Utilization of Oil Cakes: From Animal Feed to Human Food

When oil is extracted from oilseeds like soybean, groundnut, sunflower, or mustard, what remains is a solid, protein-rich residue known as an oil cake or deoiled cake. For decades, these by-products were routinely channelled into animal feed or discarded as agricultural waste. But that picture has changed significantly. Today, oil cakes are recognized as a valuable resource with wide applications – from livestock nutrition to human food products – offering a practical way to boost food security and create additional revenue for oilseed processors.

What is an oil cake? 🔗

Oil cakes are the solid residues remaining after oil is extracted from oilseeds in the edible oil industry. Depending on the extraction method used, two main types result: expeller cake (from mechanical pressing), which retains around 6-12% residual oil, and deoiled cake (from solvent extraction), which contains less than 1% residual oil. The deoiled version is more suitable for protein-focused applications due to its higher protein density.

These cakes are rich in protein, nitrogenous compounds, and minerals. Protein content varies by source: soybean cake leads with 44-48% protein, groundnut cake offers 45-50%, sunflower cake provides 28-35%, and mustard cake contains 35-40%. Beyond protein, all these cakes supply B-complex vitamins, phosphorus, potassium, and magnesium. According to FAO statistics, India alone produces over 25 million tons of oilseed cakes annually, making efficient utilization of this resource a matter of both economic and nutritional importance.

Oil cakes as animal feed 🔗

The most established and widespread use of oil cakes remains in animal nutrition. Cold-pressed cakes from rapeseed, hempseed, linseed, sunflower, camelina, and pumpkin seed have all shown promise as alternatives to conventional protein feed ingredients – particularly soybean meal, which dominates but carries significant environmental and supply chain concerns. Their high crude protein content, essential amino acids, and residual lipids make them effective energy and protein sources for both ruminants and non-ruminants.

Uses across livestock categories 🔗

In ruminant feeding (cattle, buffaloes, sheep), oil cakes serve as protein supplements that cover the nutritional needs for energy, protein, and minerals required for production. Research has shown that soybean and hempseed cakes, being rich in amino acids, support weight gain and productivity in growing cattle. In poultry and pig nutrition, cakes like sunflower and rapeseed are included in balanced feed mixtures, with studies showing that dietary inclusion can modulate fatty acid profiles in eggs and meat, resulting in higher levels of beneficial polyunsaturated fatty acids (PUFAs) for human consumers. Fish meal can also be partially replaced with fermented oilseed cakes in aquaculture diets, with fermented soybean meal and groundnut oilcake showing no adverse effects on growth or feed utilization in shrimp and carp when included at recommended levels.

To maximize the feed value of oil cakes, modern processing involves grinding and pelleting for improved digestibility, heat treatment to destroy anti-nutritional factors, and fermentation to enhance nutrient availability. Combining different cakes – for example, soybean meal with sunflower cake – also helps achieve a more balanced amino acid profile at a lower cost than using soybean meal alone.

The challenge of antinutritional factors 🔗

One of the key barriers to broader utilization of oil cakes – especially in human food – is the presence of antinutritional factors (ANFs). These naturally occurring substances can reduce protein digestibility and limit the bioavailability of macro- and micronutrients. Common ANFs include phytic acid, trypsin inhibitors, glucosinolates, tannins, and polyphenols, with the specific type and concentration varying by oilseed.

For instance, canola and rapeseed meals contain glucosinolates and sinapine, groundnut cakes are susceptible to aflatoxin contamination by Aspergillus flavus mold, and sunflower cake contains chlorogenic acid, which can inhibit digestive enzymes. Processing methods such as soaking, steaming, and fermentation have been shown to improve the nutritional quality of oilseed cakes and the bioavailability of nutrients by reducing these ANFs. Heat-based methods destroy proteinaceous inhibitors, though care must be taken to avoid damaging heat-sensitive amino acids. Industrial processes such as toasting, fractionation, and protein concentrate isolation have also demonstrated effectiveness in reducing antinutritional factors.

From feed to food: processing oil cakes for human consumption 🔗

Oil cakes are a suitable alternative protein source for human consumption – plant proteins from these cakes are non-toxic, relatively easy to digest, and cost-effective to process. The pathway from raw cake to food-grade ingredient involves several processing stages: thorough cleaning, controlled grinding, ANF removal, and where needed, protein concentration or isolation.

Protein-rich flours and concentrates 🔗

Oil cake flours are valuable sources of gluten-free proteins, making them suitable for consumers with gluten intolerance. The pressed cakes can be transformed into flour, protein concentrates, and protein isolates. Flour contains up to 65% protein; protein concentrates range from 65-90%; and protein isolates exceed 90% protein content. A comprehensive review found that oilseed cakes contain up to 56% protein and up to 66% fiber, and that enzymatic extraction methods recover 82-83% of protein – making them highly efficient for food-grade production.

Defatted soy flour, one of the most processed oil cake-derived products, is already incorporated into baked goods, breakfast cereals, and protein supplements. Texture modification through extrusion cooking can produce meat-like structures from soy flour – a technique widely used in plant-based protein products. Similarly, sunflower oilseed cakes are used in bakery items such as breads and cookies, where they contribute to softness, moisture retention, and improved crumb structure.

Functional food applications 🔗

Oilseed cakes are used as nutrient fortificants in fortified flour blends, breakfast cereals, snacks, and beverages to increase protein, fiber, and micronutrient content – directly addressing malnutrition and improving public health outcomes. Their functional properties are also leveraged in food manufacturing: they serve as natural emulsifiers, thickeners in sauces and gravies, and gelling agents in custards and puddings. In vegetarian and meat analogue products, oilseed cake proteins can mimic the texture of meat, improving the overall eating quality.

Innovative applications include gluten-free bakery products, plant-based meat alternatives such as vegan burgers, and dietary supplements made from sunflower, coconut, pumpkin, and flaxseed cakes. Research also highlights the potential for extracting bioactive peptides from oil cake proteins – compounds with antioxidant and anti-hypertensive properties that have applications in functional foods and nutraceuticals.

Combining cakes for improved amino acid profiles 🔗

A key challenge with plant-based proteins is that individual sources are often deficient in one or more essential amino acids. Research underscores that combining different oilseed cakes is necessary to meet the full protein requirement in human diets. For example, combining corn gluten meal with soybean meal is effective because the former is rich in methionine and cysteine but low in lysine, while soybean meal provides the lysine and tryptophan that corn gluten lacks. This complementary blending approach can produce protein ingredients that are nutritionally comparable to animal-derived sources.

Contribution to food security and processor economics 🔗

Production of proteins from oilseed cakes can also reduce the carbon and water footprints associated with producing animal protein, while simultaneously addressing the growing global demand for affordable nutrition. In protein-deficient regions, community-level processing of local oilseeds into oil and protein products can keep economic value within the community. School feeding programmes in several countries already incorporate oil cake-based protein supplements to address childhood malnutrition – demonstrating how an industrial by-product can be converted into a public health tool.

For processors, the financial incentive is clear. Edible oilseed cakes such as soybean, groundnut, rapeseed, sunflower, coconut, cottonseed, safflower, and flaxseed can be processed into protein concentrates, isolates, and hydrolysates – all high-value ingredients with strong demand in the food, sports nutrition, and pharmaceutical sectors. The defatted cakes can also be used in infant food products and multipurpose food supplements for undernourished populations. This transforms what was once a low-value residue into a significant revenue stream, improving the overall economics of oilseed processing operations.

Edible vs. non-edible oil cakes 🔗

Not all oil cakes are suitable for food or feed. Oil cakes fall into two broad categories: edible and non-edible. Edible cakes – from soybean, groundnut, sunflower, rapeseed, coconut, and safflower – have high nutritional value and are suitable for both animal and human consumption after appropriate processing. Non-edible cakes – from castor, jatropha, neem, and karanja – contain toxic compounds and are primarily used as organic manure, biopesticides, or biofuel feedstock. For castor oil cake, the presence of ricin makes it unsuitable for any food or feed use without extensive detoxification, though it serves as an effective soil amendment due to its nitrogen content. Jatropha cake is similarly restricted due to phorbol esters, although fermentation-based detoxification methods are being studied to unlock its protein value.

Emerging trends and future potential 🔗

Research is actively expanding the boundaries of oil cake utilization. Ultrasound-assisted extraction achieves up to 96.64% phenolic compound yield from oilseed cakes – a significant improvement over conventional methods. Nanoencapsulation technologies are being explored to protect sensitive bioactive compounds during processing and storage, preserving their nutritional and functional value in finished food products. The growing human population and escalating food prices are driving strong interest in utilizing oilseed cakes as food for humans, with a particular focus on their protein quality, functional properties, and attractive concentrations of secondary metabolites. As the global market for plant-based proteins expands, driven by both health-conscious consumers and environmental concerns, oil cake-derived ingredients are well-positioned to play a central role in sustainable food systems.

What do you think? Given that deoiled cakes already represent a protein-rich, low-cost resource, what steps do you think are most critical to scale their use from niche applications to mainstream food products? And considering the different antinutritional profiles of various oil cakes, how should processing strategies be prioritized – standardized across cakes, or tailored to each oilseed type?

References

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