NMR IMAGING OF THE WHEAT-GRAIN COOKING PROCESS

NMR imaging has been used to study the boiling and steaming of intact wheat grains by mapping the distribution of water on the central cross section of grains after various cooking times. The results show diffe rent distributions of water occurring with boiling and steaming. Boile d grains showed a front of moisture which gradually moved towards the centre of the grain, although some water was able to diffuse ahead of the front. Steamed grains showed no such front, but showed a homogeneo us distribution of water which gradually increases with cooking time. The different results for boiling and steaming imply that different me chanisms control the influx of water in each case, and provide importa nt data for modelling these processes. It is postulated that absorptio n of water during steaming is slowed by the grain temperature rising a bove that of the steam temperature as a result of the latent heat asso ciated with the condensation of steam being taken up by the grain.