Melting points, fats shortening

In many instances, TGs exist in polymorphic forms. Crystal structure is very important to the properties of margarines, shortenings, and specialty fats. The very unstable a form is readily transformed to the more stable ft form, which in some TGs has a higher melting point (more stable) than the /3 form. In single-acid TGs, the order is a — f3 — a, but some mixed TGs show a lower-melting (less stable) (3 form. This is further complicated by the existence of multiple / and /3 forms, depending upon the detailed TG structures at hand. 

Base stock consistency control is the secret to first pass yield, i.e., meeting finished product specification limits with the specified blend of base stocks. Most finished shortenings physical characteristics are controlled with solids fat index (SFI) iodine value (IV), and/or a melting point analysis. However, time restraints during hydrogenation do not allow the long elapsed times required for these results. More rapid techniques to control base stock end points are ... 

On the other hand, shortening used in biscuits should not have a melting point markedly higher than body temperature, or a waxy mouthfeel results. A shortening having an SFI profile similar to that suggested for sandwich cookie filler fat has been successfully used to accomplish all these aims. 

When it is necessary to heat fats to keep them fluid, heat should be applied to line, pumps, and tanks. Although insulation may be used to retain the necessary amount of heat, the abihty to apply heat in emergency situations is most desirable. Occasionally, even when shortenings are held above their apparent melting point, hard fractions will separate or seed out or fractionation will take place. In effect, the composition of the fat changes in different levels in the tank and possibly can block the lines. Application of heat and agitation may be necessary to correct the problem. It is recommended that experimentation on the product be carried out at the projected temperatures and times to ensure that this problem will not occur under operating conditions in the plant. 

Physical properties of a shortening include appearance, consistency, solid fat content, crystal form and size, melting point, and melting behavior. These properties are influenced by the chemical composition which in turn relates to the nature of the fatty acids present and their distribution on the glycerol molecule. 

---