Effects of Water on Aggregation and Stability of Monoglycerides in Hydrophobic Solutions

Abstract

We apply a set of different techniques to analyze the physical properties and phase transitions of monoglyceride (MG)-oil-water ternary systems. The effect of MGs on water absorption in food-grade hazelnut oil and in pure hydrocarbon oil (decane) is reported. Comparison between decane and hazelnut oil backgrounds indicates that the effect of water absorption is significant and universal in different MG ternary systems. Adding small amounts of cosurfactant (stearic acid) is necessary to stabilize the MGs in oil-water combinations by enhancing the swelling capacity of lamellar layers; as a result, the structures become sensitive to the pH of the aqueous phase used. The dramatic changes on increasing the aqueous content are recorded by the calorimetry. In samples with small quantities of water, the phase behavior is almost independent of the pH. Once the proportion of water increases, the effect of pH is prominent. At low pH, the solubility of MG in water is limited, and the ternary system retains key features of the oil-dominated environment, such as the sequence of two transitions on cooling, with the low-temperature sub-alpha crystalline phase. At high pH and a sufficient amount of water, the MG layers remain properly swollen, and the crystalline phase disappears from the phase diagram. We spend considerable effort identifying the inverse lamellar phase of MGs in an oil-dominated environment with the so-called alpha-gel phase that is well-established in water-dominated systems, and distinguishing "demixing" from water and from oil. The rheology is examined in different fluid and gel phases; the storage modulus generally decreased on increasing the water proportion, but a gel-like response is found in the high-temperature lamellar phase over a wide range of water dilution. We then focus on aging phenomena in the inverse lamellar (or alpha-gel) phase and show that the rearranging of hydrogen bonds is slowed down and disrupted by the presence of water, giving the lamellar gel longer life times.

The phase behaviour of mixed saturated and unsaturated monoglycerides in water system

“…M a n u s c r i p t 6 The data are summarised in Table 3, from which it is clear that the d spacing for L β1 phase increases continuously with water content up to 50 w/w% then the spacings do not increase further with more water addition. Thus, the maximum swelling capacity of the mixture of monoglycerides in water is obtained at 50 w/w% water content [28].…”

The supramolecular chemistry of lipid oxidation and antioxidation in bulk oils

“…When water activity is increased, metals are mobilized and oil viscosity is reduced hence oxidation is accelerated . Different water types or concentrations and levels of emulsifiers produce different shapes of association colloids and affect lipid oxidation differently . It was found that phospholipids synergize the activity of α‐tocopherol only in the presence of small amounts of water and catalysis by water‐soluble radical generators .…”

Oleogels from Glycerol‐Based Lyotropic Liquid Crystals: Phase Diagrams and Structural Characterization

“…In the oil system, below the gelation transition temperature, the inverse lamellar phase is formed with a definite hexagonal in-plane ordering and, below that point, a sub-α crystalline structure is seen [17,18]. In MAG-oilwater systems there are hydrogen bond interactions that stabilize the structure and a lamellar gel is formed [19].…”