The physical characteristics, anti-nutrient and bioactive compound contents of sorghum rice from various cultivars of different colours are presented in Table 1.
Sorghum rice textural profile
Texture analysis revealed that sorghum grain hardness ranged from 56.83 g (red) to 834.57 g (white), representing a nearly 15-fold difference across cultivars. White and black sorghum were the hardest (834.57±2.77 g and 407.00±8.19 g), while red sorghum was the softest (56.83±15.81 g). Yellow sorghum (244.67±10.50 g) and white-red sorghum (160.67±14.74 g) occupied intermediate positions closer to the texture range of conventional rice.
This variability reflects differences in starch composition, endosperm architecture and polyphenol-protein interactions. High amylose content produces harder grains through strong hydrogen bonding, whereas high amylopectin yields softer, stickier textures
(Li et al., 2016). Endosperm structure further modulates this effect: a soft endosperm absorbs water more readily than a corneous endosperm, resulting in faster gelatinisation and softer cooked texture
(Yang et al., 2024). In dark pigmented cultivars, condensed tannins may also reinforce hardness by forming tannin-protein complexes
(Pontieri et al., 2021).
Very hard cultivars such as white sorghum may be less preferred than rice in the typical 200-400 g range, whereas yellow and white-red sorghum are more likely to be accepted. For harder cultivars, prolonged soaking, pressure cooking, or pre-gelatinisation can soften the grain and improve palatability
(Yang et al., 2024).
Sorghum rice colour profile
The colour of cooked sorghum rice varied widely across cultivars. L* values ranged from 15.82 to 60.94, with black sorghum showing the highest lightness, followed by white-red, while gray sorghum was the darkest. The a* parameter ranged from -0.74 to 18.70, peaking in yellow sorghum and slightly negative in white-red sorghum, whereas b* ranged from 9.74 to 21.24 and was highest in white sorghum. Chroma values (10.05-25.29) were greatest in yellow and lowest in white-red sorghum, while hue angles (37.23°- 94.22°) placed white-red in the yellow-green region and gray sorghum closest to pure red
(Pontieri et al., 2021). Such wide cultivar-dependent variation in colour attributes, particularly in L*, a* and b* parameters, is consistent with findings reported for other small cereals;
Pawase et al., (2019) demonstrated significant differences in colour properties among finger millet and pearl millet cultivars, reflecting genotype-dependent differences in pigment composition and distribution across the grain layers.”
No direct correlation was observed between L* and phenolic or tannin content. Black sorghum, despite having the highest L* (60.94), contained high phenol (132.524 ppm) and tannin (0.01323%). Conversely, yellow and gray sorghum, both with low L*, had lower phenol levels (111.748 and 126.796 ppm) than red sorghum, which combined the highest phenol content (139.029 ppm) with only a moderate L* (23.66). This pattern indicates that cooked rice colour is shaped by multiple interacting factors rather than bioactive concentration alone.
Sorghum rice cooking time
Cooking time ranged from 19±0.5 min (white-red sorghum) to 105±2.0 min (black sorghum), an 86-min span with significant implications for energy use, practicality and commercial economics. Black sorghum required almost five times the time of white-red sorghum and over three times that of conventional rice (25-30 min). Cream sorghum (99±1.5 min) was also very long, while yellow sorghum (73±1.0 min) showed a moderate cooking time. Gray (63±1.2 min) and red sorghum (50±1.0 min) showed comparable cooking times with a difference of only 13 minutes.
This variation is primarily affected by grain physical structure, particularly endosperm hardness
(Khalid et al., 2022), the thickness of the pericarp
(Gwala et al., 2020) and starch composition
(Li et al., 2016). A compact corneous endosperm and thick pericarp slow water and heat penetration, delaying starch gelatinisation. Black sorghum’s long cooking time (105 min) likely reflects a very compact endosperm and thick pericarp, creating a mass energy transfer barrier.
Interestingly, no direct correlation existed between rice hardness and cooking time. White sorghum (834.57 g hardness) required only 61 min, less than the black sorghum (105 min, 407.00 g hardness). Likewise, red sorghum (softest at 56.83 g) needed 50 min versus 19 min for white-red sorghum (160.67 g). This suggests cooking time depends on raw grain structure and hydration rate, while cooked-rice texture depends on starch composition and retrogradation.
Anti-nutrient compound content
Phytate content ranged from 0.013±0.001% to 0.076±0.004%, varying significantly (p<0.05). Red sorghum had the highest level, nearly six times that of the lowest cultivar, indicating high genetic variability in phytic acid accumulation. Black sorghum (0.039±0.002%) and gray sorghum (0.025±0.002%) showed intermediate levels.
Yellow, cream, white-red and white sorghum had the lowest phytate content. The 0.013-0.076% range in cooked rice is far lower than that of raw sorghum grains (typically 0.5-1.5% dry weight)
(Keyata et al., 2021). This >90% reduction reflects the leaching of phytic acid into the soaking and cooking water and endogenous phytase activity, which hydrolyzes phytic acid into less-phosphorylated inositol phosphate with weaker chelating capacity.
Soaking at room temperature provides optimal conditions for endogenous phytase (pH 5.0-5.5), with 30-50% phytic acid hydrolysis achievable during prolonged soaking (
Asiri, 2025). Cooking diffuses dissolved phytic acid into the water but inactivates phytase, halting further hydrolysis. This aligns with
(Davana et al., 2021), who reported that processing of sorghum, including germination and soaking, markedly reduced phytate and tannin content, supporting the >90% reduction observed in the present study.
Tannin content ranged from 0.0174±0.0010 to 0.1323±0.0080 mg/g. Black and red sorghum had the highest content, followed by yellow and gray sorghum, while cream, white and white-red sorghum had the lowest.
Tannin content correlated with grain colour intensity: black and red sorghum had the highest tannins, while white sorghum had the lowest and the brightest cooked colour (L* = 57.22). The correlation is imperfect, however, as yellow and gray sorghum (very low cooked L*) had only moderate tannins, indicating that pigmentation depends not only on tannins but also on other phenolics, such as anthocyanins and phenolic acid, distributed differently among cultivars
(Pontieri et al., 2021).
Total phenol content and antioxidant activity
Total phenol content ranged from 90.68±1.80 ppm (white-red) to 139.03±3.50 ppm (red and black), with intermediate values for gray, yellow, white and cream sorghum. A strong positive correlation between total phenol and tannin content was observed (r=0.87, p<0.05), consistent with condensed tannins being a subset of phenolic compounds
(Pontieri et al., 2021); sorghum phenolics comprise phenolic acids, flavonoids, tannins and stilbenes (
de Morais Cardoso et al., 2017). These levels far exceed those of conventional white rice (<50 ppm), though they remain below pigmented red rice (13,000-40,000 ppm)
(Wattanavanitchakorn et al., 2025); even so, sorghum, including bright cultivars such as white-red, which offers a clear bioactive advantage over the white rice that dominates Indonesian diets, provides a strong basis for functional-food positioning.
Antioxidant activity correlated strongly with total phenol content (r=0.92, p<0.05), with minor deviation attributable to differences among phenolic classes and their synergistic interactions (
de Morais Cardoso et al., 2017). Red and black sorghum, with the highest phenol content, showed the highest DPPH scavenging capacity (82.41±1.60% and 79.86±1.50% respectively), while white-red sorghum reached 58.17±1.00%, still markedly above conventional white rice (<30%)
(Ranjkesh et al., 2021), a meaningful contribution from a staple food.
Analysis of economic feasibility for sorghum rice production
Economic feasibility analysis covered production costs per kg of sorghum rice, including raw materials, cultivar-specific water consumption, electricity (cooking-time dependent), labour and overhead (Table 2).
Structure of production cost and price components
Total production cost per kg ranged from IDR 10,909 (white-red sorghum) to IDR 20,658 (black sorghum), an 89.4% variation, nearly twofold, with corresponding contribution margins ranging from 27.3% (white-red at IDR 15,000/kg) to 34.1% (red at IDR 25,000/kg), underscoring the critical importance of cultivar selection and market positioning for economic optimisation.
Raw material was the largest cost component (73.3% for white-red Sorghum, 48.4% for black sorghum). For raw material costs of IDR 8,000/kg, operational costs ranged from IDR 2,909-9,010; for IDR 10,000/kg cultivars, from IDR 6,464-10,658.
Electricity was the largest and most variable operational cost (6.3% for white-red to 18.3% for black sorghum), scaling directly with cooking time: black sorghum (105 min) incurred IDR 3,780 against only IDR 684 for white-red sorghum (19 min), a 5.5-fold difference.
Water costs (4.1-7.3% of total) scaled with the cultivar-specific ratios, being highest for black and red sorghum (1:10) owing to greater absorption and evaporation during prolonged cooking. Labor (preparation plus cooking supervision at IDR 2,000/hour) and overhead (10% of direct costs) followed the same pattern, both lowest for white-red and highest for black sorghum (Table 2); at a commercial scale, partial automation and fixed-cost distribution would reduce both proportions substantially.
Ratio of cost efficiency and economic ranking of cultivars
The cost-effectiveness ratio (1/total cost × 1000) served as a quantitative indicator, with higher values denoting greater economic efficiency. Duncan’s test produced four statistically distinct groups. White-red sorghum achieved the highest ratio (0.0917), 89.4% more efficient than black sorghum, owing to its short cooking time and optimal water use. Gray (0.0709) and yellow sorghum (0.0673) formed the second, with moderate raw-material costs and 61-63 min cooking times. Red (0.0607) and cream sorghum (0.0588) clustered next; red’s higher raw material cost (IDR 10,000 vs. IDR 8,000/kg) was offset by its shorter cooking time (50 vs. 99 min). Black sorghum ranked lowest (0.0484), reflecting the combined penalties of high raw-material price, prolonged cooking and high water consumption.
Compared with retail rice (medium IDR 10,000-12,000/kg; premium IDR 15,000-20,000/kg), white-red sorghum (production cost of IDR 10,909/kg) can be priced competitively at IDR 15,000/kg, yielding a contribution margin of IDR 4,091/kg (27,3%) and a monthly profit of approximately IDR 8.2 milion at a production capacity of 100 kg/day. Break-even is reached at 489 kg/month (approximately 5 production days), with a payback period of approximately 6 months, assuming an initial investment of IDR 50 million, confirming its viability as a mainstream healthy alternative grain. Red sorghum, with a production cost of 16.464/kg and a selling price of IDR 25,000/kg, offers the highest contribution margin among all cultivars (34.1%, IDR 8,536/kg), with a payback period of approximately 3 months, making it the most economically attractive for the premium functional food segment. Black sorghum at IDR 25,000/kg yields a margin of 17.4% (IDR 4,342/kg) with a payback period of approximately 6 months, remaining commercially viable for health-conscious consumers. Cream sorghum, however, requires a minimum selling price of IDR 18,900/kg to recover production costs, making it less competitive at the standard market price of IDR 15,000/kg and necessitating premium positioning or further processing efficiency to improve its economic viability.
