A differential scanning calorimetry study of wheat grain cooking

Abstract

Summary A number of commercial processes involve whole grain cooking. In this study, differential scanning calorimetry (DSC) scans were taken of whole wheat grains that had been boiled or steamed for various times at either 100 d̀C or 120 d̀C. Scans were also taken of raw grains that had been soaked and equilibrated to different moisture contents. Raw grains showed peak temperatures to be dependent on moisture content, in close agreement with literature data for wheat starch/water mixtures. The two cooking methods showed different behaviour, which can be explained with reference to magnetic resonance imaging (MRI) (Stapley et al., 1997). For steamed grains with high moisture contents at longer cooking times, part of the DSC endotherm was below the cooking temperature, and conversion occurred in the cooker. DSC endotherms of steamed grains showed a clearly denned onset temperature, c. 6d̀C above the steam temperature, due to the release of latent heat. MRI shows partially boiled grains to have a high moisture content in the outer regions and an inner core of lower moisture content. The peak temperatures observed by DSC were similar to those expected of soaked grains with the same moisture contents as that of the core. It is postulated that the inner core contains unconverted starch, and that conversion has been achieved in the outer regions. The specific heat capacity for each grain was also measured, and correlated well with moisture content, but was not strongly influenced by the grain treatment.