Sorghum has a high degree of genetic diversity, and, as such, sorghum grain composition and structure can vary widely. Such variability can be of great benefit in supplying a diversity of uses but can also be a negative when uniformity is desired. Despite sharing similarities to other cereals such as maize and the millets, sorghum has several unique attributes related to the chemistry and composition of the grain. Since grain composition is linked to utilization, this chapter focuses on the basic composition and structure of major grain components and also how such attributes relate to new, upcoming, or potential uses of sorghum.

A method for fractionating sorghum proteins using extraction solvents and techniques designed to obtain polymeric protein structures (especially disulfide linked) was developed. Extraction and separation conditions were optimized in terms of completeness of protein extraction, sample stability, and analytical resolution. After pre-extraction of albumins and globulins, a 3-step sequential procedure involving no reducing agents was applied to ground whole sorghum flour. The three fractions obtained represented proportionally different protein polymer contents and molecular weight distribution as evidenced by comparative size exclusion chromatography. Protein composition also varied among the extracts with differences in kafirin composition and non-kafirin proteins detected in the fractions by RP-HPLC and SDS-PAGE analysis. The ability to quantify and further characterize sorghum polymeric protein complexes will be useful for additional studies linking protein structures with functionality and digestibility and variations for these properties within diverse sorghum germplasm.

Structure and chemistry of sorghum grain S. R. Bean, B. P. Ioerger, J. D. Wilson, M. Tilley, D. Rhodes and T. J. Herald, USDA-ARS, USA1 Introduction2 Physical grain properties3 Chemical composition of grain: starch and proteins4 Chemical composition of grain: lipids and phenolic compounds5 Chemical composition of grain: vitamins and minerals6 Factors that affect grain composition7 Summary8 Future trends9 Where to look for further information10 Acknowledgements11 ReferencesSorghum, almost always introduced as the fifth most important grain in the world, is known for its high degree of genetic diversity, with just over 43 000 accessions held in the USDA germplasm collection alone (Kimber et al., 2013). This diversity is very relevant to the discussion of sorghum grain composition since it results in phenotypes that can include virtually all aspects of grain composition and end-use quality for a wide range of uses spanning food, feed and fuel. The genetic diversity of sorghum may harbour numerous useful genes related to grain composition that, once identified, could be moved into elite adapted lines.

Sorghum is the 5th most widely grown cereal crop in the world and has desirable agronomic traits such as drought resistance and heat tolerance. Sorghum is a major food source in developing nations and is widely used as feed grain in Western countries. There is increasing interest in sorghum food products for people with celiac disease in Western countries as well. Sorghum endosperm proteins are known to have equal or lower in-vitro pepsin digestibility than other cereals in raw flour and substantially lower digestibility in cooked products. The reasons why sorghum proteins are less digestible than that of other cereals have not yet been completely elucidated. However, several factors have been identified that may play a role in determining the digestibility of sorghum including: physical grain structure, protein body structure, protein cross-linking, starch properties, and phenolic content/composition of the grain. The majority of proteins in sorghum endosperm are found in digestion resistant spherical protein bodies that have highly cross-linked outer layers. Disulfide bond mediated cross-linking increases during cooking of sorghum, resulting in the formation of highly cross-linked web-like structures of protein. Protein digestibility has a substantial impact on the nutritional properties of sorghum utilization in the production of human foods, animal feeds, and for bio-industrial uses such as ethanol production. The unique properties of sorghum proteins may also influence the digestion of sorghum starch and could play a role in development of low glycemic index foods.

Surface porous high-performance liquid chromatography (HPLC) columns were investigated for the separation of kafirins, storage proteins of grain sorghum. Kafirins were successfully separated using C3, C8, and C18 surface porous stationary phases in less than 17 min. Separations using a monolithic C18 stationary phase were also developed and were slightly faster than those achieved on the surface porous C18 stationary phase. However, the resolution was higher on the latter column. Using an ammonium hydroxide/acetonitrile mobile phase, separations were performed on a novel, alkaline stable surface porous C18 stationary phase. The resolution at alkaline pH was not as high, however, as with the traditional acidic acetonitrile mobile phases. In comparison to fully porous stationary phases, the surface porous phases provided higher resolution with much lower separation times (17 versus 40 min). Total peak areas were correlated to total protein content of sorghum (r(2) = 0.96; n = 10), and a method to measure in vitro pepsin digestibility using reversed-phase (RP)-HPLC peak areas showed good correlation to the traditional nitrogen combustion method (r(2) = 0.82; n = 20). Thus, the surface porous stationary phases could be used not only for more rapid separations but also to provide simultaneous information on total protein content and digestibility.

time points, P3 progeny had greater (P < 0.009) concentrations of circulating IgG than P1 progeny. Piglet BW did not differ between parities. These results suggest that circulating Ig concentrations in neonatal pigs may be affected by dam parity. It remains to be determined whether the increase in circulating Ig observed in P3 progeny occurred because P3 females had greater capacity to provide passive transfer of Ig during lactation. Additional work is needed to determine whether these effects afford the progeny of dams of increasing parity advantages in health and performance during subsequent growth phases.

Sorghum proteins have the potential to be used as a bio-industrial renewable resource for applications such as biodegradable films and packaging. This project was designed to evaluate the effect of interactions between sorghum protein extraction and precipitation conditions on the yield, purity, and composition of sorghum protein fractions. Proteins were extracted with 70% ethanol under nonreducing conditions, with ultrasound, or under reducing conditions using either sodium metabisulfite or glutathione as the reducing agent. Several conditions were used to isolate the extracted proteins through precipitation, including lowering ethanol concentrations alone or in combination with lowering to pH 2.5, or by adding 1M NaCl to the extract. Combinations of these conditions were also tested. All precipitation conditions effectively precipitated proteins and lowering the pH and adding 1M NaCl to the extracts enhanced precipitation in some cases. However, the conditions that precipitated the maxium amount of protein or highest purity of protein varied according to how the proteins were initially extracted. Precipitated proteins were characterized by RP-HPLC, SEC, HPCE, and SDS-PAGE to compare the protein fractions composition. Nonreduced and sonicated samples had a much wider M-w distribution than reduced extracts. Thus, extraction and precipitation conditions influenced the isolated proteins yield, purity, and composition. Because the extraction and purification processes influenced the composition, purity, and biochemical properties, it may be possible to prepare protein fractions with unique functionalities for specific end-uses.