Influence of lipid composition, crystallization behavior and microstructure on hardness of palm oil-based margarines

摘要

Two typical commercial palm oil-based margarines, denoted A (complained as with over-hardness) and B (commercially considered as with acceptable hardness), respectively, were compared in terms of hardness, solid fat content (SFC), lipid composition [fatty acid and triacylglycerol (TAG) composition], crystallization behavior and microstructure. On the basis of these results, the reason of over-hardness in margarine A was discussed. Margarine A showed higher hardness than margarine B with the differences increasing along with rise in temperature in the typical range from 15 to 30 °C. While margarine B has good quality and appropriate hardness, it showed SFCs higher than margarine A. Lipid composition analyses showed that margarine B has small amounts of medium chain fatty acids and higher content of monounsaturated TAGs [1,3-dipalmitoyl-2-oleoyl-glycerol (POP), 1,3-dipalmitoyl-2-linoleoyl-glycerol (PLP), 1-palmitoyl-2-oleoyl-3-stearoyl-glycerol (POS)]. X-ray diffraction analysis revealed that both margarines have β′ and β polymorphs with the β form being dominant in margarine B. Isothermal crystallization kinetics of both margarines under 15, 20, 25, and 30 °C, respectively, fitted using the Avrami model indicates that margarine B hardly crystallizes at temperatures ≥25 °C. Morphologic observations of the microstructure of both margarines by polarized light microscope and scanning electron microscopy showed that formation of large spherulites have an important influence on margarine texture. Occurrence of large spherulites in margarine B is considered to decrease the numbers of crystals and lessen mutual attraction with temperature increasing, which leads to weakened strength of the total network, even if margarine B has a higher SFC value. Keywords Margarine - Palm oil - Hardness - Lipid composition - Isothermal crystallization - Microstructure