3.5. Melting properties
The Onset temperature (T-onset), Peak maximum (T-peak), peak width at half height (T-width) and enthalpy of melting (ΔHmelt) were automatically calculated after integrating the melting peaks using TA Data analysis software (TA Instruments, New Castle, USA).Fig. 3 shows the DSC thermograms used for evaluating the melting properties. Peak onset corresponds to the temperature at which a specific crystal form starts to melt; peak maximum, that at which melting rate is greatest; end of melting, completion of liquefaction; and peak width at half height, an indication of how long it took (duration) a particular crystal form to melt. All these information are related to crystal type (McFarlane, 1999). All the samples exhibited similar distinct single endothermic transitions between 15 °C and 55 °C (Fig. 3). The heat capacities cp gradually and consistently increased to onset temperature (T-onset), and then progressively increased more rapidly until peak temperature (T-peak), after which it decreased to the end temperature indicating the chocolate was completely melted ( Fig. 3).
Fig. 3.
Melting profiles of sugar-free dark chocolates with inulin/polydextrose mixtures and stevia or thaumatin extracts compared to the reference chocolate with sucrose.
Figure options
Data from the DSC (Table 2) showed that sucrose substitution by the sugar replacers produced changes in crystallinity and melting properties, observed in the differences in the key DSC parameters. The onset temperature was slightly higher for the reference sample than for the sugar-free chocolates indicating a slight delay in start of melt for the reference. The enthalpy of melt was also higher for the reference than the sugar-free chocolates with the reference chocolate recording an average of 40.69 W/g. Comparing the peak width at half height for all chocolates, it was observed that, it took a slightly longer time for the sugar-free chocolates to melt with stevia and thaumatin chocolates recording average values of 3.85 °C and 3.58 °C respectively. ANOVA showed no significant differences between all samples for peak onset at the 95% confidence level. T-peak for thaumatin chocolate was significantly different from the reference but not significantly different from stevia chocolate. A similar trend was observed for the ΔHmelt. There was however no significant differences in T-width for all three chocolates at the 95% confidence level.
The above trends can be associated with the microstructural behaviour of the bulk ingredients. Earlier studies reported that chocolate formulations which contain 100% polydextrose show large crystals with dense smaller particles in between the larger crystals and minimal inter-particle spaces in comparison to formulations containing 100% inulin which revealed large crystals with more void spaces between the crystals indicating limited particle–particle interaction strength (Aidoo et al., 2014a). A combination of these ingredients will result in chocolates having large crystals with the dense smaller particles of polydextrose filling in the void spaces in the crystal network structure of chocolate formulations with inulin. The end result is chocolate with high solids packing intensity accounting for the low onset values and high peak width at half height for the sugar-free chocolates with 75:25% polydextrose: inulin ratios.
The high solids packing of the sugar-free chocolates also results in a decrease in total surface area available for fat to coat the sugar crystals hence decreasing the amount of energy needed to complete melting since most of the fat are available. Practically, although the sugar-free chocolates will begin to melt quickly than the conventional dark chocolate, it will take a much longer time for all the sugar-free chocolates than for the reference sample to completely melt. This knowledge is important as it provides information on likely oral melting behavior with an impact on temporal components of flavor release and also oral epithelial sensation
3.5. Melting propertiesThe Onset temperature (T-onset), Peak maximum (T-peak), peak width at half height (T-width) and enthalpy of melting (ΔHmelt) were automatically calculated after integrating the melting peaks using TA Data analysis software (TA Instruments, New Castle, USA).Fig. 3 shows the DSC thermograms used for evaluating the melting properties. Peak onset corresponds to the temperature at which a specific crystal form starts to melt; peak maximum, that at which melting rate is greatest; end of melting, completion of liquefaction; and peak width at half height, an indication of how long it took (duration) a particular crystal form to melt. All these information are related to crystal type (McFarlane, 1999). All the samples exhibited similar distinct single endothermic transitions between 15 °C and 55 °C (Fig. 3). The heat capacities cp gradually and consistently increased to onset temperature (T-onset), and then progressively increased more rapidly until peak temperature (T-peak), after which it decreased to the end temperature indicating the chocolate was completely melted ( Fig. 3). Fig. 3. Melting profiles of sugar-free dark chocolates with inulin/polydextrose mixtures and stevia or thaumatin extracts compared to the reference chocolate with sucrose.Figure optionsData from the DSC (Table 2) showed that sucrose substitution by the sugar replacers produced changes in crystallinity and melting properties, observed in the differences in the key DSC parameters. The onset temperature was slightly higher for the reference sample than for the sugar-free chocolates indicating a slight delay in start of melt for the reference. The enthalpy of melt was also higher for the reference than the sugar-free chocolates with the reference chocolate recording an average of 40.69 W/g. Comparing the peak width at half height for all chocolates, it was observed that, it took a slightly longer time for the sugar-free chocolates to melt with stevia and thaumatin chocolates recording average values of 3.85 °C and 3.58 °C respectively. ANOVA showed no significant differences between all samples for peak onset at the 95% confidence level. T-peak for thaumatin chocolate was significantly different from the reference but not significantly different from stevia chocolate. A similar trend was observed for the ΔHmelt. There was however no significant differences in T-width for all three chocolates at the 95% confidence level.The above trends can be associated with the microstructural behaviour of the bulk ingredients. Earlier studies reported that chocolate formulations which contain 100% polydextrose show large crystals with dense smaller particles in between the larger crystals and minimal inter-particle spaces in comparison to formulations containing 100% inulin which revealed large crystals with more void spaces between the crystals indicating limited particle–particle interaction strength (Aidoo et al., 2014a). A combination of these ingredients will result in chocolates having large crystals with the dense smaller particles of polydextrose filling in the void spaces in the crystal network structure of chocolate formulations with inulin. The end result is chocolate with high solids packing intensity accounting for the low onset values and high peak width at half height for the sugar-free chocolates with 75:25% polydextrose: inulin ratios.The high solids packing of the sugar-free chocolates also results in a decrease in total surface area available for fat to coat the sugar crystals hence decreasing the amount of energy needed to complete melting since most of the fat are available. Practically, although the sugar-free chocolates will begin to melt quickly than the conventional dark chocolate, it will take a much longer time for all the sugar-free chocolates than for the reference sample to completely melt. This knowledge is important as it provides information on likely oral melting behavior with an impact on temporal components of flavor release and also oral epithelial sensation
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