HYDRATION KINETICS OF SORGHUM GRAINS AND PHYSICOCHEMICAL PROPERTIES OF “OGI” AS INFLUENCED BY VARIETY AND GRAIN SOAKING METHODS

Abstract

The hydration kinetics of selected varieties of sorghum grains and physicochemical properties of “ogi” prepared from them were investigated .The four sorghum types used for the study were Samsorg 14, Samsorg 41, Samsorg 42 and a market sample; all obtained from the Institute of Agricultural Research (IAR), Samaru, Zaria, Kaduna State; except the market sample which was obtained from Oja Oba market, Akure. Three traditional grain soaking methods peculiar to “ogi” production were employed and these were SGCW (soaking of grains in cold water); PHWG (pouring of hot water on grains); and IBG (initial boiling of grains for 5 minutes). During soaking, the moisture uptake and density changes in the grains were determined at hourly basis and the evaluation terminated when the equilibrium moisture content (EMC) was attained. The various sorghum grains were fermented into “ogi”, a fermented paste and later oven-dried at 60 oC for 18 h. The dried samples were investigated for physicochemical properties and pasting properties using standard methods. There were variations in the proximate composition of sorghum grain types which include moisture (8.53 ─ 9.78%), ash (1.11 ─ 1.41%), fat (2.86 ─ 3.31%), fibre (2.25 ─ 2.41%), protein (13.45 ─ 14.11%) and carbohydrate (79.13 ─ 79.93). There were also variations in the amylose content (18.87 ─ 20.61%) and grain weight (2.51 ─ 3.64 g⁄ 100 grains) of the sorghum grain types. The various grain types used in the study showed that the quantity of water absorbed (y) by the soaking grains over time (x) varies widely with each other. The density changes occurring in the soaking sorghum grain types exhibited diverse regression patterns involving linear, exponential and logarithm regressions. The swelling power and solubility of “ogi” from the various sorghum grain types showed variations even at the same temperature. The swelling power of “ogi” from Samsorg 14 at 45 oC was 2.87, 2.98 and 3.10 g⁄g for SGCW, PHWG and IBG methods respectively. Similarly, the solubility of “ogi” from Samsorg 14 at 60 oC was 1.90, 2.05 and 2.10 g⁄g for SGCW, PHWG and IBG methods respectively. The pasting properties of “ogi” from the sorghum grain types using different traditional soaking methods showed variations in all the pasting properties. The variations in the pasting properties of Samsorg 14 include 16.13 ─ 54.03 RVU (peak viscosity), 1.90 ─ 6.47 RVU (breakdown viscosity) and 17.63 ─ 43.80 RVU (setback viscosity). All other samples exhibited a similar trend. The pH of “ogi” obtained from various sorghum grain types using the traditional soaking methods showed little variations. The pH of “ogi” from Samsorg 14 was 4.90, 4.86 and 4.97 using SGCW, PHWG and IBG methods respectively. The water holding capacity of “ogi” from the sorghum grain types also varied from each other, which were 282%; 292% and 284% for SGCW, PHWG and IBG methods respectively (Samsorg 14). The research work concluded that the various sorghum grain subjected to different traditional soaking methods exhibited diverse patterns in water absorption, density changes and physicochemical properties of “ogi” obtained from the grains. These observations might serve as a good tool for the industrial utilization of the sorghum grains used in this study.