Investigating the rheological, microstructural and textural properties of chocolates sweetened with palm sap-based sugar by partial replacement

Palm sugar, a natural alternative sweetener which can be made from the nectar of several species of palm tree flowers, recently gains more interest. Due to its physicochemical characteristics, utilisation of palm sugar as chocolate sweetener results in different quality attributes of chocolate. In this work, a thorough investigation about the influence of palm sugar on the rheological, microstructural and textural characteristics of chocolate was carried out through partial replacement of sucrose as chocolate sweetener. Accordingly, five sucrose-palm sugar blends with different palm sugar (PS) proportion, namely PS0, PS25, PS50, PS75, and PS100 were used as chocolate sweetener. The results showed that the Casson yield value of chocolate containing palm sugar was lower than the Casson yield value of chocolate sweetened with pure sucrose which could be attributed to the presence of agglomerates in the chocolate suspension. However, palm sugar-sweetened chocolate exhibited a higher Casson viscosity and thixotropy which could be mainly attributed to the presence of glucose and fructose and the relatively high moisture content. These factors also influenced the hardness of the chocolate to some extent. A lower melting temperature and enthalpy value of the sugar phase in chocolate were observed by DSC, whereas visualisation using SEM, polarised and normal light microscopy indicated increased agglomeration due to the presence of moisture, amorphous sugar and chemical impurities. Rheological behaviour of molten chocolate, hardness and polarised-normalised light microscopy were evaluated at a constant temperature of 40, 20, and 50 degrees C, respectively, while the melting profile was measured from 20 to 200 degrees C at a rate of 5 degrees C/min.