Factors affecting sorghum protein digestibility

In the semi-arid tropics worldwide, sorghum (Sorghum bicolor (L.) Moench) is cultivated by farmers on a subsistence level and consumed as food by humans. A nutritional limitation to its use is the poor digestibility of sorghum protein when wet cooked. The factors affecting wet cooked sorghum protein digestibility may be categorised into two main groups: exogenous factors (grain organisational structure, polyphenols, phytic acid, starch and non-starch polysaccharides) and endogenous factors (disulphide and non-disulphide crosslinking, kafirin hydrophobicity and changes in protein secondary structure). All these factors have been shown to influence sorghum protein digestibility. More than one factor may be at play at any time depending on the nature or the state in which the sorghum grain is; that is whether whole grain, endosperm, protein body preparation, high-tannin or condensed-tannin-free. It is proposed that protein crosslinking may be the greatest factor that influences sorghum protein digestibility. This may be between ?- and ß-kafirin proteins at the protein body periphery, which may impede digestion of the centrally located major storage protein, a-kafirin, or between ?- or ß-kafirin and a-kafiri

Genetic Enhancement Perspectives and Prospects for Grain Nutrients Density

Diet-induced micronutrient malnutrition continues to be a major challenge globally, especially in the developing world. With the ever-increasing population, it becomes a daunting task to feed millions of mouths with nutritious food. It is time to reorient agricultural systems to produce quality food to supply the calorie and nutrient requirements needed by the human body. Biofortification is the process of improving micronutrients density by genetic means. It is cheaper and sustainable and complements well with the nutrient supplementation and fortification— the short-term strategies that are currently deployed to address the micronutrient malnutrition. Sorghum is one of the important food crops globally, adapted to semi-arid tropics, and there is increased awareness on its nutritional importance. Further, there is great opportunity to improve sorghum for nutritional quality. This chapter deals about the genetic enhancement perspectives and prospects for improving the nutritional quality with main emphasis on grain micronutrient density in sorghum

Starch Properties of Barnard Red, a South African Red Sorghum Variety of Significance in Traditional African Brewing

Starch was isolated from Barnard Red (a South African sorghum variety) and a Chinese sorghum sample. Starch and flour properties (gelatinization, pasting, and gel texture) were compared with those of a standard corn starch. Significant findings were: 1. Barnard Red starch had lower gelatinization temperature than either Chinese sorghum or corn starch; 2. starch gels of corn and Barnard Red were of similar hardness; 3. Barnard Red starch pastes had very high viscosity compared to corn and Chinese sorghum; 4. Barnard Red starch shear-thinned more than its flour paste in the absence of amylase activity.link_to_subscribed_fulltex

Starch properties as affected by sorghum grain chemistry

To determine the relationship between sorghum grain polyphenol content, grain structure, and starch properties, starch was isolated from 10 sorghum varieties using an alkali steep and wet-milling procedure. SV2, a tannin-free variety with white pericarp, gave a white starch. Varieties having red or white pericarp and higher polyphenol levels gave pink starches. Hunter colour values (L, a, b) of starches were not correlated with grain polyphenol content. Grain appearance in terms of pericarp colour, or presence or absence of pigmented testa, did not relate to the intense pink colouration of sorghum starches. Starch amylose content was significantly negatively correlated (γ = -0.88, p < 0.001) to grain floury endosperm texture. Sorghum starches had higher peak viscosity (PV) in pasting than commercial maize starch. The time taken to reach peak viscosity from the initial viscosity rise was less for sorghum starches than maize starch. However, sorghum starches had a higher rate of shear thinning (Rst) than maize starch. There was a significant positive correlation between grain polyphenol content and starch PV (γ =0.75, p <0.05). Starch gel hardness was negatively correlated to pasting properties of Rst and paste breakdown (γ = -0.78 and -0.77 respectively) at p < 0.01. Peak gelatinisation temperature (Tp) occurred over a narrow range from 66 to 69°C. Tp was negatively correlated to the floury endosperm portion of the grain (γ = -0.77) at p <0.01. It is concluded that sorghum grain polyphenol content and grain characteristics influence its starch properties. © 2000 Society of Chemical Industry.link_to_subscribed_fulltex

Effect of steeping treatment on pasting and thermal properties of sorghum starches

Chemical treatments in wet milling could improve the physico-chemical properties of starch isolated from high-tannin sorghums. Sorghums Chirimaugute (medium-tannin), DC-75 (high-tannin), and SV2 (tannin-free) were steeped in water, dilute HCl (0.9%, v/v), formaldehyde (0.05%, v/v), and NaOH (0.3%, w/v) solutions before wet milling and starch separation. Pasting, textural, and thermal properties of starch were determined. Steeping in NaOH resulted in starches with higher peak viscosity (PV), cool paste viscosity (CPV), and setback than when water, HCl, and formaldehyde were used. The time to PV (Ptime) and PV temperature (Ptemp) were markedly reduced by treatment with NaOH. NaOH could have caused a degree of pregelatinization. HCl treatment gave starches with higher Ptemp and Ptime, presumably due to delayed granule swelling. Gel hardness was largely determined by the starch amylose content. The low hardness of DC-75 starch gels was slightly improved in NaOH-treated grains. Gelatinization temperatures of sorghum starches were generally low, regardless of steeping treatment. Starch from NaOH-treated grain generally had slightly higher gelatinization temperatures than when water, HCl, or HCHO was used. Chemical treatments during steeping of sorghum grains greatly affected starch properties. Dilute alkali steeping during wet milling could be used to improve properties of starch isolated from tannin-containing sorghums.link_to_subscribed_fulltex

FTIR and Solid State13C NMR Spectroscopy of Proteins of Wet Cooked and Popped Sorghum and Maize

Fourier transform infrared (FTIR) and solid state13C NMR spectroscopic methods were used to investigate changes in maize and sorghum proteins on wet cooking and popping. FTIR spectra indicated that wet cooking led to proteins in two normal sorghums, namely NK 283 (a red hybrid) and KAT 369 (a white variety), two sorghum mutants (P850029 and P851171) and a maize hybrid (PAN 6043) assuming more antiparallel intermolecular ß-sheet character, possibly at the expense of some a-helical conformation. Solid state13C NMR, using the technique of Cross Polarisation Magic Angle Spinning showed shifts of the protein carbonyl carbon and a-carbon resonances upfield on wet cooking in all samples, also indicating a change in protein secondary structure from a-helical to ß-sheet conformation. The extent of secondary structural change on wet cooking seemed to be greater in sorghum than in maize and may have a bearing on the inferior protein digestibility of wet cooked sorghum compared to maize. Popping produced the same secondary structural change as observed for wet cooking in both sorghum and maize. However, the extent of change on popping was less than on wet cooking in sorghum and maize