ABSTRACT Besides traditional atmospheric frying, high pressure (super-atmospheric) frying might b... more ABSTRACT Besides traditional atmospheric frying, high pressure (super-atmospheric) frying might be an alternative approach to the frying of food products. In this study, convective heat transfer coefficient during atmospheric and high pressure frying was compared. For this purpose, a pressure cooker was modified to allow the immersion of a sample into frying oil under pressure and temperature measurement of sample and oil. Heat transfer coefficient versus frying time was determined on potato slabs using changes of total mass of the experimental set-up. At the pressure of 2 bar, the results showed an almost doubled heat transfer coefficient compared to the atmospheric pressure frying. The knowledge of heat transfer coefficient during pressure frying is expected to allow accurate determination of temperature distribution and hence the kinetic calculations to lead to development of an alternative frying process.
Abstract Stability and loss of encapsulated curcumin was investigated in starch granule stabilize... more Abstract Stability and loss of encapsulated curcumin was investigated in starch granule stabilized Pickering emulsions. Heat treated and non-heat treated Pickering emulsions have been studied during storage, and during simulated oral, gastric and intestinal in vitro digestion. The amount of retained curcumin in Pickering emulsions was characterized based on spectrophotometric measurements as a function of time. Physical stability of emulsions was characterized using light microscope and light scattering particle size analyzer. Pickering emulsions showed good encapsulation efficiency (∼ 80%) and good stability. Heat treated Pickering emulsions showed better encapsulation stability than non-heat treated Pickering emulsions during 24 h storage (78.2% vs. 38.3%), and during oral (95.3% vs. 69.6%) and intestinal (86.3% vs. 40.2%) simulated in vitro digestions. In the case of simulated gastric in vitro digestion, there was no statistically significant difference in the curcumin content between non-heat treated (86.2%) and heat treated (82.4%) emulsions (P > 0.05). Moreover, comparing the physical stability of emulsions during simulated in vitro intestinal digestion with and without bile salts, it was shown that samples with bile salts showed a larger extent of changes, and these changes were more gradual in heat treated samples. Overall, this study demonstrates that Pickering emulsions stabilized with quinoa starch granules have a potential for effective delivery of bioactive compounds such as curcumin.
The effect of barrier properties on in vitro intestinal lipolysis of three different types of emu... more The effect of barrier properties on in vitro intestinal lipolysis of three different types of emulsions based on oil-in-water starch granule Pickering stabilization has been investigated including non-heat treated, heat treated (gelatinized) and heat treated and stored (retrograded) emulsions. The stability of starch covered oil-water interfaces towards in vitro intestinal lipolysis was correlated to the rate of lipid hydrolysis using a pH-stat method. The results were compared with a sodium caseinate stabilized emulsion. The shape and size of the starch granules were characterized by scanning electron microscopy and light scattering. The physical properties of the emulsions were characterized by a light scattering particle size analyzer and light microscopy. In all cases, Pickering emulsions showed lower extents of lipolysis compared to the protein stabilized emulsion. In addition, heat treated starch Pickering emulsions were more susceptible to lipolysis compared to freshly prepared emulsions with no heat treatment. This was thought to be due to the gelatinized starch barrier being more susceptible to amylase present in the pancreatin. The results of this study demonstrate the interfacial layer properties can affect the rate and extent of lipolysis.
Biochimica Et Biophysica Acta - Proteins And Proteomics, Sep 1, 1993
The N-terminal 25 amino-acid residue peptide (beta-CN 1-25) obtained from a tryptic digest of bov... more The N-terminal 25 amino-acid residue peptide (beta-CN 1-25) obtained from a tryptic digest of bovine beta-casein was studied using two-dimensional NMR techniques. Complete sequence-specific assignment of the 1H-NMR spectrum was performed both in the presence and absence of 22 mM Ca2+. The NMR data supported earlier findings that this segment of beta-casein is highly flexible and adopts multiple conformations. The observed pattern of sequential NOEs indicated that the peptide did not contain stable folded structures. However, the structure was neither that of a fully-extended peptide nor a so-called random coil. The region Ile-12 to SerP-15 showed an enhanced population of extended structure. Furthermore, addition of Ca2+ ions induced chemical-shift changes and apparently decreased the population of conformations with extended structure in the region SerP-18 to Ile-23.
Metabolite profiling was used to characterize stress responses of potato tissue subjected to reve... more Metabolite profiling was used to characterize stress responses of potato tissue subjected to reversible electroporation, providing insights on how potato tissue responds to a physical stimulus such as pulsed electric fields (PEF), which is an artificial stress. Wounded potato tissue was subjected to field strengths ranging from 200 to 400 V/cm, with a single rectangular pulse of 1 ms. Electroporation was demonstrated by propidium iodide staining of the cells nucleae. Metabolic profiling of data obtained through GC/TOF-MS complemented with orthogonal projections to latent structures (OPLS) clustering analysis showed that 24 h after the application of PEF, potato metabolism shows PEF-specific responses characterized by the changes in the hexose pool that may involve starch and ascorbic acid degradation.
Mixed cultures of different EPS-producing Streptococcus thermophilus strains in combination with ... more Mixed cultures of different EPS-producing Streptococcus thermophilus strains in combination with a Lactobacillus delbrueckii subsp. bulgaricus strain with negligible EPS-production were used for yoghurt production. The yoghurt texture was characterised with respect to sensory, rheological and microstructural properties and the EPS-concentrations were determined. The cultures resulted in yoghurts with highly different texture properties, and positive interactions between certain Streptococcus thermophilus strains were observed. The underlying properties of yoghurt texture are multidimensional, but a number of microstructural characteristics were apparent in the yoghurts with the highest mouth thickness, creaminess and viscosity. A strong protein network, not too dense and with medium size pores containing EPS, seems associated with these properties. The presence of capsular polysaccharides (CPS) also appeared to be beneficial as did a combination of EPS types, which were distributed differently in the protein network (in serum pores, respectively in association with protein). Obviously, a certain concentration of EPS must be present to provide for these effects on yoghurt texture, but other factors than concentration per se seem more important.
This chapter describes particle-stabilized emulsions, the so-called Pickering emulsions. The prin... more This chapter describes particle-stabilized emulsions, the so-called Pickering emulsions. The principles behind particle stabilization of emulsions are described. The key properties of particle-stabilized emulsions such as stability, rheology, and the influences of other ingredients on the system, as well as some additional functional properties imparted by the stabilized particles in food emulsion formulations, are highlighted.
Gels formed from milk by renneting or acidification under quiescent conditions may subsequently s... more Gels formed from milk by renneting or acidification under quiescent conditions may subsequently show syneresis, that is, expel liquid (whey), because the gel (curd) contracts. Under quiescent conditions, a rennet-induced milk gel may lose two-thirds of its volume, and up to 90%, or even more, if external pressure is applied. Often, syneresis is undesired, for example, during storage of products like yogurt, sour cream, cream cheese, or quark; hence, it is useful to know under what conditions syneresis can be (largely) prevented. In making cheese from renneted or acidified milk, syneresis is an essential step. Consequently, it is useful to understand and quantitatively describe syneresis as a function of milk properties and process conditions, particularly when new methods or process steps are introduced in cheesemaking.
ABSTRACTThe instrumental and sensory analysis of the texture and color of commercial potato chips... more ABSTRACTThe instrumental and sensory analysis of the texture and color of commercial potato chips were compared. The instrumental measurement was a puncture test with an Intron Universal Testing Machine, and the parameters used were fracture force, deformation and stiffness. The instrumental color quantification was a computerized video image analysis technique, and the color was expressed as L*a*b* values. Sensory evaluation of texture and color was performed by a sensory panel especially trained in evaluating potato chips. The sensory attributes were “hardness”, “chewiness”, “crunchiness”, and “tenderness” for texture analysis, and “yellow color”, “burnt aspect”, “sugar colored aspect” and “transparency” for color analysis. The factor analysis of the sensory attributes indicated that texture can be divided into two principal components, one represented by “hardness”, “crunchiness” and “chewiness”, and the other by “tenderness” alone. The factor analysis of the color can be divided into two principal components, one including “yellow color” and “burnt aspect”, and the other “sugar colored aspect” and “transparency”. Discriminant analysis showed that “tenderness” and “crunchiness” could predict correctly over 90% of the data. Fracture force correlated well with all of the sensory attributes (R2 > 0.76), and L* with the sensory color attributes (R2 > 0.79). The “Tenderness” was the individual sensory attribute which had the highest correlation (R2= 0.95) with fracture force.
Changes occurring in directly heated UHT milk were studied during storage at 5, 22, 30 and 40 C. ... more Changes occurring in directly heated UHT milk were studied during storage at 5, 22, 30 and 40 C. Industrially produced UHT milk samples were analysed for changes in enzymatic activity, protein modification, destabilisation of casein micelles and relocation of milk proteins in relation to sedimentation and gel formation. Sedimentation occurred at all temperatures, and the protein composition of the sediments reflected the composition of its liquid phase; however, there was no a-lactalbumin, b-lactoglobulin or k-casein present in sediments. Tendrils composed of b-lactoglobulin and k-casein were seen on casein micelles after UHT treatment and grew in length prior to gelation. High degrees of lactosylation of proteins and peptides were clearly correlated with the absence of gelation and long tendrils. Gelled samples showed complete hydrolysis of intact b-casein, and limited lactosylation of b-lactoglobulin and k-casein.
Journal of Food Science and Engineering, Jun 28, 2015
The primary interest to this study was to investigate the effect of milling parameters on the siz... more The primary interest to this study was to investigate the effect of milling parameters on the size of hydrophobically modified starch particles, aiming to produce small, uniformly sized modified starch microspheres. Octie, a commercial product originated from cornstarch modified using Octenyl Succinate Anhydride (OSA), was dispersed (3 wt%) using different media (water or ethanol) and subsequently wet-milled using a beads mill with zirconium beads at a rotation of 6,000 rpm up to 30 min. It was found that milling Octie in water dispersion for 3 min resulted in the smallest mean particle size (2.04 ± 0.91 m), compared to unmilled modified starch granules (15.2 ± 6.0 m). Granular size and morphology changed considerably with further milling. For instance, very dense clusters with variable particle sizes (20.6 ± 10.0 m) were obtained after 30 min milling. As depicted by Scanning Electronic Microscopy, a large number of particles were apparently flattened during the milling process rather than broken, forming aggregates. Ultimately, within the range of experimental conditions tested, production of sub-micron modified starch particles was not possible.
Whey proteins have several excellent functional properties and one of their most important functi... more Whey proteins have several excellent functional properties and one of their most important functions is to improve consistency of foods by forming thermally induced gels. β-Lactoglobulin, which is the major whey protein, has good gelation properties and the aim of this study was to follow the formation of heat-induced gels of an industrially fractionated β-lactoglobulin isolate at different pH and assess their properties using dynamic rheometry.
Lactoglobulin, standard whey protein concentrate (WPC 80) and cold-gelling whey protein concentra... more Lactoglobulin, standard whey protein concentrate (WPC 80) and cold-gelling whey protein concentrate (mWPC 80) were dried onto mica sheets at 0.03-3 g cm\ surface load and imaged with atomic force microscopy (AFM) in tapping mode.-Lactoglobulin and WPC 80 spread to a fairly even 2.5 nm thick layer at about monolayer surface load, while mWPC showed particle sizes of 20-30 nm laterally. There is little difference in the observed structures between 0.3 and 3 g cm\ apart from the higher surface load. At 0.03 g cm\,-lactoglobulin spread somewhat more thinly than WPC 80. With the addition of DTT, mWPC spread evenly with only few particles in evidence. AFM appears to be a convenient method for the characterization of aggregation states of sub-micrometer protein particles.
The electrical conductivity of milk at various dilutions was measured at different temperatures f... more The electrical conductivity of milk at various dilutions was measured at different temperatures from 2 to 70 C. The results showed that dilution has only a small influence on the temperature dependence of conductivity. A simple power-law model predicts that the conductivity is proportional to the milk concentration to the power of 0.84 and a two-term model describes the temperature dependency. The overall model has a standard deviation of 0.0067 mS cm À1 , which corresponds approximately to 0.1% milk at 2 C and 0.07% milk at 70 C. It was further shown that for less than about 25% milk in water Kohlrausch's law and the Debye-Hu¨ckel-Onsager theory can be used to describe the relationship between the concentration, temperature, and conductivity using a representative limiting molar conductivity of milk ions of 75 mS cm 2 mol À1 .
We have investigated whether transient permeabilization caused by the application of pulsed elect... more We have investigated whether transient permeabilization caused by the application of pulsed electric field would give rise to transient changes in the potato tissue viscoelastic properties. Potato tissue was subjected to nominal field strengths (E) ranging from 30 to 500 V/cm, with a single rectangular pulse of 10 −5 , 10 −4 , or 10 −3 s. The changes on the viscoelastic properties of potato tissue during pulsed electric fields (PEF) were monitored through small amplitude oscillatory dynamic rheological measurements. The elastic (G′) and viscous moduli (G″) were measured every 30 s after the delivery of the pulse and the loss tangent change (tan-δ) was calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of the pulse. Results show a drastic increase of tan-δ in the first 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly influenced by pulsing conditions and is independent of the total permeabilization achieved by the pulse. Our results, supported by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence of electroporation. The recovery of tan-δ to values similar to those before pulsation strongly suggests recovery of cell membrane properties and turgor, pointing at reversible permeabilization of the cells. A slight increase of stiffness traduced by a negative change of tan-δ after application of certain PEF conditions may also give an indication of events occurring on cell wall structure due to stress responses. This study set the basis for further investigations on the complex cell stress physiology involving both cell membrane functional properties and cell wall structure that would influence tissue physical properties upon PEF application.
Thermal unfolding of whey proteins and whey protein-casein mixtures in sim- ulated milk ultrafilt... more Thermal unfolding of whey proteins and whey protein-casein mixtures in sim- ulated milk ultrafiltrate was studied by differential scanning calorimetry. The re- sults are reported as transition enthalpy, temperature of peak maximum, and van't Hoff enthalpy related to the sharpness of transition. The results of earlier investiga- tions were reviewed. It is suggested that a large part of reported whey
The extraction of red pigment and conductive matters from individual red beet tissue slices follo... more The extraction of red pigment and conductive matters from individual red beet tissue slices following pulsed electric field pretreatment of different durations was compared with a two dimensional bimodal Fickian diffusion model. The process appeared to be governed by two apparent diffusion coefficients, one slow and one fast. The values of these coefficients were independent of the duration of treatment, but the yield associated with each coefficient varied. Following the treatment of longest duration and treatment by freezing and thawing of the tissue, the yield from the faster diffusion coefficient accounted completely for the mass transport. The faster apparent diffusion coefficient was 2-5 times smaller than the diffusion coefficients in dilute solution.
Skim milk was heat treated (100°C/5min) and fermented with ropy and non-ropy commencai starters, ... more Skim milk was heat treated (100°C/5min) and fermented with ropy and non-ropy commencai starters, in beaker or in rheometer cup. Yoghurt properties were followed by dynamic rheometry (Bohlin Universal Rheometer) and by penetrometry (Stevens LFRA Texture Analyzer) and the measuring methods were compared.
A review. Gels formed from milk by renneting or acidification under quiescent conditions may subs... more A review. Gels formed from milk by renneting or acidification under quiescent conditions may subsequently show syneresis, i.e., expel liq. (whey), because the gel (curd) contracts. In making cheese from renneted or acidified milk, syneresis is an essential step. Consequently, it is useful to understand and quant. describe syneresis as a function of milk properties and process conditions, particularly when new methods or process steps are introduced in cheesemaking.
ABSTRACT Besides traditional atmospheric frying, high pressure (super-atmospheric) frying might b... more ABSTRACT Besides traditional atmospheric frying, high pressure (super-atmospheric) frying might be an alternative approach to the frying of food products. In this study, convective heat transfer coefficient during atmospheric and high pressure frying was compared. For this purpose, a pressure cooker was modified to allow the immersion of a sample into frying oil under pressure and temperature measurement of sample and oil. Heat transfer coefficient versus frying time was determined on potato slabs using changes of total mass of the experimental set-up. At the pressure of 2 bar, the results showed an almost doubled heat transfer coefficient compared to the atmospheric pressure frying. The knowledge of heat transfer coefficient during pressure frying is expected to allow accurate determination of temperature distribution and hence the kinetic calculations to lead to development of an alternative frying process.
Abstract Stability and loss of encapsulated curcumin was investigated in starch granule stabilize... more Abstract Stability and loss of encapsulated curcumin was investigated in starch granule stabilized Pickering emulsions. Heat treated and non-heat treated Pickering emulsions have been studied during storage, and during simulated oral, gastric and intestinal in vitro digestion. The amount of retained curcumin in Pickering emulsions was characterized based on spectrophotometric measurements as a function of time. Physical stability of emulsions was characterized using light microscope and light scattering particle size analyzer. Pickering emulsions showed good encapsulation efficiency (∼ 80%) and good stability. Heat treated Pickering emulsions showed better encapsulation stability than non-heat treated Pickering emulsions during 24 h storage (78.2% vs. 38.3%), and during oral (95.3% vs. 69.6%) and intestinal (86.3% vs. 40.2%) simulated in vitro digestions. In the case of simulated gastric in vitro digestion, there was no statistically significant difference in the curcumin content between non-heat treated (86.2%) and heat treated (82.4%) emulsions (P > 0.05). Moreover, comparing the physical stability of emulsions during simulated in vitro intestinal digestion with and without bile salts, it was shown that samples with bile salts showed a larger extent of changes, and these changes were more gradual in heat treated samples. Overall, this study demonstrates that Pickering emulsions stabilized with quinoa starch granules have a potential for effective delivery of bioactive compounds such as curcumin.
The effect of barrier properties on in vitro intestinal lipolysis of three different types of emu... more The effect of barrier properties on in vitro intestinal lipolysis of three different types of emulsions based on oil-in-water starch granule Pickering stabilization has been investigated including non-heat treated, heat treated (gelatinized) and heat treated and stored (retrograded) emulsions. The stability of starch covered oil-water interfaces towards in vitro intestinal lipolysis was correlated to the rate of lipid hydrolysis using a pH-stat method. The results were compared with a sodium caseinate stabilized emulsion. The shape and size of the starch granules were characterized by scanning electron microscopy and light scattering. The physical properties of the emulsions were characterized by a light scattering particle size analyzer and light microscopy. In all cases, Pickering emulsions showed lower extents of lipolysis compared to the protein stabilized emulsion. In addition, heat treated starch Pickering emulsions were more susceptible to lipolysis compared to freshly prepared emulsions with no heat treatment. This was thought to be due to the gelatinized starch barrier being more susceptible to amylase present in the pancreatin. The results of this study demonstrate the interfacial layer properties can affect the rate and extent of lipolysis.
Biochimica Et Biophysica Acta - Proteins And Proteomics, Sep 1, 1993
The N-terminal 25 amino-acid residue peptide (beta-CN 1-25) obtained from a tryptic digest of bov... more The N-terminal 25 amino-acid residue peptide (beta-CN 1-25) obtained from a tryptic digest of bovine beta-casein was studied using two-dimensional NMR techniques. Complete sequence-specific assignment of the 1H-NMR spectrum was performed both in the presence and absence of 22 mM Ca2+. The NMR data supported earlier findings that this segment of beta-casein is highly flexible and adopts multiple conformations. The observed pattern of sequential NOEs indicated that the peptide did not contain stable folded structures. However, the structure was neither that of a fully-extended peptide nor a so-called random coil. The region Ile-12 to SerP-15 showed an enhanced population of extended structure. Furthermore, addition of Ca2+ ions induced chemical-shift changes and apparently decreased the population of conformations with extended structure in the region SerP-18 to Ile-23.
Metabolite profiling was used to characterize stress responses of potato tissue subjected to reve... more Metabolite profiling was used to characterize stress responses of potato tissue subjected to reversible electroporation, providing insights on how potato tissue responds to a physical stimulus such as pulsed electric fields (PEF), which is an artificial stress. Wounded potato tissue was subjected to field strengths ranging from 200 to 400 V/cm, with a single rectangular pulse of 1 ms. Electroporation was demonstrated by propidium iodide staining of the cells nucleae. Metabolic profiling of data obtained through GC/TOF-MS complemented with orthogonal projections to latent structures (OPLS) clustering analysis showed that 24 h after the application of PEF, potato metabolism shows PEF-specific responses characterized by the changes in the hexose pool that may involve starch and ascorbic acid degradation.
Mixed cultures of different EPS-producing Streptococcus thermophilus strains in combination with ... more Mixed cultures of different EPS-producing Streptococcus thermophilus strains in combination with a Lactobacillus delbrueckii subsp. bulgaricus strain with negligible EPS-production were used for yoghurt production. The yoghurt texture was characterised with respect to sensory, rheological and microstructural properties and the EPS-concentrations were determined. The cultures resulted in yoghurts with highly different texture properties, and positive interactions between certain Streptococcus thermophilus strains were observed. The underlying properties of yoghurt texture are multidimensional, but a number of microstructural characteristics were apparent in the yoghurts with the highest mouth thickness, creaminess and viscosity. A strong protein network, not too dense and with medium size pores containing EPS, seems associated with these properties. The presence of capsular polysaccharides (CPS) also appeared to be beneficial as did a combination of EPS types, which were distributed differently in the protein network (in serum pores, respectively in association with protein). Obviously, a certain concentration of EPS must be present to provide for these effects on yoghurt texture, but other factors than concentration per se seem more important.
This chapter describes particle-stabilized emulsions, the so-called Pickering emulsions. The prin... more This chapter describes particle-stabilized emulsions, the so-called Pickering emulsions. The principles behind particle stabilization of emulsions are described. The key properties of particle-stabilized emulsions such as stability, rheology, and the influences of other ingredients on the system, as well as some additional functional properties imparted by the stabilized particles in food emulsion formulations, are highlighted.
Gels formed from milk by renneting or acidification under quiescent conditions may subsequently s... more Gels formed from milk by renneting or acidification under quiescent conditions may subsequently show syneresis, that is, expel liquid (whey), because the gel (curd) contracts. Under quiescent conditions, a rennet-induced milk gel may lose two-thirds of its volume, and up to 90%, or even more, if external pressure is applied. Often, syneresis is undesired, for example, during storage of products like yogurt, sour cream, cream cheese, or quark; hence, it is useful to know under what conditions syneresis can be (largely) prevented. In making cheese from renneted or acidified milk, syneresis is an essential step. Consequently, it is useful to understand and quantitatively describe syneresis as a function of milk properties and process conditions, particularly when new methods or process steps are introduced in cheesemaking.
ABSTRACTThe instrumental and sensory analysis of the texture and color of commercial potato chips... more ABSTRACTThe instrumental and sensory analysis of the texture and color of commercial potato chips were compared. The instrumental measurement was a puncture test with an Intron Universal Testing Machine, and the parameters used were fracture force, deformation and stiffness. The instrumental color quantification was a computerized video image analysis technique, and the color was expressed as L*a*b* values. Sensory evaluation of texture and color was performed by a sensory panel especially trained in evaluating potato chips. The sensory attributes were “hardness”, “chewiness”, “crunchiness”, and “tenderness” for texture analysis, and “yellow color”, “burnt aspect”, “sugar colored aspect” and “transparency” for color analysis. The factor analysis of the sensory attributes indicated that texture can be divided into two principal components, one represented by “hardness”, “crunchiness” and “chewiness”, and the other by “tenderness” alone. The factor analysis of the color can be divided into two principal components, one including “yellow color” and “burnt aspect”, and the other “sugar colored aspect” and “transparency”. Discriminant analysis showed that “tenderness” and “crunchiness” could predict correctly over 90% of the data. Fracture force correlated well with all of the sensory attributes (R2 > 0.76), and L* with the sensory color attributes (R2 > 0.79). The “Tenderness” was the individual sensory attribute which had the highest correlation (R2= 0.95) with fracture force.
Changes occurring in directly heated UHT milk were studied during storage at 5, 22, 30 and 40 C. ... more Changes occurring in directly heated UHT milk were studied during storage at 5, 22, 30 and 40 C. Industrially produced UHT milk samples were analysed for changes in enzymatic activity, protein modification, destabilisation of casein micelles and relocation of milk proteins in relation to sedimentation and gel formation. Sedimentation occurred at all temperatures, and the protein composition of the sediments reflected the composition of its liquid phase; however, there was no a-lactalbumin, b-lactoglobulin or k-casein present in sediments. Tendrils composed of b-lactoglobulin and k-casein were seen on casein micelles after UHT treatment and grew in length prior to gelation. High degrees of lactosylation of proteins and peptides were clearly correlated with the absence of gelation and long tendrils. Gelled samples showed complete hydrolysis of intact b-casein, and limited lactosylation of b-lactoglobulin and k-casein.
Journal of Food Science and Engineering, Jun 28, 2015
The primary interest to this study was to investigate the effect of milling parameters on the siz... more The primary interest to this study was to investigate the effect of milling parameters on the size of hydrophobically modified starch particles, aiming to produce small, uniformly sized modified starch microspheres. Octie, a commercial product originated from cornstarch modified using Octenyl Succinate Anhydride (OSA), was dispersed (3 wt%) using different media (water or ethanol) and subsequently wet-milled using a beads mill with zirconium beads at a rotation of 6,000 rpm up to 30 min. It was found that milling Octie in water dispersion for 3 min resulted in the smallest mean particle size (2.04 ± 0.91 m), compared to unmilled modified starch granules (15.2 ± 6.0 m). Granular size and morphology changed considerably with further milling. For instance, very dense clusters with variable particle sizes (20.6 ± 10.0 m) were obtained after 30 min milling. As depicted by Scanning Electronic Microscopy, a large number of particles were apparently flattened during the milling process rather than broken, forming aggregates. Ultimately, within the range of experimental conditions tested, production of sub-micron modified starch particles was not possible.
Whey proteins have several excellent functional properties and one of their most important functi... more Whey proteins have several excellent functional properties and one of their most important functions is to improve consistency of foods by forming thermally induced gels. β-Lactoglobulin, which is the major whey protein, has good gelation properties and the aim of this study was to follow the formation of heat-induced gels of an industrially fractionated β-lactoglobulin isolate at different pH and assess their properties using dynamic rheometry.
Lactoglobulin, standard whey protein concentrate (WPC 80) and cold-gelling whey protein concentra... more Lactoglobulin, standard whey protein concentrate (WPC 80) and cold-gelling whey protein concentrate (mWPC 80) were dried onto mica sheets at 0.03-3 g cm\ surface load and imaged with atomic force microscopy (AFM) in tapping mode.-Lactoglobulin and WPC 80 spread to a fairly even 2.5 nm thick layer at about monolayer surface load, while mWPC showed particle sizes of 20-30 nm laterally. There is little difference in the observed structures between 0.3 and 3 g cm\ apart from the higher surface load. At 0.03 g cm\,-lactoglobulin spread somewhat more thinly than WPC 80. With the addition of DTT, mWPC spread evenly with only few particles in evidence. AFM appears to be a convenient method for the characterization of aggregation states of sub-micrometer protein particles.
The electrical conductivity of milk at various dilutions was measured at different temperatures f... more The electrical conductivity of milk at various dilutions was measured at different temperatures from 2 to 70 C. The results showed that dilution has only a small influence on the temperature dependence of conductivity. A simple power-law model predicts that the conductivity is proportional to the milk concentration to the power of 0.84 and a two-term model describes the temperature dependency. The overall model has a standard deviation of 0.0067 mS cm À1 , which corresponds approximately to 0.1% milk at 2 C and 0.07% milk at 70 C. It was further shown that for less than about 25% milk in water Kohlrausch's law and the Debye-Hu¨ckel-Onsager theory can be used to describe the relationship between the concentration, temperature, and conductivity using a representative limiting molar conductivity of milk ions of 75 mS cm 2 mol À1 .
We have investigated whether transient permeabilization caused by the application of pulsed elect... more We have investigated whether transient permeabilization caused by the application of pulsed electric field would give rise to transient changes in the potato tissue viscoelastic properties. Potato tissue was subjected to nominal field strengths (E) ranging from 30 to 500 V/cm, with a single rectangular pulse of 10 −5 , 10 −4 , or 10 −3 s. The changes on the viscoelastic properties of potato tissue during pulsed electric fields (PEF) were monitored through small amplitude oscillatory dynamic rheological measurements. The elastic (G′) and viscous moduli (G″) were measured every 30 s after the delivery of the pulse and the loss tangent change (tan-δ) was calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of the pulse. Results show a drastic increase of tan-δ in the first 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly influenced by pulsing conditions and is independent of the total permeabilization achieved by the pulse. Our results, supported by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence of electroporation. The recovery of tan-δ to values similar to those before pulsation strongly suggests recovery of cell membrane properties and turgor, pointing at reversible permeabilization of the cells. A slight increase of stiffness traduced by a negative change of tan-δ after application of certain PEF conditions may also give an indication of events occurring on cell wall structure due to stress responses. This study set the basis for further investigations on the complex cell stress physiology involving both cell membrane functional properties and cell wall structure that would influence tissue physical properties upon PEF application.
Thermal unfolding of whey proteins and whey protein-casein mixtures in sim- ulated milk ultrafilt... more Thermal unfolding of whey proteins and whey protein-casein mixtures in sim- ulated milk ultrafiltrate was studied by differential scanning calorimetry. The re- sults are reported as transition enthalpy, temperature of peak maximum, and van't Hoff enthalpy related to the sharpness of transition. The results of earlier investiga- tions were reviewed. It is suggested that a large part of reported whey
The extraction of red pigment and conductive matters from individual red beet tissue slices follo... more The extraction of red pigment and conductive matters from individual red beet tissue slices following pulsed electric field pretreatment of different durations was compared with a two dimensional bimodal Fickian diffusion model. The process appeared to be governed by two apparent diffusion coefficients, one slow and one fast. The values of these coefficients were independent of the duration of treatment, but the yield associated with each coefficient varied. Following the treatment of longest duration and treatment by freezing and thawing of the tissue, the yield from the faster diffusion coefficient accounted completely for the mass transport. The faster apparent diffusion coefficient was 2-5 times smaller than the diffusion coefficients in dilute solution.
Skim milk was heat treated (100°C/5min) and fermented with ropy and non-ropy commencai starters, ... more Skim milk was heat treated (100°C/5min) and fermented with ropy and non-ropy commencai starters, in beaker or in rheometer cup. Yoghurt properties were followed by dynamic rheometry (Bohlin Universal Rheometer) and by penetrometry (Stevens LFRA Texture Analyzer) and the measuring methods were compared.
A review. Gels formed from milk by renneting or acidification under quiescent conditions may subs... more A review. Gels formed from milk by renneting or acidification under quiescent conditions may subsequently show syneresis, i.e., expel liq. (whey), because the gel (curd) contracts. In making cheese from renneted or acidified milk, syneresis is an essential step. Consequently, it is useful to understand and quant. describe syneresis as a function of milk properties and process conditions, particularly when new methods or process steps are introduced in cheesemaking.
Uploads
Papers by Petr Dejmek