Effect of temperature and moisture on dynamic Viscoelastic properties of Soybeans

The soybean crushing industry utilizes conditioning in the temperature range of 60-90°C and moisture range of 9-12% to modify the viscoelastic properties of cracked soybeans in order to make them more deformable and to produce thin flakes for oil extraction. Viscoelastic properties of soybean cotyledons, namely G′ and tan δ in the temperature range of 30-120°C and moisture range or 9.5-12.8% were determined using DMTA. In this moisture range, G′ decreased at a rapid rate by 2-4 times due to an increase in conditioning temperature from 30°C to 72.5-81°C. Thus, flake thickness could be substantially reduced by conditioning soybeans up to 72.5-81°C. The tan δ curves showed a peak in the temperature range of 40-50°C, which shifted to a lower temperature by 2-4°C after a decrease in frequency from 1 Hz to 0.3 Hz. This indicates that the material underwent glass transition in this temperature range. In some experiments a second transition occurred at 95-105°C. However, data was insufficient to conclude that this was a glass transition. In general, G′ values below 10% moisture content were about two times greater than at higher moisture contents, which confirmed that at room temperature below 10% moisture content soybeans existed in a glassy state. Due to low deformability of soybeans in the glassy state, flaking below 10% moisture content would require higher mechanical energy and result in thicker flakes.