Low-temperature stability and the glassy state in frozen foods

Abstract

Many frozen foods contain an unfrozen phase with a very low freezing point, due to the process of freeze-concentration of the solutes as water is removed in the form of ice. Hence, many reactions that are diffusion-controlled, such as enzymatic degradation or ice recrystallization, can occur within this unfrozen phase even at very low temperatures, giving frozen foods a finite shelf life. Recent research in the area of low-temperature stability of foods has focused on the importance of the viscosity of the freeze-concentrated solution or rates of diffusion of water and solutes within the unfrozen phase. At very high viscosities (> 10 12 Pa s), an amorphous solid state or glass may form within the frozen food, thus tremendously decreasing the rates of molecular diffusion and rendering the frozen food stable for much longer periods of time. An awareness of this glass formation illustrates the importance of appropriate freezing and storage temperatures to stability and also may allow formulation of foods with a higher glass transition temperature or reduced molecular diffusion rates to improve shelf life.