Fan C. Wang

Effect of intrinsic and extrinsic factors on the stability of the α-gel phase of a glyceryl monostearate–water system

Glyceryl monostearate–water systems (MG-gels) undergo a polymorphic transition from the α-gel phase to the coagel phase. This phase transition results in destabilization and loss of water in monoglyceride-structured systems, commonly found in personal care and food products. In this study, we examined the effect of intrinsic factors (type and concentration of co-emulsifiers) and extrinsic factors (cooling rate and applied shear) on the stability of the α-gel phase. The methods used to study the polymorphic transition were differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results suggested that the transition from the α-gel phase to the coagel phase caused a change in the gels physical appearance. More specifically, opaque regions developed in the semi-translucent α-gel upon aging. The stability of the α-gel phase can be increased by using an α-tending co-emulsifier, such as sodium stearyol lactylate (SSL), and by increasing the concentration of the co-emulsifier. Slow cooling rates without shear could also increase the stability of the α-gel phase. In this work, we developed a subα Coagel Index that can be used together with the Coagel Index to characterize the degree of polymorphic transformation of MG-gels.

Nature and dynamics of monostearin phase transitions in water: stability and the sub-α-gel phase

This work examines the polymorphic transition of a glycerol monostearin–water system (GMS–water) stored at 5 °C, 25 °C and 45 °C for 100 days. Upon addition of co-emulsifiers, such as sodium stearoyl lactylate (SSL), the GMS–water system forms a metastable α-gel structure, which transforms into a coagel structure over time. The GMS–water system loses its water swelling capacity during the polymorphic transition from the α-gel phase to the coagel phase. Therefore the α-gel phase is a more favorable structure for water structuring. Powder X-ray diffraction (XRD), XRD with temperature control, differential scanning calorimetry (DSC), and microscopy were used to examine the nature and dynamics of the phase transition. Results suggest that the α-gel phase is stable for 100 days when stored at 5 °C. Increasing the storage temperature will increase the rate of transformation from the α-gel phase to the coagel phase. However, even though no phase transformation from the α-gel phase to the coagel phase took place, seemingly, fractionation took place within the α-gel structure when stored at 5 °C, altering the melting profile of the gel and affecting the calculation of the Coagel index. The GMS–water system forms a thermally reversible and metastable sub-α-gel phase when cooled below 13 °C. This work characterizes the XRD diffraction patterns and the DSC melting profiles of the sub-α-gel phase of GMS–water system for the first time. XRD patterns suggest that the water layer thickness in the sub-α-gel phase is ∼140 A. This thick layer of water may contribute to the high water swelling capacity and stability of the monoglyceride–water system at refrigeration temperatures.

Advances in the application of food emulsifier α-gel phases: Saturated monoglycerides, polyglycerol fatty acid esters, and their derivatives

Emulsifiers form complex structures in colloidal systems. One of these structures, the α-gel phase, has drawn much research interest. α-gel phases are formed by emulsifiers that are stable in the α-crystalline structure in the presence of water. The α-gel phase has shown superior functionality in a variety of applications because it has a water-rich lamellar structure. Even though studies on emulsifier α-gel phases emerged over half a century ago, there is still a knowledge gap on fundamental properties of α-gel phases formed by a variety of emulsifiers. This article summarizes recent studies on the physical and chemical properties of α-gel phases formed by several food emulsifiers, specifically saturated monoglycerides, polyglycerol monoester and diesters of fatty acid, and sodium stearoyl lactylate. Recent research has advanced the understanding of factors affecting the stability and foamability of the α-gel phases. Current and potential applications of α-gel phases in baked food products and in personal care products are also reviewed here.

Internal and external factors affecting the stability of glycerol monostearate structured emulsions

Monoglyceride (MG) structured emulsions have been developed for use in diverse food and cosmetic applications. However, these MG-structured emulsions undergo a polymorphic transformation from the α-gel phase to the coagel phase, resulting in emulsion destabilization and water syneresis. In this study, the stability of emulsions containing 60–70% (w/w) water structured with 5% (w/w) of a blend of the emulsifier glycerol monostearate (GMS) and co-emulsifier sodium stearoyl lactylate (SSL), was assessed. The internal factors examined were concentrations of co-emulsifier and the addition of the polysaccharide xanthan gum. External factors examined included cooling rate and applied shear. The methods used to study the polymorphic transition were differential scanning calorimetry, X-ray diffraction, and pulsed proton nuclear magnetic resonance. In this work, the sub-α Coagel Index was successfully used to characterize the degree of coagel formation in MG-structured emulsions. Results showed that the stability of the α-gel phase was improved by using 1 : 9 w/w SSL : GMS ratios and by adding 0.1% xanthan gum. Slow cooling rates without shear could also increase the stability of the α-gel phase in the structured emulsion system.

pH and stability of the α-gel phase in glycerol monostearate–water systems using sodium stearoyl lactylate and sodium stearate as the co-emulsifier

Changing the environmental pH alters the melting profiles of monostearate–water systems and affects the stability of the α-gel phase using sodium stearoyl lactylate (SSL) and sodium stearate (NaS) as co-emulsifiers. NaS in MG-gels may be present both in a micellar phase and in a lamellar phase. Once above the critical micellar concentration of NaS, the NaS solution and diluted MG-gels remained at a stable pH.