Effect of Span 60 on the Microstructure, Crystallization Kinetics, and Mechanical Properties of Stearic Acid Oleogels: An In‐Depth Analysis

Abstract

Modulation of crystallization of stearic acid and its derivatives is important for tuning the properties of stearate oleogels. The present study delineates the crystallization of stearic acid in stearate oleogels in the presence of Span 60. Microarchitecture analysis revealed that stearic acid crystals in the oleogels changed its shape from plate-like structure to a branched architecture in the presence of Span 60. Consequently, a significant variation in the mobility of the solute molecules inside the oleogel (Fluorescence recovery after photobleaching studies, FRAP analysis) was observed. Thermal analysis (gelation kinetics and DSC) revealed shortening of nucleation induction time and secondary crystallization with an increase in the Span 60 concentration. Furthermore, isosolid diagram suggested better physical stability of the formulations at higher proportions of Span 60. XRD analysis indicated that there was a decrease in the crystal size and the crystallinity of the stearic acid crystals with an increase in Span 60 concentration in the Span 60 containing oleogels. However, crystal growth orientation was unidirectional and found unaltered with Span 60 concentration (Avarmi analysis using DSC data). The mechanical study indicated a composition-dependent variation in the viscoelastic properties (instantaneous [τ 1 ], intermediate [τ 2 ], and delayed [τ 3 ] relaxation times) of the formulations. In conclusion, Span 60 can be used to alter the kinetics of the crystallization, crystal habit and crystal structure of stearic acid. This study provides a number of clues that could be used further for developing oleogel based formulation.Practical Application: Stearic acid can be used for the solidification of vegetable oils. This will allow easy handling, storage and transportation of the oils. The physical and the thermal properties of the oleogels can be altered by tailoring the microstructure of the oleogels using Span 60 (nonionic surfactant). The oleogels can be used for the controlled delivery of nutraceuticals and drugs.

Stearic Acid Modified Stearyl Alcohol Oleogel: Analysis of the Thermal, Mechanical and Drug Release Properties

“…The release of the drug in lower amounts in the absence and in the presence of lower amount of stearic acid was due to the entrapment of the drug molecules within the gelator fibers. An increase in the stearic acid content improved the synergistic interactions amongst the stearyl alcohol and stearic acid molecules, which did not allow the accommodation of the drug molecules within the gelator network structure [13,14]. Additionally, the alteration in the microstructure of the gelator network in the presence of stearic acid might have promoted the diffusion of the drug molecules.…”

“…Visual observation of the oleogels suggested that the addition of stearic acid results in oleogels with a homogenous matrix, which can be explained by the formation of mixed crystals when fatty acid-fatty alcohol mixtures are used for structuring of the oils [30]. A slight alteration in the crystal habit completely changes the architecture of the gelator network and hence their texture [13,14]. Microscopic results indicated that stearic acid promoted the formation of long gelator fibers.…”

“…Gelation kinetics of the oleogels was analyzed using an in-house developed instrument. The details of the in-house developed machine have been reported earlier by our group [13,14].…”

“…Based on the thermal profiles of oleogels, it is possible to determine the change in the solid fat content (SFC) of the oleogels [13,14]. The %SFC was calculated from the DSC thermograms using Proteus software (Netzsch, Germany), provided by the manufacturer.…”

“…2; Fig. 3b) to determine the rate of melting (K H ) of the gelator molecules with temperature [13,14]. The negative values of 'K H ' are due to the inverse logistic SFC profile, obtained during the heating process.…”