Publication no. C-2002-0205-04R |  VIEW ARTICLE

Influence of Fat on Expansion of Glassy Amylopectin Extrudates by Microwave Heating.

V. Ernoult (1), C. I. Moraru (1), and J. L. Kokini (1,2). (1) Food Science Department, Rutgers-The State University of New Jersey, New Brunswick, NJ 08901. (2) Corresponding author. Phone: (732)932-9611x313. E-mail: <kokini@aesop. rutgers.edu> Cereal Chem. 79(2):265-273. Accepted December 3, 2001. Copyright 2002 American Association of Cereal Chemists, Inc.

The effect of solid fat (melting point 70°C) and liquid fat (melting point -20°C) on the microwave expansion of extruded glassy amylopectin pellets was investigated. Glassy, unexpanded amylopectin extrudates containing <10% fat were equilibrated at different water activity levels (a(w)) and then expanded by microwave heating. Expanded products were characterized by analyzing degree of expansion, structure, and texture. For the a(w) range studied, expansion increased with increasing a(w) of the pellets until a maximum at a(w) = 0.605 and then decreased. Completely dehydrated samples did not expand at all. This demonstrated that moisture was the driving force in the microwave expansion of the pellets. The addition of solid fat contributed greatly to expansion. The highest degree of expansion was obtained for pellets containing 6% solid fat at all a(w) levels. Due to the effect on expansion, the addition of solid fat also affected the microstructure and texture of the expanded products. Concentrations of solid fat >2% resulted in expanded products with a large number of cells, uniform in size, with thin cell walls. Liquid fat addition had a negative effect on microwave expansion. The expanded products obtained from pellets that contained liquid fat had a lower expansion volume and a coarser structure.