Study of the polymorphism and the crystallization kinetics of tripalmitin: A microscopic approach

Abstract

The morphology and kinetics of crystallization of tripalmitin have been examined in detail by optical microeco W. The a-crystallization process is characterized by a fast heterogeneous nucleation and spherulitic growth, even at low undercooling, resulting in intense birefrlngence and smooth spheruiitie entities. Four different fJ'-microstructures have been found--grainy, fibrous, feathery and lamellar. Around 47°C, a clear change from a grainy to a fibrous/3'-microstructure is observed. This transition seems to take place without a drastic change in nucleation or in crystal growth. At 50°C, both nucleation and crystal growth exhibit a clear discontinuity, indicating interference from f~crystallization. Around 52°C, the ~'-form changes again from a fibrous to a more feathery microstructure; the transition is accompanied by a distinct decrease in crystal growth rate. The lamellar ~'~tructure exhibits the highest stability and can be obtained only v/a an accelerated nucleation at low temperature, followed by further growth at elevated temperature near the melting temperature of the ~'-form. Determination of the/~-form on the basis of its microstructure is not always precise, because the microstructure strongly depends on whether the/~-crystals are obtained from a transformation of a or f~', or whether ~.crystRllization occurs directly from the melt. Clear confirmation of the polymorphic nature of the solid state can be obtained from melting point determination.KEY WORDS: Kinetics, microscopy, polymorphism, tripAlmitin.The crystallization of triglycerides, the major constituent of oils and fats, is a key step both in the manufacture of fat products and the fractionation of fats and otis (1}. The crystnllization behavior is complex because triglycerides are characterized by the existence of multiple crystalline states. Because of the commercial importance of edible fats, intensive studies have been carried out on the crystallization properties of triglycerides for more than a century (2,3t.Determination of the polymorphic identity of a solid state is not always easy. Differential thermal analysis, X-ray diffraction and infrared spectroscopy are most commonly used to characterize the morphological forn~ Although polarizing microscopy has already found wide appreciation in the food industry, the technique has gained little attention in polymorphism and crystallization studies of fats. In many applications of edible fats however the morphology and number of glyceride crystals determine the suitability of the fat for a given purposeThe present paper is part of a fundamental study on the polymorphism of monoacid triglycerides (4). In this work, the polymorphic behavior of the triglyceride tripalmitin is studied by the optical microscopic techuiqua The study

Physicochemical properties of Brazilian cocoa butter and industrial blends. Part II Microstructure, polymorphic behavior and crystallization characteristics

“…Above this value, as the results observed in this work after 90 minutes of crystallization, the granular structure is indicative of the presence of b' polymorph, for the samples Blend A, Blend B, Blend C, Braz A and Braz B. The simultaneous presence of larger disks and spherulites (close to 50 mm) for Braz C evidences, therefore, a possible polymorphic b' → b transition, confirming a distinct crystallization pattern for this sample (Rousseau, 2007;Kellens et al, 1992). This behavior may be related to the development of crystals with undesirable dimensions hence weaker crystalline networks, which causes a decay in consistency and loss of gloss in chocolate-based products (Timms, 2003).…”

A differential scanning calorimetry study of the crystallization kinetics of tristearin‐tripalmitin mixtures

“…The polymorphic and phase behavior as well as the crystallization kinetics of pure tripalmitin and tristearin has been reported previously in the literature (6)(7)(8)(9)(10). However, relatively few studies have been performed on blends of tripalmitin and tristearin, although a phase diagram is well established (11)(12)(13).…”

Physical properties of fats in food

“…It is worthy of note that various morphologies of β -form PPP crystals have been found for different temperature treatments. In particular, the β -form showed needle-like crystals after slow crystallisation, similar to β-form crystals, which usually exhibit a long needle shape (Kellens et al, 1992).…”