Biopolymer Systems Research Articles

Controlled biopolymer phase separation in complex food matrices containing fat droplets, starch granules, and hydrocolloids

New strategies are needed to create high-quality reduced-calorie foods designed to combat the recent rise in overweight and obesity. In this study, we examined the influence of controlled phase separation and gelation of mixed biopolymer systems on the physical properties of model food matrices containing fat droplets, starch granules, and hydrocolloids. Phase separation of pectin–caseinate mixtures was induced through thermodynamic incompatibility (pH7) followed by electrostatic complexation (pH5), and then gelation was induced by adding calcium ions. The resulting model food matrices consisted of fat droplets, starch granules, and a phase separated biopolymer matrix. Confocal microscopy showed that the fat droplets were located within caseinate-rich hydrogel particles, which were present in the interstitial region around the swollen starch granules. All systems exhibited shear-thinning behavior and had yield stresses that increased with increasing biopolymer and calcium concentration. Swollen starch granules had a greater influence on the rheology of the mixed systems than other components due to their relatively high effective volume fractions, whereas fat droplets had a greater influence on the optical properties due to their stronger light scattering efficiency. Calcium ions increased the apparent viscosity of mixed systems, which was attributed to charge screening and ion-bridging effects. These findings suggest that controlled phase separation and gelation of mixed biopolymer systems have potential to create reduced calorie emulsion-based foods, or products with novel textural characteristics.

Polysaccharide gels as oil bulking agents: Technological and structural properties

Lipid and polysaccharide interactions in various polysaccharide gels prepared for use as oil bulking agents were investigated using Raman spectroscopy. Two different polysaccharide gel matrices containing olive oil were prepared using mixed biopolymer systems of alginate with inulin (OM-A/I) or dextrin (OM-A/D). Stability and textural properties were also evaluated in these matrices. Thermal stability of the different matrices was optimal. The textural behaviour of polysaccharide matrices with olive oil incorporated differed depending on the polysaccharide gels used in their formulation. OM-A/I presented the highest (P < 0.05) hardness, adhesiveness, and chewiness. These matrices were stabilized by hydrogen bonding between oil carbonyl groups and water and/or carbohydrate molecules. Lipid acyl chains are relatively fixed through hydrogen bonding and intermolecular order upon micelle formation. Raman spectroscopic results also showed carbohydrate-water hydrogen bonding, in which inulin seemed to be more strongly bonded to water than dextrin. This difference in the structural behaviour of inulin and dextrin in terms of hydrogen bonding to water may explain the differences in textural 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 600MPa for 15min 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 300MPa, whereas HPP at 600MPa 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 1480–1575cm−1, which reflect the vibrational bands of amide I and amide II, respectively.

Chitosan as matrix for bio-polymer dispersed liquid crystal systems

The obtaining of bio-polymer dispersed liquid crystal (bio-PDLC) systems based on a chitosan polymer matrix is reported here for the first time. The new PDLC composites have been obtained by encapsulation of 4-cyano-4′-pentylbiphenyl (5CB) as low molecular weight liquid crystal into chitosan, and they have been characterized by polarized optical microscopy, differential scanning calorimetry, electron and transmission scanning microscopy, Raman and fluorescence spectroscopy.Submicrometric liquid crystalline droplets with uniform size distribution and density have been obtained for low liquid crystal content into the PDLCs. The droplets have a radial configuration being anchored into chitosan matrix by an interface ordering coupling phenomenon.

Dissipative interactions in cell–matrix adhesion

The mechanical properties of cell microenvironments, cells themselves and the linking biomolecular constituents are increasingly recognized as important parameters in understanding and controlling cell behaviour. Specifically, cell adhesion – the first step of interaction – controls many processes in cell signalling. In this context the viscoelastic characteristics of involved biopolymer systems have to be considered as a key to the understanding of the underlying mechanisms. While elasticity is currently heavily addressed in biophysical and biomaterials science, studies on viscous and dissipative contributions are underrepresented and their impact is frequently neglected. In this review we point out that there is a need to overcome this imbalance and to reveal the impact of dissipative processes in cell–matrix interaction.

High-energy deformation of filaments with internal structure and localized torque-induced melting of DNA

We develop a continuum elastic approach to examining the bending mechanics of semiflexible filaments with a local internal degree of freedom that couples to the bending modulus. We apply this model to study the nonlinear mechanics of a double-stranded DNA oligomer (shorter than its thermal persistence length) whose free ends are linked by a single-stranded DNA chain. This construct, studied by H. Qu and G. Zocchi [Europhys. Lett. 94, 18003 (2011)], displays nonlinear strain softening associated with the local melting of the double-stranded DNA under applied torque and serves as a model system with which to study the nonlinear elasticity of DNA under large energy deformations. We show that one can account quantitatively for the observed bending mechanics using an augmented wormlike chain model, the helix-coil wormlike chain. We also predict that the highly bent and partially molten dsDNA should exhibit particularly large end-to-end fluctuations associated with the fluctuation of the length of the molten region, and propose appropriate experimental tests. We suggest that the augmented wormlike chain model discussed here is a useful analytic approach to the nonlinear mechanics of DNA or other biopolymer systems.

Feeling Inter‐ or Intramolecular Interactions with the Polymer Chain as Probe: Recent Progress in SMFS Studies on Macromolecular Interactions

Single-molecule force spectroscopy (SMFS) opens new avenues for elucidating the structures and functions of large coiled molecules such as synthetic and biopolymers at the single-molecule level. In addition, some of the features in the force-extension curves (i.e. force spectra) are closely related to primary/secondary structures of the molecules being stretched. For example, the long force plateau in the DNA stretching curve is related to the double-helix structure. These features can be regarded as the force fingerprints of individual macromolecules. These force fingerprints can therefore be used as indicators/criteria of single-molecule manipulation during the measurement of some unknown intra- or intermolecular interactions. By comparing the force spectra of a single polymer chain before and after interaction with other molecules, the mode/strength of such molecular interactions can be derived. This Review focuses on recent advances in AFM-based SMFS studies on molecular interactions in both synthetic and biopolymer systems using a single macromolecular chain as probe, including interactions between nucleic acids and proteins, mechanochemistry of covalent bonds, conformation-regulated enzymatic reactions, adsorption and desorption of biopolymers on a flat surface or from the nanopore of a carbon nanotube, and polymer interactions in the condensed state.

Mixed Biopolymer Systems Based on Starch

A binary mixture of starch–starch or starch with other biopolymers such as protein and non-starch polysaccharides could provide a new approach in producing starch-based food products. In the context of food processing, a specific adjustment in the rheological properties plays an important role in regulating production processing and optimizing the applicability, stability, and sensory of the final food products. This review examines various biopolymer mixtures based on starch and the influence of their interaction on physicochemical and rheological properties of the starch-based foods. It is evident that the physicochemical and rheological characteristics of the biopolymers mixture are highly dependent on the type of starch and other biopolymers that make them up mixing ratios, mixing procedure and presence of other food ingredients in the mixture. Understanding these properties will lead to improve the formulation of starch–based foods and minimize the need to resort to chemically modified starch.

NMR studies of hydration in low water content biopolymer systems

The problem of characterising the behaviour of water and biopolymers by NMR in low water content biopolymer systems is discussed. A low water content system is defined, and the problems of characterising the relaxation behaviour of the water are analysed. In the case of protons, the types of protons contributing to the signal and the exchange mechanism between them cannot be systematised in terms of existing models that have been developed for high water content systems. It is suggested that any successful model must take account of at least three separate pools of water including water vapour. Experimental results indicate that although the motion of the biopolymer is radically affected by water, the reverse is not necessarily true. It is concluded that the use of nuclei such as (13)C and (15)N may be very effectively used to characterise biopolymer motion, but the use of both (1)H and (2)H for characterising water is still problematic. Despite the formidable experimental and theoretical difficulties, (17)O NMR may be the only way to finally to untangle the problem.

Electron microscopy of gels of biopolymer systems

Structural characteristics of some gels derived from proteins and polysaccharides are examined by means of electron microscopy. It is shown that for such biopolymer systems, the results from electron microscopy and other research methods correlate.

Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate)-based biopolymer systems

Biodegradable biopolymers attract much attention in biology and medicine due to its wide application. The present review considers a biodegradable and biocompatible polymer of bacterial origin, poly(3-hydroxybutyrate), which has wide perspectives in medicine and pharmaceutics. It highlights basic properties of biopolymer (biodegradability and biocompatibility) and also biopolymer systems: various materials, devices and compositions based on the biopolymer. Application of poly(3-hydroxybutyrate)-based biopolymer systems in medicine as surgical implants, in bioengineering as cell culture scaffolds, and in pharmacy as novel drug dosage forms and drug systems are also considered.

Oligomers: Just background noise or as functional elements in structured biopolymer systems?

In their own right, oligomers of biological origin have traditionally not been looked upon as having structural capabilities. This is of course due to their limited structuring potential when present alone. In combination with high molecular weight biopolymers, on the other hand, several reports on oligomers acting as modification agents exist. This paper gives some examples on how such oligomers can impose structural modifications on such ordered biopolymer systems pointing towards the possibility to tailor new product properties.

Poly(3-hydroxybutyrate) and biopolymer systems on the basis of this polyester

Biodegradable biopolymers attract much attention in biology and medicine due to its wide application. The present review is designed to be a comprehensive source for research of biodegradable and biocompatible bacterial polymer, poly(3-hydroxybutyrate). This paper focuses on basic properties of biopolymer: biodegradability and biocompatibility, as well as on biopolymer systems: various materials, devices and compositions on the basis of biopolymer. Application of biopolymer systems based on poly(3-hydroxybutyrate) in medicine as surgical implants, in bioengineering as scaffold for cell cultures, and in pharmacy as drug dosage forms and drug systems is observed in the present review.

Self-structuring foods based on acid-sensitive mixed biopolymer to impact on satiety

A novel approach that may impact on satiety is the use of hydrocolloids that respond to the environmental (acidic) conditions inside the human stomach by self-structuring. This study focuses on the “structuring” (acid-gelation) process of acid-sensitive mixed biopolymer systems; low-methoxy pectin and low-acyl gellan gum. Our preliminary work tends to suggest that, by tailoring the strength of the acid gels produced in the stomach, structure breakdown, allowing gastric emptying, digestion and eventually the return of the feeling of hunger, can be controlled by taking advantage of the “natural forces” applied by the stomach.

Hydrolytic Degradation of Biopolymer Systems Based on Poly-3-hydroxybutyrate. Kinetic and Structural Aspects

The aim of the present work is to record and compare long-term kinetic curves of the hydrolytic degradation of polymer systems: bacterial poly-3-hydroxybutyrate (POB), its copolymer with hydroxyvalerate, and also a composite mixture of POB and polylactide (PLA). To monitor the degree of hydrolytic degradation, use was made of the total weight loss of the specimen and the change in the viscosity-average molecular weight (MW). Atom force microscopy was used to assess the surface state of POB films. It was shown that the rate of hydrolytic degradation depends on the incubation medium (the nature of the buffer), temperature, the chemical composition of the biopolymer, and its molecular weight. Atom force microscopy confirmed that, along with volumetric processes of POB hydrolysis, surface hydrolysis of the polymer also occurs.

On the hydrodynamic analysis of conformation in mixed biopolymer systems

AbstractA brief review is given of some of the advances in hydrodynamic methodologies for studying the conformation and flexibility of biomacromolecules in mixed systems. We consider first of all the evaluation of conformation type and flexibility in polymer systems with a quasi‐continuous distribution of molecular weight, using polysaccharides and mucin glycoproteins as our main examples, and then conformation determination in discrete or paucidisperse systems such as aggregated antibody preparations. Copyright © 2010 Society of Chemical Industry

Hydration water dynamics in biopolymers from NMR relaxation in the rotating frame

Assuming dipole–dipole interaction as the dominant relaxation mechanism of protons of water molecules adsorbed onto macromolecule (biopolymer) surfaces we have been able to model the dependences of relaxation rates on temperature and frequency. For adsorbed water molecules the correlation times are of the order of 10 −5 s, for which the dispersion region of spin–lattice relaxation rates in the rotating frame R 1 ρ = 1/ T 1 ρ appears over a range of easily accessible B 1 values. Measurements of T 1 ρ at constant temperature and different B 1 values then give the “dispersion profiles” for biopolymers. Fitting a theoretical relaxation model to these profiles allows for the estimation of correlation times. This way of obtaining the correlation time is easier and faster than approaches involving measurements of the temperature dependence of R 1 = 1/ T 1. The T 1 ρ dispersion approach, as a tool for molecular dynamics study, has been demonstrated for several hydrated biopolymer systems including crystalline cellulose, starch of different origins (potato, corn, oat, wheat), paper (modern, old) and lyophilized proteins (albumin, lysozyme).

Biodegradation kinetics of poly(3-hydroxybutyrate)-based biopolymer systems

The aim of this study was to evaluate and to compare the long-term kinetics curves of biodegradation of poly(3-hydroxybutyrate) (PHB), its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and a PHB/polylactic acid composite. The total weight loss and the change of average viscosity molecular weight were used as the parameters reflecting the biodegradation degree. The rate of biodegradation was analyzed in vitro in the presence of lipase and in vivo after film implantation in animal tissues. The morphology of the PHB film surface was studied by the atomic force microscopy technique. It was shown that PHB biodegradation involves both polymer hydrolysis and its enzymatic biodegradation. The results obtained in this study can be used for the development of various PHB-based medical devices.

Scaling behaviour of hyaluronic acid in solution with mono- and divalent ions.

The effect of the simultaneous presence of mono- and divalent cations on the thermodynamics of polyelectrolyte solutions is not fully understood. In physiological conditions, combinations of these ions affect structure formation in biopolymer systems. It is known that divalent counterions form a tight sheath around the polymer backbone, while monovalent ions are distributed in a diffuse cloud. Dynamic light scattering measurements of the collective diffusion coefficient D and the osmotic compressibility of semi-dilute hyaluronan solutions containing different ratios of sodium and calcium ions are compared with simple polyelectrolyte models. Scaling relationships are derived in terms of polymer concentration and ionic strength J of the added salt. Differences in the effects of sodium and calcium ions are expressed only through J.

Polysaccharide determination in protein/polysaccharide mixtures for phase-diagram construction

The effect of protein removal from protein–polysaccharide mixtures on the determination of total sugar concentration for phase-diagram construction was explored by response surface methodology. Phenol–sulphuric acid method was used to estimate the total sugar concentration whereas phase separation and microstructure of biopolymers in the mixtures were probed by means of fluorescent microscopy. All the factors studied (trifluoroacetic acid (TFA) volume, protein concentration, precipitation time) had significant influence on the polysaccharide recovery from the mixtures. The overall pattern of protein precipitation with TFA was also found to highly depend on protein–time interactions. Images taken at different mixture concentrations and with two different filter sets revealed a phase-separated system with the guar gum domains surrounded by a continuous protein phase. Experimental measurements as well as microscopical evidence suggests that, for greater than 60% polysaccharide recovery (±6% error), the protein content in the mixtures should be < ∼5.5% (w/v) with less than 0.5 mL TFA combined with more than 30 min rest under the influence of TFA. The results of the present investigation showed that when attempting to construct phase diagram of mixed biopolymer systems the equilibrium phases must be diluted to a protein content < ∼5% (w/v) before TFA treatment if the maximum polysaccharide concentration is to be determined.