Characterization of the glass transition of commercial confections selected from each sugar cooking stage

The stages of sugar cooking are widely used in the confectionery industry as a practical tool for producing confections with a wide range of physical and textural properties. However, the range of glass transition temperatures (T_g) associated with each sugar cooking stage requires further investigation. Thus, the objective of this study was to characterize the T_g of commercial confections from each sugar cooking stages, thread to hard crack. Twenty-four representative confections were selected from across the six stages. Vacuum oven moisture content, chilled mirror hydrometer water activity, and differential scanning calorimetry T_g parameters were measured. Principle Component Analysis (PCA) and cluster analysis were performed, categorizing the confections based on their physical and thermal properties. Generally, T_g increased with increasing sugar cooking stage, with noted exceptions. Overall, rubbery confections exhibited a much wider variation in moisture content, a_w, and T_g values compared to glassy confections, in agreement with the PCA and cluster analysis results. Water activity proved to be a better predictor of T_g midpoint values for the confections studied herein than moisture content, as a_w better reflected the amorphous solid-water interactions within the confectionary matrix. While moisture content and a_w did not correlate to T_g in the same fashion, PCA revealed that both parameters assist in characterizing the confections. The confections did not cluster by stage, but the glassy and rubbery confections did cluster separately, yielding one glassy and two rubbery clusters. This research underscores the significant role formulation plays in impacting the physical and thermal properties of confections.