Instability of low‑moisture carrageenans as affected by water vapor sorption at moderate storage temperatures

摘要

Isothermal microcalorimetry was used to study the exothermic heat flow caused by the absorption of water into carrageenansand a furcellaran, leading to their thermodynamic instability under moderate storage conditions (35°C, τ = 12 h),where τ is the reaction time (h). The net heats evolved by furcellaran, ι-carrageenan, κ-carrageenan, and a mixture ofκ/λ-carrageenan were 43.5 J/g, 45.9 J/g, 31.6 J/g, and 28.1 J/g, respectively. The pronounced exothermic behavior of furcellaranwas attributed to the enthalpic association of water molecules with the thermally degraded carbohydrate matrix.The responses of a heat treatment of carrageenans at 55 °C, 85°C, and 105°C for 15 min on exothermic heat Q (J/g) atdifferent water activities (a_w = 0.26, 0.51, 0.76, and 1.0) were measured. The dependence of the net recorded heat Q onwater activity can be satisfactorily approximated by the equation Q = a[1 − (1 − a_w)~b], where a and b are the coefficientsfound by the nonlinear least-squares method. It was concluded that carrageenans affected by excessive heat treatmentshould be preferably stored with limited water access.