GLASS TRANSITIONS IN AQUEOUS CARBOHYDRATE SOLUTIONS AND THEIR RELEVANCE TO FROZEN FOOD STABILITY

During the freezing of aqueous low molecular weight carbohydrate (suga r) solutions, the solute is freeze-concentrated into a supersaturated solution of high viscosity that is capable of undergoing a transition into the vitreous (glassy) state. If the freezing process follows the equilibrium liquidus line, maximal ice formation results in a glass tr ansition temperature known as the T'(g). However, it is apparent from freezing rate studies that the concentration of solute in the glass ma y be lower than expected as a result of less than maximal ice formatio n, resulting in a T-g < T'(g). The addition of polysaccharides to suga r solutions has no significant effect on T'(g), but increases the mech anical properties of the solution at T > T'(g). Sugar and sugar/polysa cchharide solutions can be used as model systems to determine the beha viour of several categories of frozen foods, such as fruits, frozen da iry desserts, or other types of sugar-added food systems. Storage of s uch frozen foods under conditions where the unfrozen, freeze-concentra ted phase is in the vitreous state may greatly improve stability and s helf-life. An examination of the low-temperature thermal behaviour of carbohydrate solutions also provides considerable insight into the act ion of polysaccharides in improving the stability of frozen foods to i ce recrystallization.