Thermodynamic and Kinetic Study on Phase Behavior of Binary Mixtures of POP and PPO Forming Molecular Compound Systems

Abstract

The phase behavior of PPO (sn-1,2-dipalmitoyl-sn-3-oleoylglycerol) and POP (sn-1,3-dipalmitoyl-sn-2-oleoylglycerol) binary mixture was examined using differential scanning calorimetry, conventional and synchrotron radiation X-ray diffraction (XRD), and highly pure samples. A molecular compound, βC, was formed at the 1:1 concentration ratio of PPO and POP, giving rise to two monotectic phases of PPO/compound and compound/POP in a juxtapositional way. βC has a long spacing value of 4.1 nm of double chain length structure. In the PPO/compound region, the DSC melting peak increased with increasing PPO concentration, whereas the DSC melting peak increased with increasing POP concentration in the compound/POP region. The melting point of βC was lowest at 31.2 °C. Time-resolved XRD study unveiled the formation of molecular compounds in metastable forms, αC and β‘C, having the same PPO/POP concentration ratio as βC. αC and β‘C exhibited monotectic phases with corresponding metastable forms of the pure components. In αC, two hexagonal packing XRD short spacing peaks were obtained for αC, corresponding to a differently packed hexagonal subcell of two leaflets. A structure model of the PPO/POP molecular compound is proposed, involving separation of palmitoyl chain leaflet and palmitoyl−oleoyl mixed-acid chain leaflet in the double chain length structure. This model justifies the structure of βC of SOS/SSO proposed by Engstrom (Engstrom, L. J. Fat Sci. Technol. 1992 94, 173−181), in which the saturated and unsaturated chains are packed in the same leaflet of the double chain length. The present work additionally proved that the formation of the molecular compound was present in the αC and β‘C metastable forms, as directly proved by dynamic X-ray diffraction study using synchrotron radiation.

Crystallization of Fully Hydrogenated and Interesterified Fat and Vegetable Oil

“…Molecular compound formations, were observed in the binary mixture systems of the symmetric/ asymmetric saturated/unsaturated mixed-acid TAGs, such as POP/PPO and SOS/SSO 15,17 . The mechanism of such molecular compound formation was discussed in a study on POP/OOP binary systems 18 , in which a eutectic phase was formed.…”

Crystallization of model fat blends containing symmetric and asymmetric monounsaturated triacylglycerols

“…6a) is not greatly influenced by the isothermal time. Looking at the peak maxima and the TAG composition, the observed melting peak probably corresponds to the melting of a diluted (with OOO) mixed crystal consisting of PPP and POP or even of PPP-POP-POO [18][19][20][21][22]32].…”

Solidification and phase transformation behaviour of food fats — a review

“…The fat solidification processes so far examined by SR-XRD were the solidification and transformation of PPP (tripalmitin), SSS (tristearin), and their mixtures [16][17][18], cocoa butter [19,20], SOS (sn-1,3-distearoyl-2-oleoyl glycerol) [21,22], POP (sn-1,3-dipalmitoyl-2-oleoyl glycerol) and its mixing phases with other TAGs [23][24][25]. A recent review summarised the fundamental aspects obtained by the above SR-XRD studies [26].…”