Chemical and Physical Properties of Breakfast Cereals and Snacks Made from Specialty Sorghums and Sorghum Bran Using Twin Screw Extruder
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Whole ground white, high tannin and black sorghum with and without additional high tannin sorghum bran were used in different proportions to develop ready to eat breakfast cereals and snacks. The effect of extrusion on the phenolic compounds and on in vitro starch digestibility of sorghum based cereals and snacks were observed. Gluten free and gluten containing breakfast cereal and snacks were developed with different physical, chemical and sensory characteristic. By increasing the sorghum and bran level in the formulations, the bulk density of extrudates was increased while expansion ratio was decreased. Bowl life of extrudates was increased up to 18 min. when 60% whole ground white sorghum was used with additional 10% high tannin sorghum bran. Water soluble index was significantly higher for the extrudates without additional bran and decreased as bran was added. A positive correlation between water soluble index and expansion ratio (R^2=0.89) indicated that the more expansion ratio provided a large surface area for water to interact with starch and other soluble components. The retention of total phenols in these extrudates varied from 13-41% and it was found that extrudates with additional high tannin sorghum bran had more total phenols than extrudates without it. Sorghum extrudates showed a significant reduction in antioxidant activity varied from 21-83%. Similarly, the effect of extrusion on condensed tannins was detrimental, and their retention was ranged from 12-28%. The smaller particle size of ground sorghum increased the surface area of contact between composite flour components and extruder barrel which promoted interactions during extrusion, lowering condensed tannins and antioxidant activity. All sorghum based extrudates had significantly (P<0.05) lower starch digestibility than that of corn flour extrudates. All types of sorghum had non-significant difference in starch digestibility from 0.5-2hrs. After 16 hrs., high tannin sorghum extrudates had the lowest starch digestibility (79%), which was significantly different from other sorghum types. There was a negative correlation between the rapid digestible starch and tannin contents (R^2=0.62). Breakfast cereals made from different types of sorghum and bran levels were statistically equally rated in taste and overall acceptability.