The protein content in sorghum can be comparable to the protein content of wheat [5,16]. However, Tasie and Gebreyes [17] found a wide range of 8.20–16.48% between different sorghum whole grain varieties. Attempts have often been made to identify correlations between nutrients and the sorghum kernels color. Whether the protein content differs between red and white sorghum is still poorly understood. A research of Galan et al. [18] detected a higher protein content in red whole grain sorghum flour, while Yousif et al. [19] and Srichuwong et al. [20] figured out a higher protein content in whole grain white sorghum flour.

In sorghum protein the predominant fraction is the prolamin fraction, which is called kafirin. According to a study almost half of the sorghum protein belonged to the kafirin fraction (47.7%), followed by the glutelin fraction (24.1%) and the albumin and globulin fraction (18.8%) [21]. Regarding the kafirins, four types of kafirins, occurring in form of protein bodies, can be mentioned: alpha-, beta-, gamma-, and delta-kafirin. Alpha-kafirins are the most common kafirins found in sorghum [10,22]. Detailed amino acid analyses have been carried out by Mohapatra et al. [23]. The most common amino acids found in whole grain sorghum were glutamic acid (44.38 mg/100 g protein), arginine (28.34 mg/100 g protein), aspartic acid (20.50 mg/100 g protein), leucine (16.50 mg/100 g protein) and glycine (16.22 mg/100 g protein) [23]. The limiting acid is lysine, as for most other true cereals [24].

Sorghum proteins have been gaining much attention due to their ability to crosslink, in particular upon cooking. Authors believe that this kafirin cross linking is connected to low protein digestibility of sorghum. In this context a comparison of the digestion of kafirins and zeins was performed by Emmambux and Taylor [9]. The authors analyzed the digestibillity of sorghum and maize meal as well as the digestibillity of aqueous tertiary butanol extracted kafirin and zein. In order to evaluate the influence of heat on sorghum and maize digestibillity, the samples were undertaken a boiling and a pressure cooking treatment. Already in the untreated state, the maize meal and extracted zeins showed a higher digestion rate than the sorghum meal and kafirins. However, after boiling and pressure cooking this difference was even more obvious. Authors detected that sorghum kafirins (obtained from decorticated sorghum kernels) were more polymerized by disulfide bridges during the cooking process than the zeins [9]. Same authors further pointed out, that sorghum proteins were not only able to form complexes between each other, but also had the ability to connect with condensed tannins and tannic acids [25]. This leads to the suggestion that sorghum kernel dehulling or the usage of condensed tannin free sorghum varieties might offer a higher digestibillity. However, crosslinking interactions According to Hamaker and Bugusu [10] sorghum proteins are embedded within protein bodies and therefore hard to access, but on the other hand they may show viscoelastic behavior in food. However, several questions remain unanswered at present. Fundamental investigations are still needed in order to determine the properties of kafirins.

Carbohydrate amounts between 67.5–76.4% were found in different whole grain sorghum varieties from Ethiopia [17]. Pontieri et al. [26] found that five varieties of refined sorghum, which were grown in Italy, the USA or Uganda, had an average carbohydrate content of 75.23% in dry matter. Starch is the main component of carbohydrates and is located in the endosperm. Srichuwong et al. [20] reported a starch content of 72.2% and 73.8% in dry matter in white and red whole grain sorghum, with amylose contents of 25.8% and 24.6% respectively. However, there is a wide range of amylose content in sorghum varieties, and even waxy varieties, which have high amylopectin contents occur in the wild [27]. The diameter of starch granules was measured to be between 5–35 µm and they appeared as polygonal and spherical [20], but also more unusual granules shapes, which researchers called “doughnut-shaped”, were occasionally discovered in sorghum kernels [28]. Miafo et al. [29] determined the content of free sugars in sorghum refined flour of 30.35 mg/g sorghum flour. Sucrose made up the largest proportion (12.42 mg/g), followed by maltose (4.25 mg/g) and fructose (4.22 mg/g). The usage of sorghum flour might offer a sugar reduction possibility in bakery products as it has already a unique sweet taste itself. As humans are tending more and more towards balanced diets, sensory trials are required in order to state if sorghum can partially replace household sugar.

Whole sorghum contains a notable amount of dietary fibers, which is mostly located in the outer layers of the sorghum kernel. A study carried out in 2012 showed a total dietary fiber content between 9.13–15.09 g/100 g that has been detected in eight sorghum varieties, whereby the soluble fiber part ranged between 0.15–0.88 g/100 g [30]. Authors compared the fiber content determined in whole grain sorghum, dehulled sorghum and sorghum bran. It was found that the bran fraction had the highest value with 41.38 g/100 g, followed by 26.34 g/100 g in whole grain sorghum and 11.53 g/100 g in hulled sorghum [31].

Whole grain sorghum flour is known for its high fat content (3.5%) especially compared to wheat (2% in whole wheat) [3]. Fat is mostly located in the sorghum germ (Taylor, 2003). The most common fatty acids are linoleic acid (18:2), followed by oleic acid (18:1) and palmitic acid (16:0), with average contents of 43.86%, 37.98% and 13.07% in refined sorghum flour, respectively [26]. The ratio of saturated to unsaturated fatty acids was found to be 0.27–0.37 [32]. Knowledge is lacking if high fat contents in sorghum flour play a crucial role within shelf life. However, [33] were able to extend the storage time of sorghum flour from 15 days to several months by means of heat treatments. As sorghum is mostly harvested in Africa, knowledge about sorghum milling in the Western countries was rare until very recently. It was not clear whether a high fat content in sorghum brings difficulties within a milling process. However, in 2021 authors concluded that sorghum flour can be provided via commercial wheat mills [15].

Sorghum is known for having a valuable micronutrient profile. Istianah et al. [5] determined 1.64% ash in dehusked sorghum. However, it seems that micronutrient contents vary to a great extend among different varieties [17,34]. Tasie and Gebreyes (2020) identified ash contents between 1.1–2.3% in dry matter of different whole grain sorghum flours from Ethiopia. Regarding the micronutrients, amounts of phosphorus ranged between 112.5–327.7 mg/100 g, of sodium between 2.2–6.2 mg/100 g, of magnesium between 62.0–207.5 mg/100 g and of calcium between 9.5–67.2 mg/100 g [17]. Varieties with a particularly high mineral content exist, like for example the variety Tabat with phosphorus quantities of 350 mg/100 g, sodium of 14.5 mg/100 g, magnesium of 329 mg/100 g and calcium of 24.5 mg/100 g extracted sorghum flour [35].

Although people in the Western hemisphere are increasingly turning to alternative cereals with valuable ingredients, like amaranth or buckwheat, sorghum is still unknown. However, sorghum also offers a lot of promising health-promoting components. A review pointed out that especially sorghum polyphenols, as they have antioxidative effects, can help preventing chronic diseases, like improvement of insulin sensitivity, reduction of fat accumulation, or reduction of mild chronic inflammation [36]. Therefore, many research studies are interested in measuring the polyphenol content of sorghum, regardless of the research question. It can be stated with certainty, that polyphenols vary enormously among the biodiversity of sorghum. However, despite this interest, little research tended to focus on the context between polyphenols and sorghum colors. While researchers found that the polyphenol content of whole grain wheat (92.4 mg/100 dry matter) and whole grain white sorghum (95.2 mg/g dry matter) was similar, whole grain red sorghum had a significantly higher content of 203.5 mg/g dry matter [20]. Higher polyphenol levels in whole grain red sorghum flour than in whole grain white sorghum flour were confirmed by further studies [19,37]. If polyphenols are determined in more detail, flavonoids and phenolic acids are mainly mentioned. Wide ranges of phenolic acids were reviewed in the past. However, in red sorghum, as well as in white sorghum, ferulic acid was found to be the most predominant phenolic acid [38]. Among all flavonoids, special attention has been paid to the tannins, chemically named proanthocyanidins. Tannins are known to reduce sorghum digestibility [8]. There are low tannin and high tannin sorghum varieties, both naturally occurring. Tasie and Gebreyes [17] examined 35 whole grain sorghum flours from Ethiopia and detected tannin contents between 1.3–3337.2 mg/100 g dry matter. They also reported that condensed tannins and tannin acids in sorghum can form complexes with kafirins. Such a complex formation is one reason to lower sorghum protein digestibility. There was no evidence that other phenolic compounds, such as catechin or flavonoids, can bind kafirin [9]. A decreased protein digestion of tannin containing sorghum compared to non-tannin sorghum was also detected by Wedad et al. [39]. As condensed tannins are not present in wheat [14], it is questionable if using tannin rich sorghum varieties in a wheat blend leads to nutritional advantages. Besides phenolic acids and flavonoids, carotenoids also offer antioxidant properties. Luteolin, zeaxanthin and beta-carotene were found in amounts of 122.3 mg/kg, 25.2 mg/kg and 27.0 mg/kg, respectively, in white sorghum [40].