In this study, the relationship between microstructure, fracturing behaviour and sound upon breakage was evaluated for four cocoa butter alternatives. Sound emission plays an important role in the sensory perception of snap, a key attribute for many chocolate and confectionery products. However, the correlation between microstructure, mechanical properties and the acoustic properties of fats used in the chocolate and confectionery industry has not been elucidated. SOS, PSO, PPO and POP rich fats were studied and characterised by SAXS/WAXS and confocal laser scanning microscopy. Simultaneous texture and acoustic analysis was conducted by the use of a texture analyser combined with an acoustic envelope detector system, augmented by a broad band microphone (2-200 kHz), and a digital sampling oscilloscope. A significant effect of triacylglycerol (TAG) composition on the sound pressure level upon breakage of fats was shown (p<0.05), whereas no effect of the crystallisation procedure was found. On the contrary, the maximum force at fracture was significantly affected by TAG-composition as well as crystallisation procedure. No significant correlation was found between force at fracture and the sound pressure level. A more detailed evaluation of force-displacement curves showed a high correlation between the negative values of the 2nd derivative of the force curve, providing a measure of the rate of energy release upon breakage, and the sound pressure level (r=0.89, p<0.05), demonstrating a link between mechanical properties and acoustic emission. No relation between polymorphic behaviour, determined by x-ray diffraction, and the acoustic properties of fats was found. All fats was found to crystallised into the β’ phase within an hour storage at 20°C and subsequently the PPO and POP rich fats transformed into the β form after 1 week. Further, analysis of the microstructure by confocal laser scanning microscopy showed no direct relation between acoustic properties and crystal size or crystal morphology. An evaluation of the strength of links within the fat crystal network, based on how orderly and dense packed crystals/crystal clusters appear on microscopic images, indicated an important role of the strength of inter-particle links for the sound emission, whereas intra-particle links were found to be less important. It is hypothesized that strong inter-particle links provide a strong rigid structure resulting in build-up of energy during compression and a fast energy release upon breakage accompanied by sound emission. The absence of large areas of liquid fat might also be important, especially when the contact areas between probe and sample is small, as such areas might act as crack stoppers providing local fracturing and preventing the build-up of energy.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)