Promotion of stable polymorphs and molecular compound formation in mixtures of a high melting fraction of extra virgin olive oil and cocoa butter

Abstract

The complex polymorphic crystallization and melting behavior of mixtures of the high melting fraction (HMF) of extra virgin olive oil (EVOO) and cocoa butter (CB) was analyzed in the present work. All the mixtures prepared for every 10 % concentration ratio were subjected to a cooling procedure from the molten state (50 ◦C) to -50 ◦C at a rate of 2 ◦C/min, and a subsequent heating to the starting temperature at the same rate. Time-resolved synchrotron radiation X-ray diffraction (SR-XRD) experiments, based on simultaneous small- (SR-SAXD) and wide- (SR-WAXD) angle measurements was used to describe the polymorphism exhibited by single HMF and CB, and selected blends of 30CB/70HMF, 50CB/50HMF and 70CB/30HMF. Six (α-2 L, β’3–2 L, β’2–2 L, β’1–2 L, β’2–3 L, β’1–3 L) and two (Forms I and II) polymorphic forms were encountered in single HMF of EVOO and CB, respectively, at the experimental conditions examined. By contrast, in the blends, HMF crystallized in just two phases (β’3–2 L, β’2–2 L), whereas CB was detected in Forms I, II, IV and V. Many difficulties arose in phase identification, due to the large similarities between polymorphs of the raw materials. The addition of CB resulted in a relevant increase of the crystallization and melting temperatures in the mixtures, which were caused by the formation of Forms IV and V of CB, but also the occurrence of a molecular compound (MC) structure. The promotion of more stable forms of CB may be due to the presence of liquid oil (HMF), which accelerated polymorphic transformations by thermodynamic solvent effects. The results obtained in this work may be suitable for the reduction of saturated fats, favoring the predominance of the monounsaturated ones, like oleic acid.