Effects of sucrose addition on the rheology and structure of iota-carrageenan

Sucrose addition contributes to the rheology of carrageenan, which improves the quality of food that includes carrageenan as an additive. In the present study, the rheological behaviours of sucrose-supplemented iota carrageenan at different concentrations (0–20%, w/v) were determined. Easier gelation with a higher gelling temperature (51.4–57.4 °C) could be achieved by sucrose addition, and the trend could be predicted using mathematical models. Application of the Kirkwood-Buff theory demonstrated that exclusion effects of water and direct binding between sucrose and iota carrageenan are the possible mechanisms for the stabilisation, which act by providing significantly greater |ΔGu2| than |ΔGu1| from all samples using Clausius-Clapeyron equation (|ΔGu1| and |ΔGu2| are calculated KB parameters representing the contribution of the rearrangement of water and cosolvent around the solute to the thermodynamics of sol-gel transition). Fourier transform infrared spectroscopy further confirmed the bindings by detecting band shifts (from 845 to 835 cm−1). The gel was the strongest (251.71 Pa) at 5% (w/v) sucrose; however, too much sucrose decreased the gel strength. The Winter-Chambon equation provided the fractal dimension df (2.22) and critical gel strength Sg (12.52 Pa•sn) at 5% (w/v) sucrose concentration, indicating the highest density and critical strength. The zeta potential (−0.92 mV) and confocal laser scanning microscopy images also showed the most abundant aggregates at 5% sucrose. Excess sucrose may form sucrose-sucrose hydrogen bonds that loosen the iota carrageenan network. A schematic representation was provided to show how sucrose could affect the structure and gelation of iota carrageenan (differs from kappa carrageenan) and the potential bonds related to the effect. [Display omitted] •Sucrose addition stabilised the gel of iota carrageenan.•Exclusion effect contributed to the stabilisation.•Direct binding between sucrose and iota carrageenan enhanced stabilisation.•The strongest gels were formed at 5% (w/v) sucrose addition.•Too much sucrose loosened the structure of the iota carrageenan network.