Screening Assay For Impacts Of Soaking And Malting On Functional Properties And Macromolecular Changes Of Sorghum "Sorghum Bicolor L. (Moench)"

Sorghums are rich sources of micronutrients such as minerals and vitamins; and macronutrients like carbohydrates, proteins and fat. Sorghum has a resistant starch, which makes it interesting for obese and diabetic people. In addition, sorghum may be an alternative food for people who are allergic to gluten. Malts sorghum display a-amylase andβ-amylase activities comparable to those of barley, making them useful for various agro-industrial foods. The feature of sorghum as a food in developing as well as in developed countries is discussed. This work makes a particular emphasis on the impact of soaking and malting on sorghum macromolecules in the use of sorghum for infants thin porridges, granulated foods, local beer, as well agro-industrial foods such as lager beer and bread.The work starts by optimizing steeping and germination condition and their effect on sorghum grain in term of malt loss, soluble solid (SS) yield, cold paste viscosity, amylase activity, tannin and protein content. The factors studied included time and temperature of soaking with temperature and time of germination. Germination significantly affected the increase in malt loss, SS yield, amylase activity, and protein content with a decrease in cold paste viscosity and tannin content of sorghum. Optimum conditions for sorghum were:steeping time for 24 h at 31℃and 4.5-days of germination at 30℃. Values predicted at optimum conditions by the response surface model for all responses were experimentally tested and close agreement between experimental and predicted values was observed. The flour yield was evaluated and sorghum flour was significantly enhanced by 3-days germination of the seeds. The increase in flour yield resulted from the brittle nature of the malted seeds which improved flour extraction. Volatile compounds were detected in the sorghum flour and 16 peaks were detected in raw seed with 14 volatile compounds. Soaking and germination generated some new volatiles and 20,23 and 25 peaks were identified in SSG,3DGS and 5DGS respectively. Some aldehydes, ketones, esters and acids were generated and increased during the time of germination. Malted sorghum flour was sweet and floral due to the higher content of ethyl acetate,3-methylbutanal, pentanal,2-pentanone, acetic acid,2-methylpropyl ester, butyl acetate, hexanal, 1-octen-3-ol, benzaldehyde.Sorghum grains have naturally occurring anti-nutritional factors, such as phytic acid, tannin that decrease their dietary availability. This work determined the effect of wooden ash extract on anti-nutritional factors and also was conducted to assess the effect of soaking and malting on nutritional properties of sorghum flour. The addition of wooden ash extract during 24 h of soaking resulted in significant decrease in tannin by 50.2% and the decrease was observed to be progressive as malting time increases. Five days of malting resulted in significant decrease in tannin by 69.3% and phytic acid by 66.4% with slight decrease in ash, lipid, fiber and starch. Malting significantly improved the quantity of protein and essential amino acids and sugars analysis showed a significant increase of maltose, glucose and fructose. In vitro protein digestibility was markedly increased with the malting time increases and structural analysis of sorghum starch showed porosity on granule's surface susceptible to the amylolysis.Influence of grain germination on functional properties of sorghum flour was evaluated for five days and protease and amylase activities were measured. Results showed that flour obtained from the 3-days germinated sorghum grain had high protease and amylase activities. The functional properties of flours derived from the germinated sorghum seeds were studied and ungerminated seeds were used as a control. Germinated samples had a higher protein solubility compared with the control, and the highest solubility occurred at pH 6. Germination also increased the protein solubility index of sorghum flour. Germinated sorghum flour had a least gelation concentration of 8% compared with 18% for the control. The bulk densities of germinated flours were lower compared to the ungerminated one. Water and oil capacities were increased by germination from 131% and 90% to 142% and 108%, respectively after three days of germination. The emulsifying activities and stabilities of the germinated samples increased significantly. In addition, germination improved the foamability of sorghum flour from unfoam flour to a flour with foam after three days of germination; and the foaming capacity and stability increased significantly with increasing germination time. Thus, the study indicated that germination improved the functional properties of sorghum and it would be possible to design new foods using germinated sorghum.Ultrasonic technology was applied for starch extraction from the malted sorghum and response surface methodology (RSM) was used to optimize the effects of processing parameters on starch yields. Three independent variables were ultrasonic power (X1), extraction time (X2) and ratio of water to raw material (X3), respectively. The statistical analysis indicated that three variables and the quadratic of X1 and X2 had significant effects on the yields, and followed by the significant interaction effects between the variables of X2 and X3 (p<0.05). A mathematical model with high determination coefficient was gained and could be employed to optimize starch extraction. The optimal extraction conditions of starch were determined as follows:Ultrasonic power 600 W, extraction time 4 min, ratio of water to raw material 30:1 (v/w). Under these conditions, the experimental yield of starch was 17.08±0.33%, which was agreed closely with the predicted value 17.06%. Extracted starch from soaked and malted sorghum was studied to understand their physicochemical and functional properties. The swelling power (SP) and the water solubility index (WSI) of both starches were nearly similar at temperatures below 50℃, but at more than 50℃, the starch isolated from malted sorghum showed lower SP and high WSI than those isolated from raw and soaked sorghum. The pasting properties of starches determined by rapid visco-analyzer (RVA) showed that malted sorghum starch had a lower viscosity peak value (86 BU) than raw sorghum starch (454 BU). For both sorghum, X-ray diffractograms exhibited an A-type diffraction pattern, typical of cereal starches and the relative degrees of crystallinity ranged from 9.62 to 15.50%. Differential scanning calorimetry (DSC) revealed that raw sorghum starch showed an endotherm with a peak temperature (Tp) at 78.06℃and gelatinization enthalpies of 2.83 J/g whereas five-day malted sorghum starch had a Tp at 47.22℃and gelatinization enthalpies of 2.06 J/g. Storage modulus (G') and loss modulus (G") of all starch suspensions increased steeply to a maximum at 70℃and then decreased with continuous heating. The structural analysis of malted sorghum starch showed porosity on the granule's surface susceptible to the amylolysis. The results showed that physicochemical and functional properties of sorghum starches are influenced by soaking and malting methods.A mathematical model with high determination coefficient was gained and could be employed to optimize protein extraction of malted sorghum flour. Four independent variables were ultrasonic power, pH, extraction time and solvent/meal ratio was used. Selected response which evaluated the extraction process was protein yield and the second-order model obtained from protein yield revealed a coefficient of determination of 0.967%. The optimal extraction conditions of protein were determined as follows: Ultrasonic power, pH, and extraction time and solvent/meal ratio were 400 W,8,40 min, and 20:1 (v/w), respectively. Protein yield was primarily affected by ultrasonic power, pH and solvent/meal ratio. These conditions resulted in protein yield of 5.43 g of soluble protein from extract/100 g malted sorghum flour which was agreed closely with the predicted value 5.36%. The adequacy of the model was confirmed by extracting the protein under optimum values given by the model and the results may help in designing the process of optimal protein extraction from malted sorghum flour. Sorghum protein extracted was followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The quantitative measurement of free amino acids in the sample was made using the ninhydrin reaction and thermal properties of protein were evaluated using DSC. The SDS-PAGE results showed that levels of high-molecular-weight aggregates increased after soaking. This behavior shows the enhancement of prolamin extractability and concentration in sorghum as a result of starch degradation. The 66.2 kDa oligomer concentration remained constant when sorghum is soaked and showed a significant decrease after 3 days of germination and remain constant after 5days malting. The 43.0 kDa oligomer concentration remained constant when the sorghum is soaked thereafter decreases slightly, reaching 31.0 after 3 and 5 days of germination. It was also found that 5 day malt led to a fourfold increase in free amino acid content. These modifications are due to intrinsic lipases, proteases and amylases. Germinated sorghum protein possessed the highest differential scanning calorimetry result (peak temperature of 84.30℃, delta H = 3.05 J/g) and raw seed protein had the lowest (peak temperature 70.83℃, delta H= 3.09 J/g). Germinated sorghum proteins are potential functional food ingredients.To estimate the antioxidant activity of soaked and malted sorghum, the DPPH and ABTS were used. Antioxidant activity was significantly affected by sorghum soaking and germination. As studied before raw sorghum grain had high content (p<0.05) in tannin and phytic acid. These sorghums had significantly high antioxidant activity. Raw sorghum grain had the highest (P< 0.05) DPPH radical scavenging activity (21.0μM Trolox/100 g of dw), followed by soaked sorghum (18.8μM Trolox/100 g of dw), then 3-days malted sorghum (13.0μM Trolox/100 g of dw) and lastly 5-days malted sorghum (11.2μM Trolox/100 g of dw). Malted sorghum had significantly decreased antioxidant activity. Antioxidant activities of malted sorghum as measured by ABTS ranged from 3.1μM Trolox/100 g of dw for the raw sorghum grain to 2.3μM Trolox/100 g of dw for the soaked sorghum. The 5-days malted sorghum gave the lowest ABTS radical scavenging (1.6μM Trolox/100 g of dw) followed by 3-days malted sorghum grainThese findings show that it is possible to use the sorghum macromolecules and selecting the most suitable sorghum flour properties for specific food processing.