Showing papers in "Food Biophysics in 2008"

Solid Lipid Nanoparticles as Delivery Systems for Bioactive Food Components

Abstract: The inclusion of bioactive compounds, such as carotenoids, omega-3 fatty acids, or phytosterols, is an essential requisite for the production of functional foods designed to improve the long-term health and well-being of consumers worldwide. To incorporate these functional components successfully in a food system, structurally sophisticated encapsulation matrices have to be engineered, which provide maximal physical stability, protect ingredients against chemical degradation, and allow for precise control over the release of encapsulated components during mastication and digestion to maximize adsorption. A novel encapsulation system initially developed in the pharmaceutical industries to deliver lipophilic bioactive compounds is solid lipid nanoparticles (SLN). SLN consist of crystallized nanoemulsions with the dispersed phase being composed of a solid carrier lipid–bioactive ingredient mixture. Contrary to larger colloidal solid lipid particles, specific crystal structures can be “dialed-in” in SLN by using specific surfactant mixtures and ensuring that mean particle sizes are below 100–200 nm. Moreover, in SLN, microphase separations of the bioactive compound from the solidifying lipid matrix can be prevented resulting in an even dispersion of the encapsulated compound in the solid matrix thereby improving chemical and physical stability of the bioactive. In this review article, we will briefly introduce the structure, properties, stability, and manufacturing of solid lipid particles and discuss their emerging use in food science.

Designing food structure to control stability, digestion, release and absorption of lipophilic food components

Abstract: The bioavailability of dietary lipophilic components may be either increased or decreased by manipulating the microstructure and/or physicochemical properties of the foods that contain them. This article stresses how knowledge of the molecular, physicochemical, and physiological processes that occur during lipid ingestion, digestion, and absorption can be used to rationally design food structures to control these processes and therefore impact the rate or extent of lipid digestion and/or absorption. These approaches include controlling the molecular characteristics of the lipid molecules, altering lipid droplet size or interfacial properties, and manipulating food matrix structure and composition. Improved knowledge of the molecular, physicochemical, and physiological processes that occur during lipid ingestion, digestion, and absorption will facilitate the rational design and fabrication of functional foods for improved health and wellness.

Applications of Microfluidic Devices in Food Engineering

Abstract: The design of novel food micro-structures aimed at the quality, health and pleasure markets will probably require unit operations where the scale of the forming device is closer to the size of the structural elements (i.e., 1–100 μm). One emerging possibility is microfluidics or devices that employ small amounts of fluids (10−6 to 10−9 l) flowing in channels where at least one dimension is less than 1 mm. However, under these conditions, the predominant effects are not necessarily those present in conventional macroscopic unit operations. Dominant physical effects at the microfluidic scale are introduced through the use of dimensionless numbers. Different types of geometries to generate multi-phase flows in micro-channels, techniques and materials to construct the micro-devices, principally soft lithography and laser ablation, as well as methods used to modify surface properties of channels, are reviewed. The operation of micro-devices, the role of flow regimes, rheological behaviour of fluids in micro-channels and of transient time is discussed. Finally, systems developed to generate emulsions and foams, fluid mixing and dispersion, and future applications of these devices in food processing and food analysis are presented.

Influence of Surfactants on Lipase Fat Digestion in a Model Gastro-intestinal System

Abstract: In the present study, we use a model gastro-intestinal system to study the influence of different food-grade surface-active molecules (Sn-2 monopalmitin, β-lactoglobulin, or lysophosphatodylcholine) on lipase activity. The interfacial activity of lipase and surfactants are assessed with the pendant drop technique, a commonly used tensiometry instrument. A mathematical model is adopted which enables quantitative determination of the composition of the water–oil interface as a function of bulk surfactant concentration in the water–oil mixtures. Our results show a decrease in gastric lipolysis when interfacially active molecules are incorporated into a food matrix. However, only the Sn-2 monopalmitin caused a systematic decrease in triglyceride hydrolysis throughout the gastro-intestinal tract. This effect is most likely due to exclusion of both lipase and triglyceride from the water–oil interface together with a probable saturation of the solubilization capacity of bile with monoglycerides. Addition of β-lactoglobulin or lysophopholipids increased the hydrolysis of fat after the gastric phase. These results can be attributed to an increasing interfacial area with lipase and substrate present at the interface. Otherwise, β-lactoglobulin, or lysophopholipids reduced fat hydrolysis in the stomach. From the mathematical modeling of the interface composition, we can conclude that Sn-2 monopalmitin can desorb lipase from the interface, which, together with exclusion of substrate from the interface, explains the gradually decreased triglyceride hydrolysis that occurs during the digestion. Our results provide a biophysics approach on lipolysis that can bring new insights into the problem of fat uptake.

Effect of Structural and Physicochemical Characteristics of the Protein Matrix in Pasta on In Vitro Starch Digestibility

Abstract: Pasta is a popular carbohydrate-based food with a low glycemic response. A continuous protein matrix which entraps starch granules and/or limits/retards starch hydrolysis by α-amylase is thought to be an important factor in explaining the slow digestion of starch in pasta. The characteristics of the protein matrix may also play an important role in determining the rate of starch digestion in pasta and therefore its glycemic response. In this study, the structural and physicochemical characteristics of the protein matrix of pasta were modified by varying the number of passes through sheeting rollers to investigate their effect on in vitro starch digestibility. The results show that the proteins dissociated from the starch granules with increasing sheeting passes thereby allowing an increased degree of digestion of starch.

Effect of Hydrophilic and Lipophilic Compounds on Zein Microstructures

Abstract: Zein, the prolamine of corn, contains nearly an equal amount of hydrophilic and lipophilic amino acid residues. Its tertiary structure has a regular geometry measuring 17 × 4.5 × 1.2 nm. The structure of zein allows it to function as a polymeric amphiphile. Zein had been observed to self-assemble into periodic bilayer structures and nanotubes. This work investigated the structural development of zein self-assemblies as affected by the hydrophilic–lipophilic balance (HLB) of the system. The formation of several structures, including spheres, sponge, and lamellae, were identified. Images were obtained by SEM, AFM, and FIB/SEM. The radius of curvature of the observed assemblies was affected by the HLB of the components in the system. Thus, lipophilic flavor oils increased the curvature of zein spheres producing smaller spheres. Curvature decreased in the presence of amphiphilic fatty acids forming sponges with interconnected channels. Hydrophilic compounds decreased the curvature to the point of forming smooth films. The results of this study see a future in microencapsulation and controlled release systems for flavor and bioactive compounds in the food industry.

Formulation and Characterization of Phytophenol-Carrying Antimicrobial Microemulsions

Abstract: Phytophenols were solubilized in nonionic surfactant micelles to form antimicrobially active and thermodynamically stable microemulsions. Formulation of phytophenols in microemulsions has previously been shown to improve their antimicrobial activity in model microbiological and food systems. Carvacrol and eugenol were incorporated in micellar solutions of two nonionic surfactants (Surfynol® 485W and Surfynol® 465) by mixing at room temperature. Particle size of formed microemulsions was determined by dynamic light scattering, and structural information about the mixed micellar system was obtained by nuclear magnetic resonance spectroscopy (NMR). Uptake of carvacrol and eugenol in surfactant micelles as determined by ultrasonic velocity measurements was very rapid, e.g., below the maximum additive concentration, the phytophenols were completely solubilized in the micelles in less than 30 min. Depending on the surfactant–phytophenol combination, the self-assembled surfactant–phytophenol aggregates had mean particle diameters between 3 and 17 nm. Elucidation of the structure of aggregates by 1H NMR studies indicated that micelles had a “bracket-like” structure with phytophenols being located inside the palisade layer of the micelle in direct contact with adjacent surfactant monomers. Encapsulation of phytophenols in surfactant micelles enables the incorporation of large amounts of hydrophobic antimicrobials in aqueous phases. Formulation of antimicrobial microemulsions may thus offer a means to deliver high concentrations of phytophenols to the bacterial surfaces of foodborne pathogens to affect kill.

Structural Behaviour of Lipid Droplets in Protein-stabilized Nano-emulsions and Stability of α-Tocopherol

Abstract: A stearin-rich milk fraction was used, alone or in combination with α-tocopherol, for the preparation of oil-in-water sodium caseinate-stabilized nano-emulsions. Fat droplets in these two emulsions were characterized for their size distribution and physical stability against aggregation–coalescence, for their heat-induced structural behaviour, and for their ability to protect α-tocopherol during oxidation. Inclusion of α-tocopherol led to changes in the particle size distributions of fat droplets: in the presence of α-tocopherol, approximately 75% of fat droplets were lower than 1 μm, instead of 100% in the absence of α-tocopherol. On the other hand, thermal transitions observed by differential scanning calorimetry showed that supercooling (the increase in differences between temperature of initial crystallization and melting completion) was higher in the emulsified milk fat samples containing α-tocopherol. In addition to a decrease in the temperature of fat crystallization leading this change in the supercooling effect of α-tocopherol, small- and wide-angle X-ray diffraction patterns (SAXS and WAXS, respectively) observed under cooling and re-heating cycles showed that heat-induced polymorphic transitions from $${\text{2L}}_{\text{ $ \alpha $ }} \to {\text{2L}}_{{\text{ $ \beta $ }}\prime } $$ forms were more impeded in the emulsion containing α-tocopherol. Immobilisation of α-tocopherol in fat droplets composed by high melting temperature milk fat triglycerides seemed to lead to its protection against degradation.

Stability of Biopolymer Particles Formed by Heat Treatment of β-lactoglobulin/Beet Pectin Electrostatic Complexes

Abstract: The purpose of this study was to examine the stability of biopolymer particles formed by heating electrostatic complexes of β-lactoglobulin and sugar beet pectin together (pH 5, 80 °C for 15 min). The effects of electrostatic interactions on the formation and stability of the particles were investigated by incorporation of different salt levels (0 to 200 mM NaCl) during the preparation procedure. Biopolymer particles were characterized by turbidity, electrophoretic mobility, dynamic light scattering, and visual observance. Salt inclusion (≥25 mM) prior to heating β-lactoglobulin/pectin complexes led to the formation of large biopolymer particles (d > 1,000 nm) that rapidly sedimented, but salt inclusion after heating (0 to 200 mM) led to the formation of biopolymer particles that remained relatively small (d < 350 nm) and were stable to sedimentation. The biopolymer particles formed in the absence of salt remained stable over a wide range of pH values (e.g., pH 3 to 7 in the presence of 200 mM NaCl). These biopolymer particles may therefore be suitable for application in a number of food products as delivery systems, clouding agents, or texture modifiers.

Antioxidant and Neuroprotective Properties of Sour Tea (Hibiscus sabdariffa, calyx) and Green Tea (Camellia sinensis) on some Pro-oxidant-induced Lipid Peroxidation in Brain in vitro

Abstract: Oxidative stress is the cause of neurodegenerative disorders such as Lou Gehrig’s disease, Parkinson’s disease, and Huntington’s disease; one practical way to prevent and manage neurodegenerative diseases is through the eating of food rich in antioxidants (dietary means). This present study sought to compare the ability of aqueous extract of sour tea (Hibiscus sabdariffa, calyx) and green tea (Camellia sinensis) to prevent some pro-oxidant [Fe (II), sodium nitroprusside, quinolinic acid]-induced lipid peroxidation in rat’s brain in vitro. Aqueous extracts of both teas were prepared (1 g tea in 100 ml of hot water). Thereafter, the ability of the extracts to prevent 25 μM FeSO4, 7 μM sodium nitroprusside, and 1 mM quinolinic acid-induced lipid peroxidation in isolated rat’s brain tissue preparation was determined in vitro. Subsequently, the total phenol content, reducing power, Fe (II) chelating and OH radical scavenging ability were determined. The results of the study revealed that both teas significantly (P < 0.05) inhibit lipid peroxidation in basal and pro-oxidant-induced lipid peroxidation in the rat’s brain homogenates in a dose-dependent manner. Also, the teas had high total phenol content [sour (13.3 mg/g); green (24.5 mg/g)], reducing power, and Fe (II) chelating and OH radical scavenging ability (except sour tea). However, green tea had a significantly higher (P < 0.05) ability to inhibit lipid peroxidation in both the basal and pro-oxidant-induced lipid peroxidation in rat’s brain homogenates in vitro. Therefore, it is obvious from the study that both teas had high antioxidant properties and could inhibit Fe2+, sodium nitroprusside, and quinolinic acid-induced lipid peroxidation in brain. However, green tea had a higher inhibitory effect, which may probably be due to its high total phenol content, reducing power, Fe (II) chelating ability, and OH radical scavenging ability.

Rheology and Stability of Beverage Emulsions in the Presence and Absence of Weighting Agents: A Review

Abstract: Cloudiness or opacity (cloudy appearance) is an important property in citrus beverages, since it enhances their juice-like appearance and gives it a natural fruit juice appeal. This property is achievable through the addition of oil-in-water emulsions known as clouding agents. These emulsions are thermodynamically unstable and tend to break down during storage. Moreover, product and legal constraints put severe limits on materials that can be used to insure emulsion stability, particularly the introduction of weighting agents into the oil phase. Weighing agents (density-adjusting agents) are lipophilic compounds with specific gravity higher than that of water and have a restricted use because of the perceived health risk disadvantage, undesirable taste, and oxidative instability. The stability of beverage emulsions is a problem of serious concern faced by the flavor and beverage industry. This paper provides an overview of research carried out by the authors on basic factors affecting the physical stability of beverage cloud emulsions having a bearing on droplet size/distribution, rheological properties of emulsion and phases components, and the stability of emulsion in concentrated and diluted forms with or without addition of weighting agents.

Effect of Cooling and Heating Rates on Polymorphic Transformations and Gelation of Tripalmitin Solid Lipid Nanoparticle (SLN) Suspensions

Abstract: Solid lipid nanoparticle (SLN) suspensions undergo a phase transition from the α- to β-polymorphic forms, which is accompanied by particle aggregation and gel formation These processes are both time and temperature dependent, and so it is important to study the impact of cooling rates (CRs) and heating rates (HRs) on polymorphic transformations, particle aggregation, and gelation Rheology measurements indicated that the temperature where gelation was first observed during cooling (T gel) decreased with increasing CRs, with SLN suspensions remaining fluid at HR ≥ 5 °C/min On the other hand, the temperature where gelation was first observed during heating of stable SLN suspensions increased with increasing HRs: 18, 24, 31, and 45 °C at 2, 5, 10, and 20 °C/min, respectively When the melted SLN suspensions were cooled again, two exothermic peaks were observed in the differential scanning calorimetry scans at 39 (which was attributed to coalesced oil) and 19 °C (which was attributed to stable SLN) With increasing CR, the enthalpy of the coalescence peak (ΔH CO) decreased, while that of the supercooled SLN (ΔH SLN) increased With increasing HR, ΔH CO decreased and ΔH SLN increased, with no coalescence being observed at HR ≥ 10 °C/min These results show that increasing the CRs or HRs retard the α→β polymorphic transformation, which increased the stability of SLN against aggregation and retarded gelation In addition, this study shows that the careful selection of HRs and CRs is required to examine polymorphic transformations and the stability of SLN suspensions

Creating Novel Structures in Food Materials: The Role of Well-Defined Shear Flow

Abstract: Structure formation in food materials is influenced by the ingredient properties and processing conditions. Until now, small structural elements, such as fibrils and crystals, have been formed using self-assembly, while processing was applied to create relatively large structures. The effect of self-assembly under flow is rarely studied for food materials, but it is widely studied for non-food systems. The use of well-defined flow, often simple shear, turned out to be essential to study and control the structure formation process in foods as well. This observation encouraged us to develop a number of different shearing devices that allowed processing of biopolymer systems under simple shear flow. This paper reviews our main findings. In the case of protein fibrillization, the shear rate was found to control the growth rate as well as the properties of the fibrils formed. In the case of dough processing, simple shear flow made the product more process tolerant and induced gluten migration. The use of shear flow for dense caseinate dispersions led to hierarchically structured and fibrous material. Based on the presented results, we conclude that introducing simple shear flow in food structuring processes can lead to a much broader range of structures, thereby better utilizing the full potential of food ingredients.

Encapsulation of Lipophilic Bioactive Molecules by Microchannel Emulsification

Abstract: Currently, much effort is being invested in novel formulations of bioactive molecules, such as emulsions, for pharmaceutical, food, and cosmetic applications. Therefore, methods to produce emulsions with controlled-size droplets of uniform size distribution have been developed. On this concern, a microfluidic device called the microchannel (MC) was used in this work for emulsification. This is a novel method for producing monodispersed emulsion droplets with very narrow droplet size distribution and low energy input, due to the spontaneous droplet generation basically driven by the interfacial tension, unlike other conventional emulsification processes. This technology provides the formulation of oil-in-water (O/W) emulsions containing lipophilic active molecules with increased bioavailability, which may be readily absorbed by the human body. MC emulsification enables the preparation of highly monodispersed O/W emulsions, which may be applied as enhancer on active molecules delivery systems, as well as in foodstuff. In this study, formulations of O/W emulsions loaded with bioactive molecules, such as β-carotene and γ-oryzanol, were prepared by the MC emulsification process. Refined soybean oil containing the dissolved lipophilic molecule and either sugar ester or gelatin solution (1 wt.%) were used as the dispersed and continuous phases, respectively. The emulsification process conducted using the asymmetric straight-through MC plate enabled the production of monodispersed O/W emulsions, resulting in β-carotene-loaded O/W emulsions with average droplet size (dav) of 27.6 μm and coefficient of variation (CV) of 2.3% and γ-oryzanol-loaded droplets with dav of 28.8 μm and CV of 3.8%. The highly monodisperse β-carotene-loaded droplets were physically stable throughout the storage period observed, resulting in droplets with dav 28.2 μm and CV of 2.9% after 4 months storage in darkness at 5 °C. Single micrometer-sized monodisperse emulsions loaded with β-carotene were successfully formulated using the grooved MC emulsification, resulting in droplets with dav of 9.1 μm and CV of 6.2%.

Molecular Gastronomy: A Food Fad or an Interface for Science-based Cooking?

Abstract: A review is given over the field of molecular gastronomy and its relation to science and cooking. We begin with a brief history of the field of molecular gastronomy, the definition of the term itself, and the current controversy surrounding this term. We then highlight the distinction between molecular gastronomy and science-based cooking, and we discuss both the similarities and the distinctions between science and cooking. In particular, we highlight the fact that the kitchen serves as an ideal place to foster interactions between scientists and chefs that lead to benefits for the general public in the form of novel and high-quality foods. On the one hand, it can facilitate the implementation of new ideas and recipes in restaurants. On the other hand, it challenges scientists to apply their fundamental scientific understanding to the complexities of cooking, and it challenges them to expand the scientific understanding of many chemical and physical mechanisms beyond the common mass-produced food products. In addition, molecular gastronomy forms an ideal base to educate the general public about the basic principles of science and cooking and how they can be utilized to improve the awareness of the role of food and nutrition for the quality of life.

Application of Supercritical Anti-Solvent Technologies for the Synthesis of Delivery Systems of Bioactive Food Components

Abstract: To develop edible delivery systems suitable for food applications, regulations require that solvents and ingredients are either generally recognized as safe or listed by the Food and Drug Administration as processing aids. In this work, we studied a food grade polymer-corn zein, a category of alcohol-soluble proteins, as the carrier material for microencapsulating bioactives. Zein is insoluble in aqueous solutions; zein-based delivery systems may thus maintain the integrity in aqueous food products during processing and storage. Three alcohols, i.e., ethanol, methanol, and isopropanol, with an appropriate amount of water were used to dissolve zein. A supercritical anti-solvent process was applied to synthesize micro- and nanoparticles of zein for edible delivery systems of bioactive compounds. We studied critical variables during the particle formation: polymer concentration, CO2 flow rate, and co-solvent chemistry. Particles were produced only when mass transfer was fast enough that the co-solvent in the atomized droplets could be extracted by the reservoir CO2 and polymers could nucleate and grow into particles. Manipulation of the above variables enabled the production of micro- and nanoparticles, which can be used as bases for microencapsulating bioactives. Our results demonstrated promising applications of the supercritical anti-solvent technology to synthesize food grade delivery systems of bioactive food ingredients that can enhance the healthfulness, safety, and quality of food products.

Rheological behavior of food emulsions mixed with saliva: Effect of oil content, salivary protein content, and saliva type

Abstract: In this paper, we studied the effect of saliva on the rheological properties of β-lactoglobulin- and lysozyme-stabilized emulsions, prepared at pH = 6.7 in relation to variation of emulsions- and saliva-related parameters. The effect of oil–volume fraction (2.5% w/w to 10% w/w), salivary protein concentration (0.1 to 0.8 mg ml−1), and the use of both stimulated and unstimulated saliva was investigated. Viscosity and storage modulus were measured before (ηemul and G′emul, respectively) and after addition of saliva (ηmix and G′mix). To better estimate the changes due to saliva-induced flocculation of the emulsions, the ratios ηmix/ηemul, G′mix/G′emul were calculated. In addition, tan δ (=the ratio of the loss and storage moduli) was investigated to evaluate the viscoelastic behavior of the emulsion/saliva mixtures. Increasing the oil–volume fraction and salivary protein concentration resulted in an increase in ηmix/ηemul and G′mix/G′emul, while a decrease in tan δ of the emulsion/saliva mixtures is occurring. When compared with unstimulated saliva, mixing β-lactoglobulin-stabilized emulsions with stimulated saliva led to a reduction in ηmix/ηemul and G′mix/G′emul, and an augment of tan δ at all measured deformations. In case of lysozyme-stabilized emulsions, the use of stimulated saliva increased G′mix/G′emul for γ < 3 when compared to unstimulated saliva. The effect of stimulated saliva on the ηmix/ηemul and tan δ in this mixture is similar to that of unstimulated saliva. These results indicate that the influence of stimulated saliva on the rheological parameters of emulsion/saliva mixtures largely depends on the type of emulsions. To conclude, our findings demonstrate that the rheological behavior of emulsions upon mixing with saliva is greatly affected by both saliva and emulsion properties.

Mechanical and Barrier Properties of Avenin, Kafirin, and Zein Films

Abstract: Biodegradable and renewable materials can be manufactured from prolamins, which are the major storage protein fraction of cereals. This paper investigates the material properties of oat prolamin (avenin), corn prolamin (zein), and sorghum prolamin (kafirin). Glass transition temperature, dry solid content, stress at break, strain at break, oxygen permeability, and water vapor permeability were analyzed at different plasticizer contents. Avenin was plasticized with glycerol, and kafirin and zein were plasticized with a mixture of polyethylene glycol, glycerol, and lactic acid. Avenin displayed potential, although it did not exhibit the mechanical qualities of gluten, which resembles avenin at the molecular level. Compared to kafirin and zein, avenin was more extensible at low plasticizer contents, while kafirin and especially zein were more extensible at the highest plasticizer content. Avenin was far weaker than the other two at all plasticizer contents. Kafirin and zein displayed similar barrier properties, whereas avenin was notably more permeable.

Physical Properties Giving the Sensory Perception of Whey Proteins/Polysaccharide Gels

Abstract: Establishing relationships between physical and sensorial properties of semi-solid foods is essential to develop tailored products. Whey protein/polysaccharide mixed gels were used to model both natural and fabricated semi-solid foods. The presence of various polysaccharides modulated the microstructure and large deformation properties of the mixed gels. The gels exhibited a large spectrum of sensorial properties as evaluated by panellists in a quantitative descriptive analysis. Mouthfeel attributes that discriminated best between the gels were wateriness, crumbliness, and spreadability. Wateriness strongly correlated with the amount of exuded phase (serum) measured during uniaxial compression. Serum release may have a positive effect on, for instance, the juiciness of a product. Large deformation measurements showed that highly crumbly gels fracture readily via a free-running crack. Low serum release is a requirement for that. Low crumbly gels fracture slowly, often releasing a high amount of serum. Spreadability related to the occurrence of multiple microcracks during deformation as observed by confocal laser scanning microscopy, which resulted in a large number of pieces after oral processing.

Drying and Rehydration of Calcium Alginate Gels

Abstract: In this paper, we study the rehydration properties of air-dried calcium alginate gel beads. Rehydration is shown to depend on alginate source (i.e. mannuronic to guluronic acid ratio) and the salt concentration in the rehydration medium. Rehydration curves are described adequately by the empirical Weibull equation. Wide-angle X-ray diffraction measurements are performed to obtain information on the microstructure of dried alginate gels. The X-ray diffraction patterns provide evidence for formation of ordered domains in which alginate polymers are laterally associated. Formation of ordered structures during drying is found to have a large impact on rehydration properties. Lateral association of alginate chains is reduced (and rehydration improved) by removing excess calcium ions from the gel beads in a washing step prior to air drying. In addition, rehydration properties of mixed alginate–carboxymethyl cellulose (CMC) gel beads are investigated. The presence of CMC in the gel matrix is found to reduce lateral association of alginate chains during drying and to improve rehydration properties.

Rheology of Mixed Pectin Solutions

Abstract: The effects of sucrose (S) and pectin (P) concentrations and the ratio between two distinct pectins (R) on the rheological behavior of diluted pectin systems were evaluated simultaneously using the surface response methodology. The systems were composed of a mixture of two high methoxy pectins with different degree of methyl esterification values (HM1/HM2) and of a mixture of a high-methoxy with an amidated low-methoxy pectin (HM1/LMA). For the HM1/HM2 systems, the multivariate analysis showed that the sucrose and pectin concentrations exerted statistically significant (p < 0.05) linear effects on the consistency index k and viscosity, the influence of pectin being about five times higher than that of sucrose. The pectin concentration and the ratio between the different pectins were shown to be significant with respect to the rheological parameters of the HM1/LMA systems. Evaluating the influence of the ratio between the different pectins, a synergistic effect on the structure reinforcement was observed when mixing HM1 and LMA in similar proportions, indicating the importance of the presence of hydrophobic interactions between methyl ester groups in addition to the stronger hydrogen bonding in junction zone stabilization. In general, the conditions in which hydrogen bonds were favored in relation to hydrophobic interactions led to systems with higher pseudoplasticity.

Exploring Metabolic Responses of Potato Tissue Induced by Electric Pulses

Abstract: In this study, we investigated the metabolic responses of potato tissue induced by pulsed electric field (PEF). Potato tissue was subjected to field strengths ranging from 30 to 500 V/cm, with a single rectangular pulse of 10 μs, 100 μs, or 1 ms. Metabolic responses were monitored using isothermal calorimetry, changes on electrical resistance during the delivery of the pulse, as well as impedance measurements. Our results show that the metabolic response involves oxygen consuming pathways as well as other unidentified events that are shown to be insensitive to metabolic inhibitors such as KCN and sodium azide. The metabolic response is strongly dependent on pulsing conditions and is independent of the total permeabilization achieved by the pulse. Evidence shows that calorimetry is a simple and powerful method for exploring conditions for metabolic stimulation, providing information on metabolic responses that can not be obtained from electrical measurements. This study set the basis for further investigations on defense-related consequences of PEF-induced stress.

Enzyme-Induced Formation of β-Lactoglobulin Fibrils by AspN Endoproteinase

Abstract: This paper describes a low temperature, enzymatic route to induce fibrillar structures in a protein solution. The route comprises two steps. First, β-lactoglobulin was hydrolyzed into peptides at pH 8 and 37 °C with the enzyme AspN endoproteinase, which resulted in the formation of random aggregates. After hydrolysis, the pH was lowered to 2. As a result, long fibrillar aggregates were formed which was observed using transmission electron microscopy and Thioflavin T fluorescence measurements.

Effects of Modification of Encapsulant Materials on the Susceptibility of Fish Oil Microcapsules to Lipolysis

Abstract: The aim of the study was to assess the effects of modification of encapsulant materials before emulsion formation on the viscosity and interfacial properties of the emulsions and their influence on the susceptibility of emulsions to in vitro lipolysis. Emulsions (oil/protein ratio 2:1) were prepared by homogenizing mixtures containing fish oil and non-heated or heated (100 °C/120 min) dispersions comprising (a) sodium caseinate (NaCas), (b) mixtures of NaCas and a high amylose-resistant starch (Hylon VII; 1:1 mass ratio), and (c) mixtures of NaCas and previously modified resistant starch (heat/microfluidized [MF] Hylon VII; 1:1 mass ratio), followed by freeze drying. Reconstituted emulsion containing heated mixture of NaCas and heat/MF Hylon VII was the most viscous. The extent of lipolysis was the same in all emulsions stabilized by non-heated NaCas or non-heated mixtures of NaCas with resistant starch. Heat treatment of NaCas increased lipolysis of emulsions stabilized with protein alone, but heating NaCas with Hylon VII or heat/MF Hylon VII before emulsion formation reduced lipolysis. The emulsion stabilized with the heated NaCas–heat/MF Hylon VII mixture was the most resistant to lipolysis. Overall, the resistance to lipolysis was considered to be primarily dependent on the interfacial properties of the microcapsules. These findings of in vitro lipolysis of NaCas-resistant starch formulated oil powders may be relevant to an understanding of in vivo digestibility of the oil powders. The insights may be used as a guide to formulate oil systems for altering the susceptibility to lipolysis of ingested oil emulsions.

In situ Imaging of Pea Starch in Seeds

Abstract: A method has been developed for the in situ imaging of starch in dry seeds by exploiting the tight packing of the starch and protein storage reserves within the cells of the embryo. The method can be adapted to prepare seed samples which are suitable for light microscopy (birefringence and iodine staining), scanning electron microscopy and atomic force microscopy. Its potential for imaging the internal structure of starch granules without any prior isolation process is demonstrated for round smooth peas. Using a standard ultramicrotome, thin sections were cut directly from selected regions of dry pea seeds and examined by light microscopy before and after hydration. The sectioning procedure left a planed surface with the internal structure of the starch granules exposed. This material was examined by scanning electron microscopy and atomic force microscopy directly or after controlled hydration. In the hydrated pea samples, the growth ring structure and blocklet sub-structure of individual starch granules within the seed were visualised directly by atomic force microscopy. Furthermore, the effects of hydration and staining were monitored and have been used to introduce contrast into the images. The observations have revealed new information on the blocklet distribution within pea starch granules and the physical origins of the growth ring structure of the granules: the blocklet distribution suggests that the granules contain alternating bands with different levels of crystallinity, rather than alternating amorphous and crystalline growth rings.

Influence of the Dispersed Particulate in Chocolate on Cocoa Butter Microstructure and Fat Crystal Growth during Storage

Abstract: The dispersed particulates present in chocolate are shown to influence the microstructural development and fat crystal growth of cocoa butter (CB) during storage. Atomic force microscopy of both chocolate and CB showed that surface crystal growth on both materials was similar during isothermal (25 °C) storage over 4 weeks. However, unique micron-scale amorphous mounds also appeared on the surface of chocolate. With time, these regions increased in number and diameter and eventually solidified into clustered crystalline masses. X-Ray diffraction, solid fat content, and whiteness index measurements substantiated the observed crystal growth, with gradual increases in the proportion of the form VI polymorph, solid fat, and whiteness over time. Overall, these findings suggest that typical chocolate refining and tempering protocols result in a heterogeneously distributed particulate network that has a substantial impact on the morphology and crystallization pathway of the fat phase.

Antioxidant Properties of Fruits and Vegetables Shots and Juices: An Electron Paramagnetic Resonance Study

Abstract: The antioxidant activity of some commercially available fruit and vegetable juices was evaluated with regard to their radical scavenging activity against the stable free radical 4-hydroxy-2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPOL) monitored by electron paramagnetic resonance (EPR) spectroscopy. TEMPOL is a stable nitroxide free radical characterized by a well-defined EPR spectrum consisting of three peaks. The integral intensity of the EPR spectra of TEMPOL was decreased upon juice addition, and the decrease was dose dependent. EPR spectroscopy using stable free radicals provides a simple, rapid, and sensitive method for the determination of antioxidant activity of fruit and vegetable juices. The method was standardized by using the standard antioxidant compound Trolox, and the antioxidant activity of the juices was expressed as Trolox equivalents. When concentrated juices of fruits and vegetables (shots) were considered, the evaluated antioxidant activity was almost twofold higher than that of the conventional, non-concentrated ones. Fruits and vegetables shots also showed very good stability during storage. This finding indicates that natural antioxidant compounds contained in commercially available concentrated juices are not eliminated or inactivated when the juices are kept refrigerated according to the instructions of the manufacturer.

Starch Granule Hydration—A MAS NMR Investigation

Abstract: Starch is the most important energy resource in human diet, and starch is used extensively as a food ingredient to manipulate the quality of our food. In both applications, starch functionality is intimately related to its hydration level. This paper aims at elucidating the starch granule hydration by investigating genotype-specific differences for native wheat, maize, and potato starches by 1H high-resolution (HR) magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The preparations as analyzed in D2O suspensions at room temperature provided NMR spectra with large differences in signal-to-noise (S/N) ratio ranging over several orders of magnitude. It was possible to assign a wide range of components including anomeric α-1,4 and α-1,6-protons from reducing and non-reducing ends, respectively. We utilized the effect that only mobile protons (e.g, dissolved or partially hydrated) are observed using 1H HR-MAS spectroscopy, whereas immobile protons (e.g., in water-inaccessible regions) of the starch granule are not observed due to strong homonuclear interactions to verify the hypothesis that the variations in signal intensities between the different starches are caused by genotype-specific variations in assembly of the starch granules and that the signal intensity, thus, indicates the extent of accessible granule hydration surfaces. Moreover, events taking place during thermal starch granule hydration (gelatinization) were investigated for ten representative starches. NMR spectra of suspended samples were acquired at 30, 45 and 70 °C and again after cooling at 30 °C. A substantial increase in NMR signal intensity occurs above the gelatinization temperature due to extensive proton mobilization in the starch granule assembly. The relative integrated spectral intensities at 30 °C before and after gelatinization at 70 °C showed differences in gain factors between 4 and 193. Also, 31P MAS NMR spectra displayed a similar significant intensity gain upon gelatinization. The results showed that the phosphate groups in the starch granule are mobilized concomitantly with the protons and thus deeply “buried” in the immobile (water inaccessible) domains.

Characterization of Fish Gelatin at Nanoscale Using Atomic Force Microscopy

Abstract: Atomic force microscopy (AFM) was used as a meaningful tool to characterize the nanostructure of gelatin from catfish (Ictalurus punctatus) skin. The gelatins extracted with pretreatments including acid pretreatment, alkaline pretreatment, and alkaline followed by acid pretreatment (optimized extraction conditions). The resulting gelatins were imaged using AFM and their nanostructure was studied. The AFM images showed that gelatin extracted with acid pretreatment had a coacervate structure while with alkaline pretreatment there were separate aggregates. Spherical aggregates and annular pores were observed in AFM images of gelatin with the optimized extraction conditions. AFM imaging of gelatin with a relative high concentration (0.5%) was successfully done and the results help researchers to understand gelatin structures at the nanoscale.

Product Composition, Structure, and Bioavailability

Abstract: Bioavailability is the fraction of an administered dose that reaches the systemic circulation. Health claims for functional foods can only be made if the ingredient reaches the target site to trigger the physiological action, hence substantiation requires good bioavailability. This is also expressed in the European Regulation on Health Claims. Albeit not new at all, a full understanding of the controlling factors for bioavailability in foods is still lacking. Foods are complex systems and can be part of a meal. The impact of product composition and the interplay with human physiology during fed or fasted state has to be understood: a functional ingredient has to be released from the product matrix into a molecularly dispersed state, either in classic solution or in micellar state. Only in the dispersed state can actives cross the gut wall. Release and dissolution are depending on both molecular physicochemical properties of the active and those of the entire product. More complex is the uptake of hydrophobic, poorly water-soluble substrates. As they do not dissolve in the aqueous intestinal environment, presence of fat, release of bile, enzymes, and gut motility to induce lipolysis are required. Surface-active bile salts together with lipolysis products create micelles containing the hydrophobic active. This imposes limitations on the formulation space for hydrophobic compounds. Finally, many ingredients are not fit for straightforward use as they compromise the stability or sensory characteristics of the product. Compartmentalization strategies, like encapsulation, may offer solutions to the problem; it should, however, not be forgotten that encapsulates themselves may effect bioavailability through the changed dynamics of the uptake processes. To explore and build a better understanding of these factors, a range of models are available and used in product formulation and claim substantiation. A structured approach and the selection of proper models will help to improve functional food formulations in the future.