the tissue. No cell wall damage and tissue particle alterations were observed upon dehydration. The effect of osmotic dehydration (OD) using different sugar solutions without PME and Ca++ on the texture and structure of frozen-then-thawed samples was limited and sometimes negative. The added PME and Ca++ however positively influenced the volume and shape of the thawed samples, which could be related to slightly higher relative hardness values and, for the Elsanta strawberry fruits, also to the reduced (up to 81%) drip loss upon thawing. Upon freezing the dehydrated fruits, no cell wall disruption was observed. Tissue distortion caused by freezing and indicated by a decrease in particle size, convexity and roundness, was compensated by the use of PME and Ca++ during OD.

Structure/processing relation of vacuum infused strawberry tissue frozen under different conditions

Strawberry halves were infused with pectinmethylesterase (PME) and calcium and subsequently frozen by slow, rapid, cryogenic or high-pressure shift freezing (HPSF). A microscopic procedure including detailed image analysis was used to study the effect of vacuum infusion (VI) and/or freezing on the strawberry tissue structure. Hereto, parameters characterizing the size, the shape and/or smoothness of tissue particles were compared for the different samples. It was found that VI seemed to stabilize the cell walls and the cell–cell contact and did not affect the integrity of the strawberry tissue. Structural damage of untreated strawberry tissue due to freezing was large for all freezing methods applied. Rapid and cryogenic freezing conditions were most favorable. VI was effective to minimize the structural damage of rapidly, cryogenically and high-pressure shift frozen strawberries. Infused strawberries frozen by HPSF showed the most smooth and largest particles from all the frozen samples, indicating the importance of both infusion and a high and homogenous degree of undercooling to obtain maximal structure retention of frozen strawberries.

Effects of locust bean, xanthan and guar gums on the ice crystals of a sucrose solution frozen at high pressure

Hydrocolloids are added in ice-creams and frozen desserts to produce smooth texture and protect the product during its storage. The high-pressure freezing techniques also aimed to enhance product qualities. In this work, both the hydrocolloid and the high-pressure processing actions are combined. A 0.3% (w/w) of guar gum (viscous solution) or of locust bean gum plus xanthan gum (gel) was mixed in sucrose solutions (16% w/w) to analyze whether water mobility affected ice crystal formation. Sucrose solutions with or without hydrocolloids were frozen by high-pressure assisted freezing (HPAF) at 100 MPa and by high-pressure shift freezing (HPSF) from 210 MPa to 0.1 and 100 MPa, to compare their effects on the ice crystal characteristics. Ice crystal sizes were determined from images obtained by low temperature scanning microscopy (LT-SEM). Ice crystals were smaller after HPSF than after HPAF, due to greater supercooling following expansion and to shorter phase transition times. As regards the hydrocolloids, ice crystals were smaller when the mixture of locust bean and xanthan gums were added irrespective of the freezing method. The formation of a gel-like structure at ambient temperature strengthened by a cryo-gelation effect in the frozen state may limit water molecule diffusion and ice crystal growth.

Influence of Low-temperature Blanching Combined with High-pressure Shift Freezing on the Texture of Frozen Carrots

: Freezing causes texture loss of tissue-based systems such as fruits and vegetables. To evaluate the potentials of high-pressure freezing for minimizing freezing damage, the effects of high-pressure shift freezing and regular freezing conditions on the texture of carrot cylinders were investigated. To improve the strength of the plant material by a pectin-based network, carrot cylinders were submitted to different pretreatment conditions before freezing. The reduced freezing time of high-pressure shift freezing compared with conventional freezing results in a limited positive effect on the hardness of non-pretreated carrots. A pronounced hardness improvement was obtained when calcium soaking followed by thermal (30 min at 60°C) or high-pressure (15 min at 60°C and 300 MPa) pretreatment was combined with high-pressure shift freezing. During subsequent frozen storage at -18°C, the increased hardness values of pretreated, high-pressure frozen carrots could not be maintained.

Minimizing texture loss of frozen strawberries: effect of infusion with pectinmethylesterase and calcium combined with different freezing conditions and effect of subsequent storage/thawing conditions

Vacuum infusion (VI), freezing, frozen storage and thawing conditions were optimized in order to minimize the texture loss of frozen strawberries. Slow freezing caused severe loss in textural quality of the strawberries. This quality loss could not be prevented by the application of VI prior to slow freezing, or by the application of rapid, cryogenic or high-pressure shift freezing conditions on non-infused fruits. A remarkable texture improvement was noticed when infusion of pectinmethylesterase (PME) and calcium was combined with rapid or cryogenic freezing. The highly beneficial effect of PME/Ca-infusion followed by HPSF on the hardness retention of frozen strawberries was ascribed to the combined effect of the infused PME (53% reduction in degree of esterification (DE) of the strawberry pectin) and the high degree of supercooling during HPSF. During frozen storage, textural quality of PME/Ca-infused high-pressure frozen strawberries was maintained at temperatures below −8 °C, whereas the texture of PME/Ca-infused strawberries frozen under cryogenic freezing conditions was only preserved at temperatures below −18 °C. Thawing at room temperature seemed to be an appropriate method to thaw strawberries. Fast thawing by high-pressure induced thawing (HPIT) did not prevent textural quality loss of frozenstrawberries.

High-pressure shift freezing versus high-pressure assisted freezing: Effects on the microstructure of a food model

Gelatin gel samples (10% gelatin, w/w) were frozen by high-pressure shift freezing (HPSF) and by high-pressure assisted freezing (HPAF) with the phase transition at identical pressure conditions (0.1, 50, and 100 MPa) so as to allow valid comparisons. The corresponding temperature/pressure profiles were recorded in order to characterize the processes. Also, the ice crystal distributions were analyzed to estimate the effects of both freezing methods on the food microstructure. Results clearly showed that high-pressure shift freezing is the more advantageous method. The supercooling attained after the expansion and the consequent instantaneous freezing of water, together with the temperature drop in the pressure medium, induced short phase transition times (5.9, 8.6, and 13.7 min in HPSF versus 14.8, 14.1, and 23.1 min in HPAF at 0.1, 50, and 100 MPa, respectively) and a homogeneous distribution of small ice crystals throughout the sample.

High-pressure-shift freezing: Main factors implied in the phase transition time

We have studied the dynamics of the high-pressure-shift freezing (HPSF) process and the main parameters implied. Conventional freezing experiments at atmospheric conditions and HPSF experiments were carried out at identical temperatures and different pressures and the phase transition times compared. Phase transition times in HPSF experiments were lower than their homologues at atmospheric pressure in all cases. The reduction depends on the pressure and temperature conditions before expansion. These variables are highly involved in the supercooling reached and govern both the percentage of ice formed during the pressure release and the temperature drop in the pressure medium. After expansion, the pressure medium plays a significant role in the heat removal from the sample. Good predictions of plateau times can be made from initial pressure and temperature values, both process parameters that can be readily adjusted in the food industry.

Modelling heat transfer in high pressure food processing: a review

The most claimed advantage of high-pressure food processing as compared to thermal processing is that pressure acts instantaneously and uniformly through a mass of food independently of its size, shape or composition. Nevertheless, thermal gradients are established in the products after compression and cause inhomogeneities in the pursued pressure effect. Modelling heat transfer in high-pressure food processes can be a useful tool to homogenise and optimise these treatments. The main difficulty is the lack of appropriate thermophysical properties of the processed materials under pressure. When modelling high-pressure processes at subzero temperatures, pressure/temperature phase transition data and latent heat are also needed. Those for water are known, but there is a total lack for those corresponding to components relevant to foods. Moreover, the precise mechanisms that rule high-pressure shift freezing and induced thawing are not yet clear and so it hinders modellisation. This review collects the difficulties found and the advances made up to date in modelling heat transfer in high-pressure processes, including those performed at subzero temperatures.