Structural, Microstructural and UV-Vis spectroscopy studies of Gamma–irradiated starch from Dioscorea Rotundata,

Abstract

Starch from Dioscorea rotundata (white yam) of Kwasi species was irradiated with gamma rays at different doses (0.05, 0.1, 0.2, 0.6 and 1.0 kGy) from Cesium-137 gamma source. The native and irradiated specimens were characterised by X-ray diffraction, SEM and UV-Vis spectroscopy. Proximate analyses shows it contains moisture of ~9.77%, crude protein of 1.18%, crude fat of 0.39%, ash content of 1.13%, crude fibre 1.09%, crude carbohydrate 86.44% and Amylose content of 22.48%. The effect of increased irradiation shifted the 2θ values below the native sample peak which implies increase in the size of the unit cell. The strongest diffraction peaks are all at ~17° 2θ and confirms that Kwasi starch has typical B-type diffraction pattern. Their microstructure has average grain size maximum of 31.70 µm for 1kGy and minimum of 15.28 µm 0.6 kGy samples, all of which are either characterised by ellipsoidal, ovoid or oval-shaped grains. The crystallize sizes determined from Willamson–Hall plots are 27.79 ±16.01 nm maximum, for native and 13.72±4.48 nm minimum, for 0.1 kGy. UV-Vis spectroscopy studies show maximum absorbance of 1.373 at 290 nm for 0.2 kGy sample. The TGA plot shows that kwasi starch is stable from 699oC with a weight loss of ~14.19 %. All the doses absorbed are in the ultra-violet region (190-400 nm) and thus no indication of absorbed light which makes Kwasi starch colourless. It is concluded that kwasi starch structure is not altered in any significant way by gamma irradiation at the applied dose and may thus be suitable for applications in the food and non-food industries.