The crystal size is also affected by the rate of cooling and larger crystals were shown to be formed when fat was cooled at a slower cooling rate83. However the samples were not subjected to changes in the rate of cooling in this study. At higher temperatures (or lower supercooling conditions) due to decrease in the driving force, less crystals are formed although the crystals are larger in size as compared to those formed at lower temperatures83. At lower temperatures, due to the higher driving force, nucleation is favored and a lot of small crystals are generated in the system83. Also, the microstructure of sample with higher agitation speed had smaller crystals83. The crystals can vary in shape from spherulites to needle like or clusters84.
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The SFC can be measured either isothermally to determine the change in the SFC over time or measure the SFC over a range of temperatures to determine the melting profile of the samples 84. The instrument exposes the sample to a high radio frequency zone and causes excitation of the H nuclei. The SFC of the sample is measured based on the relaxation time of the H nuclei. The H nuclei in the solid state relax faster than those in the liquid form and thus based on the ratio, the amount of solid fat in the sample can be calculated88. The SFC of the samples is an indicator of the spreadability 87, mouthfeel and palatability of the fat 70. The SFC also relates to the hardness of the fat 87. A higher rate of cooling has also shown to increase the isothermal SFC of the lard and AMF samples 87. Fat samples after HIU application have shown to have steeper melting profile 70, 71, although broader melting profiles may also be obtained depending on the packing or the polymorphic form generated in the sample 70. Depending on the TAGs or the polymorphic transformations in the fats, the fat can sometimes crystallize isothermally in two steps. This could be due to the crystallization of the higher melting fractions followed by the lower melting fractions or crystallization of a certain polymorphic form followed by its isothermal crystallization to a more stable form. …show more content…
Rheology of food is an important factor that affects the organoleptic properties of foods as it determines the texture and the mouthfeel 94. Foods in which texture plays a major role are potato chips, cookies, emulsion based beverages, pickled cucumbers, etc. Bourne lists descriptors of texture in US, Austria and Japan and some of the common ones include Crisp, Crunchy, Hard, Soft and Creamy among others 95. Hydrocolloids such as gums and stabilizers are widely used to manipulate the texture of foods by changing the viscosity 96 although fats also affect the rheological properties of foods as well 97 depending on the type and the amount of fat. Increase in viscosity can be used as tool to inhibit sedimentation in beverages. An increase in the G’ and G’’ of the ice cream mix was shown with an increase in the fat content 98. Marangoni and Rousseau found that the hardness index and the G’ of the fat increased with the increase in the SFC. Also, upon interesterification, the HI and G’ was higher for the interesterified lard canola oil samples, while it was not affected for the Palm oil-soybean oil blend 31. Veereckren et. al. showed that the hardness of the fat was also dependent on the composition of the fat and the crystallization conditions 99 including the rate of crystallization 87.
The SFC can be measured either isothermally to determine the change in the SFC over time or measure the SFC over a range of temperatures to determine the melting profile of the samples 84. The instrument exposes the sample to a high radio frequency zone and causes excitation of the H nuclei. The SFC of the sample is measured based on the relaxation time of the H nuclei. The H nuclei in the solid state relax faster than those in the liquid form and thus based on the ratio, the amount of solid fat in the sample can be calculated88. The SFC of the samples is an indicator of the spreadability 87, mouthfeel and palatability of the fat 70. The SFC also relates to the hardness of the fat 87. A higher rate of cooling has also shown to increase the isothermal SFC of the lard and AMF samples 87. Fat samples after HIU application have shown to have steeper melting profile 70, 71, although broader melting profiles may also be obtained depending on the packing or the polymorphic form generated in the sample 70. Depending on the TAGs or the polymorphic transformations in the fats, the fat can sometimes crystallize isothermally in two steps. This could be due to the crystallization of the higher melting fractions followed by the lower melting fractions or crystallization of a certain polymorphic form followed by its isothermal crystallization to a more stable form. …show more content…
Rheology of food is an important factor that affects the organoleptic properties of foods as it determines the texture and the mouthfeel 94. Foods in which texture plays a major role are potato chips, cookies, emulsion based beverages, pickled cucumbers, etc. Bourne lists descriptors of texture in US, Austria and Japan and some of the common ones include Crisp, Crunchy, Hard, Soft and Creamy among others 95. Hydrocolloids such as gums and stabilizers are widely used to manipulate the texture of foods by changing the viscosity 96 although fats also affect the rheological properties of foods as well 97 depending on the type and the amount of fat. Increase in viscosity can be used as tool to inhibit sedimentation in beverages. An increase in the G’ and G’’ of the ice cream mix was shown with an increase in the fat content 98. Marangoni and Rousseau found that the hardness index and the G’ of the fat increased with the increase in the SFC. Also, upon interesterification, the HI and G’ was higher for the interesterified lard canola oil samples, while it was not affected for the Palm oil-soybean oil blend 31. Veereckren et. al. showed that the hardness of the fat was also dependent on the composition of the fat and the crystallization conditions 99 including the rate of crystallization 87.