Characterisation of Fat Crystal Polymorphism in Cocoa Butter by Time-Domain NMR and DSC Deconvolution.

Arnout Declerck,Paul Van Der Meeren,Veronique Nelis,Koen Dewettinck,Sabine Danthine

doi:10.3390/foods10030520

Arnout Declerck, Paul Van Der Meeren + Show 3 more

Open Access

https://doi.org/10.3390/foods10030520

Copy DOI

Abstract

The polymorphic state of edible fats is an important quality parameter in fat research as well as in industrial applications. Nowadays, X-ray diffraction (XRD) is the most commonly used method to determine the polymorphic state. However, quantification of the different polymorphic forms present in a sample is not straightforward. Differential Scanning Calorimetry (DSC) is another method which provides information about fat crystallization processes: the different peaks in the DSC spectrum can be coupled to the melting/crystallisation of certain polymorphs. During the last decade, nuclear magnetic resonance (NMR) has been proposed as a method to determine, qualitatively and/or quantitatively, the polymorphic forms present in fat samples. In this work, DSC- and NMR-deconvolution methods were evaluated on their ability to determine the polymorphic state of cocoa butter, with XRD as a reference method. Cocoa butter was subjected to two different temperature profiles, which enforced cocoa butter crystallization in different polymorphic forms. It was found that XRD remains the best method to qualitatively determine the polymorphic state of the fat. Whereas the quantitative NMR and DSC deconvolution results were not fully in line with the XRD results in all cases, NMR deconvolution showed great promise both in a qualitative and quantitative way.

Highlights

In food science and industry, it is well known that the polymorphic state of fat is an important quality parameter of the lipid phase in the food product
The three basic subcell packing structures of TAG acyl chains are a hexagonal, orthorhombic and triclinic subcell, known as α, β’ and β packing, respectively, of which the thermodynamic stability, the packing density, the melting point and the melting enthalpy increase in consecutive order [8,9,10,11]. These differences in physical properties can be exploited for elucidation of the polymorphic form using various analytical techniques, e.g., Differential Scanning Calorimetry (DSC), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), or infrared spectroscopy
The absence of a short spacing (SS) around 4.20 Å indicated the melting and/or polymorphic transition of α-and β2’-crystals to more stable phases. This is in line with Marangoni and McGauley [25], who found that the stable β polymorphic form was only observed at higher crystallization temperatures (20–26 ◦C) and through polymorphic transition from β’ to β

Summary

Introduction

In food science and industry, it is well known that the polymorphic state of fat is an important quality parameter of the lipid phase in the food product. The three basic subcell packing structures of TAG acyl chains are a hexagonal, orthorhombic and triclinic subcell, known as α, β’ and β packing, respectively, of which the thermodynamic stability, the packing density, the melting point and the melting enthalpy increase in consecutive order [8,9,10,11]. These differences in physical properties can be exploited for elucidation of the polymorphic form using various analytical techniques, e.g., Differential Scanning Calorimetry (DSC), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), or infrared spectroscopy. Access to XRD equipment is not straightforward in an (industrial) research & development and/or quality control unit, which is not the case for DSC and low field(LF)-NMR

Objectives

Methods

Results

Discussion

Conclusion