Phase Behavior of Binary Mixture Systems of Saturated-Unsaturated Mixed-Acid Triacylglycerols: Effects of Glycerol Structures and Chain–Chain Interactions

Abstract

We systematically examined the phase behavior of binary mixtures of mixed-acid triacylglycerols (TAGs) containing palmitic and oleic acid moieties 1,3-dioleoyl-2-palmitoyl-glycerol (OPO), 1,2-dipalmitoyl-3-oleoyl-rac-glycerol (PPO), and 1,2-dioleoyl-3-palmitoyl-rac-glycerol (OOP), which are widely present in natural fats and are employed in the food, pharmaceutical, and cosmetic industries. Differential scanning calorimetry and X-ray diffraction methods were applied to observe the mixing behavior of PPO/OPO, OOP/OPO, and PPO/OOP under metastable and stable conditions. The results led to three conclusions: (1) Eutectic behavior was observed in PPO/OPO. (2) Molecular compound (MC) crystals were formed in the mixtures of OOP/OPO and PPO/OOP. (3) However, the MC crystals occurred only under metastable conditions and tended to separate into component TAGs to form eutectic mixture systems after 17 months of incubation. These results were contrary to those of previous studies on 1,3-dipalmitoyl-2-oleoyl glycerol (POP)/OPO and POP/PPO in which the MC crystals were thermodynamically stable. We determined that specific molecular interactions may cause this different phase behavior (stability of POP/OPO and POP/PPO MC crystals and metastability of OOP/OPO and PPO/OOP MC crystals). All results confirm the significant effects of molecular structures of glycerol groups, interactions of fatty acid chains, and polymorphism of the component TAGs on the mixing behavior of mixed-acid TAGs.

Crystallization Behavior of Molecular Compound in Binary Mixture System of 1,3‐Dioleoyl‐2‐Palmitoyl‐sn‐Glycerol and 1,3‐Dipalmitoyl‐2‐Oleoyl‐sn‐Glycerol

“…In this study, we studied the crystallization of a binary mixture of 1,3-dioleoyl-2-palmitoyl-sn-glycerol (OPO) and 1,3-dipalmitoyl-2-oleoyl-sn-glycerol (POP) with an interest in using the two TAG for edible fats, having advantageous properties of no-trans, low-saturated, and high-oleic fats. Previous studies have shown that OPO and POP form molecular compound (MC) crystals at the ratio of OPO: POP = 1:1 mixture (Bayés-García, Calvet, Cuevas-Diarte, Ueno, & Sato, 2015;Ikeda, Ueno, Miyamoto, & Sato, 2010;Ikeda-Naito, Ogawa, & Ueno, 2017;Larsson, Quinn, Sato, & Tiberg, 2006;Minato et al, 1997;Moran, 1963;Sato & Ueno, 2014;Sibbald, Carney, & Marangoni, 2016). Its stable polymorphic form is β, which has a double-chainlength structure.…”

Polymorphism and Mixing Phase Behavior in Ternary Mixture Systems of SOS–SSO–OSO: Formation of Molecular Compound Crystals

“…Quite interestingly, the formation of MC crystals of POP/OPO and POP/PPO was confirmed in both neat liquid and in diluted n ‐dodecane solutions (Ikeda, Ueno, Miyamoto, & Sato, ; Ikeda‐Naito, Hondoh, Ueno, & Sato, ). Table indicates that the diversified mixing behavior of the major TAG is influenced by fatty acid moieties (chain length, saturated or unsaturated) and glycerol structures (chair or tuning fork) as thoroughly discussed by Bayes‐Garcia, Calvet, Cuevas‐Diarte, Ueno, and Sato (). The importance of the glycerol structures is clearly seen in POP/OOP (eutectic) and POP/OPO (MC forming), since the glycerol structures of POP and OPO are of tuning‐fork type, whereas OOP reveals chair‐type structure.…”

Binary Phase Behavior of Saturated-Unsaturated Mixed-Acid Triacylglycerols—A Review

“…More experimental and modeling work is required to understand the mechanism. Binary phase behaviors of various saturated-unsaturated mixed-acid TAGs are summarized in Table 2 6, 9, 11 16,20,24,25,30 .…”

“…With a basic understanding of the MC formation mechanism, the phase behaviors of the binary mixtures of OPO, PPO, and OOP were recently examined systematically by Bayés-García et al 30 . It should be noted that OPO, PPO, and OOP are the counterpart TAGs of POP, OOP, and PPO, in which the positions of palmitic acid and oleic acid interchanged.…”

“…However, experimental results indicate the metastability of the MC PPO/OOP. Bayés-García et al suggested that the metastability is probably due to the racemicity of PPO and OOP 30 . The importance of chirality for understanding their mixing behaviors was thus evidenced.…”