EFFECT OF DECORTICATION METHODS ON NUTRIENTS OF SORGHUM GRAINS

Abstract

The main goal of this study is to evaluate the changes in chemical composition, and the losses of macro and micro-elements of sorghum grains due to the effect of the different methods of decortication and to suggest a method which leads to high quality product as well as retains most of the nutrients indigenous to sorghum grains. Three Sudanese cultivar grains, namely Tetron, Hageen and Feterita- Gedarif, were randomly obtained from the local market of Khartoum North. They were carefully cleaned and freed from dirt, broken, shrunken, immature and infected seeds. Each of the three cultivar grains was decorticated by the different methods of decortication, traditional (Dec. 1), mechanical: familiar (Dec. 2) and the most advanced machine Schule (Dec. 3). All samples, including whole meal, were investigated for their physical and chemical composition, mineral matter and anti-nutritional factors such as tannin and phytic acid. They were also used to prepare a thick porridge (aceda), which was subjected to organoleptic evaluation using the ranking method. The analysis of variance (ANOVA) was performed to examine the significant effect in all parameters measured. Least significant difference (LSD) was used to separate the means. Decortication process was found to decrease significantly the macronutrient contents of sorghum grains, when any of the three methods of decortication was used. The average losses were 13.01, 21.88 and 12.65% in protein; 20.44, 39.26 and 23.32% in ash; 25.14, 42.10 and 30.21% in fat, whereas the average loss in fibre was found to be 27.64, 26.59 and 35.18% and an increase of 4.02, 8.52 and 6.06% in carbohydrates, when the three methods of decortication (Dec. 1, Dec. 2 and Dec. 3) were used, 15 respectively. The higher reduction in nutrients was observed when Dec. 2 was used. The losses in minerals, during decortication, differed in percentages from one mineral to another depending on sorghum cultivar as well as on method of decortication. The decortication process was found to have significant positive effect (P≤0.05) on antinutritional factors such as tannin and phytic acid. The reduction in tannins was found to be 8.95, 13.43 and 9.90%, and 56.09, 37.83 and 52.79% in phytic acid, when Dec. 1, Dec. 2 and Dec. 3 were used, respectively. Sensory evaluation showed preference for colour and texture of aceda prepared from decorticated sorghum flour but not taste or odour. Anyhow, most panelists preferred aceda prepared from decorticated sorghum flour. Based on the results above, it becomes obvious that the best method for decortication which removes only pericarp and may be testa leads to the best quality of product which retains most nutrients indigenous to sorghum and at the same time decreases the antinutritional factors such as tannin and phytic acid is by using the most modern decortication method (Dec. 3), the Vertical Shelling Machine (Schule). 16