Numerical computation of relaxation spectra from mechanical measurements in biopolymers

In the present investigation, a computational methodology to treat relaxation spectra from mechanical data is developed. To calculate the spectral function that represents the relaxation process of the material, three different regularization algorithms were tested using MATLAB. Two algorithms employ Tikhonov’s regularization whereas the third investigative tool is an implementation of the CONTIN algorithm. These efforts improved the ability to look at data hence allowing utilization of the L-curve criterion in order to locate the optimum regularization parameter for accurate data inversion. Algorithms were first evaluated with hypothetical data followed by experimental datasets of hydrated gluten as a model biopolymer system. Essentially, algorithms converge on a specific relaxation spectrum that unveils the molecular features of gluten structure. The methodology described is not limited to mechanical measurements but should be used with any type of exponential decay in studies of relaxation processes.     

Structure,sensory and nutritional aspects of soluble-fibre inclusion in processed food products

The food industry relies increasingly on soluble fibre to formulate products with superior structural properties, mouthfeel and potential health benefits. In this paper, we have compiled experimental data from a wide range of high-solid foodstuffs in order to demonstrate the utility of fibre inclusion in such preparations. Recent studies have mapped out the structural properties of soluble-fibre polysaccharides (e.g., κ-carrageenan, agarose and deacylated gellan) in the presence of increasing levels of co-solute with application to the confectionery and ice cream industries. One of the incentives to understand the behaviour of such systems is the prospect of providing an alternative to gelatin since the protein is increasingly falling “out of fashion” with consumers and producers alike. This rather underresearched area has other applications, for example, flavor encapsulation and preservation of bioactive molecules in glassy polysaccharide matrices.     

Structuring dairy systems through high pressure processing

This review highlights the current knowledge on gelation of hydrocolloids induced by high pressure processing (HPP) of dairy products. Pressure-induced gelation of single systems (casein rich, whey protein rich, gelatin, and polysaccharide solutions) as well as rheological and thermo-mechanical effects of HPP on mixture systems are discussed. The mechanism of dairy protein gelation under pressure, their properties and microstructure, and potential application of HPP to improve physical properties of dairy products (cheese, yoghurt, and ice cream) are included. HPP is a promising tool for future manufacturing of structured dairy products with unique sensorial properties.     

Phase separation in biopolymer gels: a low- to high-solid exploration of structural morphology and functionality

Phase separation in protein and polysaccharide gels remains one of the basic tools of achieving the required structural properties and textural profile in food product formulations. As ever, the industrialist is faced with the challenge of innovation in an increasingly competitive market in terms of ingredient cost, product added-value, and expectations of a healthy life-style to mention but a few. It appears, however, that a gap persists between the fundamental knowledge and a direct application to food related concepts with a growing need for scientific input. Furthermore, within the context of materials science, there is a tendency to examine research findings in either low- or high-solid systems without considering synergistic insights/benefits to contemporary needs, spanning the full range of relevant time-, length-, and concentration scales. This review highlights the latest attempts made to utilize and further develop fundamental protocols from the advanced synthetic polymer research as a source of inspiration for contemporary bio-related applications in low- and intermediate-solid composite gels. Then, it takes advantage of this school of thought to "force a passage" through the phase topology and molecular dynamics of binary biopolymer mixtures at high levels of co-solute. It is hoped that these phenomenological and fundamental tools should be able to bridge the divide in the analysis of the two "types" of composite materials (from low to high solids) thus dealing effectively with the specific and often intricate problems of their science and applications.     

Advanced topics in the application of the WLF/free volume theory to high sugar/biopolymer mixtures: a review

The vitrification properties of mixtures of several biopolymers with sugars have been investigated in this laboratory using the technique of small deformation dynamic oscillation. It was demonstrated that the free volume followed a reciprocal relationship with the number average molecular weight of the biopolymer, which should be associated with imperfect intermolecular associations around the ends of the molecules. The effect of free volume on the kinetics of vitrification is quantified by the friction coefficient (ζ_o) per monomer unit of the biopolymer. The magnitude of the coefficient ζ_o increases with the extent of intermolecular associations and enhanced network cohesion diminishes the free volume thus elevating the rheological glass transition temperature (T_g). The approach was also applied to high solids starch systems where moisture loss owing to heating above 100°C results in viscoelastic properties characteristic of the glass transition region. These can be described by the Williams-Landel-Ferry equation modified with a ‘moisture term’. For all samples, the temperature dependence of shear moduli was described by the method of reduced variables. The generated shift factors (a_T) were used to engineer a state of ‘iso-free-volume’ thus demonstrating that, within the glass transition region, viscoelastic rate processes are solely governed by free volume. Practical applications include the construction of a state diagram for food materials, which utilizes the rheological T_g to follow the concentration dependence of the metastable vitrification events.     

Structure and phase behaviour of microcrystalline cellulose in mixture with condensed systems of potato starch

It has been suggested that microcrystalline cellulose (MCC) can be used in biodegradable films to improve techno‐functionality by providing bulk and enhancing mechanical strength. This study aimed to investigate the effect of MCC addition on the structural properties of potato starch films. Samples were prepared by hot pressing at 120 °C for 7 min to produce systems that covered a broad range of moisture content and relative humidity. Complimentary experimental techniques, including thermomechanical analysis, FTIR, wide‐angle X‐ray diffraction and SEM, were employed to examine the micro‐ and macromolecular characteristics in these mixtures. Both moisture content and the presence of MCC have a plasticising effect on the composites yielding a reduction in its glass transition temperature. It appears that there is no specific and nontrivial interaction between potato starch and MCC, an outcome which indicates that the cellulose fibres act as inert filler in the polymeric composite.     

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

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

Biochemical and thermo-mechanical analysis of collagen from the skin of Asian Sea bass (Lates calcarifer) and Australasian Snapper (Pagrus auratus), an alternative for mammalian collagen

Australasia has a large fish industry, and fish skin by-products from the processing industry could be used for the commercial production of fish collagen. The aim of this study was to characterize collagen extracted from the Asian sea bass (Australian barramundi) (Lates calcarifer) and snapper (Pagrus auratus) skin as an alternative to mammalian-derived collagen in gelatin products. The acid-soluble fractions of collagen from Asian sea bass and snapper skin were extracted and yielded about 8 and 7.5 % collagen (on a dry weight basis), respectively. The electrophoretic and chromatography patterns indicated that both collagens comprise of α1, α2, α3, and β chains, corresponding to the properties of calf skin collagen type I. Amino acid analysis and peptide mapping of digested collagen suggested differences in their amino acid sequences and collagen primary structure. Fourier transform infrared spectroscopy demonstrated that the helical structure of collagen was completely maintained in Asian sea bass and partially in snapper. Transition temperatures for the completion of the melting process in the two collagen networks were confirmed with differential scanning calorimetry and dynamic oscillatory rheology to be about 29 °C. Zeta potential analysis identified the isoelectric points (pI values) of collagen from Asian sea bass and snapper skin at pH 6.90 and 7.75, respectively. Thus, Asian sea bass and snapper skin could be an important alternative source of collagen to replace mammalian collagen for industrial applications.     

Glass Transition and Water Activity of Freeze-Dried Shark

Glass transition temperatures and water activity as a function of moisture content were determined for freeze-dried shark to further compare the two distinct criteria of food stability. The adsorption experiments were carried out at controlled water activity, at 21, 40, and 50°C using an isopiestic method and they were modeled using BET and GAB equations. Glass transition temperatures were measured by dynamic oscillation on shear. Results indicate that there is a difference in the temperature-related stability criteria predicted by the concepts of water activity (a _w ) and the glass phenomenon (T _g ). The glass transition concept tends to accommodate higher levels of moisture within the framework of a safe storage of a dried product.