Sorghum: An Underutilized Cereal Whole Grain with the Potential to Assist in the Prevention of Chronic Disease

Exploring the nutritional and phytochemical potential of sorghum in food processing for food security

Purpose

Sorghum is quite comparable to wheat, rich source of nutrients with various health benefits, and therefore considered as a grain of future. The purpose of this paper is to review the bioactive active compounds, health benefits and processing of the sorghum. Sorghum is utilized for animal feeding rather than the human food usage. Therefore, this paper focuses on the emerging new health foods with benefits of the sorghum.

Design/methodology/approach

Major well-known bibliometric information sources searched were the Web of Science, Google Scholar, Scopus and PubMed. Several keywords like nutritional value of sorghum, bioactive compounds present in sorghum, health benefits of sorghum and processing of sorghum were chosen to obtain a large range of papers to be analyzed. A final inventory of 91 scientific sources was made after sorting and classifying them according to different criteria based on topic, academic field country of origin and year of publication.

Findings

From the literature reviewed, sorghum processing through various methods, including milling, malting, fermentation and blanching, bioactive compounds, as well as health benefits of sorghum were found and discussed.

Originality/value

Through this paper, possible processing methods and health benefits of sorghum are discussed after detailed studies of literature from journal articles.

Low-tannin white sorghum contains more digestible and metabolisable energy than high-tannin red sorghum if fed to growing pigs

The present study was conducted to determine and compare the digestible (DE) and metabolisable energy (ME) and the apparent total tract digestibility (ATTD) of gross energy (GE) in yellow-dent corn, three low-tannin white sorghum cultivars and three high-tannin red sorghum cultivars when fed to growing pigs. Forty-two barrows (34.8 ± 3.1 kg bodyweight) were housed in metabolic crates and allotted to one of seven diets with six pigs per diet in a completely randomised design. The seven diets were formulated to contain 969 g/kg of corn or one of the six sorghum cultivars as well as 31 g/kg vitamin and minerals. Faeces and urine were collected for 5 days following a 7-day adaptation period. The DE and ME were lower (P < 0.05) for red sorghum than for corn while the values for corn were lower (P < 0.05) than those obtained for white sorghum. The ATTD of GE for pigs fed corn was higher (P < 0.05) than for pigs fed red sorghum but was lower (P < 0.05) than the ATTD of GE for pigs fed white sorghum. Tannin had a high negative correlation with DE and ME (both, r = –0.99; P < 0.01) and the ATTD of GE (r = –0.92; P < 0.01). The DE, ME and ATTD of GE were positively correlated with CP (P < 0.05), and negatively with kafirin/CP and phenols (P < 0.05). However, tannin was negatively correlated with CP (r = –0.85; P < 0.05), or positively with kafirin/CP (r = 0.88; P < 0.01) and phenols (r = 0.77; P < 0.05). Therefore, tannin content in sorghum may be the main anti-nutritional factor. The overall results of this study indicate that low-tannin white sorghum varieties are superior to high-tannin red sorghum varieties for use as an energy source in diets fed to growing pigs, and high-tannin red sorghum varieties should be incorporated into pig diets to ease the demand pressure on corn only if favourably priced in terms of their DE and ME values.

Parboiling of sorghum grains as a strategy to improve endosperm yield and mineral content of refined flours

The aims were (i) to optimize the parboiling/decorticating process by assessing the effects of parboiling soaking temperature (60-80 ℃) and pearling time (4-6 min and 5.5-9.5 min for red and white sorghum) on endosperm yield and ash content, to obtain pregelatinized refined flours from parboiling sorghum (RF-PS) and (ii) to evaluate the final content of selected nutrients in RF-PS obtained in these optimal conditions. Endosperm yield decreased with the increase of pearling time, and a maximum around 70 ℃ soaking temperature was observed. Ash content decreased with increasing soaking temperature and pearling time. The optimal conditions of soaking temperature-pearling time were 73.3 ℃-4.8 min for red sorghum and 67.9 ℃-8.6 min for white sorghum, considering maximum endosperm yield and ash content lower than 0.65 g/100 g. In RF-PS obtained under optimal conditions, protein, lipid, Cu, and free polyphenols were higher in red sorghum than white sorghum (10.16 ± 0.62 vs. 9.42 ± 0.61 g/100 g, 0.89 ± 0.16 vs. 0.62 ± 0.11 g/100 g, 2.08 ± 0.21 vs. 1.88 ± 0.20 mg/kg, 79.51 ± 14.51 vs. 63.82 ± 4.33 mg/100 g). Fe, Zn, Ca, and Na were higher in white sorghum than red sorghum (20.61 ± 2.92 vs. 17.56 ± 0.98 mg/kg, 11.94 ± 0.84 vs. 9.58 ± 1.65 mg/kg, 87.45 ± 12.91 vs. 75.31 ± 12.57 mg/kg, 129.62 ± 9.03 vs. 102.69 ± 28.34 mg/kg). No difference was observed in the contents of ash, Mg, and K. It was possible to improve endosperm yield using a parboiling process prior to decortication. In addition, this process contributes to increase the mineral content in RF-PS.

Effect of different processing conditions on proximate composition, anti-oxidants, anti-nutrients and amino acid profile of grain sorghum

The effect of different processing conditions (B: boiling; F: LAB fermentation; FS: fermentation and steaming; FSF: fermentation, steaming, flaking) of whole grain sorghum on the proximate composition, antioxidants, anti-nutrients, and amino acids (AAs) was evaluated. A marginal increase in the protein content and a decrease in the fat content was observed in the F-sample. Total phenolics reduced by 28%; DPPH scavenging activity and CUPRAC activity increased by 1.4 and 6 times, respectively during fermentation. Tannin content reduced by 30-39%, for the F, FS and FSF samples; highest reduction in trypsin inhibitory activity (58%) was observed in the FS-sample. Total AAs increased by 2.9 folds in FSF samples. Grain sorghum contained mostly hydrophobic AAs (30-34%). The ratio of Essential amino acid to total amino acid and predicted protein efficiency ratio were highest in the F-sample, whereas predicted biological value of the FSF was 3 times than that of the control.

Extruded sorghum (Sorghum bicolor L.) reduces metabolic risk of hepatic steatosis in obese rats consuming a high fat diet

The study investigated the effect of extruded sorghum flour (ESF) in a high fat diet (HFD) on biometric measurements and hepatic lipogenesis. Male Wistar rats were fed a normal diet (AIN-93M), HFD, HFD plus ESF replacing 50% cellulose and 100% corn starch (HFDS50), or HFD plus ESF replacing 100% cellulose and 100% corn starch (HFDS100) for eight weeks. ESF reduced the body mass index and liver weight of obese rats. Additionally, ESF reduced hepatic lipogenesis by increasing adiponectin 2 receptor gene expression and gene and protein expressions of peroxisome proliferator-activated receptor α (PPARα), while reducing the gene expression of sterol regulatory element-binding transcription factor 1. Molecular docking analysis revealed the affinity of ESF compounds (luteolinidin, apigeninidin, 5-methoxy-luteolinidin, and 7-methoxy-apigeninidin) with the PPAR-α receptor. Histological analysis confirmed the decreased grade of hepatic steatosis in obese rats. These data indicate the potential of ESF to reduce metabolic risk of hepatic steatosis associated with lipogenesis and obesity.

Downregulation of α-Melanocyte-Stimulating Hormone-Induced Activation of the Pax3-MITF-Tyrosinase Axis by Sorghum Ethanolic Extract in B16F10 Melanoma Cells

Ultraviolet irradiation-induced hyperpigmentation of the skin is associated with excessive melanin production in melanocytes. Tyrosinase (TYR) is a key enzyme catalyzing the rate-limiting step in melanogenesis. TYR expression is controlled by microphthalmia-associated transcription factor (MITF) expression. Sorghum is a cereal crop widely used in a variety of foods worldwide. Sorghum contains many bioactive compounds and is beneficial to human health. However, the effects of sorghum in anti-melanogenesis have not been well characterized. In this study, the biological activity of sorghum ethanolic extract (SEE) on α-melanocyte-stimulating hormone (α-MSH)-induced TYR expression was evaluated in B16F10 melanoma cells. SEE attenuated α-MSH-induced TYR gene promoter activity through the downregulation of the transcription factor MITF. We found that paired box gene 3 (Pax3) contributes to the maximal induction of MITF gene promoter activity. Further analysis demonstrated that SEE inhibited α-MSH-induced Pax3 expression. The collective results indicate that SEE attenuates α-MSH-induced TYR expression through the suppression of Pax3-mediated MITF gene promoter activity. Targeting the Pax3-MITF axis pathway could be considered a potential strategy to increase the efficacy of anti-melanogenesis.

Subcritical water extraction of polyphenolic compounds from sorghum (Sorghum bicolor L.) bran and their biological activities

Subcritical water extraction (SWE), an environment-friendly technique, was applied to extract polyphenolics from sorghum bran. Extraction temperatures (°C), time (min), and solid-liquid ratio (mL/g) were investigated and optimized by Box-Behnken design. The optimized conditions for SWE was 144.5 °C of temperature, 21 min of time, and 35 mL/g of solid-liquid ratio, with a polyphenolics yield of 47.253 ± 0.375 mg GAE/g dw, which was in good agree with the predicted value. Comparing with hot water extraction (HWE), SWE resulted in a higher yield of polyphenolics, higher radical scavenging activities, and more efficient antiproliferative activity. Furthermore, major polyphenolic compositions of the extracts were identified and quantified by HPLC-ESI-MS/MS. Taxifolin, taxifolin hexoside, oligomeric procyanidins, and epicatechin were the most abundant polyphenolic compounds in the extracts. Taken together, SWE can be used as a effective extraction method for polyphenolics from sorghum bran, which could be used as a potential source of natural antioxidants.

Bioaccessibility of hydroxycinnamic acids and antioxidant capacity from sorghum bran thermally processed during simulated in vitro gastrointestinal digestion

Sorghum is a source of hydroxycinnamic acids (HCA), which have shown antioxidant, anti-inflammatory and anti-proliferative capacities. However, a high proportion of them have low bioaccessibility due the complex structural disposition of the plant's cell wall. The effects of boiling and extrusion processes on sorghum bran and their effects on the antioxidant capacity and bioaccessibility of HCA during simulated in vitro gastrointestinal digestion were investigated. The bioaccessibility of phenolic compounds was significantly higher in extruded sorghum bran (38.4%) than that obtained by boiling (29.5%). This is consistent with the increase of the antioxidant capacity after in vitro digestion. In contrast, a low bioaccessibility of pure monomeric HCA was observed when they were exposed to in vitro gastrointestinal digestion. There were significant bioaccessibility reductions of 36.8, 19.5, 13.5, 62.1% for caffeic, ρ-coumaric, ferulic and sinapic acids, respectively, when unproccessed sorghum bran was added. Although the bioaccessibility of monomeric HCA was low, the total phenolic compounds and antioxidant capacity increased during the digestion simulation due to the thermal processes of extrusion and boiling. Extrusion and boiling could be utilized to produce food based on sorghum bran with biological potential.

The comprehensive analysis of sorghum cultivated in Poland for energy purposes: Separate hydrolysis and fermentation and simultaneous saccharification and fermentation methods and their impact on bioethanol effectiveness and volatile by-products from the grain and the energy potential of sorghum straw

The aim of this work was to study the potential of sorghum crop cultivated in European climate as an energy material. The investigation showed strong interaction between the fermentation method and the sorghum cultivar. It was also noted that the cultivar with the highest grain yield showed the highest yield of ethanol per hectare, achieving 1269 L/ha in SHF (separate hydrolysis and fermentation) and 1248 L/ha in SSF (simultaneous saccharification and fermentation). Chromatographic analysis of raw spirits showed that smaller amounts of impurities are formed in the SSF process than in the SHF process. The calorific value of sorghum straw was also measured, and amounted to 16,050-16,840 kJ/kg. The results have demonstrated the high value of sorghum as grain for bioethanol production and as straw as a valuable feedstock for forming pellets or briquettes.

Losses of nutrients and anti-nutrients in red and white sorghum cultivars after decorticating in optimised conditions

The aims were to optimise pearling process of red and white sorghum by assessing the effects of pearling time and grain moisture on endosperm yield and flour ash content and to assess nutrient and anti-nutrient losses produced by pearling different cultivars in optimised conditions. Both variables significantly affected both responses. Losses of ashes (58%), proteins (9.5%), lipids (54.5%), Na (37%), Mg (48.5%) and phenolic compounds (43%) were similar among red and white hybrids. However, losses of P (30% vs. 51%), phytic acid (47% vs. 66%), Fe (22% vs. 55%), Zn (32% vs. 62%), Ca (60% vs. 66%), K (46% vs. 61%) and Cu (51% vs. 71%) were lower for red than white sorghum due to different degree of extraction and distribution of components in the grain. Optimised pearling conditions were extrapolated to other hybrids, indicating these criteria could be applied at industrial level to obtain refined flours with proper quality and good endosperm yields.

Phenolic profile and content of sorghum grains under different irrigation managements

Sorghum grain is widely consumed in Sub-Saharan Africa and Asia, as a staple food due to its adaptation to harsh environments. The impact of irrigation regime: full irrigation (100%); deficit irrigation (50%); and severe deficit irrigation (25%) on phenolic profile and content of six sorghum grain genotypes was investigated by high performance liquid chromatography coupled with diode array detection and electrospray ionization mass spectrometry (HPLC-DAD-ESI-MS). A total of 25 individual polyphenols were unequivocally or tentatively identified. Compared to the colored-grain genotypes, the white grained sorghum var. Liberty had a simpler polyphenol profile. The concentrations of the sorghum-specific 3-deoxyanthocyanidins luteolinidin and apigeninidin, were higher under deficit irrigation compared to the other two regimes in all genotypes. These findings will be valuable for the selection of sorghum genotypes for grain production as human food under water deficit conditions, since polyphenol levels can affect the grain's nutritional value and health properties.

Comparing sorghum and wheat whole grain breakfast cereals: Sensorial acceptance and bioactive compound content

The sensory acceptance and the content of bioactive compounds of whole-sorghum and whole-wheat breakfast cereals were compared. Sensory acceptance was assessed using the Food Action RatingScale. 3-Deoxyanthocyanidins, flavones and flavanones were determined by high-performance liquid chromatography (HPLC) with diode array detection, and vitamin E by HPLC with fluorescence detection. Total phenolics and antioxidant activity were determined by spectrophotometry. The sorghum breakfast cereal had better sensory acceptance (70.6%) than wheat breakfast cereal (41.18%). Sorghum had higher 3-deoxyanthocyanidin content (100% higher), total phenolic compounds (98.2% higher) and antioxidant activity (87.9% higher) than wheat breakfast cereal. Flavones and flavanones were not detected in both breakfast cereals. Total vitamin E content was 78.6% higher in wheat than in sorghum breakfast cereal. Thus, consumption of whole sorghum breakfast cereal should be encouraged, since it had good sensory acceptance and is a source of bioactive compounds that can promote benefits to human health.

Effect of sorghum consumption on health outcomes: a systematic review

CONTEXT

Sorghum, an ancient grain originating in Africa, may have health-protective properties that could encourage its consumption among those who do not traditionally consume it.

OBJECTIVE

The aim of this systematic review was to evaluate the health effects associated with the consumption of sorghum among humans.

DATA SOURCES

Academic databases were searched for relevant studies published between 1985 and November 2015.

STUDY SELECTION

Nineteen studies -13 interventional and 6 observational - were identified for inclusion.

DATA EXTRACTION

Participant characteristics, study country, health outcomes, main findings, and study quality were reported. Interventional and observational studies were summarized separately.

RESULTS

Studies were divided into those that investigated the effect of sorghum on chronic disease and those that investigated other effects of sorghum on health. There was evidence that the consumption of sorghum attenuated blood glucose responses and decreased the expression of markers of oxidative stress. Sorghum was also observed to be a suitable ingredient for the formulation of oral rehydration solutions and showed potential for use as a medical adjunct to boost immune responses in HIV-positive patients CONCLUSIONS: The implication is that sorghum may have attributes superior to those of other staple grains, indicating its potential for innovative uses in commercial foods. More work is required to elucidate the health effects of sorghum when consumed by population groups that have not been traditional consumers of the grain.

Changes in whole grain polyphenols and antioxidant activity of six sorghum genotypes under different irrigation treatments

Sorghum grain containing elevated polyphenolic antioxidant content may provide foods with benefits to human health. A study was undertaken to determine the potential role of irrigation on the content of polyphenols and antioxidant levels in sorghum grain. Bound, free and total polyphenols were investigated in six diverse sorghum genotypes grown under either full irrigation or a deficit irrigation regime. Results showed genotype, irrigation and their interaction had a significant effect on polyphenols and antioxidant activity (P⩽0.05). The deficit irrigation treatment significantly increased polyphenol content and antioxidant activity compared to the full irrigation treatment. Of the six genotypes Shawaya black short 1 and IS1311C (brown) showed the highest polyphenols levels and antioxidant activity. Therefore, both irrigation treatments and genotype need to be considered by sorghum breeders and farmers during sorghum production to produce grain with the required levels of polyphenolics and antioxidant activity for targeted end-use.

Identification and characterization of phenolic compounds in hydromethanolic extracts of sorghum wholegrains by LC-ESI-MS(n)

Hydromethanolic extracts of brown, red, and white sorghum whole grains were analysed by LC-MS(n) in negative ESI mode within the range m/z 150-550amu. Besides the flavonoids already reported in sorghum, a number of flavonoids were also identified in the sorghum grain for the first time, including flavanones, flavonols and flavanonols, and flavan-3-ol derivatives. Various phenylpropane glycerides were also found in the sorghum grain, the majority of them are reported here for the first time, and a few of them were detected with abundant peaks in the extracts, indicating they are another important class of phenolic compounds in sorghum. In addition, phenolamides were also found in sorghum grain, which have not been reported before, and dicaffeoyl spermidine was detected in high abundance in the extracts of all three type sorghum grains. These results confirmed that sorghum is a rich source of various phenolic compounds.

Flaked sorghum biscuits increase postprandial GLP-1 and GIP levels and extend subjective satiety in healthy subjects

SCOPE

Sorghum grain components may play a role in mechanisms that protect against development of obesity-related chronic diseases. We conducted a randomized, cross-over trial (40 healthy subjects) using whole grain sorghum flaked biscuits to investigate mechanisms related to satiety.

METHODS AND RESULTS

Subjects were tested on four occasions after a 12-h fast. At baseline, they consumed 50 grams of one of four treatment meals: white, red, or brown sorghum biscuits or a wheat control. Subjective satiety was measured at 8 time-points over four hours. In a subset of 20 subjects, plasma glucose, insulin, gastric inhibitory peptide (GIP), glucagon-like peptide-1 (GLP-1), peptide-tyrosine-tyrosine (PYY), and ghrelin were measured. Subjects reported significantly lower subjective satiety ratings after consuming wheat compared to sorghum biscuits. Incremental area under the plasma concentration-time curve of postprandial GLP-1, GIP and in males, PYY, were significantly higher (p = 0.018, p = 0.031, p = 0.036, respectively) for sorghum breakfasts compared to wheat. Energy intake at a subsequent meal did not differ between treatments.

CONCLUSIONS

Sorghum whole grain is a promising novel ingredient in foods targeting satiety as an adjunct for weight control. Evidence is now required from randomized controlled trials that aim to examine specific effects on health outcomes from a sorghum-enriched intervention diet.

Growth temperature and genotype both play important roles in sorghum grain phenolic composition

Polyphenols in sorghum grains are a source of dietary antioxidants. Polyphenols in six diverse sorghum genotypes grown under two day/night temperature regimes of optimal temperature (OT, 32/21 °C and high temperature (HT, 38/21 °C) were investigated. A total of 23 phenolic compounds were positively or tentatively identified by HPLC-DAD-ESIMS. Compared with other pigmented types, the phenolic profile of white sorghum PI563516 was simpler, since fewer polyphenols were detected. Brown sorghum IS 8525 had the highest levels of caffeic and ferulic acid, but apigenin and luteolin were not detected. Free luteolinidin and apigeninidin levels were lower under HT than OT across all genotypes (p ≤ 0.05), suggesting HT could have inhibited 3-deoxyanthocyanidins formation. These results provide new information on the effects of HT on specific polyphenols in various Australian sorghum genotypes, which might be used as a guide to grow high antioxidant sorghum grains under projected high temperature in the future.