Influence of processing on digestibility and nano-molecular basis of sorghum grain

Thermal process reduces protein digestibility in the rumen via denaturing the protein and formation of protein-protein and protein-carbohydrate bonds (Anonymous 2001). Dandy et al. (1995) also concluded wet sorghum baking reduced digestibility. Preston (1998) reported that processing and steaming of corn and sorghum grains reduced solubility of proteins. Also, access to lysine amino acids reduced by flakes density reduces. Scanning electron micrographs in all three treatments showed that processing destructed protein matrix and increased enzymes access to starch granules and increased their digestibility. In steam flaking treatment, granule surfaces were attacked by microorganisms and protein matrix destructed more than other treatments. Also, terminal processing in all three treatments gelatinated the starch and increased average of scale of granules. In addition to the importance of starch digestion, the increase in viscosity during gelatinization may also positively affect physical quality of processed feeds through increasing in binding between feed particles. Svihus et al. (2004) reported that pelleting can improve feed integrity by increasing binding between particles. Gelatinization of starch greatly increases α-amylase accessibility to amylose and amylopectin glucose chains and so, increases the rate of starch digestion. The number of created orifices is explanatory for degradability values. Benmoussa et al. (2006) concluded that number and scale of granules have positive effects on digestive properties. In this study, despite of smaller number and smaller size of orifices in steam flaking treatment than other treatments (against further degradability of steam flaking than others treatments), SEM images of incubated steam flaking showed that granules were processed completely. Therefore, lots of uniformity and meltingcan be justified as its high degradability. Conclusion: Electron microscopy images showed that the number and size of holes (nano-sized) per unit area of ​​treatments were highly correlated with the degree of degradability. Steam flaked treatment has caused more gelatinization in starch granules as the size of the granules has increased more than the control treatment and other treatments. Steam flake processing shows better degradability properties than other treatments and provides higher amounts of nutrients to microorganisms.