Effects of Different UV Irradiations on Properties of Cassava Starch and Biscuit Expansion

Abstract

Commercial cassava starch was modified by using 1%(w/w) lactic acid solution for 15 min and the drained starch was irradiated with different UV wavelengths of either UVBA (280-420 nm), UVB (310-330 nm) or UVC (254 nm) for 7 to15 h. The acidified starch, irradiated with UVB or UVC for 7 and 9 h, achieved the desired baking expansion. No significant change in the specific volumes was shown for the starch irradiated with UVB for 9 h, UVC for 7 and 9 h. The starch which has been irradiated with UVB for 9 h gave the highest specific volume of 12.23 ± 0.12 cm³/g, while UVC irradiated samples of 7 and 9 h gave 12.10 ± 0.75 and 11.33 ± 0.62 cm³/g, respectively. The specific volumes of the samples were significantly correlated to the losses of dough weights during baking (r² = 0.94). As for the rapid visco analysis, the peak viscosity of the samples irradiated with UVB for 7 and 9 h were 196.55 ± 2.41 and 195.67 ± 0.83 RVU, while those of the UVC irradiated samples were 176.55 ± 1.83 and 169.54 ± 3.24 RVU, respectively. These values were higher than the values obtained from the other treatments but lower than the commercial starch. In addition a linear relationship between the peak viscosity and the specific volume of the samples, was observed (r² = 0.81), pointing that the starch irradiated with UVB or UVC for 7 to 9 h was capable of absorbing and holding water during gelatinization and responded for the baking expansion. A significant increase in the pasting temperatures indicated formation of network structure which occurred in the amorphous regions, due to no change in the typical A-pattern of the X-ray diffractions of the samples obtained. A reduction in amylose contents of the irradiated starches was also observed. From the scanning electron micrographs, fracture appearance and sight exocorrosion on the surface of the starch granules were similar in the different treatments. The texture profile analysis showed the deformation curves of the biscuits made by the UVB irradiated starch similar to those of the wheat rolls. The satisfactory sensory qualities in the biscuits were obtained.