Sequential crystallization of high and low melting waxes to improve oil structuring in wax-based oleogels

Abstract

The main objective of this study was to investigate the effect of combining a high-melting wax (sunflower wax or rice bran wax) with a low-melting wax (berrywax or BEW) on the crystallization and gelation behavior of the corresponding wax-based oleogels in rice bran oil (RBO). Sunflower wax (SW) and rice bran wax (RBW) have a similar chemical composition but a very different crystallization behavior. Therefore, SWand RBW were also combined in a wax-based oleogel to examine the occurrence of co-crystallization and/or crystal coexistence. The thermal and gelation behavior of the binary blends in rice bran oil (5% w/w total concentration of wax) were investigated with differential scanning calorimetry (DSC) and rheological measurements, showing sequential crystallization and gelation for the SW/RBW : BEW wax-based oleogels and simultaneous crystallization and gelation for the SW : RBW wax-based oleogels. Oscillatory shear and hardness measurements revealed the reinforcement of the high-melting wax crystal network with the addition of the low-melting berry wax. X-ray diffraction (XRD) measurements in both the long-spacing and the short-spacing region showed the occurrence of crystal co-existence, rather than co-crystallization, which was confirmed with polarized light microscopy (PLM). Two different crystal morphologies could be discerned for all three combinations (RBW : SW, SW : BEW and RBW : BEW). We hypothesized that the improved rheological properties could be attributed to sintering, a process in which the low-melting BEW crystals form solid bonds between the crystals of the high-melting waxes. As such, a cohesive network is formed, resulting in an increased hardness of the bi-wax-based oleogels. This research provides the opportunity to minimize the amount of wax necessary in creating semi-solid materials with a wide variety in rheological and textural properties

Physical Properties of Beeswax, Sunflower Wax, and Candelilla Wax Mixtures and Oleogels

“…Because the spherulites seem to be present in oleogels with higher HC, they may be result of WE crystallization, which may be inducing nucleation of HC crystals, resulting in smaller platelets and a denser network. The spherulites could also be serving as junction points for the platelet network and are increasing firmness in this manner, similar to the bridging observed between high melting RBW and SFW crystals and low melting BEW at certain ratios in binary oleogels (Tavernier et al, ). In oleogels with lower than median firmness, the WE tended to form either haystack clusters or large agglomerates, indicating that small levels of HC inhibited platelet and network formation.…”

“…This type of interaction may be beneficial for applications where a firmer product is needed that will still have low solids content at body temperature. Synergistic interactions resulting in higher oleogel firmness as well as higher elastic modulus ( G ′) have been observed in several other mixed gelator systems and were also shown to be related to changes in the crystal microstructure (Gandolfo et al, ; Jana and Martini, ; Schaink et al, ; Tavernier et al, ).…”

“…Pseudophase diagrams (Craven and Lencki, ; Jana and Martini, ; Serrato‐Palacios et al, ; Tavernier et al, ) were drawn for the DSC endotherms by plotting a line through the lowest endothermic peak T on to represent the solidus line, below which everything is solid, and through the T p of the highest melting peak to represent the liquidus line, above which everything is liquid. These diagrams are considered pseudophase diagrams because the two waxes are not made up of pure components but are rather mixtures of wax components.…”

“…Investigating the phase behavior of binary mixtures of pure waxes (BW, PW, RBW, and SFW), Jana and Martini () demonstrated that when two waxes are made up of different components, they tend to form eutectic or monotectic systems, and these mixed compositions tended to form smaller and denser crystal morphologies. Tavernier et al () recently evaluated binary blends of high melting point waxes (RBW and SFW) with a low melting point wax, BEW, in rice bran oil oleogels. The high melting waxes formed monotectic systems with BEW, but interestingly there was a synergistic interaction at various ratios of the wax mixtures that resulted in stronger solid properties and firmness compared to oleogels made from either wax alone.…”

Tailoring Properties of Mixed-Component Oleogels: Wax and Monoglyceride Interactions Towards Flaxseed Oil Structuring

“…However, lower TC1,onset values were observed at in same proportions of GMS to SHW (GMS50:50SHW). Moreover, a greater difference between ΔHmI and ΔHmII indicates that the crystalline species takes longer to develop (i.e., sequential crystallization), which can be interpreted as a positive interaction of these oleogelators taking place at this specific ratio (1:1) [32]. This positive interaction was corroborated by rheological results, because, in this condition, the gels were stronger.…”