Crystallization and polymorphic behavior of shea stearin and the effect of removal of polar components

Abstract

The crystallization of shea stearin was investigated both before and after pre‐treatment with silica to remove a small amount (0.7 wt%) of diacylglycerols (DAGs) and oxidized material. NMR (for solid fat content), X‐ray diffraction (XRD), polarized light microscopy, confocal Raman microscopy, and non‐isothermal, isothermal and “stop‐and‐return” differential scanning calorimetry (DSC) techniques were used. Four major polymorphs previously found with 1,3‐distearoyl‐2‐oleoyl‐sn‐glycerol (StOSt) were detected: α, γ, β′, and β; whilst evidence for a further (δ) polymorph was found by DSC and possibly XRD but not Raman spectroscopy. Isothermal crystallization of shea stearins by DSC at 20°C produced α and δ forms within 5 min which then transformed to γ. Microscope images showed that after 1 day these had transformed into β′ with a few crystals of β, with further conversion to β after one week. Silica treated samples showed a faster initial crystallization, with faster transformation or direct crystallization into δ and then γ and β′ forms. Non‐isothermal DSC also showed a faster transformation into γ from α on the subsequent remelt. However, further transformation into β appeared to occur at reasonably similar rates for both types, suggesting that DAGs have less influence on this transformation and may be excluded from higher forms. Practical applications: This paper has two main practical applications: (i) Provides knowledge and understanding of the crystallization and polymorphic behavior of commercial shea stearin, which is a widely used fat in the confectionery, cosmetic, and pharmaceutical industries. (ii) The presence of small amounts of DAGs significantly delays the crystallization process of shea stearin, particularly of the lower polymorphs.

Production of High‐Melting Symmetrical Monounsaturated Triacylglycerol‐Rich Fats from Mango Kernel Fat by Acetone Fractionation

“…Such diunsaturated and triunsaturated triacylglycerols might be ideal sources for producing cooking oils, frying fats and other structured lipids by further blending or interesterification [17,18]. Furthermore, relatively high content of diacylglycerol in MKF (2.7-5.8%) would give chocolate its undesirable physical properties [1,5,19]. As reported in SOS-rich fats or CB systems, the presence of diacylglycerol delayed the transition of Hm-SMT into a more stable polymorph, resulting in difficulties in the tempering of the fat [2,19,20].…”

“…Furthermore, relatively high content of diacylglycerol in MKF (2.7-5.8%) would give chocolate its undesirable physical properties [1,5,19]. As reported in SOS-rich fats or CB systems, the presence of diacylglycerol delayed the transition of Hm-SMT into a more stable polymorph, resulting in difficulties in the tempering of the fat [2,19,20].…”

Determination of Physical Properties and Crystallization Kinetics of Oil From Allanblackia Seeds and Shea Nuts Under Different Thermal Conditions

“…This was then placed on the microscope in a temperature-controlled cabinet to investigate the microstructure of the fat after crystallization (1 h). [21] Data obtained from the study clearly shows that the content and composition of fatty acids found in the ASO and SNO are different. The results show that ASO contains stearic and oleic acid with a small percentage (less than 1%) representing palmitic acid and arachidic acid.…”

“…The presence of oleic and linoleic acids in the SNO accounts for its high level of unsaturated fatty acids. [22] Ray et al reported the presence of 1-stearoyl-3-oleoyl-glycerol and 1-stearoyl-2-oleayl-glycerol DAGs in shea stearin, [21] therefore the broadening of peaks may be attributed to the inhibitory effect on crystallization/ recrystallization of DAGs present in the SNO. The fatty acid composition of ASO and SNO were comparable to their iodine values of 36.86 (mg I 2 100 g À1 ) and 52.06 (mg I 2 100 g À1 ), respectively.…”

Current update on the influence of minor lipid components, shear and presence of interfaces on fat crystallization

“…As for the polymorphic transition, the presence of minor components can have one or more of these effects: (a) stabilization of unstable polymorphs; (b) destabilization of stable polymorphs and (c) increase in the energy barrier for transformation (slowing down the transformation) [10 ,11,23]. Interestingly, recent studies on silicon treated shea stearin showed that the slowing down effect of DAGs was limited only to lower polymorphs while, the transformation to higher polymorphs was unaffected [23]. Acevedo and Marangoni recently demonstrated that it is possible to functionalize blends of fully hydrogenated oil and liquid oil by using specific emulsifiers under controlled crystallization conditions.…”