Physical Properties of Cooked Wheat Grains as Affected by Cooking Temperature and Duration

Abstract

The physical properties of soft and hard wheat grains, cooked with steam under pressure, were investigated. These included water uptake, rheological properties as observed by modulus of elasticity (E) and maximum compressive contact stress (Smax), color in CIE L*a*b* system and pasting properties by Rapid Visco Analyzer (RVA). Four cooking temperatures (110, 120, 130 and 1408 C) and six cooking durations (20, 40, 60, 80, 100 and 120 min) for each temperature were studied. Water uptake (WU) and rheological properties were analyzed immediately after cooking conditions were achieved. For color and pasting properties, cooked wheat grains were dried at low temperature and ground before analysis. It was found that WU increased proportionally with cooking temperatures and durations. Hard wheat grains tended to absorb more water than soft wheat grains. Both E and Smax decreased rapidly when wheat grains were cooked. Such decreases were found to be more rapid in hard wheat grains. Wheat grains became darker when cooked, resulting in the decrease of L* values and increase of a* and b* values. Cooked wheat grains lost their natural pasting properties compared to uncooked grains, resulting in the decrease of viscosity in their RVA profiles. The experimental data fitted well in second-order polynomial models (p # 0.0001). The built models were sufficiently accurate for most of the studied properties (R2 ranging from 0.58–0.97).