30E-14 |
Influence of moisture on microwave expansion of glassy corn pellets in the presence of hydrocolloids |
M. Besnard1, C. I. MORARU2, and J. L. Kokini2. (1) ENSBANA, Dijon, France, (2) Food Science Department, Rutgers University, New Brunswick, NJ 08901 Microwave expansion is emerging as a promising technique in the manufacturing of third generation snacks. Previous studies showed that moisture is the driving force in microwave expansion of glassy cereal pellets and that gums have the potential to improve the structure of the expanded products. The objective of this research was to study the microwave expansion of glassy corn pellets in the presence of high molecular weight xanthan gum and CMC, at different levels of moisture. Unexpanded corn pellets were obtained by extruding corn flour at the following levels of gums (xanthan gum and CMC): 0%, 0.5%, 1% and 1.5%. A ZSK-30 self-wiping, intermeshing, twin-screw extruder (W&P, Ramsey, NJ) was used to produce the samples. The pellets became glassy upon cooling and drying and then were equilibrated at five relative humidities: 0%, 11%, 33%, 58% and 69%. The equilibrated pellets were expanded by microwave heating, using an AVCTM-80 model microwave oven with a constant power of 600W and a frequency of 2450 MHz (CEM Corporation). The volumetric changes, textural and microstructural characteristics of the expanded products were determined. The moisture sorption isotherms of the pellets at 25°C, 50°C, 70°C and 87°C were built. The results showed that expansion was strongly dependent on water activity/moisture content, with maximum expansion taking place at Aw=0.55, for all gum concentrations. CMC and XG resulted in slightly lower expansion, but improved structural uniformity of the expanded products. This had direct effects on the textural properties of the expanded samples, which were less variable in the presence of fats than for corn flour alone. At the concentrations used in this study, the addition of gums did not change the moisture sorption properties of the extruded pellets. This study contributes to a better understanding of the effects of gums on microwave expansion of cereal pelets.
Session 30E, Food Engineering: Rheology and texture
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