Bi-cheng Wu

Soft matter strategies for controlling food texture: formation of hydrogel particles by biopolymer complex coacervation

Soft matter physics principles can be used to address important problems in the food industry. Starch granules are widely used in foods to create desirable textural attributes, but high levels of digestible starch may pose a risk of diabetes. Consequently, there is a need to find healthier replacements for starch granules. The objective of this research was to create hydrogel particles from protein and dietary fiber with similar dimensions and functional attributes as starch granules. Hydrogel particles were formed by mixing gelatin (0.5 wt%) with pectin (0 to 0.2 wt%) at pH values above the isoelectric point of the gelatin (pH 9, 30 °C). When the pH was adjusted to pH 5, the biopolymer mixture spontaneously formed micron-sized particles due to electrostatic attraction of cationic gelatin with anionic pectin through complex coacervation. Differential interference contrast (DIC) microscopy showed that the hydrogel particles were translucent and spheroid, and that their dimensions were determined by pectin concentration. At 0.01 wt% pectin, hydrogel particles with similar dimensions to swollen starch granules (D3,2 ≈ 23 µm) were formed. The resulting hydrogel suspensions had similar appearances to starch pastes and could be made to have similar textural attributes (yield stress and shear viscosity) by adjusting the effective hydrogel particle concentration. These hydrogel particles may therefore be used to improve the texture of reduced-calorie foods and thereby help tackle obesity and diabetes.

Creation of reduced fat foods: Influence of calcium-induced droplet aggregation on microstructure and rheology of mixed food dispersions

The impact of calcium-induced fat droplet aggregation on the microstructure and physicochemical properties of model mixed colloidal dispersions was investigated. These systems consisted of 2 wt% whey protein-coated fat droplets and 4 wt% modified starch granules heated to induce starch swelling (pH 7). Optical and confocal microscopy showed that the fat droplets were dispersed within the interstitial region between the swollen starch granules. The structural organisation of the fat droplets within these interstitial regions could be modulated by controlling the calcium concentration: (i) at a low calcium concentration the droplets were evenly distributed; (ii) at an intermediate calcium concentration they formed a layer around the starch granules; (iii) at a high calcium concentration they formed a network of aggregated droplets. Paste-like materials were produced when the fat droplets formed a three-dimensional network in the interstitial region. The properties of fat droplet-starch granule suspensions can be modulated by altering the electrostatic interactions to alter microstructure.

Stabilization of biopolymer microgels formed by electrostatic complexation: Influence of enzyme (laccase) cross-linking on pH, thermal, and mechanical stability

Biopolymer microgels formed by electrostatic complexation are often susceptible to disintegration when environmental conditions are changed, and so methods are required to improve their stability. In this study, microgels were formed by electrostatic complexation of a protein (type-B gelatin) and a polysaccharide (beet pectin). The impact of enzyme (laccase) crosslinking of the ferulic acid groups on the beet pectin was then studied as a method to improve microgel stability to environmental stresses. Gelatin-beet pectin (1:0.25w/w) microgels were formed at 35°C and pH4.4, and then the pH dependence of the ζ-potential, size, turbidity, and microstructure of the microgels was measured in the absence and presence of laccase cross-linking. Our results suggested that crosslinking occurred within the microgels (rather than between them) since no particle aggregation was observed after enzyme treatment. Enzyme crosslinking did not affect the ζ-potential of the microgels, but it did decrease their size. Both cross-linked and non-cross-linked microgels were stable to aggregation at low (2-3) and high (4.4-7) pH values, but not at intermediate values (3-4.4), which was attributed to their low surface charge. Cross-linking improved the resistance of the microgels to shearing-induced disruption (300rpm for 24h) and to thermal-induced disruption (50°C for 2min). These cross-linked biopolymer microgels may have applications for texture modification, encapsulation, or controlled release.

Design of reduced-fat food emulsions: Manipulating microstructure and rheology through controlled aggregation of colloidal particles and biopolymers

The objective of this study was to develop model reduced-calorie food emulsions with desirable textural and optical properties based on controlled aggregation of food-grade colloidal particles and biopolymers. The model food emulsion consisted of fat droplets (5wt.%), starch granules (4wt.%), and xanthan gum (0 to 0.02wt.%) under acidic conditions (pH3). The fat droplets were stabilized by a protein-based emulsifier (whey protein isolate). Fat droplet aggregation was induced by adding anionic xanthan gum to promote bridging flocculation of the cationic protein-coated fat droplets. Thermal processing (95°C) did not have a major impact on fat droplet aggregation, but it did promote starch granule swelling. The structural organization of the fat droplets could be regulated by altering xanthan levels. Relatively small droplet aggregates were formed at low xanthan concentrations that coated the starch granule surfaces. Conversely, large irregular shaped droplet aggregates were formed throughout the system at higher xanthan levels. The rheological and optical properties of the model emulsions could therefore be controlled by altering fat droplet organization. Addition of low levels of xanthan significantly increased the viscosity, yield stress, and complex modulus of the model food emulsions. However, high levels of xanthan led to the formation of large visible aggregates that would negatively impact on sensory quality. This study has important implications for the development of cost-effective and clean-label reduced-fat products with desirable quality attributes, such as dressings and sauces.

Modulating the morphology of hydrogel particles by thermal annealing: mixed biopolymer electrostatic complexes

Biopolymer hydrogel particles formed by electrostatic complexation of proteins and polysaccharides have various applications within the food and other industries, including as delivery systems for bioactive compounds, as texture modifiers, and as fat replacers. The functional attributes of these electrostatic complexes are strongly influenced by their morphology, which is determined by the molecular interactions between the biopolymer molecules. In this study, electrostatic complexes were formed using an amphoteric protein (gelatin) and an anionic polysaccharide (pectin). Gelatin undergoes a helix-to-coil transition when heated above a critical temperature, which impacts its molecular interactions and hydrogel formation. The aim of this research was to study the influence of thermal annealing on the properties of hydrogel particles formed by electrostatic complexation of gelatin and pectin. Hydrogel particles were fabricated by mixing 0.5 wt% gelatin and 0.01 wt% pectin at pH 10 (where both were negatively charged) at various temperatures, followed by acidification to pH 5 (where they have opposite charges) with controlled acidification and stirring. The gelation () and melting temperature () of the electrostatic complexes were measuring using a small amplitude oscillation test: °C and °C. Three annealing temperatures (5, 30 and 50 °C) corresponding to different regimes (, , and ) were selected to control the configuration of the gelatin chain. The effects of formation temperature, annealing temperature, and incubation time on the morphology of the hydrogel particles were characterized by turbidity, static light scattering, and microscopy. The results of this study will facilitate the rational design of hydrogel particles with specific particle dimensions and morphologies, which has important implications for tailoring their functionality for various applications.

Development of hydrocolloid microgels as starch granule mimetics: Hydrogel particles fabricated from gelatin and pectin

In this study, hydrocolloid microgels fabricated by electrostatic complexation of gelatin and pectin were developed as possible starch mimetics. The impact of covalent cross-linking on the physicochemical and structural properties of the microgels was investigated. Microgels were formed by acidifying a mixture of gelatin (0.5wt.%) and pectin (0.01wt.%) from pH10 to 5 at 40°C, followed by cross-linking with glutaraldehyde (0 to 2mM). At low glutaraldehyde levels (<0.5mM), cross-linking occurred primarily within the microgels and did not affect particle dimensions, whereas at high levels (2mM), cross-linking connected adjacent microgels leading to the formation of large flocs. Rheological and microscopic analysis showed that the degree of cross-linking impacted the thermal transitions of the microgels. A simulated oral processing study indicated that the melt-in-the-mouth behavior of the hydrocolloid microgels could be made to be similar to that of starch granules by controlling the degree of cross-linking. This study may be useful for designing starch mimetics with improved texture-modifying properties and reduced-calories.

Engineering Hydrogel Microspheres for Healthy and Tasty Foods

Hydrogel microspheres made with food-grade biopolymers, such as proteins and polysaccharides, have become a highly active research area in both applied and fundamental food science studies. This is because hydrogel particles can be formulated with a diverse range of microstructures, rheological properties, and responses to environmental stimuli. The tunable nature of the physicochemical properties of hydrogel particles leads to many potential applications in texture control, encapsulation, and/or targeted delivery of bioactive components. This chapter provides a brief overview of the molecular characteristics of common biopolymers used to assemble hydrogel particles, the major principles of structural formation used to assemble these particles, and the functional properties of hydrogel particles in food applications.