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The effect of diglycerides (DG) on the phase transition of various polymorphic forms of normal triglycerides (TG) of sal fat was investigated by differential scanning calorimetry. Three levels of DG, 5, 10 and 15%, were used. DG delayed the phase transition of lower melting crystal forms to higher forms of TG when the samples were brought to a congealed state by rapid cooling (20 C/min) and heated at rates ranging from 1.25 to 10 C/min; the extent depended on the level of DG and the rate of heating. As the level of DG and the rate of heating increased, the delay in phase transition of crystal forms I → II → III was more pronounced. The phase transition of crystal forms I, II and III to form IV was delayed at 5 and 10% levels of DG, while at the 15% level the phase transition of form I to higher forms was completely stopped when the samples were tempered at 0 C for 18 hr and heated at 10 C/min. DG at 10 and 15% levels retarded the phase transition of form IV to the most stable (V) form of TG when the samples were tempered at 0 C for 1 hr followed by 3 hr at 26 C. |
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