Revalorization of the Residual Cake from Moringa Seeds as an Alternative Source of Plant-Based Proteins ^†

Abstract

The residual cake obtained after extracting oil from Moringa oleifera seeds is a promising source of plant-based proteins due to its high content of proteins, dietary fibre and essential minerals. However, its food applications are limited by a strong bitter taste that affects consumer acceptance and antinutritional compounds that reduce mineral bioavailability such as phytates. This study aimed to evaluate the effect of saline and ethanol treatments of moringa cake—reported in the literature as improving its sensory properties—on its nutritional profile. Proximal composition was determined by gravimetry for moisture, muffle incineration for ash, and solvent extraction with the Randall method for lipids. Protein content was analyzed using the Dumas combustion method. Mineral elements (calcium, iron, zinc, sodium) were quantified by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and phytates by High-Performance Liquid Chromatography (HPLC). The untreated cake revealed a favourable nutritional profile, mainly due to its protein content, but also contained high phytate levels. Both treatments slightly reduced phytates (5–12%), with saline extraction proving more effective. Nevertheless, mineral loss was observed, while there was a notable increase in sodium in the saline-treated samples. Ethanol treatment, in contrast, led to a statistically marked reduction in residual lipids. Importantly, both treatments diminished the bitter taste, improving sensory acceptability. Although neither method completely eliminated phytates, the overall improvements in protein quality, mineral profile, and sensory properties highlight the potential of moringa residual cake as a valuable ingredient. Thus, it emerges as a sustainable, high-nutritional-value source of plant proteins for the development of innovative food products.

1. Introduction

Moringa oleifera, native to the Himalayan region and now cultivated in tropical and semiarid areas, is notable for its drought tolerance and high yields under irrigation and fertilization. It is a plant of substantial nutritional value and versatility: its leaves, seeds, flowers, and roots are utilized [1]. The leaves, rich in essential amino acids, are used as food fortificants, while the seeds can be eaten fresh or roasted; however, their principal value lies in the oil (35–40% of seed weight) [2], which is similar to olive oil. The moringa press cake remaining after oil extraction has applications as a fertilizer, in animal feed, and especially as a natural flocculant for water purification [3]. Nevertheless, this protein-rich cake additionally has potential for human nutrition—particularly in regions with protein deficits—by enabling partial substitution of starchy staples with a plant-based protein ingredient. Its nutritional value is due primarily to proteins, vitamins, and minerals, although it may be limited by its antinutrient content and strong bitterness [4,5]. Against this background, the present study proposes to evaluate debittering treatments with saline and ethanolic solutions and their effects on the nutritional value of the treated cake in terms of proximate composition and potential improvement in mineral bioavailability via phytate reduction in comparison with the source seed and the untreated residual cake.

2. Materials and Methods

2.1. Materials

Materials for this study consisted of moringa seeds and the residual press cake Q’omer^® obtained after cold oil extraction, originating from Mozambique (Q’omer BioActive Ingredients S.L., Valencia, Spain). Prior to raw material characterization, the seeds—previously manually dehulled (Figure 1)—were ground (75–425 um), as was the residual cake, to obtain homogeneous flours with reduced particle size for subsequent chemical analyses. The seeds and milled samples were stored in polyethylene bags at refrigeration temperature until analysis.

2.2. Methods

2.2.1. Proximal Composition

The samples were characterized in terms of moisture, dietary fibre, starch, and lipids according to approved AOAC methods, yielding 925.09, 991.43, 996.11, and 945.16, respectively. Protein determination was carried out by the Dumas combustion method. The carbohydrate content, excluding fibre, was calculated by difference.

2.2.2. Nutritional Value Evaluation

Phytic acid was determined by HPLC [6]. The Ca, Fe, Zn and Na concentrations were determined using ICP-Ms. Each sample was digested with HNO₃ and H₂O₂ using a microwave-assisted digestion system [7]. The prediction of mineral availability was determined using InsP₆/mineral molar ratios [8]. The phytate/iron ratio should be below 0.4 [9], and phytate/zinc molar ratios < 5, between 5 and 15, and >15 have been associated with high, moderate, and low zinc bioavailability, corresponding to approximately 50%, 30%, and 15% of total zinc, respectively [10]. The contribution to the Dietary Reference Values/Intakes (DRV/DRI)/Adequate Intakes (AI) of Ca, Fe, Zn, proteins, and dietary fibre was also evaluated for the adult group.

2.2.3. Physicochemical Treatments of Moringa Residual Cake After Oil Extraction

Two treatments proposed by Silva-Jaimes et al. [5] were performed according to the scheme shown in Figure 2, with some modifications after the preliminary trials. Prior to sample treatments, preliminary pre-treatments were conducted using either intact or ground pellets, with or without agitation and with or without filtration.

2.2.4. Statistical Analysis

To detect significant differences among samples, a multiple-sample comparison of means using Analysis of Variance (ANOVA) and Fisher’s Least Significant Differences (LSD) was employed. Statistical analysis was conducted using Statgraphics Plus 7.1 software (Bitstream, Cambridge, MN, USA), and differences were deemed significant at p < 0.05.

3. Results and Discussion

3.1. Proximal Composition of Raw Materials

Dehulled moringa seeds showed a protein content consistent with previous studies, with higher levels in the defatted sample as a result of cold pressing, which enriches the residual cake in proteins (

Table 1. Proximate composition of dehulled moringa seeds and cake after cold-press oil extraction ⁽¹⁾.

Component	Units	Dehulled Moringa Seeds	Reference Values	Residual Cake after Oil Extraction	Reference Values
Moisture	g/100 g	7.39 ± 0.03 a	4.70 a; 7.0 g; 5.7–8.9 h	8.16 ± 0.03 b	5.03 a; 5.39 d; 8.4 g
Proteins f: 5.4975 (2); (f: 6.25)	g/100 g d.m.	33.7 ± 0.1 a (38.3)	28.04 (f: NI) a 36.4 (f: 5.4975) g; 41.1 (f:6.25) g; 29.4–33.3 h	45.83 ± 0.0.02 b (52.1)	50.80 (f: NI) a; 43.82 (f: NI) d; 47.6 (f: 5.4975) g; 54.1 (f:6.25) g
Total dietary fibre (TDF) Insoluble (IDF) Soluble (SDF)	g/100 g d.m.	TDF: 8.28 ± 0.21 a IDF: 5.82 ± 0.29 a SDF: 2.45 ± 0.50 a	7.73 a (3); 6.8–8.0 (TDF) h; 6.5 (TDF)/5.9 (IDF)/0.6 (SDF) g	TDF: 13.0 ± 0.3 b IDF: 10.48 ± 0.04 b SDF: 2.52 ± 0.28 a	2.54 d (3); 12.96 a (3); 12.8 (TDF)/11.9 (IDF)/0.89 (SDF) g
Lipids	g/100 g d.m.	38.5 ± 0.5 a	30–40 b; 39.0 g; 34.7–40.4 h	9.66 ± 0.06 b	11.2 b; 26.99 d; 10.5 g
Ash	g/100 g d.m.	3.56 ± 0.04 a	4.10 a; 3.6 g; 4.4–6.9 h	6.09 ± 0.13 b	3.96 d; 10.0 a; 5.0 g
Carbohydrates not included in fibre (4)	g/100 g d.m.	16.7	10.59 a; 14.5 g; 16.5–19.8 h	26.5	17.3 d; 18.15 a; 24.1 g

⁽¹⁾ Mean ± SD, n = 3. Values in the same row followed by different letters are significantly different (p < 0.05); ⁽²⁾ f: conversion factor from N to proteins considering the average factors of oilseeds: 5.4975; ⁽³⁾ crude fibre; ⁽⁴⁾ calculated by difference; ^a Abiodun et al. [4]; ^b Cattan et al. [1]; ^d Silva-Jaimes et al. [5]; ^g previous results from Q’omer; ^h Leone et al. [2]. d.m.: dry matter; NI: not informed; TDF: total dietary fibre; IDF: insoluble dietary fibre; SDF: soluble dietary fibre.

). Regarding dietary fibre, total values were in line with the literature, with an increase in the insoluble fraction after oil extraction, while the soluble fraction tended to decrease due to mechanical losses or refining. The lipid profile was higher in the seeds, whereas the cake presented a greater ash content, reflecting a concentration of minerals bound to proteins and polysaccharides. Finally, the carbohydrate content, excluding fibre, also remained consistent with reported values in the literature.

3.2. Nutritional Value of Raw Materials

Phytic acid and its salts are the main phosphorus reserve in plants, but in human and monogastric animals they limit the bioavailability of divalent and trivalent minerals by forming insoluble complexes in the intestinal tract. In the samples analyzed, phytate content was high and greater in the defatted cake, in line with expectations and literature data (

Table 2. Mineral content, phytic acid, and lower myo-inositol phosphates in dehulled moringa seeds and residual cake after oil extraction *.

Myo-Inositol Phosphate, g/100 g d.m.	Dehulled Moringa Seeds	Reference Values	Residual Cake after Oil Extraction	Reference Values
InsP6, (Phytic Acid)	0.74 ± 0.14 a	0.059 a; 1.85 f; 0.175–1.381 g	1.39 ± 0.26 b	0.149 a; 2.18 f
InsP5	0.0019 ± 0.0008	0.110 f	N.D.	0.247 f
InsP4	N.D.	0.020 f	N.D.	0.043 f
InsP3	N.D.	0.006 f	N.D.	0.007 f
Mineral, mg/100 g d.m.
Ca	33.3 ± 0.8 a	20.4 a; 87.6 f; 150–260 g	61.0 ± 2.3 b	25.0 a; 265.5 c; 144 f
Fe	1.96 ± 0.01 a	3.1 a; 4.85 f; 44.8 g	4.02 ± 0.18 b	2.5 c; 3.7 a; 16.2 f
Zn	2.36 ± 0.03 a	0.81 a; 3.83 f; 7.3 g	3.84 ± 0.12 b	1.21 a; 7.30 f
Na	0.985 ± 0.002 a	15.5 a	3.42 ± 0.05	13.8 c; 18.4 a

* Mean ± SD, n = 3. Values in the same row followed by different letters are significantly different (p < 0.05); d.m.: dry matter; InsP_3–6: myo-inositol phosphates with 3, 4, 5 and 6 phosphate groups; N.D. not detected; ^a Abiodun et al. [4]; ^c Cattan et al. [1]; ^f previous results from Q’omer; ^g Amad & Zentek [3].

). No significant hydrolysis of InsP₆ was detected, indicating that the seeds were new and free of fungal contamination. This lower phytate content slightly improves mineral bioavailability, but prolonged fermentation or the use of phytases is still recommended to reduce it during processing. In animal feeding, phytase supplementation or mineral addition remains necessary, since extrusion only achieves partial reductions. Regarding minerals, higher concentrations were found in the cake compared to seeds, especially sodium, possibly due to processing contamination. These variations are consistent in magnitude with previous studies and are mainly influenced by agronomic factors and seed origin.

Nutrient reference intakes (DRIs) from FAO/WHO and EFSA aim to prevent deficiencies and promote health, though values may vary by population habits. For dietary fibre, the Adequate Intake (AI) for adults is 25 g/day, and 100 g of moringa seeds or cake can supply roughly one-third to half of this requirement. The seeds show a favourable soluble/insoluble ratio, while the cake is richer in insoluble fibre (

Table 3. Percentage contribution of dehulled moringa seeds and residual cake to the Adequate Intake of dietary fibre ^a.

Moringa Material	Total Dietary Fibre g/100 g w.b. b	% Contribution to Adequate Intake c	Ratio SDF/IDF d, g/g
Seeds	7.61 ± 0.19 a	30 ± 1	1/2.4
Residual Cake	12.1 ± 0.3 b	49 ± 1	1/4.2

Mean ± SD, n = 3. Values in the same column followed by different letters are significantly different (p < 0.05); ^a dietary fibre and % contribution to Adequate Intake from moringa samples do not include the hull. ^b w.b.: wet basis; ^c % contribution to Adequate Intake (AI) for an average daily intake of 100 g of seeds or cake. The reference value used for calculation was the Adequate Intake of dietary fibre in adults >18 years: 25 g/day [11]. Soluble/insoluble fibre ratio: 1:3 [12]; ^d SDF: soluble dietary fibre; IDF: insoluble dietary fibre.

). Regarding protein, both the seeds and cake provide over 50% of daily needs, highlighting their potential as valuable plant-based ingredients for enriching foods or developing protein-rich formulations (

Table 4. Percentage contribution of dehulled moringa seeds and residual cake to PRI and Recommended Dietary Allowance.

Moringa Material	Proteins g/100 g w.b. a	% Contribution to PRI b, Adults	% Contribution to RDA c, Adults
Seeds	31.2 ± 0.1 a	53.7 ± 0.2	55.8 ± 0.2
Residual Cake	42.1 ± 0.0 b	72.4 ± 0.0	75.2 ± 0.0

Mean ± SD, n = 3. Values in the same column followed by different letters are significantly different (p < 0.05); ^a w.b.: wet basis; ^b % of contribution to PRI (Popular Reference Intake), 0.83 g of proteins/kg body weight [13]; ^c Recommended Dietary Allowance of proteins, 0.8 g of proteins/kg body weight [14], assuming an average daily intake of 100 g in a healthy adult (≥18 years, male or female) with a body weight of 70 kg.

).

The contribution of moringa seeds and defatted cake to mineral intake was evaluated considering phytic acid effects. Calcium absorption is not inhibited, though its dietary contribution is low. Iron bioavailability is strongly limited by high InsP₆/Fe ratios, despite the higher iron content in the cake. Zinc remains bioavailable, with InsP₆/Zn below the inhibitory threshold, and the cake provides a higher contribution than seeds. Overall, 100 g of seeds or cake can partially meet daily Ca and Zn needs, but iron absorption is restricted, highlighting the potential benefit of phytase or processing treatments to improve mineral availability (

Table 5. Contribution to the mineral Dietary Reference Intake and prediction of its bioavailability in humans from dehulled moringa seeds or residual cake.

Mineral	DRI (1) mg/day	% of Contribution to the DRI (2)	Threshold Molar Ratio InsP6/Mineral (3)	Molar Ratio InsP6/Mineral
Ca
Seeds	Adults, 1000	3.3	>0.24	0.15
Residual Cake		6.1		0.15
Fe
Seeds	Male/Female,	25/11	>0.4	3.20
Residual Cake	8/18	50/22		2.93
Zn
Seeds	Male/Female,	22/29	>5	3.03
Residual Cake	11/8	35/48		3.51

⁽¹⁾ DRI: Dietary Reference Intake (mg/day) in adults—Ca (1000) for 19–70-year-olds (y); Fe male/female (8/18) for 31–≥70 y/19–50 y, respectively; Zn male/female (11/8) for 31–50 y/19–≥70 y, respectively [15,16]; ⁽²⁾ % contribution to DRI based on a daily intake of 100 g of grains assuming the absence of mineral bioavailability inhibitors. ⁽³⁾ Threshold molar ratios of InsP₆/mineral (InsP₆/Ca; InsP₆/Fe; InsP₆/Zn), indicating onset of mineral bioavailability inhibition in humans [8,9,10].

).

3.3. Preliminary Trials

In the evaluation of treatments with saline and ethanolic solutions, the use of ground moringa cake resulted in low recoveries (35–54%) due to significant losses despite applying centrifugation and/or filtration; therefore, intact pellets were selected as the working matrix. In ethanolic solution, after 4 h without agitation, the pellets maintained their integrity and recovery reached 77 ± 2%, with filtration being employed to reduce losses caused by leaching. In contrast, treatments with saline solution led to complete disintegration of the pellets after 24 h of immersion, with low recoveries (38–44%) regardless of agitation; in this case, filtration after treatment caused fewer material losses compared with decantation or centrifugation. Overall, preliminary trials indicated that ethanolic treatment without agitation constitutes the most efficient strategy, whereas the use of saline solution entails unavoidable material losses. It was concluded that subsequent experiments should be carried out using pellets in their native form, without agitation and with filtration as the recovery method, acknowledging that the soluble and leached fraction remains in the treatment solutions, which become enriched with nutrients and bioactive compounds.

3.4. Proximal and Nutritional Composition of Defatted Moringa Residual Cake Treated with Saline and Ethanol Solutions

Ethanol treatment enriched the protein content, whereas the saline treatment maintained protein proportions despite substantial solid losses (

Table 6. Proximate composition of cake after cold-press oil extraction and after treatments with saline solution and ethanolic solution ⁽¹⁾.

Component	Units	Saline Solution	Ethanolic solution
Moisture	g/100 g	8.31 ± 0.03 b	6.89 ± 0.01 a
Proteins, f: 5.4975 (2) (f: 6.25)	g/100 g, d.m.	45.4 ± 1.9 a (51.6)	49.0 ± 0.0 b (55.7)
Total dietary fibre (TDF) Insoluble (FI) Soluble (FS)	g/100 g, d.m.	TDF: 30.5 ± 3.1 b IDF: 27.9 ± 3.3 b SDF: 2.61 ± 1.34 a	TDF: 17.4 ± 1.5 a FI: 14.1 ± 1.7 a SDF: 3.29 ± 0.17 a
Lipids	g/100 g, d.m.	18.9 ± 0.8 b	6.29 ± 0.66 a
Ash	g/100 g, d.m.	4.68 ± 0.15 a	5.86 ± 0.12 b
Carbohydrates not included in fibre (3)	g/100 g, d.m.	0.52	21.5
InsP6	g/100 g, d.m.	2.98 ± 1.2 b	1.71 ± 1.3 a
InsP6, not accounting for solid losses, % reduction	g/100 g, d.m. %	1.22 ± 0.29 a 12	1.32 ± 0.28 a 5
Ca	mg/100 g d.m.	99.2 ± 28 b	65.5 ± 3.7 a
Fe	mg/100 g d.m.	5.50 ± 0.20 b	3.72 ± 0.21 a
Zn	mg/100 g d.m.	8.55 ± 0.27 b	4.33 ± 0.29 a
Na	mg/100 g d.m.	73.3 ± 6.7 b	2.58 ± 0.16 a

⁽¹⁾ Mean ± SD, n = 3. Values in the same row followed by different letters are significantly different (p < 0.05). ⁽²⁾ f: Conversion factor from N to proteins considering the average number of oilseeds: 5.4975; ⁽³⁾ calculated by difference. d.m.: dry matter; TDF: total dietary fibre; IDF: insoluble dietary fibre; SDF: soluble dietary fibre.

). Both treatments increased insoluble fibre, particularly in the saline sample, while soluble fibre experienced significant reductions. Lipid content rose with saline but decreased under ethanol, indicating partial extraction of polar lipids. Ash content declined moderately, as minerals remained bound to proteins, fibres, and lipids. Carbohydrates were mainly lost with saline, while ethanol caused only a slight decrease. Phytates became more concentrated, indicating they were neither extracted nor hydrolyzed during treatment. Minerals (Ca, Fe, Zn, and Na) increased significantly with saline, primarily due to the salt and other mineral components, whereas in ethanol-treated samples they remained similar to the control, reflecting differences in solubility and binding to macronutrients.

4. Conclusions

Oil extraction enriches the seeds and residual cake in proteins, fibre and minerals, although it also increases phytates. Moringa and its cake emerge as sources of plant-based proteins and fibre, with minerals whose Fe bioavailability is limited, while Ca and Zn remain available. Treatments with saline or ethanol solutions cause losses of solids and nutrients, affecting the final composition. The nature of the treatment solution influences nutrient retention or loss, determining the final applicability of the cake as a nutritious by-product. Phytate concentration did not change significantly or decreased slightly—if solid losses during treatment were not considered—indicating that endogenous phytases did not act and that phytates remained bound to the protein fraction.