Yellowhorn (Xanthoceras sorbifolium): A Climate-Resilient Oilseed for Industrial Applications

Abstract

Xanthoceras sorbifolium (Yellowhorn) is an underutilized, multipurpose, climate-resilient oilseed with emerging food and industrial potential. This review consolidates current knowledge on its botany, agronomy, kernel composition, extraction technologies, protein and bioactive functionality, food uses, regulatory considerations, and sustainability challenges. Yellowhorn offers high-quality oil with ≈94% unsaturated fatty acids (notably 3.5–4% nervonic acid), while defatted kernel meal contains 31–37% protein (w/w). The matrix also carries bioactives such as tocopherols in the oil (70–530 mg/kg), phytosterols (1420–2970 mg/kg), and saponins (up to 11.62%), alongside flavonoid extracts that show promising antioxidant activity (DPPH EC₅₀ ≈ 10.7 µg/mL). Extraction methods, including cold pressing, solvent systems, and supercritical CO₂, present trade-offs in yield (≈87.8%, ≈60.4–98.04%, and ≈56.5–89.63% respectively), bioactive retention, and scalability, while co-product valorization can improve economic and environmental performance. Regulatory acceptance in the U.S. will likely depend on a refined-oil, specification-driven Generally Recognized as Safe (GRAS) pathway supported by compositional and toxicological evidence. Sustainability priorities include breeding improvements and supply-chain development on marginal lands, valorization of co-products, and integration of life cycle assessment (LCA), both of which are currently under-reported for Yellowhorn. Future directions emphasize process optimization for simultaneous oil-protein recovery, selective purification of functional lipids, encapsulation for stability, and human studies to substantiate claims. Collectively, Yellowhorn represents a promising climate-ready ingredient system requiring targeted research to enable safe, scalable, and sustainable adoption.

1. Introduction and Rationale

Yellowhorn (Xanthoceras sorbifolium) is a woody oilseed native to northern China and the sole species of the genus Xanthoceras within the Sapindaceae (soapberry) family, with historical documentation in the Jiu Huang Ben Cao (1406 AD) and longstanding local use for edible oil and clean illumination [1,2]. Recent agronomic and genomic studies highlight its resilience to heat, drought, salinity, and alkalinity, enabling cultivation on marginal lands and positioning the crop for climate-adapted agriculture [3,4,5]. Botanically, the species exhibits unusual andromonoecious floral morphology with functional monoecy and self-incompatibility, features relevant to pollination management and yield stabilization [6].

From a food science perspective, Yellowhorn kernels combine high oil content (≈55–70%) with an unsaturated dominant profile (≈94%), typically enriched in linoleic and oleic acids and distinguished by nervonic acid (≈3.5–4%) and erucic acid (≈9%) [7,8,9]. Beyond lipids, the defatted meal contains ≈31–37% protein, and the matrix carries tocopherols, phytosterols, saponins, and diverse flavonoids, supporting antioxidative and techno-functional roles [10,11,12]. Together, these attributes suggest potential for edible oil, protein ingredients, and bioactive side streams; however, successful translation requires thoughtful management of erucic acid levels, oxidation control, and minor constituent standardization through germplasm selection and process design.

Extraction routes such as cold pressing, solvent extraction, and supercritical CO₂ offer distinct trade-offs in yield, compositional integrity, sustainability, and scalability [12,13,14,15]. In parallel, a plausible U.S. pathway is a refined oil, specification-driven GRAS strategy, supported by manufacturing controls, compositional datasets, exposure estimates, and a weight-of-evidence safety narrative [16,17,18]. Finally, realizing sustainability potential demands attention to breeding bottlenecks, supply chain development, and LCA beyond current biology-focused research [19,20].

This review synthesizes botany and agronomy, kernel composition and oil chemistry, extraction and processing, protein and bioactive functionality, food applications, safety/regulatory considerations, and sustainability/value chain challenges for Yellowhorn. Our objectives are to: (i) consolidate contemporary evidence across disciplines; (ii) identify process- and specification-based strategies that enable food-grade development while managing erucic and oxidative risks; (iii) map functional opportunities for proteins and bioactives; and (iv) outline regulatory and sustainability roadmaps to support credible commercialization. In doing so, we aim to transition Yellowhorn from a promising niche oilseed to a viable, climate-ready ingredient system grounded in evidence-based manufacturing, safety, and performance. Existing studies on Yellowhorn have largely progressed in disciplinary silos, emphasizing agronomy, oil chemistry, or bioactivity in isolation, while offering limited critical comparison of processing conditions, minimal engagement with U.S. food regulatory requirements and little integration of life-cycle perspectives needed to evaluate scalability and sustainability. As a result, the field lacks a unifying framework that connects compositional promise with process design, regulatory feasibility, and supply-chain analytics. To our knowledge, this is the first cross-disciplinary synthesis that links extraction choices, GRAS-ready specifications, and LCA gaps for Yellowhorn.

2. Botanical and Agronomic Snapshot

Yellowhorn is a woody perennial oilseed native to northern China and the sole species of Xanthoceras within the Sapindaceae family (soapberry) [1]. Historical records trace its use to the famine-relief materia medica Jiu Huang Ben Cao (1406 AD), with long-standing cultivation near temples and dwellings for edible oil and clean-burning illumination [1,2]. The modern binomial Xanthoceras sorbifolium was established by Alexander Bunge in 1833 [21].

Agronomically, Yellowhorn is heat- and drought-tolerant, performing optimally near 35 °C and tolerating up to ≈38 °C, with successful cultivation reported under low precipitation regimes (≈14–18 inches per year) and on marginal soils, including high salinity (≈3% NaCl) and alkaline substrates [3,4,5]. Its floral biology is unusual among angiosperms: inflorescences are morphologically andromonoecious (male and bisexual flowers co-occurring), yet the bisexual flowers are functionally monoecious, with only the pistillate organs fertile [6]. Despite this, the species is self-incompatible; selfed ovules abort within ≈10 days, necessitating cross-pollination for fruit set [6]. Figure 1 illustrates the morphological progression of X. sorbifolium, from pollinated inflorescences (A) through the fruiting stage (C). Once mature, the fruits/capsules are opened to remove the seeds (E), which are then shelled to obtain the kernels (B) used for oil pressing (D).

3. Kernel Composition and Oil Chemistry

Yellowhorn kernels exhibit high lipid accumulation (≈55–70% oil), with unsaturated fatty acids constituting ≈94% of total fatty acids across reports [7,8,22]. As summarized in Table 1, the profile is linoleic- and oleic-dominant, accompanied by longer-chain monoenes, most notably nervonic acid (≈3.5–4%) and erucic acid (≈9%). The erucic acid content merits explicit consideration for food applications; variability among accessions and process fractions may influence intended use levels, labeling, and alignment with edible-oil precedents, even when the overall unsaturation resembles conventional seed oils [7,8,9,22,23,24,25,26,27,28]. Beyond lipids, seeds present low moisture (≈4.4%, [12]), which supports postharvest stability under appropriate storage, and comparatively high protein (≈31–37%), highlighting the potential of defatted meal as a protein-rich co-product pending functionality and safety characterization [10,11].

Nervonic acid (24:1 n-9), a very-long-chain fatty acid (VLCFA) and a key component in myelin biosynthesis, distinguishes Yellowhorn relative to common edible oils. This acid contributes to membrane thickness, rigidity, and packing of myelin bilayers. Sources and production routes span oilseeds, microalgae, and engineered platforms, with literature exploring its potential roles in neurodevelopment and demyelinating conditions; however, translational efficacy requires cautious interpretation and further clinical substantiation [29,30,31]. Table 1 shows the comparison between Yellowhorn and common edible oils, distinguishing Yellowhorn as an oil with higher amounts of nervonic acid (3.5–4%) than its counterparts with <1% concentration. Oleic acid (18:1 n-9) contributes to oxidative stability and broad utility (edible applications, biodiesel), with cardiometabolic relevance discussed in the literature; the oil’s oleic predominance therefore supports both technological performance and nutritional positioning [32,33]. Linoleic acid (18:2 n-6) is diet-essential and must be obtained exogenously; population-level adequacy typically requires low single-digit percent energy, though specific requirements vary by life stage and dietary context [34,35].

Table 1. Fatty acid composition of Yellowhorn kernels compared to soybean, canola, coconut, palm, olive, and avocado oils.

Fatty Acid (%)	Yellowhorn [7,8,22]	Soybean [8,23]	Canola [24]	Coconut [26,27]	Palm [8,28]	Olive [27,36]	Avocado [9,25]
Oleic acid (18:1 n-9)	30.7–31.0	23	61.60	6.9–10.1	30–56	66–75	36–42
Linoleic acid (18:2 cis-9,12)	40.6–44	54	21.70	1.90	10–21	7–13	14–18
Nervonic acid (24:1 n-9)	3.5–4	n.r.	n.r.	0.37	n.r.	0.39	n.r.
Erucic acid (22:1 n-9)	9	0.30	0.20	0.09	n.r.	0.09	n.r.
Palmitic acid (16:0)	5.20	11	n.r.	9.50	19–55	29.80	25–26
Stearic acid (18:0)	2.20	4	1.50	2.80	1–5.5	13.95	0.5–0.6
Linolenic acid (18:3)	0.50	8	9.60	0.35	0–0.5	0.39	0.5–0.8
Arachidic (20:0)	0.40	0.30	0.60	15.0	0.1–1	0.38–0.46	n.r.

n.r.: Not reported.

Table 1. Fatty acid composition of Yellowhorn kernels compared to soybean, canola, coconut, palm, olive, and avocado oils.

Fatty Acid (%)	Yellowhorn [7,8,22]	Soybean [8,23]	Canola [24]	Coconut [26,27]	Palm [8,28]	Olive [27,36]	Avocado [9,25]
Oleic acid (18:1 n-9)	30.7–31.0	23	61.60	6.9–10.1	30–56	66–75	36–42
Linoleic acid (18:2 cis-9,12)	40.6–44	54	21.70	1.90	10–21	7–13	14–18
Nervonic acid (24:1 n-9)	3.5–4	n.r.	n.r.	0.37	n.r.	0.39	n.r.
Erucic acid (22:1 n-9)	9	0.30	0.20	0.09	n.r.	0.09	n.r.
Palmitic acid (16:0)	5.20	11	n.r.	9.50	19–55	29.80	25–26
Stearic acid (18:0)	2.20	4	1.50	2.80	1–5.5	13.95	0.5–0.6
Linolenic acid (18:3)	0.50	8	9.60	0.35	0–0.5	0.39	0.5–0.8
Arachidic (20:0)	0.40	0.30	0.60	15.0	0.1–1	0.38–0.46	n.r.

n.r.: Not reported.

Minor lipid classes reported in Yellowhorn oil include triacylglycerols (e.g., TG 52:2, TG 54:4, TG 56:7), cholesteryl esters (e.g., CE 18:2, CE 20:4, CE 22:6), phosphatidylethanolamines (PE 18:0/20:4, PE 18:1/18:1), lysophosphatidylcholines (LPC 16:0, LPC 18:1), and phosphatidylcholines (PC 16:0/18:2, PC 18:0/20:4). In an animal model, these components were associated with the attenuation of hyperlipidemia, warranting further mechanistic and clinical study before food-use claims [37]. The kernel matrix also contains antioxidants, notably tocopherols (γ-dominant), phytosterols (β-sitosterol, Δ⁷-stigmastenol), and vitamins A and C [11,12]. Reported totals include ≈24.3 mg/100 g of tocopherols (γ-tocopherol predominant), representing early evidence of these micronutrients in Yellowhorn oil and inviting confirmation across accessions and processing conditions [11].

4. Extraction and Processing Routes

4.1. Cold Pressing

Cold pressing represents a mechanical, solvent-free extraction approach that minimizes thermal and chemical stress, thereby preserving native bioactive compounds and reducing environmental burden [38]. For Yellowhorn, cold-pressed oil retains a favorable fatty acid profile (rich in oleic and nervonic acids) and exhibits strong nutritional attributes. However, the yield is comparatively lower than that of solvent-based methods (87.81%), emphasizing its positioning as a minimally processed, health-oriented oil rather than a high-throughput industrial option [12]. Despite its promise, research gaps remain in optimizing process parameters, refining strategies for bioactive recovery (e.g., tocopherols, phytosterols), and developing encapsulation technologies to enhance oxidative stability and broaden functional applications in food and nutraceutical systems [32].

4.2. Solvent Extraction

Solvent extraction is the industrial benchmark for oil recovery, particularly for low-oil seeds, due to its high efficiency and scalability. Conventional practice employs non-polar solvents, predominantly hexane, owing to its strong solvating power, low boiling point (≈69 °C), and chemical stability. This method achieves near-complete oil removal (<1% residual in meal), far exceeding mechanical pressing (10–15% residual), with reported yields for Yellowhorn around 60.4% under typical conditions [39,40]. However, extraction cycles are lengthy (5–10 h at ≈70 °C), and reliance on petrochemical solvents raises concerns regarding residual contaminants, thermal degradation of thermolabile lipids, and environmental impact. Emerging research explores green solvent systems (e.g., ethanol, isopropanol) and hybrid approaches integrating thermal or enzymatic pretreatments to mitigate these drawbacks while maintaining efficiency [13]. Future directions include solvent recovery optimization, residue control, and process intensification to align with sustainability and food safety imperatives.

4.3. Supercritical Fluid Extraction

Supercritical fluid extraction, most commonly employing carbon dioxide (CO₂), is regarded as a green technology for oil recovery due to its efficiency and absence of toxic solvent residues. Above CO₂’s critical point (31 °C, 74 bar), the fluid exhibits gas-like diffusivity and liquid-like solvating power, enabling effective extraction of non-polar lipids while minimizing thermal degradation [14]. For Yellowhorn, supercritical fluid extraction has demonstrated the ability to recover high-quality oils enriched in bioactive compounds, positioning it as a promising alternative to conventional methods [15]. Its adoption is expanding across the food, pharmaceutical, and cosmetic sectors, reflecting growing interest in sustainable processing [41].

Despite these advantages, supercritical fluid extraction presents notable constraints. Capital investment is substantial due to the need for high-pressure equipment and stringent safety systems [14,42]. Furthermore, oil yields, reported at ≈56.5% for Yellowhorn, may fall below those achieved via solvent extraction unless pressure, temperature, and co-solvent conditions are carefully optimized [40,41]. These factors limit scalability for small-scale or cost-sensitive operations, highlighting the need for process intensification strategies and economic modeling to support broader industrial adoption.

4.4. Water-Based Extraction Methods

Water-based extraction methods, such as hot water flotation and aqueous enzymatic extraction, offer environmentally friendly alternatives to traditional solvent-based techniques for edible oil recovery. Hot water flotation, one of the oldest methods, involves boiling crushed oilseeds in water, allowing oil to rise to the surface and be skimmed off. Unlike solvent extraction and supercritical extraction, water-based extraction is low-cost and has an average oil yield of about 58.74%, requiring 1–2 h at 40–60 °C [39]. While inexpensive and free of chemical solvents, this method often results in moderate oil recovery and presents operational challenges such as emulsion formation and high fuel consumption [43].

More advanced aqueous approaches, such as enzymatic-assisted extraction, use enzymes to break down cell walls and release oil and protein fractions into water. This technique increases oil yield (sometimes exceeding 90%) and enables co-extraction of valuable proteins, supporting sustainable processing systems [44]. However, aqueous enzymatic extraction can be costly due to enzyme requirements and may require additional demulsification and separation steps [39].

For Yellowhorn specifically, ref. [32] notes that aqueous enzymatic extraction (AEE) is one of the primary extraction methods studied for Yellowhorn oil, alongside pressing, solvent extraction, ultrasound-assisted extraction, microwave-assisted extraction, and supercritical CO₂ extraction. AEE is highlighted as particularly promising because it improves oil recovery efficiency while maintaining the integrity of bioactive compounds, especially nervonic acid, a key component of Yellowhorn oil with neurological health significance. These findings suggest that water-based and enzymatic approaches may be especially well-suited for Yellowhorn due to their ability to preserve sensitive functional lipids while reducing environmental impact [32].

Emerging water-based techniques such as subcritical water extraction (SWE) and ultrasound-assisted extraction further expand the potential of water as an extraction medium. SWE uses high-temperature, pressurized water to recover oil without organic solvents, though it requires more complex and energy-intensive equipment [45]. Ultrasound-assisted extraction improves yield and reduces processing time through enhanced mass transfer and cell disruption, though prolonged sonication can degrade heat- or oxidation-sensitive compounds [39]. Together, these water-based techniques reflect a growing movement toward greener oil extraction, balancing process efficiency with environmental and health considerations.

A comparative summary of the operating conditions, yields, advantages, and research needs of these extraction methods is presented in

Table 2. Comparison of oil extraction technologies.

Method	Cold Pressing	Solvent Extraction	Supercritical Fluid Extraction	Water-Based Extraction
Principle/Solvent	Mechanical pressing; solvent-free [38]	Non-polar solvents (mainly hexane); emerging green solvents (ethanol, isopropanol) [39]	Supercritical CO2 (sometimes with co-solvents) [14,41]	Water-based processes using heat, enzymes, or mass transfer [40,45]
Typical Conditions	Single screw press with 60 ± 4 °C running temperature; ambient or low temperature; minimal thermal stress [12,37]	≈50 °C; 4 h extraction cycle; solvent to solid ratio 1:5 (w/v) [12]	28 MPa, 42 °C for 192 min; >31 °C; >74 bar; high-pressure operation [12,14]	40–60 °C; 1–2 h processing time (hot water flotation); solvent-to-solid ratio 1:5 (w/v) [40]
Oil Yield	87.81%; Lower than solvent methods (significant residual oil remains) [12]	98.04% [12]; ≈60.4%; <1% residual oil in meal [39]	89.63% [12]; ≈56.5% (can increase with optimization) [40]	Hot water flotation: ≈58.74% Aqueous enzymatic extraction: up to >90%; 68.74% [40,44]
Advantages	Preserves native bioactive compounds; favorable fatty acid profile (oleic, nervonic acids); environmentally friendly; minimally processed [38]	Highest efficiency; scalable; industrial benchmark; suitable for low-oil seeds [13,39]	No toxic solvent residues; mild thermal conditions; high-quality oil enriched in bioactives; sustainable technology [15,41]	Environmentally friendly; improved retention of bioactives; potential co-extraction of proteins (AEE); potentially high yield [32,44]
Limitations	Lower extraction efficiency; not suitable for high-throughput industrial production [12,32]	Long extraction time; solvent residues; thermal degradation of labile lipids; environmental and safety concerns [13,39]	High capital and operating costs; complex equipment; yields may be lower than solvent extraction without optimization [15,42]	High fuel inputs; high operating costs for enzymes; demulsification often needed [39,43,45]
Key R&D Needs	Optimization of process parameters; improved recovery of bioactives (tocopherols, phytosterols); encapsulation strategies to enhance oxidative stability and functionality [32]	Green solvent development; solvent recovery optimization; residue control; hybrid thermal/enzymatic pretreatments; process intensification [40]	Optimization of pressure, temperature, and co-solvents; economic modeling; scalability and process intensification strategies [42]	Improvement of demulsification and separation efficiency; development of lower cost, and energy efficient AEE systems [39,43]
Scale of Yields	Laboratory- and industrial-scale experiments [12]	Laboratory-scale experiments [12]	Laboratory- and pilot-scale experiments [12]	Laboratory-scale experiments [12]
Seed Moisture	4.43% [12]	4.43% [12]	4.43% [12]	4.43% [12]
Particle size	Whole kernels, 10% shell added as backfill [12]	Ground kernels [12]	Ground kernels [12]	Ground kernels [12]
Recovery efficiency	Oil yield vs. crude fat; gravimetric [12]	Oil yield vs. crude fat; gravimetric [12]	Oil yield vs. crude fat; gravimetric [12]	Oil yield vs. crude fat; free oil recovered after demulsification/centrifuge [12]

.

4.5. Assessment of Extraction Methods for Food-Grade Applications

Considering the full range of extraction pathways outlined in Section 4.1, Section 4.2, Section 4.3 and Section 4.4, no single method meets all criteria for food-grade production. Each technique presents distinct trade-offs in yield, cost, sustainability, and preservation of bioactive compounds. Solvent extraction currently offers the highest and most consistent yields (≈60.4%) and remains the most economically viable approach for large-scale manufacturing, but its reliance on petrochemical solvents necessitates additional refining steps and raises concerns regarding thermolabile lipid degradation. Cold pressing, in contrast, provides the cleanest and most natural product, preserving key bioactive components such as tocopherols and nervonic acid; however, its relatively low extraction efficiency limits its applicability for high-volume industrial use.

Supercritical CO₂ extraction produces high-quality oil while protecting sensitive compounds, aligning well with sustainability goals highlighted in previous sections. However, its high equipment and operational costs restrict accessibility for many food-grade processors. The addition of water-based methods, including hot-water flotation and aqueous enzymatic extraction, introduces an increasingly relevant category of solvent-free options. While traditional hot-water extraction yields moderate oil recovery, enzymatic-assisted aqueous extraction offers high efficiency and is particularly promising for Yellowhorn due to its ability to retain functional lipids and support cleaner processing. However, enzyme cost and additional separation requirements currently limit its widespread adoption.

Overall, solvent extraction remains the most practical large-scale method for food-grade applications under current industrial conditions, while cold pressing and supercritical CO₂ extraction cater to premium markets emphasizing minimal processing and bioactive integrity. Water-based extraction, especially enzymatic approaches, represents a growing and environmentally aligned alternative with strong potential for future food-grade Yellowhorn oil production as technological and economic barriers continue to be addressed.

5. Functional Streams: Protein and Bioactives from Yellowhorn

Yellowhorn is an underutilized oilseed with dual value streams: (i) protein, primarily from kernels and defatted press cake, and (ii) bioactives distributed across kernels, leaves, husks, and flowers. Reported constituents include saponins, polyphenols/flavonoids, tocopherols, phytosterols, and select vitamins that exhibit antioxidant, antimicrobial, and putative neuroprotective properties, while kernel proteins are relevant for food structuring [10,11,46].

5.1. Protein Content, Fractions, and Amino Acid (AA) Profile

Kernel protein content is ≈26.0–26.3%, in raw seeds and ≈53.5–62.0% in defatted meal, supporting protein isolate production [47,48]. Isolates/fractions from defatted kernels attain ≈80.3–80.8% (w/w) purity, consistent with commercial specifications [47,48]. Major fractions include albumin (≈40–49% of total protein; 21.50–34.63% under sequential/direct extraction), globulin (≈23–30%; 26.38–75.57% by process), glutenin (≈2.49%), and prolamins/gliadin (1.99–7.26%) [10,48]. Albumin predominance reflects water solubility; globulin and glutenin serve as storage proteins.

AA composition is nutritionally balanced. Across seven accessions, essential amino acids (EAAs) (Figure 2) represent 6.91 ± 0.78%, and non-essential amino acids (NEAAs) 15.9 ± 1.8% [11]. Aspartic acid + asparagine, glutamic acid + glutamine, and arginine dominate (collectively up to ≈43% of total AAs), with branched-chain EAAs (leucine, isoleucine, valine) comparable to or exceeding those in soybean meal; lysine levels align with monogastric feed requirements (3–6% for pigs/poultry) [2,10,11]. While methionine and tryptophan can be limiting, sulfur amino acids (methionine + cysteine) are relatively abundant, enabling partial substitution for non-cereal plant proteins [11,47]. The EAA/NEAA (0.37–0.38) and EAA/total AA (0.27–0.28) ratios (mg/g of dietary protein) exceed FAO/WHO recommendations for adults but fall short for young children in threonine and lysine [47].

5.2. Bioactive Compounds: Content and Profile

Different bioactive compounds reported in different parts of Yellowhorn are shown in Table 3 and Table 4. Comprehensive phytochemical surveys identify ≈278 compounds across plant parts: 124 terpenoids, 48 flavonoids, 14 phenylpropanoids, 17 steroids, 17 phenols, 29 fatty acids, 9 alkaloids, 4 quinones, and others [2].

Saponins concentrate in seed hulls (≈7.2 mg/g), defatted kernels (≈3.4 mg/g), and crude oil (≈0.64 mg/g), with microwave-assisted extraction yielding up to 11.62 ± 0.37% from defatted kernels and 5.03–7.33% (dry wt.%) from leaves [10,49,50]. Leaf saponins include ginsenoside-Rg1, ginsenoside-F, ginsenoside-Rg2, α-hederin, hederagenin, licoricesaponin G2, betulinic/ursolic/betulonic acids, and dehydro(11,12)-ursolic acid lactone; husks can reach ≈14.95 mg/g saponin yield [50,51].

Flavonoids and polyphenols are abundant in husks (37 compounds), leaves, and flowers (leaves: 948 non-volatile, 638 volatile metabolites; flowers: 976 non-volatile, 636 volatile) [46,52,53]. Reported molecules include chrysoeriol, diosmetin, hispidulin, kaempferol, luteolin, quercitrin, gallocatechin, eriodictyol, epicatechin, rutin, multiple myricetin conjugates, kaempferitrin, and myricetin, which appear relatively abundant [46,53,54]. Phenylpropanoids (especially coumarins: fraxin, scopoletin, esculetin) dominate leaves and bark [54].

Kernel oil contains tocopherols (vitamin E) in the range ≈70.19–530.15 mg/kg, typically with γ-tocopherol being dominant (≈65.37 ± 2.57–361.37 mg/kg), along with α- (≈1.22 ± 0.13–94.51 mg/kg) and δ- (≈3.6 ± 0.06–74.27 mg/kg) isoforms [11,12,55]. Phytosterols total ≈142–297 mg/100 g, including Δ⁷-stigmastenol, Δ⁷-avenasterol, 24-methylcholest-7-en-3-β-ol, β-sitostanol, stigmasterol, ergosterol, Δ^5,24(25)-stigmastadienol, campesterol, and 24-methylenecycloartanol [11,55]. Vitamins A and C have been detected at low levels (≈0.133 and ≈0.277 mg/100 g, respectively), representing preliminary evidence warranting confirmation across accessions and processing conditions [11].

Table 3. Major classes of phenolic compounds and other secondary metabolites reported in Yellowhorn and co-products.

	Major Phenolic Compounds Reported in Yellowhorn Co-Products
Compound Class	Plant Part	Identified Compounds/Content	Extraction Method	Key Conditions	Pharmacological Significance
Phenolic acids	Husks	Protocatechuic acid: 6.01 mg/100 g [52]	Solvent reflux extraction	75% aqueous ethanol, 65 °C, 2 h [52]	Ethanolic extract, anti-Alzheimer’s, in vivo (AD rat model), 2.5–10 mg/kg/day, improved cognitive function [2,56]
Flavonoids	Leaves	≈55 mg/g [46]	Ultrasound-assisted	71.49% ethanol, liquid:solid ratio: 13.87 mL/g, ultrasonic power: 157.49 W, for 30 min [46]	Catechin: Anti-inflammatory/anti-neuroinflammatory, in vitro (LPS-induced BV2 cells), IC50 3.08 µM, NO production strongly inhibited [2] Quercetin-3-O-β-D-glucopyranoside: Anti-inflammatory/anti-neuroinflammatory, in vitro (LPS-induced BV2 cells), IC50 13.39 µM, NO production inhibited [2] Mixed Flavonoids: Antibacterial, in vitro (S. aureus, E. coli, B. subtilis), 2.14–8.56 mg/mL, dose-dependent bacterial growth inhibition [2,56]
	Husks	41.99 mg Rutin/g dry weight [57]	Conventional solvent extraction	Tetrapropylammonium bromide—lactic acid, liquid–solid ratio: 20 mL/g, Temp: 60 °C, for 30 min [57]
		Epicatechin = 5.24 mg/100 g, Catechin = 3.34 mg/100 g, Rutin = 2.81 mg/100 g, Myricetin-3-O-rutinoside = 1.37 mg/100 g, Quercentin = 1.19 mg/100 g, Quercitrin = 1.12 mg/100 g [52]	Solvent reflux extraction	75% aqueous ethanol, 65 °C, 2 h [52]

Table 3. Major classes of phenolic compounds and other secondary metabolites reported in Yellowhorn and co-products.

	Major Phenolic Compounds Reported in Yellowhorn Co-Products
Compound Class	Plant Part	Identified Compounds/Content	Extraction Method	Key Conditions	Pharmacological Significance
Phenolic acids	Husks	Protocatechuic acid: 6.01 mg/100 g [52]	Solvent reflux extraction	75% aqueous ethanol, 65 °C, 2 h [52]	Ethanolic extract, anti-Alzheimer’s, in vivo (AD rat model), 2.5–10 mg/kg/day, improved cognitive function [2,56]
Flavonoids	Leaves	≈55 mg/g [46]	Ultrasound-assisted	71.49% ethanol, liquid:solid ratio: 13.87 mL/g, ultrasonic power: 157.49 W, for 30 min [46]	Catechin: Anti-inflammatory/anti-neuroinflammatory, in vitro (LPS-induced BV2 cells), IC50 3.08 µM, NO production strongly inhibited [2] Quercetin-3-O-β-D-glucopyranoside: Anti-inflammatory/anti-neuroinflammatory, in vitro (LPS-induced BV2 cells), IC50 13.39 µM, NO production inhibited [2] Mixed Flavonoids: Antibacterial, in vitro (S. aureus, E. coli, B. subtilis), 2.14–8.56 mg/mL, dose-dependent bacterial growth inhibition [2,56]
	Husks	41.99 mg Rutin/g dry weight [57]	Conventional solvent extraction	Tetrapropylammonium bromide—lactic acid, liquid–solid ratio: 20 mL/g, Temp: 60 °C, for 30 min [57]
		Epicatechin = 5.24 mg/100 g, Catechin = 3.34 mg/100 g, Rutin = 2.81 mg/100 g, Myricetin-3-O-rutinoside = 1.37 mg/100 g, Quercentin = 1.19 mg/100 g, Quercitrin = 1.12 mg/100 g [52]	Solvent reflux extraction	75% aqueous ethanol, 65 °C, 2 h [52]

Table 4. Other secondary metabolites reported in Yellowhorn and co-products.

Other Major Secondary Metabolites Reported in Yellowhorn Co-Products
Compound Class	Plant Part/ Co-Product	Content	Extraction Method	Key Conditions	Pharmacological Significance
Saponins	Leaves	5.03–7.33% DW [46]	Conventional solvent extraction and Ultrasound-assisted extraction [46]	Conventional: 70% ethanol, 60 °C, 1 h UAE: 71.56% ethanol, Liquid/solid ratio = 30.67 (v/m) [46]	Anti-obesity/lipid-lowering at dose of 50–200 mg/kg, in vivo study on high-fat mice, TC, TG, and LDL reduced, pancreatic lipase inhibited [56]
	Husks	7.2 mg/g [2] 14.95 mg/g [51] 72.1 mg Re/g DW [57]	Conventional solvent extraction [2] Ultrasound-assisted extraction [51] Conventional extraction [57]	Vanillin-H2SO4 method [2] 65% ethanol, solvent-to-solid ratio: 35:1, 200 W ultrasonic power, at 50 °C for 35 min [51] Tetrapropylammonium bromide-lactic acid (TPMBr-La), 28 min, liquid–solid ratio: 26 mL/g, water content: 35% [57]	Anti-Alzheimer’s/cognitive improvement, in vitro, ICR mice, 0.02–0.32 mg/kg, memory improvement, TLR2/MAPK/NF-κB pathway inhibited [2] Neuroprotection, in vitro (PC12 cells), 0.01–0.1 mg/mL, protected cells against Aβ toxicity [2]. Antidepressant, 0.02 to 0.32 mg/kg, in vitro, C57BL/6J mice, activation of hippocampal BDNF signaling pathway [2].
	Press Cake	3.2 mg/g [2]	Conventional solvent extraction [2]	Vanillin-H2SO4 method	Kernel Antioxidant, IC50 0.782 mg/mL, in vitro, strong free-radical scavenging activity [2] Anti-hepatoma, in vitro (HepG2 cells), 9.7 mg/L, induced apoptosis of liver cancer cells [1,2]
	Press cake	11.62% [49]	Microwave-assisted extraction [49]	42% (v/v) ethanol, 51 °C, 7 min, 900 W, 32 mL/g, 3 cycles [49]
Tocopherol	Seed Oil	530.15 mg/kg [12] 390–427 mg/kg [10] 10.2–35.9 mg/100 g [11] 70.19 mg/100 g [51]	Oil extraction: Solvent extraction (n-Hexane) [12] Oil extraction: Extrusion followed by Soxhlet extraction (n-Hexane) [10] Oil used: Cold press [11]	Oil extraction: Sample:solvent ratio: 1:5 (w/v), ratio: 1:5 (w/v), 50 °C, 4 h [12] 60 MPa, below 30 °C for 1 h [11]	Seed Oil Anti-oxidation: 0.1–1.4 g/mL, good scavenging effect on hydroxyl radical, superoxide anion radical, and DPPH radical [2] 0.15–0.195 mg/mL, lipid peroxidation inhibitory activity with IC50, notable scavenging effect on DPPH radical [2]
Sterols	Seed Oil	2104.07 mg/kg [12] 1393–2066 mg/kg [10] 142–297 mg/100 g [11]	Oil extraction: Solvent extraction [12] Oil extraction: Extrusion followed by Soxhlet extraction (n-Hexane) [10] Oil extraction: Soxhlet extraction (petroleum ether) [11]	Oil extraction: (n-Hexane), sample: solvent ratio: 1:5 (w/v), ratio: 1:5 (w/v), 50 °C, 4 h [12] 10 h at 60 °C [11]

Table 4. Other secondary metabolites reported in Yellowhorn and co-products.

Other Major Secondary Metabolites Reported in Yellowhorn Co-Products
Compound Class	Plant Part/ Co-Product	Content	Extraction Method	Key Conditions	Pharmacological Significance
Saponins	Leaves	5.03–7.33% DW [46]	Conventional solvent extraction and Ultrasound-assisted extraction [46]	Conventional: 70% ethanol, 60 °C, 1 h UAE: 71.56% ethanol, Liquid/solid ratio = 30.67 (v/m) [46]	Anti-obesity/lipid-lowering at dose of 50–200 mg/kg, in vivo study on high-fat mice, TC, TG, and LDL reduced, pancreatic lipase inhibited [56]
	Husks	7.2 mg/g [2] 14.95 mg/g [51] 72.1 mg Re/g DW [57]	Conventional solvent extraction [2] Ultrasound-assisted extraction [51] Conventional extraction [57]	Vanillin-H2SO4 method [2] 65% ethanol, solvent-to-solid ratio: 35:1, 200 W ultrasonic power, at 50 °C for 35 min [51] Tetrapropylammonium bromide-lactic acid (TPMBr-La), 28 min, liquid–solid ratio: 26 mL/g, water content: 35% [57]	Anti-Alzheimer’s/cognitive improvement, in vitro, ICR mice, 0.02–0.32 mg/kg, memory improvement, TLR2/MAPK/NF-κB pathway inhibited [2] Neuroprotection, in vitro (PC12 cells), 0.01–0.1 mg/mL, protected cells against Aβ toxicity [2]. Antidepressant, 0.02 to 0.32 mg/kg, in vitro, C57BL/6J mice, activation of hippocampal BDNF signaling pathway [2].
	Press Cake	3.2 mg/g [2]	Conventional solvent extraction [2]	Vanillin-H2SO4 method	Kernel Antioxidant, IC50 0.782 mg/mL, in vitro, strong free-radical scavenging activity [2] Anti-hepatoma, in vitro (HepG2 cells), 9.7 mg/L, induced apoptosis of liver cancer cells [1,2]
	Press cake	11.62% [49]	Microwave-assisted extraction [49]	42% (v/v) ethanol, 51 °C, 7 min, 900 W, 32 mL/g, 3 cycles [49]
Tocopherol	Seed Oil	530.15 mg/kg [12] 390–427 mg/kg [10] 10.2–35.9 mg/100 g [11] 70.19 mg/100 g [51]	Oil extraction: Solvent extraction (n-Hexane) [12] Oil extraction: Extrusion followed by Soxhlet extraction (n-Hexane) [10] Oil used: Cold press [11]	Oil extraction: Sample:solvent ratio: 1:5 (w/v), ratio: 1:5 (w/v), 50 °C, 4 h [12] 60 MPa, below 30 °C for 1 h [11]	Seed Oil Anti-oxidation: 0.1–1.4 g/mL, good scavenging effect on hydroxyl radical, superoxide anion radical, and DPPH radical [2] 0.15–0.195 mg/mL, lipid peroxidation inhibitory activity with IC50, notable scavenging effect on DPPH radical [2]
Sterols	Seed Oil	2104.07 mg/kg [12] 1393–2066 mg/kg [10] 142–297 mg/100 g [11]	Oil extraction: Solvent extraction [12] Oil extraction: Extrusion followed by Soxhlet extraction (n-Hexane) [10] Oil extraction: Soxhlet extraction (petroleum ether) [11]	Oil extraction: (n-Hexane), sample: solvent ratio: 1:5 (w/v), ratio: 1:5 (w/v), 50 °C, 4 h [12] 10 h at 60 °C [11]

5.3. Physicochemical Properties

Yellowhorn’s pressed cake protein (isolate and albumin) solubility is reported to follow a pH-dependent U-shaped curve, with minimum solubility at pH 4–6 and solubility increasing (>50%) up to ≈80% in alkaline conditions at pH 9–10 (Figure 3a) [47,58]. Although the protein isolate exhibited a moderately high protein solubility value at neutral pH, albumin did not possess this characteristic (Figure 3a) [47]. Kernel proteins show isoelectric points at pH 4.0–5.0, denaturation temperatures of 87.7–92.1 °C, and enthalpy changes (ΔH) of 96.8–106.3 J/g, indicating thermal stability [47]. Water absorption (3.21–3.83 g/g) and oil absorption (2.45–2.52 g/g) capacities suit viscous food matrices; solubility is minimal near pH 4.0 but adequate at neutral pH, favoring non-acidic systems. Foaming is limited, yet the emulsifying activity index (1.11–4.01 m²/g) and stability (20.2–69.5 min) indicate utility as emulsifiers (Figure 3b and Figure 4) [47]. With ultrasonication (20 kHz, ≤600 W, 10 min), Yellowhorn protein’s β-sheet structures dropped from 42.3% to undetectable levels, whereas α-helix content increased from ≈31.7% to 51.9%. In contrast, natural protein had trace amounts of random coils (≈22.9%) and β-turns (≈3%), improving stability, emulsification, and protein solubility (from ≈43.1% to ≈73.0% at pH 7) [58].

Bioactive functionality includes antioxidant and antimicrobial activities. Saponins exhibit DPPH/ABTS scavenging of ≈88.7–91.4% and ≈82.6–90.2% at 0.025–0.50 mg/mL, with Fe²⁺ chelation at ≈88.0% at 0.10 mg/mL [50,51]. Flower/leaf flavonoids show EC50 for DPPH of ≈10.69 µg/mL and for ABTS of ≈14.23 µg/mL, outperforming rutin but slightly falling short of vitamin C [46,54]. Saponins inhibit E. coli and S. aureus (MIC 1.88 and 0.94 mg/mL; MBC 3.75 mg/mL) [50]. Kernel oil quality indices (acid value 0.19–0.51 mg KOH/g, peroxide value 0.47–1.36 mol/kg, OSI 7.85–9.20 h, ω-6/ω-3 29.98, O/L 12.23) indicate oxidative stability consistent with a linoleic/oleic-rich oil [12,55].

Extraction and processing conditions differed substantially between studies. Cao et al. used Osborne fractionation, extracting albumin with water and preparing the isolate under alkaline conditions (pH 10, 50 °C), followed by petroleum–ether defatting (residual lipid ≈13–15%), acid precipitation (pH 4.0–5.0), and freeze-drying [47]. In contrast, Yu et al. produced a single alkali isolate (pH 7, 25 °C) from defatted meal that was not dried, and some treatments applied high-intensity ultrasonication (20 kHz, 150–600 W, 10 min) [58]. Emulsion evaluation protocols also differed, including oil type and ratio as well as homogenization intensity. Thus, the heterogeneity in the methodology should be considered while making comparisons.

Overall, the functional evidence suggests that Yellowhorn’s proteins and bioactive fractions offer promising but application-specific utilities. Protein isolates perform best in neutral pH systems, such as beverages, sauces, and emulsified foods, because solubility and emulsifying activity are markedly reduced near the isoelectric point at pH 4–6. Ultrasonication-induced structural shifts (increased α-helix, reduced β-sheets) significantly enhance solubility and emulsification, supporting their use in high-value formulations. Saponins and flavonoids contribute to strong antioxidant and antimicrobial activities, but their bitterness, foaming behavior, and dose-dependent biological effects require careful control of inclusion levels. Together, current data indicate that Yellowhorn’s proteins are best suited for neutral pH, thermally stable food matrices, while its bioactives show potential as natural preservatives or functional additives, pending further characterization of bioavailability, sensory impacts, and regulatory limits.

6. Current and Potential Applications

Defatted pressed cake proteins are suitable for animal feeds, with AA profiles permitting partial soybean meal substitution in pig and poultry diets [10,11]. Protein isolates function as emulsifiers in beverages, creams, and sauces; ultrasonication enhances their performance [47,58].

Saponins and flavonoids serve as natural antioxidants/antimicrobials. Leaf saponins at ≈0.3% improve whey protein foaming under acidic pH 3.0, producing compact bubbles suitable for dairy foams [50]. Flower flavonoids inhibit E. coli, S. aureus, and B. subtilis, suggesting their utility as preservatives [54]. Leaf/flower volatiles (e.g., 2-furanmethanol, β-ionone) support green tea formulations for lipid-lowering/cardiovascular benefits [53].

Oil applications include culinary use (with a high smoke point reported), bakery systems (e.g., biscuits made using 40% Yellowhorn oil with 3% tea powder), confections, and beverages for nutritional enhancement [32]. Additional uses include kernel beverages/juices, leaf teas for blood pressure/lipid management, and fried kernels for direct consumption [2].

Husks yield polyphenols with in vitro cytotoxicity (A549, HepG2, MGC803, MFC), indicating pharmaceutical potential [52]. Besides food and pharmaceutical potential, evidence of increased sunscreen SPF (16.44 → 30.5) while reducing zebrafish embryo toxicity with the use of starch–oil composites (enzyme-modified corn starch + Yellowhorn oil) indicates the potential use of Yellowhorn oil in cosmetic applications [59].

Technological Limitations and Mitigation Strategies

Key constraints include low protein purity in pressed cake (linked to ≈10% seed residue retained for friction in mechanical extraction), bitterness/foaming from saponins, and oxidation of highly unsaturated lipids (>94%) during processing/storage [32,48]. The bioavailability of triterpenoids/polyphenols is curtailed by molecular complexity and limited pharmacokinetic data; long-term human trials substantiating safety/efficacy are lacking [2,32]. Supply chain scalability is impacted by growth cycle length and underutilization of coproducts (leaves/husks) [32]. Toxicology data indicate low acute/genetic toxicity, with no poisoning observed in 30-day feeding studies under recommended doses [60].

Mitigation strategies encompass fractionation (sequential/direct extraction; yields ≈84.06%, purity ≈83.92%), microwave-assisted extraction and ultrasound–enzyme–ethanol routes for saponins (11.62–14.95 mg/g), aqueous enzymatic extraction for simultaneous oil/protein recovery (enzyme cost remains a barrier), encapsulation (e.g., linoleic acid microcapsules) and low-temperature processing for oxidative stability, as well as ultrasonication to improve protein solubility/emulsification [32,48,49,58,61]. Molecular distillation/urea inclusion enables nervonic acid enrichment to ≈30.4–86.76%, supporting targeted functional lipid formulations [32].

7. Safety and Regulatory Considerations

7.1. Regulatory Framework and Status in the U.S.

In the United States, safety assessment and regulatory acceptance of Yellowhorn oil for food use are governed by the U.S. Food and Drug Administration (FDA) under Title 21 of the Code of Federal Regulations (21 CFR). This framework emphasizes ingredient-specific evaluation rather than botanical origin or traditional use outside the U.S. food system [16,17]. FDA precedent for edible oils demonstrates that compositional safety, rather than plant source alone, is central to regulatory acceptance, as illustrated by the distinction between low-erucic-acid rapeseed (canola) oil and traditional high-erucic-acid rapeseed or mustard oils, which are not permitted for general food use [62,63]. Erucic acid (cis-13-docosenoic acid; 22:1 n-9) is inefficiently β-oxidized in cardiac mitochondria, leading to myocardial lipidosis, the accumulation of neutral lipids in heart muscle that can impair contractile function, identified as the principal toxic effect in risk assessments [64]. Animal studies across multiple species (rats, piglets, monkeys) show that chronic, higher-dose exposures produce dose-dependent myocardial lipidosis with mitochondrial ultrastructural changes and, at still higher intakes, necrosis and fibrosis, with greater susceptibility in neonates and young animals [64,65]. In consequence, EFSA derived a tolerable daily intake (TDI) of 7 mg/kg body weight/day from a no-observed-adverse-effect level (NOAEL) of 0.7 g/kg body weight/day for myocardial lipidosis in young animals and noted that high-percentile exposures in infants and children may approach or exceed this level [64]. In edible oils, the general consensus regarding erucic acid limits it to 2% in the U.S. [63] and Europe [65]. Reports place Yellowhorn at ≈9% erucic acid, which exceeds the ≤2% limit that defines low-erucic edible oils (e.g., canola) and sits squarely within the EFSA toxicological concern that limits a TDI of 7 mg/kg body weight/day; therefore, a GRAS-credible specification will require substantial reduction toward ≤2% and control of total very long chain fatty acid (VLCFA) exposure [63,64]. A practical route mirrors canola: (i) classical breeding/selection for low-erucic acid alleles at FAE1 to depress VLCFA formation, (ii) precision breeding (e.g., CRISPR knockout of FAE1, optionally stacked with FAD2) to drive near-zero erucic acid/high-oleic profiles within a few generations, and (iii) refining to specification (full refining with optional post-refining separations) to manage residual erucic acid in the interim. It should be recognized that aggressive refining can also reduce nervonic acid, which should be addressed via separate enrichment streams if pursued for non-edible uses [66]. These steps can provide a decision-ready framework to bring Yellowhorn oil into regulatory alignment (≤2% erucic acid) while preserving a path for differentiated value streams.

In the absence of a documented history of consumption in the U.S., and without inclusion among affirmed GRAS or prior-sanctioned substances, Yellowhorn oil cannot be presumed safe by common use. Therefore, a defined regulatory pathway is required to support its incorporation into conventional foods [67].

7.2. GRAS as the Practical Pathway

Among the viable regulatory options, the establishment of Generally Recognized as Safe (GRAS) status is widely regarded as the most practical and scientifically appropriate route for an edible oil. By contrast, a food additive petition is typically disproportionately burdensome for vegetable oils and is rarely pursued in modern practice [18]. FDA treatment of edible oils containing potentially hazardous minor constituents, such as erucic acid, further illustrates that GRAS determinations hinge on demonstrated control of compositional risk, often through plant selection, processing, and refining [63]. Central to a GRAS determination is the demonstration that the oil, as manufactured and used, does not present safety concerns, with particular attention to how extraction and refining influence the presence of co-extracted minor constituents [64].

7.3. Role of Refining and Specifications

Fully refined oils generally exhibit a lower regulatory risk profile than cold-pressed or minimally processed counterparts because refining steps reduce potentially undesirable constituents and improve compositional consistency [68]. Therefore, manufacturers face a deliberate trade-off: fully refined oils optimize regulatory certainty and compositional consistency for conventional food use, whereas bioactive-rich fractions are more appropriately developed as separate ingredients under alternative regulatory or non-food pathways. Alignment of product specifications with those established for GRAS vegetable oils, through control of oxidation markers, residual solvents, heavy metals, process contaminants, and pesticide residues, represents a critical risk-management strategy [69]. A comprehensive GRAS dossier would further integrate manufacturing descriptions, batch-to-batch compositional data, dietary exposure estimates, and a weight-of-evidence safety narrative supported by toxicological information and published literature, including comparative bridging arguments to structurally and functionally similar edible oils [67].

7.4. Dietary Supplement Pathway

Although marketing Yellowhorn oil as a dietary supplement would invoke the New Dietary Ingredient notification process, this pathway does not authorize inclusion in conventional foods and therefore offers limited applicability for food ingredient development [17].

Collectively, these considerations indicate that a refined oil, specification-driven, GRAS strategy, ideally supported by a voluntary notification to the FDA, provides the most credible pathway for enabling the safe and regulatory-compliant use of Yellowhorn oil in the U.S. food supply.

8. Sustainability, Value Chain and Challenges

The sustainability of Yellowhorn as a biodiesel feedstock depends on addressing constraints across the value chain, including supply chain limitations, breeding bottlenecks, agronomic resilience, co-product valorization, and gaps in TEA and LCA. Current challenges stem from low fruit yield, limited high-quality germplasm, and insufficient large-scale cultivation systems, which collectively suppress yields and elevate costs, forming the primary bottleneck of the Yellowhorn biodiesel industry [19]. Although Yellowhorn exhibits high genetic diversity, as evidenced by genome-wide simple sequence repeat identification and population structure analyses, wild populations remain fragmented and genetically isolated, with low gene flow. These factors render cultivar improvement slow and resource-intensive [20,22]. Despite these limitations, the species plays a significant role in desertification control, soil stabilization, and wind erosion reduction through its deep and resilient root system, contributing to long-term soil and water conservation [8]. Yellowhorn demonstrates strong agronomic resilience, thriving on marginal lands, including arid and semi-arid regions of northern China, where annual precipitation ranges from 200 to 700 mm (8–28 inches) [20]. Additionally, biodiversity is supported by the creation of stable microhabitats that establish other plant and animal species in degraded ecosystems. Its drought and cold tolerance enable cultivation in landscapes unsuitable for food crops, reducing land-use conflict and supporting sustainability goals.

From an input-output perspective, Yellowhorn seeds contain 55–70% oil, with up to 94% unsaturated fatty acids, positioning the crop as a high-quality feedstock for both food and energy applications [70]. Co-product valorization offers significant opportunities to enhance economic and environmental performance: hulls, leaves, shells, and defatted meal can be utilized in medicine, animal feed, industrial chemicals, and functional foods, offsetting production costs and reducing waste across the value chain [19]. Yellowhorn’s multifunctionality strengthens its value, with high oil content providing renewable feedstock for edible oils and biodiesel production, while its byproducts such as protein-rich meal and bioactive compounds can be valorized for animal feed, fertilizers, or pharmaceutical applications. This combined utilization supports circular economy principles and reduces waste across the value chain. Furthermore, the perennial growth habit of Yellowhorn likely enhances carbon sequestration and climate change mitigation because of the greater accumulation of soil organic carbon (SOC) compared to annual crops, due to persistent root systems and reduced soil disturbance. Global empirical evidence indicates that transitions from annual to perennial cropping systems tend to increase SOC stocks over time, emphasizing their value in climate-smart agriculture [71].

Integrating LCA into Breeding and Supply-Chain Development

To further guide researchers toward a decision-grade LCA of Yellowhorn oil, we outline an operational framework that integrates LCA principles directly into breeding and supply chains based on previously published LCAs for edible oils [72,73,74,75]. We recommend fixing the functional unit at 1 kg of refined, food-grade Yellowhorn oil at the factory gate under a cradle-to-gate boundary spanning orchard establishment and management on marginal lands, harvest, dehulling/shelling, kernel transport, extraction (cold-press, hexane/green solvents, supercritical CO₂, aqueous enzymatic), and refining to specification, with utilities and solvents modeled as explicit unit operations. This mirrors best practices in vegetable oil LCAs, where unit-operation mass/energy balances drive gate-to-gate burdens and reveal actionable improvement levers [74].

We further advise treating co-products (protein-rich meal, bioactive streams) via economic allocation, with mass/energy sensitivity analyses and transparent revenue shares, consistent with comparable oilseed studies showing that co-product handling materially shifts outcomes [72,75]. For perennial systems, subsequent work should also consider biogenic carbon accounting and land occupation (and clearly state assumptions on yield gains vs. area expansion), aligning with olive oil LCA guidance that highlights agricultural stages (irrigation, fertilization, phytosanitary treatments) as dominant contributors and emphasizes the need for consistent sequestration assumptions [73]. To populate such a model, future researchers should capture plot-level agronomic data (planting density, juvenile years to bearing, kernel yield per ha on marginal sites, kernel-to-husk ratio, kernel moisture at harvest, and logistic metrics (drying, shelling energy, storage losses)), and side-by-side process datasets for each extraction route, reporting energy usage per kg of crude oil, yield vs. crude fat, solvent make-up and losses, and recoverable heat by unit operation. These parameters, used in soybean LCAs, dominate processing impacts and, in edible oil case studies such as coconut oil, explain hotspots in global warming potential, acidification, eutrophication, and net-energy performance [72,74].

We suggest these indicators prospectively as design constraints: breeding programs can rank accessions by expected reductions in kg CO₂ per kg of refined oil via kernel yield per ha, favorable kernel-to-husk ratios that result in lower dehulling energy, lower kernel moisture that reduces drying requirements, improved pollination efficiency resulting in lower yield variance, and stable fatty acid profiles that allow for milder refining (reducing energy use and loss of target lipids); process development can prioritize extraction trains with demonstrated leverage (e.g., heat recovery in hexane systems; compressor work reduction, or membrane-assisted solvent recovery for supercritical CO₂) before scale-up [74].

By providing these recommendations, we aim to convert this review into a research blueprint that future researchers can use to produce a comprehensive, comparable LCA of Yellowhorn oil, directly informing breeding and supply-chain choices.

9. Future Directions and Conclusions

Advancing Yellowhorn from a niche oilseed to a viable food and nutraceutical platform requires integrated progress in processing, safety, and sustainability. Immediate priorities include optimizing simultaneous oil-protein recovery (e.g., aqueous enzymatic extraction), refining nervonic acid purification, and developing encapsulation systems to improve bioavailability and stability. Human clinical studies are essential to substantiate functional claims, while valorizing underutilized parts such as leaves for teas and husks for polyphenols can reduce waste and enable novel products like antioxidant beverages and sunscreens. Proteomic and metabolomic profiling will further accelerate targeted applications.

Regulatory acceptance hinges on a specification-driven GRAS strategy, supported by compositional data, toxicological evidence, and bridging arguments to similar edible oils. Managing erucic acid levels, oxidative stability, and minor constituents through refining and germplasm selection is critical. However, refining can reduce the nervonic acid content of the finished oil, so nervonic acid-based functional claims may not apply to fully refined products. At the same time, addressing breeding bottlenecks, improving pollination, and embedding LCAs into supply-chain design will position Yellowhorn within global sustainability frameworks. Yellowhorn is a climate-resilient source of healthy oil, useful proteins, and natural antioxidants. With safe refining, proof of performance in real foods, and sustainable production, it can transition from promise to dependable products.

To enable credible commercialization of Yellowhorn as a food-grade, climate-resilient oilseed, three near-term priorities are critical. First, refining specifications and erucic acid controls must be established in alignment with GRAS precedents, supported by compositional datasets and toxicological bridging to similar edible oils. Second, protein and bioactive profiles should be standardized across accessions and processing methods to ensure consistent functional performance and to reduce variability that limits formulation. Third, co-product valorization and LCAs should be integrated into supply-chain development to quantify sustainability benefits, improve economic feasibility, and guide breeding and processing investments.