Improving the nutritional quality, and contribution to recommended dietary allowances of cassava and orange-fleshed sweet potato fufu flour blends for adults and children

Abstract

Cassava-based fufu is widely consumed but nutritionally limited, particularly in micronutrients. Incorporation of orange-fleshed sweet potato (OFSP) may enhance its nutritional value. This study evaluated the nutrient composition, microbial safety, functional properties and contribution to recommended dietary allowance (RDA) of cassava-orange-fleshed sweet potato composite fufu flour for adults and children. Four blends were formulated: CONTROL (100% CF, Control), CSF1 (90% CF:10% OFSPF), CSF2 (80% CF:20% OFSPF), and CSF3 (70% CF:30% OFSPF). Nutrient composition, functional properties, microbial safety, pasting behavior, carotene content, and sensory attributes were analyzed using standard methods. Moisture (5.54–6.41%), ash (1.05–2.10%), crude fiber (0.23–1.91%), fat (1.80–9.96%), protein (2.02–7.82%), and carbohydrates (77.60–87.32%) varied significantly (p < 0.05) across blends. Pasting properties revealed: peak time (46.4 -5.63 s), pasting temperature (74.47–77.53 °C). Peak viscosity (26.0–44.6 RVU), minimum viscosity (12.67–14.83RVU), Ultimate viscosity (18.1–31.5 RVU), Attenuation value (142.5–354.5 RVU), and regeneration value (63.0–208 BVU). These results indicate that the inclusion of OFSPF modifies starch gelatinization behavior and improves paste stability. Microbial counts remained within safe limits during storage, with sample CSF2 (80% CF:20% OFSPF) and CSF1 (90% CF:10% OFSPF) having no fungal growth at 35 days. Although CSF3 exhibited the highest carotene (276.87 µg/g) and protein contents (7.82%), CSF2 provided a more balanced combination of nutrient enhancement and functional properties, and was therefore considered the most suitable formulation. This product has potential as a food-based strategy to combat micronutrient deficiencies in vulnerable populations.

Introduction

Cassava (Manihot esculenta Crantz) is a major staple crop in sub-Saharan Africa, serving as a primary source of calories for millions of people. One of its most popular products is fufu, a fermented flour or dough widely consumed across West and Central Africa. Despite its importance, cassava is predominantly composed of carbohydrates and contains limited amounts of protein, essential fatty acids, vitamins, and minerals [11]. Consequently, long-term reliance on cassava-based foods can contribute to micronutrient deficiencies, particularly vitamin A deficiency, which remains a major public health concern in sub-Saharan Africa [38].

Orange-fleshed sweet potato (OFSP, Ipomoea batatas) has been reported as a biofortification strategy for addressing vitamin A deficiency in several studies [34]. It is rich in β-carotene, a precursor of vitamin A, and contains significant levels of protein, fiber, and minerals [15]. Incorporating OFSP into traditional staples such as fufu could improve their nutritional quality without altering their cultural acceptability. Previous studies have demonstrated that composite flours made from cassava and OFSP enhance carotenoid retention, increase protein and fat content, and contribute to improved sensory properties of food products [18, 22, 31]. However, limited research has explored the integration of OFSP into fufu flour specifically, with emphasis on its proximate composition, functional characteristics, microbial safety, and sensory acceptability. Understanding these properties is critical to ensuring that nutritional improvements do not compromise product quality, storability, or consumer preference.

Orange-fleshed sweet potato was selected as a fortifying ingredient due to its high β-carotene content, affordability, adaptability to tropical agroecological conditions, and established role in food-based approaches for combating vitamin A deficiency in sub-Saharan Africa [22]. While OFSP has been incorporated into bakery and complementary foods, limited information exists on its utilization in fermented cassava fufu flour systems, particularly regarding the combined effects on nutrient density, pasting behavior, microbial stability, and dietary contribution to recommended nutrient intakes.

Therefore, the present study was designed to evaluate the chemical composition, physicochemical and pasting properties and microbial quality of cassava/OFSP composite fufu flours. The findings aim to promote the development of nutrient-enhanced, shelf-stable, and consumer-acceptable fufu flour blends, contributing to food diversification and the reduction of vitamin A deficiency in regions where cassava is a dietary staple.

Materials and methods

Materials

Fresh cassava roots of TME 419 variety (12 months maturity) and orange-fleshed sweet potato roots of UMUSPO3 (4 months maturity) were obtained from Eke-Ukwu Market, Owerri, Imo State, Nigeria. Samples were transported under ambient conditions and processed within 24 h of procurement.

Methods

Preparation of flour samples

Cassava flour (CF): Traditionally, the unit operations of cassava blends are peeling, washing, grating, pressing and fermentation, sieving and roasting as described by [29]. Fresh cassava roots were peeled manually with sharp knives. The peels were dried for animal feed. The peeled roots were washed thoroughly and grated by rubbing on the rough surface of a perforated galvanized metal sheet fixed to a wooden board support. The grated cassava mash was packed into jute bags and the open ends tied securely with rope. The bags were placed on a wooden rack and heavy stones placed on them to press out the starch juice. The fermentation process lasted for a period of two days. The pressed fermented dough was oven-dried (model LBN-DO161, Labnic, USA-based Supplier) at 60 °C and cooled. Diagrammatic presentation of the process is shown below in Fig. 1.

Fig. 1.

Processing of cassava/OFSP fufu

OFSP flour (OFSPF): Following the method described in [17], OFSP roots were washed, peeled manually with a sharp knife and sliced into thin pieces. The uniformity of the slices helps ensure consistent drying. The sliced sweet potatoes were dried in an oven (model LBN-DO161, Labnic, USA-based Supplier) at 60.⁰C for 12 h to reduce their moisture content. The dried slices were milled into a fine powder using milling machines. The flour was sieved with a wooden mesh (40 mesh sieve) to achieve a finer texture and remove any larger particles or impurities. The final sweet potato flour was packaged in high density polyethylene (HDPE) bag for storage. The dried cassava and OFSP flours attained moisture contents below 10%, suitable for shelf-stable flour production. Diagrammatic presentation of the process is shown below in Fig. 1

Formulations

Four (4) samples of the fufu flour were formulated by mixing two types of flour, Cassava flour (CF) and orange-fleshed sweet potato flour (OFSPF), into different ratios (CF: OFSPF). The samples formulated are as follows: CONTROL (100:0) Control, CSF1 (90:10), CSF2 (80:20) and CSF3 (70:30) as presented in Table 1.

Table 1.

Composition (%) of Cassava flour (CF) and orange-fleshed sweet potato flour (OFSPF) (CF/OFSP) Fufu flour Samples

Samples	CF	OFSP
Control	100	0
CSF1	90	10
CSF2	80	20
CSF3	70	30

CSF Cassava flour (CF) and orange-fleshed sweet potato flour (OFSPF) fufu flour blend

Proximate analysis

The proximate analysis (moisture, ash, protein, fat, fiber, and carbohydrate) of the Fufu samples was determined using the official method of analysis of the Association of Official Analytical Chemists [5].

Physicochemical properties

Physicochemical characteristics (bulk density, swelling capacity, water/oil absorption, pH) were assessed using the method described in [30]. The least gelation concentration was determined using the method described by Finney et al. [12].

Pasting properties

The method as described by [7] was used in determining the pasting properties of the fufu flour using Rapid Visco Analyser (RVA).

Determination of total carotene content

The Harvest Plus procedure for carotene analysis was used to analyze the total carotenoid content of fufu flour made from fresh cassava roots and orange-fleshed sweet potatoes with Spectrophotometry (λ = 450 nm) [29].

Total Carotenoid (μg/g) = Total Carotenoid (μg/g) = 

Where, A = absorbance,

Volume = total volume of extract (50 ml),

A^1% = absorption coefficient of β-carotene in P.E. (2592).

β-carotene to RAE

Conversion of β-carotene to RAE was done using WHO/FAO conversion which is 12 μg β-carotene = 1 μg RAE as described by [35].

Determination of viscosity

The viscosity of the samples was determined using the method described by [30]. 10% of each formulated sample was suspended in distilled water and mechanically stirred for 2 h at room temperature. Oswald-type viscometer was used to measure the viscosity of the mixture.

Microbial analysis of the samples

The microbial safety of the Fufu flour was evaluated by measuring the total bacteria count (TBC) and total fungal count (TFC) at different time points, including Days 0, 1, 14, 28, and 35 [23]. Total viable bacterial count and fungal count were determined using standard plate count procedures according to ISO 4833–1:2013 and ISO 21527–2:2008, respectively.

Statistical analysis

All analyses were conducted in duplicate and results expressed as mean ± standard deviation. Data were subjected to one-way analysis of variance (ANOVA) using SPSS version 25.0 under a completely randomized design. Mean separation was performed using Fisher’s Least Significant Difference (LSD) test at p < 0.05 as described by [33]. Assumptions of normality and homogeneity of variance were verified prior to analysis.

Results and discussions

Nutrient and physicochemical composition of fufu flour blends

The proximate and physicochemical composition of cassava and OFSP blends (Table 2) shows significant changes (p > 0.05) with increasing OFSP levels. Moisture content increased slightly but remained below 10% in all samples, indicating good storage stability and low susceptibility to microbial spoilage [13]. The ash content which is an indication of the mineral content of the products (24), was highest (2.10%) in the 20% OFSP blend (CSF2). This value is higher than those reported for cassava granules by [2], but aligns with the high ash content (1.78%) reported for fermented OFSP flour by [28].

Table 2.

Nutrient and physicochemical composition of fufu flour blends (% dry weight)

Sample	Moisture (%)	Ash (%)	Crude fiber (%)	Crude fat (%)	Protein (%)	Carbohydrates (%)	pH	Total Carotene (µg/g)
Control	5.54b ± 0.04	1.52b ± 0.04	1.00b ± 0.04	6.12b ± 0.02	2.31b ± 0.00	83.52b ± 0.02	5.15c ± 0.07	8.86d ± 0.00
CSF1	5.77b ± 0.06	1.05c ± 0.02	0.62c ± 0.08	2.71c ± 0.31	2.54b ± 0.00	87.32a ± 0.18	4.90d ± 0.00	139.71c ± 0.28
CSF2	6.42a ± 0.08	2.10a ± 0.01	1.91a ± 0.06	9.96a ± 0.03	2.02b ± 0.01	77.60d ± 0.13	5.35b ± 0.07	255.13b ± 0.27
CSF3	6.39a ± 0.21	1.46b ± 0.04	0.23d ± 0.03	1.80d ± 0.26	7.82a ± 0.40	82.31c ± 0.34	7.05d ± 0.07	276.87a ± 0.40

Values are means ± standard deviation of duplicate determination. Means bearing different superscript within the same column are significantly (p ≤ 0.05) different

Crude fiber was highest (1.91%) in the CSF2 (80%CF, 20% OFSPF) blend. A low-fiber diet is undesirable and linked to colon diseases [16]. However, moderate fiber content is also desirable for young children, as excessive fiber can reduce energy density [32]. Sample CSF2 will contribute less than 8% of the RDA (25–30 g/day), indicating that while OFSP slightly boosts fiber, additional fiber-rich soup or sauce (such vegetables and legumes soups) is needed to balance the diet. The crude fat content more than doubled in the 20% OFSP blend (9.96%) compared to the control (6.12%), significantly enhancing the energy density of the fufu blend. Lipids are important for the absorption of beta-carotene abundant in OFSP [1]. The increased fat content may also facilitate formation of amylose–lipid complexes, which influence starch gelatinization and paste stability. RDA for adults and children in Table 3, shows that sample CSF3 with the highest OFSP blends (9.96 g/100 g) will supply 12–16% of daily fat needs for adults and 20–30% of daily fat requirement (10 g/100 g) for children.

Table 3.

Recommended daily nutrient requirements for adults and children

Nutrient	WHO/FAO Adult Standard/RDA	WHO/FAO Children (1–3) Standard/RDA
Protein (g)	50–60 g/day	13 g/day
Fat (g)	60–80 g/day	33–58 g/day
Fibre (g)	25–30 g/day	130–200 g/day
Carbohydrate (g)	225–325 g/day	10–14 g/day
Vitamin A (Beta carotene)	900–700	400 μg/day

WHO/FAO 39, 40, 38, UNICEF/WHO child feeding guidelines

Protein content showed the most notable improvement, protein content rose from 2.31% (Control) to 7.82% in CSF3 (30% OFSP), a 238% increase. Although still below RDA values, 200–300 g could cover 25–40% of adult protein needs, and smaller portions of 2–8 g per 100 g could meet 50% of needs for children. Cassava is especially low in protein, and this result demonstrates that OFSP fortification can effectively address this major nutritional limitation. Similar reports from Ojo and Akande [26] and [36] support that OFSP fortification enhances protein quality in cassava-based foods in sub-Saharan Africa.

As expected, the carbohydrate content decreased significantly as the proportion of nutrient-dense OFSP (with its higher protein, fat, and fiber) increased. The 20% OFSP blend (CSF2) had the lowest carbohydrate content at 77.60%. This indicates a shift from a purely high-energy cassava flour to a more nutritionally balanced composite flour. This inverse relationship between fortification level and carbohydrate content is an expected outcome, as documented in previous studies on composite flours [4] and [24]. The values for all blends, however, remain high, confirming that the product retains its primary function as a staple energy source. A 100 g portion would supply about one-third of the adult daily carbohydrate requirement, aligning with WHO’s guidance that 45–65% of energy should come from carbohydrates [38]. pH values (4.90–7.05) declined with OFSP inclusion, likely due to its organic acids. This would contribute to shelf stability [18]. Similarly, [17], also noticed that the pH values of sorghum/orange-fleshed sweet potato composite flour rose as the proportion of OFSP flour increased (5.72 −6.15). Total carotene content showed an obvious increase with OFSP substitution, ranging from 8.86 μg/g in the control to 276.86 μg/g in CSF3 (70:30). Based on β-carotene conversion factors, approximately 17–20 g of CSF3 would theoretically provide the daily vitamin A requirement of young children, excluding processing and bioavailability losses. This confirms OFSP as an effective pro-vitamin A enrichment source in fufu flour. Similar observations have been made in previous studies [6, 17, 19] for flour or complementary food substituted with OFSP. The significant rise in carotene content aligns with [10] reports and highlights the potential of OFSP to combat vitamin A deficiency through staple food fortification.

Functional properties of fufu flour blends

The Functional properties of cassava-OFSP blends (Table 4) showed significant variation with increasing OFSP levels. Bulk density ranged from 0.77–0.90 g/ml, highest in was observed in CSF3 (70:30) and the lowest in the Control. The higher values compared to cassava granules (0.57–0.65 g/cm³) in [2] for Bio-fortified and Traditionally Prepared Cassava Granules may be due to denser OFSP starch granules, reported in [17]. Higher bulk density supports packaging and transport efficiency [21].

Table 4.

Functional properties of fufu samples

Sample	Bulk Density (g/ml)	WAC (g/ml)	OAC (g/ml)	Least Gelation Conc. (°C)	Gelation Temp (°C)	Swelling Capacity (g/ml)
Control	0.77b ± 0.03	2.00b ± 0.00	1.50a ± 0.12	3.50a ± 0.71	69.00b ± 1.41	48.48c ± 2.78
CSF1	0.79b ± 0.01	1.85b ± 0.07	1.23b ± 0.00	3.00a ± 1.41	70.25b ± 1.06	31.26d ± 1.30
CSF2	0.80b ± 0.71	1.95b ± 0.07	1.54a ± 0.06	2.00a ± 0.00	72.25ab ± 0.35	79.04b ± 1.03
CSF3	0.90a ± 0.00	2.25a ± 0.07	1.63a ± 0.06	4.00a ± 0.00	74.25a ± 0.77	97.49a ± 1.16

Values are means ± standard deviation of duplicate determination. Means bearing different superscript within the same column are significantly (p ≤ 0.05) different

Water absorption capacity (1.85–2.25 g/g) and oil absorption capacity (1.23–1.63 g/g) increased with OFSP addition, reflecting greater hydrophilicity from starch/fiber hydroxyl groups [37]; [41] and more protein-lipid binding sites [8, 25]. These properties are desirable for dough reconstitution and flavor retention. The temperature at which gelatinization of starch take place is known as the gelatinization temperature [8]. Gelation temperature ranged from 69.00 to 74.25 °C, showing slight but consistent increase with increasing OFSP levels.

The swelling capacity of a flour sample, points at the collective effects of starch quality, specifically amylose/amylopectin ratio as reflected by the volume of gel formed when heated with an excess of water [24]. The increase in swelling capacity with OFSP inclusion may be associated with differences in amylopectin-rich starch fractions and enhanced water-binding capacity of OFSP starch granules. Results rose from 31.26–97.49 g/ml with OFSP content, indicating improved starch hydration and gelatinization [24]. This enhances dough elasticity and soft texture [18].

Effect of temperature on the extraction of phenolic compounds

Pasting properties of fufu samples

The pasting characteristics of cassava-OFSP fufu blends are shown in Table 5. Peak time (4.64–5.63 min) and peak temperature (74.47–77.53 °C) indicate that OFSP inclusion did not largely alter gelatinization onset but slightly reduced the time required to reach maximum viscosity. This is consistent with starch, protein and fiber interactions in composite flours [7]. Pasting temperature values suggest that OFSP blends gelatinize at lower energy input compared to cassava alone. The control had a lower pasting temperature (77.53 °C), while blends showed slightly higher values, likely due to amylose–amylose and amylose–lipid interactions. These temperatures were lower than those reported for instant yam fufu (81.57 °C; [37]) and unfermented cassava–guinea corn–plantain fufu (93.17 °C; [27]), indicating that the cassava-OFSP blends cook faster with reduced energy requirements.

Table 5.

Pasting properties of fufu flour blends

Samples	Peak Time (s)	Peak Temp (°C)	Peak Viscosity (RVU)	Minimum Viscosity (RVU)	Ultimate Viscosity (RVU)	Attenuation Value (RVU)	Regeneration Value (BVU)
Control	5.63	77.53	26.0	14.17	31.5	142.5	208.0
CSF1	4.69	74.47	44.62	14.83	23.21	354.5	100.5
CSF2	4.64	75.03	39.12	12.67	20.92	317.5	99.0
CSF3	4.65	75.53	35.42	12.83	18.08	271.5	63.0

Peak viscosities ranged from 26–44.62 RVU, with the control recording the lowest (26 RVU). Higher peak viscosities in the blends reflect greater water absorption and starch swelling [37], leading to rapid dough formation which is desirable for consumer convenience. Attenuation was highest (354.5RVU) in sample CSF1 (90:10). Attenuation measures dough stability under shear, and higher values indicate susceptibility to structural collapse [8]. The higher breakdown in CSF1 (90:10) suggests that the partial inclusion of OFSP starch initially promotes greater swelling but leads to weaker granule integrity during continued heating. While the control exhibited the lowest breakdown, attributed to the relative stability of cassava starch. However, increasing OFSP to 20–30% in sample CSF2 and CSF3 reduced breakdown compared to CSF1 (90:10), indicating that paste stability may improve with higher OFSP proportions through starch, fiber, and protein interactions.

Regeneration values ranged between 63.0 and 208.0 BVU. It is also referred to as Setback, and it reflects the tendency of amylose molecules to reassociate during cooling [9, 17]. The high setback in the control suggests stronger retrogradation and firmer gel formation, which may yield less elastic fufu when reconstituted. The lower setback values in OFSP blends, especially in CSF3, indicate reduced retrogradation and softer gels. This attribute is desirable in fufu that is intended to be smooth and elastic. The reduction in setback viscosity with OFSP incorporation suggests reduced amylose reassociation during cooling, possibly due to interference from fiber and lipid components present in OFSP. These findings imply that OFSP substitution moderates’ starch retrogradation, improving the textural qualities of the product while reducing the tendency to harden during storage [25].

Microbial safety of the fufu samples

Table 6 shows the microbial activity in the fufu flour samples. Total fungi count and bacterial count ranges from 4 × 10¹⁰- 4.8 × 10¹⁰ and 6.55–7.12 × 10¹⁰ from week 1 to week 35. The microbial counts observed remained below the maximum acceptable limits for dried flour products (< 10⁵ CFU/g) recommended by ICMSF and Codex Alimentarius standards, indicating acceptable microbiological safety during storage. It was observed that the microbial load of the fufu samples increases as the time extends but was still within the safe limit after 5 weeks. The total fungi and bacterial count were lowest in control at day 1 and 35. Lowest microbial count in the control may be attributed to the fermentation of cassava and no presence of OFSP. The fermentation (3 days) process applied in the production of 100% cassava (control) sample may have contributed to the low microbial growth count observed. Similar studies have reported that fermentation extends shelf life and level of safety of food products [1, 3]. also reported that the drying process involving heat also minimizes the microbial load in the fufu samples. At most times, shelf life is duration during which a product maintains acceptable quality before it deteriorates [20]. The fungi and bacterial growth counts observed in the fufu sample after a period of 5 weeks were found to be within acceptable limits for ready-to-eat foods [14].

Table 6.

Total fungi and microbial count of fufu flour blends

Sample	WK1		Wk28		Wk35
	Total Fungi count	Total Bacterial count	Total Fungi count	Total Bacterial count	Total Fungi count	Total Bacterial count
Control	0 × 103	6.55 × 103	4 × 103	6.66 × 103	4.3 × 103	6.75 × 103
CSF1	4 × 103	6.85 × 103	4.3 × 103	6.94 × 103	4.3 × 103	6.86 × 103
CSF2	4 × 103	6.94 × 103	4 × 103	6.97 × 103	4.3 × 103	7.01 × 103
CSF3	0 × 103	6.89 × 103	4 × 103	7.11 × 103	4.8 × 103	7.12 × 103

Conclusions

Blending cassava with OFSP at optimal ratios (particularly 80:20 and 70:30) enhances the nutritional profile, functionality and storage stability of fufu flour. This study contributes to United Nations Sustainable Development Goals, particularly SDG 2 (Zero Hunger), by enhancing the nutritional quality of fufu staple and contributing to recommended dietary allowances for both adults and children. OFSP serves as a functional ingredient. The 70:30 cassava-OFSP blend (CSF3) demonstrated optimal nutritional enhancement (high carotenoids, protein), and desirable pasting properties while the 80:20 cassava-OFSP blend CSF2 had more balanced combination of nutrient enhancement and functional properties, and was therefore the more suitable blend. The formulated blends demonstrate potential as food-based approaches for improving dietary vitamin A intake. The microbial count of the fufu samples remained within a safe limit after a period of 5 weeks. Future work should explore industrial-scale production and consumer adoption strategies.

Authors’ contributions

G.K.E and C.O.U. wrote the main manuscript text, J.M.E prepared Tables 1–5 and U.A.O supervised. All authors reviewed the manuscript.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.