INFLUENCE OF ULTRASOUND TEMPERING ON FLOUR QUALITY OF WHITE AND SUMAC SORGHUM MILLED ON A ROLLER MILL

A BSTRACT . Sorghum, a nutritious and gluten-free cereal crop, is currently underutilized. The absence of standardized milling technology contributes to the low utilization of sorghum in food. Most existing milling methods adopted from other crops yield inferior flour quality with excessive endosperm loss. However, implementing appropriate tempering techniques prior to roller milling can enhance flour characteristics and yields. In this study, a roller milling technology was developed using a laboratory-scale roller mill to produce high-quality sorghum flour suitable for gluten-free applications. Ultrasound treatments were conducted using a probe-type ultrasound device with a frequency of 20 kHz and a power level of 600 W. The kernels were soaked in water (1:1 w/v) and subjected to ultrasound treatment set at 75% amplitude for 1, 1.5, and 2 min. After treatment, the kernels were drained, surface dried, and tempered for 24 h in sealed polythene bags to achieve a target moisture level of 17%. The effect of UST on milling and flour characteristics of a non-tannin white and red-tannin sorghum was investigated. The results were compared to sorghum milled using a standard tempering process (17% moisture). Ultrasound tempering (UST) significantly impacted milling and flour quality in terms of milling yield, particle size, damaged starch, and ash content. UST resulted in a significant reduction in the hardness index of both the white sorghum (72.6-73.6 from 79.02 (control)) and the red-tannin sumac sorghum (76.2-78.29 from 84.5 (control)). Notably, the milling yield of the white sorghum showed a significant increase with treatment durations, from 73.3% (control) to 76.6%-78.2%. The red-tannin sumac sorghum milled using the 1 min UST resulted in a higher bran yield (5.8%) compared to the standard tempering method (1.7%), indicating an improvement in milling efficiency. The 1 min UST resulted in efficient bran separation and improved ash contents for both the white (0.87%) and red-tannin sumac (0.69%) sorghum, as compared to their respective controls (1.05% and 1.4%). The principal component analysis clearly defined the inter-relationship among the treatment groups and analyzed parameters for both kernel and flour properties. Overall, the developed milling flowsheet was suitable for both the white and red-tannin sumac varieties, regardless of their differences in physical properties, and the use of UST has significantly improved the flour quality of both samples.