37-9

C. I. MORARU¹, T. C. Lee², M. Karwe², and J. L. Kokini². (1) Department of Food Scince, Rutgers University, 65 Dudley Road, New Brunswick, NJ 08901, (2) Department of Food Science, 65 Dudley Road

Besides water, other small molecules can play a plasticizing role in food matrices. In intermediate-moisture foods, where the plasticization effect of water is limited, the use of plasticizers becomes an important tool for achieving the desired texture. Glycerol and propylene glycol are generally recognized as safe substances which, when added in small concentrations, can determine the softening of food matrices.

This paper investigates the effect of plasticizers on the textural properties of intermediate-moisture extruded carbohydrate-protein matrices. The required concentration of additives that determines the desired plasticization of the matrix is also evaluated.

Different concentrations of glycerol and propylene glycol were added to starch-protein mixtures. The final mixes were extruded with a twin-screw extruder under high-shear conditions, and the texture of the extrudates was assessed using mechanical and structural methods (SEM). The study was performed on fresh extrudates and during their storage, carried out both at room temperature and under accelerated conditions.

The addition of glycerol and propylene glycol led to a noticeable softening of the extrudates, expressed by a significant decrease of the storage modulus E' and loss modulus E" for the freshly extruded samples. The plasticization effect was also present during long-term storage, meaning that the use of these substances can lead to improvement in the quality and shelf life of extruded starch-protein foods. Another important effect of these plasticizers was the depression of water activity of the extrudates to values that could ensure the microbiological stability and safety. The structural investigations have clearly revealed the effect of plasticizers on the microstructure of the extrudates.

The results show that the addition of glycerol and propylene glycol, in small concentrations, can be used to control the texture of extruded carbohydrate-protein mixtures. Also, by reducing water activity, they help the general stability of the extrudates.