Triacylglycerols crystallizing

Figure 4. Typical variations in the chain-length structures of triacylglycerol crystals. An arrow means a leaflet.

Fig. 3. Illustration of molecular interactions most irrfluential to structural stabilization of triacylglycerol crystals.

DeJong, S. (1980). Triacylglycerol Crystal Structures and Fatty Acid Conformations, A Theoretical Approach, Dissertation, Amsterdam. 

In the analysis of sterols and other components of CBAs, in particular the minor components it must be borne in mind that it is selected fractions of the parent fats obtained by crystallization that are used in confectionery and are potential adulterants. These fat fractions are produced with a view to obtaining desired physical properties, which depend on the triacylglycerol composition, and while they do contain measurable levels of some minor components of varying polarity their composition is likely to vary significantly from that of the parent fat. 

The principal determinant of butter consistency is the ratio of solid to liquid fat (Rohm and Weidinger, 1993). Therefore, the extent of crystallization is critical to the texture of butter. Milk fat is composed of literally hundreds of unique and varied triacylglycerol (TAG) species (Jensen et al, 1991). This results in milk fat having complicated crystallization, melting, and rheological behaviour (Mulder, 1953 Hannewijk and Haighton, 1957). 

The crystallization behavior of milk fat (which contains minor lipids) and a pure triacylglycerol fraction of milk fat were compared by Herrera et al. (1999). The results suggested that minor lipids delay nucleation but promote crystal growth. Other workers who examined the effects of added phospholipids on palm oil, suggested that some phospholipids delayed nucleation while others had more significant effects on the rate of growth of fat crystals (Smith, 2000),... 

Studies on the addition of standard diacylglycerols demonstrated that their racemic purity had a significant influence on crystallisation behavior of milk fat triacylglycerols. Differences in the observed effects on crystallization... 

A reduced level of low molecular weight monounsaturated triacylglycerols (C36 and C38) and increased levels of trisaturated triacylglycerols (C44-C50) was obtained on undirected chemical interesterification of milk fat with sodium methoxide (0.5%) as catalyst, resulting in a wider temperature range for crystallization compared to native milk fat (Parviainen et al., 1986). 

Sugiura, M., Oikawa, T., Hirano, K., Inukai, T. 1977. Purification, crystallization and properties of triacylglycerol lipase from Pseudomonas fluorescens. Biochim. Biophys. Acta 488, 353-358. 

Ueno, S., Yano, J., Seto, H., Amemiya, Y., Sato, K. 2000. Synchrotron radiation X-ray diffraction study of polymorphic crystallization in triacylglycerols. In, Physical Properties of Fats, Oils and Emulsifiers (N. Widlak, ed.), pp. 64-78, AOCS Press, Champaign. 

Fig. 34.1. Drawings of two- and three-chain triacylglycerol layers (a) saturated monoacid SSS-type (b) saturated symmetrical PSP-type where 2 chain differs from 1 and 3 chains in length (c) symmetrical POP-type where 2 chain is unsaturated and (d) symmetrical OPO-type where 1 and 3 chains are unsaturated. Crystals grow in bilayer units.

---