Crystalline Phase Identification of Cocoa Fat Triacylglycerol Using X-ray Diffraction and Rietveld Refinement

Introduction

Cocoa butter exhibits polymorphism, a crystallographic property that strongly influences its physicochemical behavior. This feature is crucial for the quality, stability, and sensory characteristics of chocolate, where cocoa butter is a primary component. Polymorphism stems from the molecular packing of specific fatty acids and triacylglycerols (TAGs). Understanding these crystalline forms provides deeper insight into the structural behavior of cocoa fat.

Methods

This study characterizes the crystalline phases of cocoa fat in three samples using X‑ray diffraction (XRD) combined with Rietveld refinement. Analyses were performed on a PANalytical  X’Pert³ Powder XRD system with CuK‑α radiation (λ = 1.5418 Å), a step time of 5 s per step, 30 mA of current, and 40 kV of voltage. Diffraction patterns were compared against reference data from the Crystallography Open Database (COD) for phase identification.

Results and Conclusion

The diffraction patterns matched two TAGs and one fatty acid—1,3‑distearoyl‑2‑oleoyl‑glycerol (C₅₇H₁₀₈O₆), 1‑palmitoyl‑2‑oleoyl‑3‑stearoyl‑glycerol (C₅₃H₁₀₂O₆), and cis‑9‑octadecenoic acid (C₁₈H₃₄O₂)—with match scores of 48, 59, and 44, respectively. These compounds crystallized in monoclinic, triclinic, and orthorhombic systems, respectively, as determined by Rietveld refinement. The XRD results confirm the coexistence of multiple polymorphic forms, underscoring the molecular heterogeneity of cocoa fat. This study demonstrates the utility of Rietveld refinement in structural food chemistry as an effective tool for phase analysis and compositional assessment.