Study on the properties of peanut stearins

Peanut stearins (PeS), the winterisation product of peanut oil in the plant, were used as raw materials to study their properties and to solve the problems of insufficient research, limited application and low added value of PeS. The physicochemical properties of the three PeS were analysed, and their thermodynamic properties, crystal polymorphism and crystal micromorphology were investigated by differential scanning calorimetry (DSC), X-ray diffraction and polarized light microscopy.The major fatty acids of PeS determined by gas chromatography were oleic (O, 31.56%-35.77%), linoleic (L, 33.40%-35.98%) and palmitic (P, 11.94%-14.11%) acids, followed by stearic (St, 7.00%-8.83%), behenic (Be,4.69%-6.27%), arachidic (Ad,2.74%-3.52%), lignoceric (1.31%-1.89%) and eicosenoic (0.44%-0.59%) acids, and the iodine values (IVs) of PeS were in the range of 85.33-93.53 g/100 g. PeS is mainly composed of tri-unsaturated triglycerides and mono-saturated di-unsaturated triglycerides. Due to the high content of unsaturated triglycerides, PeS had relativelly low SFC and crystallized slowly. In the range of 0-25 ℃, SFCs of PeS increased with the saturated fatty acids increasing at a given temperature. The slip melting points of PeS increased with IV decreasing and ranged from 22.1 ℃ to 26.3 ℃. The results of the thermal analysis exhibited that PeS showed two strong and wide endothermic peaks in the range of -30-0 ℃ and 0-25 ℃ in the melting process while presenting one wide exothermic peak in the range of -20-20 ℃ during the crystallization process. Two distinct diffraction peaks close to 4.10 and 3.70 Å presented in PeS were attributed to the β' form crystal. The crystal cluster of PeS with lower IV was feather blade-like and the aggregates of the clusters of them were rosette-like. However, PeS with higher IV showed cloud-like morphology. PeS exhibited one-step crystallization with various lag periods at 15 ℃. PeS could be used as base stock in plastic fat preparation through blending or interesterification with other hard fats.