Effect of thermal and high pressure processing on antioxidant activity and instrumental colour of tomato and carrot purées

Total antioxidant activity, levels of bio-active compound groups and instrumental colour of tomato and carrot purée subjected to high pressure treatment (400–600 MPa/15 min/20 °C) and thermal treatments (70 °C/2 min) were measured. Antioxidant activity in tomato and carrot purée was significantly higher (p < 0.05) than in untreated or thermally processed samples. High pressure treatments at 600 MPa retained more than 90% of ascorbic acid as compared to thermal processing in tomato purées. Heat treatments caused a rapid decrease in ascorbic acid (p < 0.05). Phenolic contents were in general un-affected by thermal or high pressure treatments. Colour parameters were significantly affected (p < 0.05) by thermal and high pressure processing. Principal component analysis (PCA) revealed that the first two components represented 97% and 92% of the total variability in instrumental colour parameters with respect to processing for tomatoes and carrots respectively.Industrial relevanceThis research paper provides scientific evidence of the potential benefits of high pressure processing in comparison to thermal treatments in retaining important bioactive compounds. Antioxidant activity (ARP), ascorbic acid, and carotenoids after exposure to high pressure treatments (400–600 MPa) were well retained. Our results also show that redness and colour intensity of purées were better preserved by high pressure processing than conventional thermal treatment. It would appear from a nutritional prospective, high pressure processing is an excellent food processing technology which has the potential to retain compounds with health properties in foods. Therefore high pressure processed foods could be sold at a premium over their thermally processed counterparts as they will have retained their fresh-like properties.     

Effect of high pressure processing on rheological and structural properties of milk–gelatin mixtures

There is an increasing demand to tailor the functional properties of mixed biopolymer systems that find application in dairy food products. The effect of static high pressure processing (HPP), up to 600 MPa for 15 min at room temperature, on milk–gelatin mixtures with different solid concentrations (5%, 10%, 15% and 20% w/w milk solid and 0.6% w/w gelatin) was investigated. The viscosity remarkably increased in mixtures prepared with high milk solid concentration (15% and 20% w/w) following HPP at 300 MPa, whereas HPP at 600 MPa caused a decline in viscosity. This was due to ruptured aggregates and phase separation as confirmed by confocal laser scanning microscopy. Molecular bonding of the milk–gelatin mixtures due to HPP was shown by Fourier-transform infrared spectra, particularly within the regions of 1610–1690 and 1480–1575 cm⁻¹, which reflect the vibrational bands of amide I and amide II, respectively.     

High pressure–low temperature processing of foods: impact on cell membranes,texture, color and visual appearance of potato tissue

To design and optimize high pressure processes at low temperatures, a quantification of the effects of different processing steps on the food structure is required. Beside pressure-shift freezing, the processes of freezing to ice III and ice V, as well as storage at −27 °C and 250 MPa up to 24 h (metastable liquid state of water) of potato samples were examined. Analyses of the structural changes of the plant tissue included impedance measurements, texture analysis, color measurements and the evaluation of the optical appearance. Storage at subzero temperatures without phase transitions resulted in low membrane damage; however, cell lysis was triggered. Freezing to ice III resulted in the lowest damaging effect on the tissue compared to the other phase transition processes investigated. Samples frozen to ice V and pressure-shift frozen were more deteriorated compared to those frozen to ice III. However, considerable improvements compared to conventional freezing were found. The direction of solid–solid phase transitions (phase transition of ice I to ice III or phase transition of ice III to ice I) influenced the result of high pressure–low temperature processing significantly.Industrial relevanceIt was previously shown that pressure supported phase transitions of ice I like pressure shift freezing are able to preserve the fragile stucture of biological samples like food better than conventional freezing. The present study extends the knowledge of pressure supported phase transitions to a higher pressure domain with the participation of other ice modifications. The authors demonstrate the influences of high pressure phase transitions of water on plant tissue material depending on the processing conditions. The study opens the way to new industrial processing concepts based on high pressure low temperature applications.     

Disintegration efficiency of pulsed electric field induced effects on onion (Allium cepa L.) tissues as a function of pulse protocol and determination of cell integrity by ¹H-NMR relaxometry

The influence of electrical pulse protocol parameters on cell rupture of onion tissues was investigated in order to improve fundamental understanding and to enhance the processing of plant tissues with pulsed electric fields (PEFs). The impact of PEF parameters on cell integrity of 20 mm dia, 4-mm thick disks of Don Victor onions (Allium cepa L.) was determined by ion leakage measurements. Electric field strength, pulse width, total pulse duration, and frequency effects were determined in relation to their effects on cell damage as a function of pulse protocol. Electric field strengths up to 500 V/cm increased the damage efficiency but there was no significant difference in efficiency beyond this field strength. Larger pulse widths increased the degree of tissue disintegration at a constant pulse number. Higher PEF efficiency was achieved with shorter pulse widths and a larger number of pulses at a constant total treatment time. Lower frequencies caused a greater degree of disintegration at constant number of pulses. 1H-NMR experiments were performed to determine the proton relaxation components of the PEF-treated onion samples and to obtain cell damage information nondestructively. Paramagnetic ion uptake by the onion sample was used to identify different proton relaxation components. Five different proton relaxation components were observed and changes in the 2 components representing different proton environments showed high correlations with ion leakage results (R2= 0.99), indicating that T(2) distributions can be used to obtain information about cell membrane integrity in PEF-treated samples. 1H-NMR proved to be an effective method for nondestructive quantification of cell membrane rupture in onions.     

Effect of high pressure processing on the gel properties of salt-soluble meat protein containing CaCl2 and κ-carrageenan

The effects of high pressure processing (HPP) on the water-binding capacity and texture profile (TPA) of salt-soluble meat protein (SSMP) containing 0.2% CaCl₂ and 0.6% κ-carrageenan (SSMP-CK) gels were investigated. The results showed that 300–400 MPa improved water-binding capacity and decreased TPA parameters of SSMP-CK gels (P < 0.05), while 100 MPa could increase hardness and chewiness of the gels. The thermal transition temperature peak for the myosin head (T_peak1) of SSMP disappeared on addition of CaCl₂ and κ-carrageenan. 300 MPa produced a new peak, and caused a shift of the NH-stretching left peak and amide I and the disappearance of NH-stretching right peak. The destruction of network structure and the weakening of molecular interaction within the pressurized gels could result in the decrease of TPA parameters. Thus gelling properties could be modified by HPP, κ-carrageenan and Ca^2 +. It is of interest to develop low-fat and sodium-reduced meat products.     

High pressure processing effects on the molecular structure of ovalbumin,lysozyme and β-lactoglobulin

Structural changes to the three sensitive food proteins, ovalbumin, β-lactoglobulin and lysozyme were examined following a series of high pressure processing experiments. The proteins prepared at specific pH were pressurized up to 600 MPa and held for periods of up to 30 min. Changes to the secondary and tertiary by examination of circular dichroism spectra revealed that the structure of the three proteins behaved differently to both the applied pressure and holding time. The notable effects were found to occur to both ovalbumin and β-lactoglobulin while lysozyme was found to be the most pressure resistant. For each of the proteins, it also appears that the processing conditions applied at specific pH act in combination to bring about structural change.     

Effects of high hydrostatic pressure on the structure of bovine α-lactalbumin

The effects of high hydrostatic pressure (HHP) processing (at 200 to 600 MPa, 25 to 55°C, and from 5 to 15 min) on some structural properties of α-lactalbumin was studied in a pH range of 3.0 to 9.0. The range of HHP processes produced a variety of molten globules with differences in their surface hydrophobicity and secondary and tertiary structures. At pH values of 3 and 5, there was a decrease in the α-helix content concomitant with an increase in β-strand content as the pressure increased. No changes in molecular size due to HHP-induced aggregation were detected by sodium dodecyl sulfate-PAGE. All samples showed higher thermostability as the severity of the treatment increased, indicating the formation of a less labile structure related to the HHP treatment.     

Effects of high pressure,microwave and ultrasound processing on proteins and enzyme activity in dairy systems — A review

High-pressure processing (HPP), microwaves (MW) and ultrasound (US) are used for pasteurization with minimum heat input. They also alter physico-chemical properties of milk proteins and enzymes. This article aims at identifying the important changes in milk proteins imparted by these three processing technologies. HPP dissociates casein micelles at low pH (<6.7) and concentrations (<4% w/w), while β-LG is the most pressure sensitive whey protein due to the presence of free thiol groups. Milk enzyme activity is inhibited at higher pressures (>400 MPa). MW treatment denatures whey proteins rapidly, even below their thermal denaturation temperatures. High-power MW treatment (e.g. 60 kW) deactivates enzymes by denaturing them. However, low-power controlled MW irradiation (e.g. 30 W) improves enzyme activity. Ultrasound can homogenize protein aggregates in dairy systems and cause whey protein denaturation. Sonication under applied pressure and heat (e.g. 3.5 kg/cm², 126.5 °C) causes enzyme inhibition while mild sonication conditions can improve enzyme activity.Industrial relevanceHPP, MW and US are gaining popularity in the dairy industry due to their ability to pasteurize and functionalize dairy streams with minimal heat input. This review offers insights into how these technologies can be used in isolation or in combination to alter milk proteins and enzyme activity for different academic and industrial applications. However, to fully understand the potential of HPP, MW and US treatment on dairy systems, further research is required in several areas including health related nutritional changes in milk and milk products caused by these technologies.     

Investigation on the influence of high protein concentrations on the thermal reaction behaviour of β-lactoglobulin by experimental and numerical analyses

In this study, treatments at various temperature–time profiles were performed for β-lactoglobulin samples at different concentrations (50–70%) using a special rheometer as processing device. Rheological measurements, offline protein chemical analyses, and molecular dynamics analyses were performed to investigate the influence of high protein concentrations and treatment temperature on the denaturation and aggregation behaviour of β-lactoglobulin. Under these conditions, the degree of denaturation and aggregation decreased with increasing protein concentration. This corresponded to a strongly decreased diffusion and increased stability of exposed surface protein regions at high concentrations. Irreversible denaturation was observed for temperatures above 60 °C. Increasing thermal treatment intensity resulted in an increase of aggregation. Depending on the thermal treatment conditions, different protein–protein interactions were measured. By increasing the treatment temperature, the resulting aggregates were increasingly stabilised by covalent bonds. In addition to disulphide bonds, non-disulphide covalent cross-links were formed at temperatures above 100 °C.     

Barley: Impact of processing on physicochemical and thermal properties—A review

Barley (Hordeum vulgare L.) is a nutritious cereal but very little (only about 2%) of this grain is used as human food. However, it has attracted the attention of researchers and food processors in the last 15 years for its potential health benefits. It is also recognized as a functional grain because it contains high levels of β-glucan and phytochemicals. Therefore, a number of barley processing research and animal/clinical trials have been performed over the last 15–20 years. Also, health claims have been approved by a number of government agencies including the Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) about consumption of β-glucan, an important component of barley. Barley must undergo various processing steps before human consumption, which greatly affect their composition and physicochemical properties. These properties play an important role in the development of new products. Therefore, the present article reviews the literature on the effect of processing on the physicochemical and thermal properties of barley.     

Retinol binding to β-lactoglobulin or phosphocasein micelles under high pressure: Effects of isostatic high-pressure on structural and functional integrity

Embedding of bioactive molecules in food matrices is of interest for food industry to develop new foods or ingredients. The present study aims at deepening understanding of ligand binding to dairy proteins regarded as nano-vehicles, using pressure-assisted technological tools. We compared effects of isostatic high-pressure up to 350–400 MPa on the stability and the retinol-binding capacity of β-lactoglobulin (β-LG) or phosphocasein (PC) at pH 6.5–6.6. Retinol binding to β-LG changed the intrinsic protein and retinol fluorescence, characterised by fluorescence resonance-energy-transfer (FRET). After correction for inner filter effects, the FRET level estimated for the β-LG–retinol complex at pH 6.5 and P_atm was compatible with a retinol position at the β-LG surface cleft. Pressurisation of the β-LG–retinol complex induced an irreversible loss of the retinol-ligand above 150 MPa. Pressurisation of PC dispersion up to 200 MPa induced a marked decrease in the PC intrinsic fluorescence intensity with a concomitant red-shift of the spectral mass centre (CSM) explained by Trp residues exposure to aqueous solvent. The pressure-induced CSM half-transition (P_1/2) was 116 MPa for PC instead of 183 MPa for β-LG. Retinol binding to PC also resulted in important FRET, but PC assemblies partly retained retinol after pressure-release from 400 MPa. Interestingly, the pressure-induced dissociation rate of PC assemblies in the 15–35 °C temperature range was significantly accelerated at lower temperature, reflecting non-Arrhenius behaviour. PC particle sizes evaluated by dynamic light-scattering, confirmed that the pressure-induced dissociation was practically achieved at 200 MPa. Thus PC dissociation paralleled the structural changes determined by fluorescence spectroscopy.     

Effects of high hydrostatic pressure on color of spinach purée and related properties

BACKGROUND: Changes in instrumental color parameters, chlorophyll a and b, activity of chlorophyllase, Mg‐dechelatase, peroxidase and polyphenol oxidase, total phenolic compounds and pH of spinach purée were assessed after high hydrostatic pressure (HHP) (200, 400 and 600 MPa for 5, 15 and 25 min) treatments at room temperature. RESULTS: HHP treatments induced a better retention of visual green color (?a* and L* values) and chlorophyll contents of spinach purée. As for chlorophyll degradation‐related enzymes, the results indicated that chlorophyllase activity decreased at all pressures; however, Mg‐dechelatase activity was dramatically activated after HHP treatment at 400 and 600 MPa. Peroxidase exhibited higher resistance to HHP; however, polyphenol oxidase, which is responsible for enzymatic browning, was suppressed progressively with increase in pressure level from 200 to 600 MPa. In addition, the pH value of HHP‐treated spinach purée was increased to be close to neutral pH, which could effectively inhibit chlorophyll degradation. No significant differences (P > 0.05) were found after extending the treatment times at the same level of pressure. CONCLUSION: HHP treatments effectively prevent chlorophyll degradation and enzymatic browning in spinach purée and retain a better original fresh green color of spinach compared with conventional thermal treatment. Copyright © 2012 Society of Chemical Industry     

Impact of high pressure processing on total antioxidant activity,phenolic, ascorbic acid,anthocyanin content and colour of strawberry and blackberry purées

The present study was undertaken to assess the effect of high pressure treatments and conventional thermal processing on antioxidant activity, levels of key antioxidant groups (polyphenols, ascorbic acid and anthocyanins) and the colour of strawberry and blackberry purées. Bioactive compounds (cyanidin-3-glycoside, pelargonidin-3-glucoside, ascorbic acid) and antioxidant activity were measured in strawberry and blackberry purées subjected to high pressure treatment (400, 500, 600 MPa/15 min/10–30 °C) and thermal treatments (70 °C/2 min). Samples were assessed immediately after processing. Different pressure treatments did not cause any significant change in ascorbic acid (p > 0.05). In contrast, following thermal processing (P₇₀ ≥ 2 min) ascorbic acid degradation was 21% (p < 0.05) as compared to unprocessed purée. However, no significant changes in anthocyanins were observed between pressure treated and unprocessed purées (p > 0.05), whereas conventional thermal treatments significantly reduced the levels (p < 0.05). In general, antioxidant activities of pressure treated strawberry and blackberry purées were significantly higher (p < 0.05) than in thermally processed samples. Colour changes were minor (ΔE) for pressurised purées but the differences were slightly higher for thermally treated samples. Redness of purées was well retained in high pressure treated samples. Therefore processing strawberry and blackberry by high pressure processing could be an efficient method to preserve these products quality. Hence high pressure processing (HPP) at moderate temperatures may be appropriate to produce nutritious and fresh like purées.Industrial relevanceThis research paper provides scientific evidence of the potential benefits of high pressure processing in comparison to thermal treatments in retaining important bioactive compounds. Antioxidant activity (ARP), ascorbic acid, and anthocyanins after exposure to high pressure treatments (400–600 MPa) were well retained. Our results also show that redness and colour intensity of strawberry and blackberry purées were better preserved by high pressure processing than conventional thermal treatment. From a nutritional perspective, high pressure processing is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products. Therefore high pressure processed foods could be sold at a premium than their thermally processed counterparts as they will have retained their fresh-like properties.     

Carotenoids and lipophilic antioxidant capacities of tomato purées as affected by high hydrostatic pressure processing

The effect of high hydrostatic pressure (HHP) (450–550–650 MPa/5–10–15 min) on the carotenoid profile of purées obtained from commercial tomato varieties (Maliniak, Cerise, Black Prince and Lima) was investigated. The carotenoids profile was analysed using high performance liquid chromatography (HPLC-DAD). Photochemiluminescence (PCL_ACL), ferric-reducing antioxidant power (FRAP) and cyclic voltammetry (CV) assays were used to determine the antioxidant capacity of the lipophilic extracts. The results demonstrated that at certain processing conditions, HHP distinctly enhanced antioxidant capacity of the studied material. A significant reduction in lycopene and β-Carotene concentration was observed for all the HHP-treated purées. In contrast, lutein found in the purée extracts of Cerise and Black Prince tomatoes was slightly affected at 550 MPa/5 min and 650 MPa/5 min. Among all the carotenoids studied, lutein strongly and significantly affected PCL_ACL and CV parameters. In contrast, lycopene had a negligible effect on the examined parameters.     

Effect of thermal and high-pressure processing on the nutritional value and quality attributes of a nectarine purée with industrial origin during the refrigerated storage

The application of hydrostatic high pressure on an industrial line of nectarine (Prunus persica L.) purées was assessed in comparison with the traditional thermal treatment of pasteurization. Changes after thermal processing (85 °C, 5 min) and after high-pressure processing (HPP: 450 or 600 MPa for 5 or 10 min) and during the refrigerated storage (60 d) of an industrially produced nectarine purée were evaluated. Conventional heat pasteurization as well as HPP showed similar microorganisms' inactivation and maintained the microbial stability of purées until the end of the refrigerated storage (60 d). In general, thermally treated purée and HP-treated purée at 600 MPa showed more intense color changes after processing than the other treatment. In addition, thermally treated purée showed more intense color changes during storage than HPP. The highest carotenoids extractability was found in those purées treated at the lowest high-pressure-treatment intensity and holding time (450 MPa/5 min), but at the end of the storage (day 60), no differences in individual or total carotenoid levels were found between the purées. HPP at 600 MPa/10 min showed the highest polyphenols content after the treatment and during the storage. At day 0, significantly higher values were found of total antioxidant activity in purée HP-treated at 450 MPa/10 min than in untreated purée; while at the end of the storage, HP-treated purée at 600 MPa/10 min had the highest antioxidant activity. Hydrostatic high-pressure application in the industrial line of nectarine purée presented some advantages compared to the thermal treatment; however, some of the changes found were lessen during the storage period. In addition, more studies need to be carried out for HP-treatment intensity optimization.     

Effect of glucono-δ-lactone and κ-carrageenan combined with high pressure treatment on the physico-chemical properties of restructured pork

In this study, response surface methodology (RSM) was used to evaluate the combined effects of NaCl, glucono-δ-lactone (GdL), and κ-carrageenan concentration (0.25%, 0.5%, and 0.75%) on the binding properties of restructured pork under hydrostatic pressure. All the generated RSM models showed no lack-of-fit and significance at the 0.001 level. The addition of both NaCl and GdL had a significant effect on color. A significant decrease in pH was shown when the GdL level increased, and subsequently led to a decrease in WHC. However, increasing the GdL level increased the binding strength. Therefore, the results indicate that a reduction in the NaCl level during meat restructuring, under pressure treatment, can be achieved by using GdL; and even a low GdL concentration allows for palatable binding properties in meat restructuring when κ-carrageenan is added.     

Effect of pulsed-light processing on the surface and foaming properties of β-lactoglobulin

Pulsed-light processing was used to treat β-lactoglobulin (BLG) solutions. The impact of pulsed light (PL) on the structural properties of this protein was explored through far-UV, CD spectral analysis, size exclusion chromatography, surface hydrophobicity and NMR spectroscopy. Changes on these physicochemical properties were related to surface rheology, surface tension, foam stability and foam capacity of the non-treated and treated BLG to elucidate adsorption mechanism and consequences on foaming capacity. Conformational modification of BLG was related with PL total fluence as important conformational changes increased when total fluence was higher. Consequently, adsorption rate of treated BLG at the air/water interface was faster than native BLG. Additionally, treated BLG formed highly elastic interfaces. This was found to have an impact on the foam stability. Pulsed-light treatment seemed to enhance the overall strength of the interface, resulting in more stable foams.