Cooking behaviour of potatoes

Rectangular potato pieces (dimensions: thickness 3 mm, cross-section 10 x 15 mm) were then cooked in boiling water at different cooking times. The potato pieces had nearly identical sizes and were cooked for 3 min, 6 min and 9 min. A raw potato piece (cooking time: 0 min) was used for reference purposes. The cubic shaped potato slices were tested in uniaxial dynamic compression mode by applying a static pre-strain of 10 % (approx. 200 - 300 µm) of the sample's height (approx. 2 to 3 mm). Thereafter a dynamic strain sweep at an interval from 0.1 % to 1 % of the initial length was carried out (test frequency: 20 Hz). The superposed dynamic amplitudes correspond to mechanical deformations of approx. 2 µ up to 20 µm. A decrease of the storage modulus E‘ with increasing dynamic strain amplitude is to be observed. As expected the raw potato demonstrates the largest E‘ modulus. E‘ decreases with increasing cooking times and the potato softens.

Cooking behaviour of noodles

5 different cubic samples, 5 mm wide and 7 mm long, have been cut from a ribbon noodle made of durum wheat. In uncooked state the noodle was 1.5 mm thick. The prepared noodles were then cooked for 2 min, 8 min and 10 min. Thereupon an uniaxial dynamic compression test was carried out on the noodle pieces. The cubic noodle pieces were placed between 2 parallel compression plates and were imposed with a static pre-compression of 10 % (approx. 150 to 250 µm) in relation to the sample's thickness (of approx. 1.5 mm). Swelling of the noodle is automatically taken into consideration by the spectrometer and included in the analysis. Thereafter the dynamic load amplitude was systematically increased from 0.05 % to 5 % of the initial length. The dynamic deformation was imposed by a test frequency of 20 Hz. The resulting amplitudes for the imposed dynamic deformations ranged from approx. 1 µm to 100 µm. These investigations were carried out at the cold noodle at ambient temperature. With rising dynamic amplitude the storage modulus E‘ decreases. As expected the sample cooked for only 2 min is the hardest one. Consequently the E‘ (or hardness) shows the highest absolute values and decrease with increasing cooking time.