Ricky S.H. Lam

Food proteins: A review on their emulsifying properties using a structure-function approach

Proteins are of great interest due to their amphiphilic nature, which allows them to reduce the interfacial tension at the oil-water interface. The incorporation of proteins at the oil-water interface has allowed scientists to utilise them to form emulsions (O/W or W/O), which may be used in food formulations, drug and nutrient delivery. The systematic study of the proteins at the interface and the factors that affect their stability (i.e., conformation, pH, solvent conditions, and thermal treatment) has allowed for a broader use of these emulsions tailored for various applications. In this review, the factors affecting the stability of emulsions using food proteins will be discussed. The use of polysaccharides to complex with proteins will also be explored in relation to enhancing emulsion stability.

A molecular insight into the nature of crystallographic mismatches in self-assembled fibrillar networks under non-isothermal crystallization conditions

The lengths of the 12-hydroxystearic acid (12HSA) fibers are influenced by crystallographic mismatches resulting from the incorporation of 12HSA monomers into the crystal lattice in an imperfect manner. On a molecular level, this can be differentiated using synchrotron Fourier transform infrared (FTIR) spectroscopy by monitoring the change in area of the 1700 cm−1 and 3200 cm−1 peaks, corresponding, respectively, to the dimerization of the carboxylic acid groups and hydroxyl non-covalent interactions, during crystallization. The crystallographic mismatch is attributed to a plateau in the apparent rate constant for the dimerization of the carboxylic acid head groups while the hydroxyl interactions linearly increase as a function of cooling rate (ϕ). The rate constant for hydroxyl interactions linearly increases as a function of cooling rate while a plateau is observed for the rate of dimerization at cooling rates between 5 and 7 °C min−1. At cooling rates greater than 5 to 7 °C min−1 12HSA monomers do not effectively dimerize before being incorporated into the crystal lattice causing crystal imperfections impeding linear epitaxial crystal growth and produces branched fibers. At slow cooling rates (i.e., less than 5 to 7 °C min−1), long fibers are produced with a fractal dimension between 0.95 and 1.05 and for rapid cooling rates (i.e., greater than 5 to 7 °C min−1) short branched fibers are produced with a fractal dimension between 1.15 and 1.32.

Influence of chirality on the modes of self-assembly of 12-hydroxystearic acid in molecular gels of mineral oil

The gelating abilities of enantiopure, racemic, and different enantio-enriched mixtures of 12-hydroxystearic acid (12HSA) have been compared in order to clarify conflicting reports in the literature (1) concerning their ability to gelate organic liquids. Less than 1.0 wt % of optically pure (D)-12HSA was found to gelate mineral oil. The gel matrix was comprised of high aspect ratio fibers in which the 12HSA molecules were organized as head-to-head dimers and the 12-hydroxyl groups formed an H-bonding network along the axis transverse to the longitudinal growth. Below 2 wt %, racemic 12HSA in mineral oil did not reach the percolation threshold. Its organogels were comprised of platelet-like crystals with a molecular arrangement of single, in-plane, hydrogen-bonded acyclic dimers that prevent longitudinal growth and limit the ability of the polar groups to phase separate during nucleation.

Experimental validation of the modified Avrami model for non-isothermal crystallization conditions

The modified Avrami model was found to accurately predict the induction time, maximum phase volume and dimensionality of crystal growth for stearic acid containing molecules when the experimental method employed measures as a function of phase volume. Four methods were examined to validate the model including: Fourier transformed infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), small deformation rheology and polarized light microscopy (PLM). PLM and FT-IR were able to detect the nucleation event prior to DSC and rheology. FT-IR and PLM provided the most accurate data due to the similarities between the experimental and fitted induction times (x0), maximal phase change (ymax) and the Avrami exponent (n). Further, the Avrami exponent, obtained from FT-IR, was sensitive to both the mode of nucleation and the dimensionality of crystal growth. Therefore, the apparent rate constants (kapp) obtained by FT-IR and PLM are useful in providing further insights into the kinetics of non-isothermal crystallization. The calculated apparent rate constants suggest a diffusion limited crystallization at slow cooling rates (i.e., below 5–7 °C min−1) and at cooling rates greater than 5–7 °C min−1, the incorporation of the gelator molecules onto the crystal lattice becomes limited by the reaction rate constant.

The effect of pH and temperature pre-treatments on the structure, surface characteristics and emulsifying properties of alpha-lactalbumin

The effect of pH (5.0 or 7.0) and temperature (25.0, 65.0 and 95.0 °C) on the physicochemical and emulsifying properties of type-1 (with calcium, ALA-1) and type-3 (without calcium, ALA-3) alpha-lactalbumin (ALA) were examined. By increasing the temperature of pre-treatment, changes in ALA conformation allowed for greater surface hydrophobicity and caused changes in its surface charge. pH also influenced surface charge for ALA where enhanced repulsion at pH 7.00 was observed resulting in reduced aggregation despite having greater hydrophobicity. Findings indicate that changes to protein conformation using various pH and temperature pre-treatments influenced their surface chemistry, aggregation and ability to align at the oil-water interface. Overall, emulsions were found to be more stable at pH 7.0 than 5.0 due to the greater amount of electrostatic repulsive forces between droplets present at pH 7.0. Under the conditions examined in this study, ALA-3 pre-treated at 65 °C and at pH 7.00 resulted in the best emulsifying properties.

Effect of the Biopolymer Mixing Ratio on the Formation of Electrostatically Coupled Whey Protein−κ- and ι-Carrageenan Networks in the Presence and Absence of Oil Droplets

The rheological properties of 1.0% (w/w) whey protein isolate (WPI)-κ-/ι-carrageenan (CG) mixtures were investigated during a slow acidification process by glucono-δ-lactone from pH 7.00 to ∼4.20 as a function of biopolymer mixing ratio and in the presence and absence of oil droplets. In all cases, electrostatic coupled biopolymer and emulsion gel networks were formed at pH values corresponding to where attractive interactions between WPI and CG began. Formed WPI-CG complexes were found to be surface active, capable of lowering interfacial tension and forming viscoelastic interfacial films within emulsion-based systems. Both biopolymer and emulsion-based gels increased in strength and elasticity as the CG content increased, regardless of the type of CG present. However, WPI-ι-CG coupled networks were stronger than WPI-κ-CG networks, presumably due to the higher number of sulfate groups attracting the WPI molecules.