Thermal characteristics and state diagram of freeze-dried broccoli: Freezing curve, maximal-freeze-concentration condition, glass line and solids-melting

Abstract

Stability of foods during processing and storage can be determined from their phase and state diagrams. In this study, state diagram of broccoli was developed considering freezing curve, glass line, maximal-freeze-concentration conditions, solids-melting and BET-monolayer line. The freezing point, glass transition and solids-melting were measured and modeled by Chen's model, Gordon-Taylor model, and Flory-Huggins model, respectively. The ultimate maximal-freeze-concentration conditions (Tm′)u (i.e. end temperature of freezing) and (Tg′′′)u [i.e. end glass transition at (Tm′)u] were found as −30.0 °C and −32.2 °C, respectively, and solids content (i.e. Xs′) at this point was 0.70 g/g sample. The solids-water interaction (χ) during melting was estimated as 0.69 (dimensionless) from Flory-Huggins model, and BET-monolayer was observed as 0.089 g/g dry-solids at 20 °C.