Food Science & Technology · Commodity Processing Technologies · also Legume Technology, Pulse and Oilseed Processing, Plant Protein Technology
Turning legumes and oilseeds into foods and protein ingredients: dehulling and splitting, removal of anti-nutritional factors, traditional legume products, soy foods, and protein concentrates and isolates and their functional properties.
In the exams: ICAR AICE 35.a Unit 2 (pulses, oilseeds, protein concentrates and isolates, dairy analogues); GATE XE-G Section 3 (oil processing)
Pulses and oilseeds are the protein crops of the plant kingdom. Pulses, the dry edible seeds of legumes such as chickpea, pigeon pea, lentil, black gram, green gram, peas and dry beans, are a staple protein source for much of the world, above all in South Asia, where dal is eaten daily. Oilseeds such as soybean, groundnut, rapeseed-mustard, sunflower, cottonseed and sesame are grown mainly for oil, but the meal left after oil extraction is rich in protein. Plant protein technology turns both into foods and ingredients: dals and flours, traditional fermented and roasted products, soy milk and tofu, protein concentrates and isolates, textured proteins, meat and dairy analogues, and nut products.
The subject has gained importance with the global interest in plant-based diets and sustainable protein. Legumes fix nitrogen, need less fertiliser and water per gram of protein than animal products, and complement cereals nutritionally, because cereal protein is limited in lysine while legume protein is limited in the sulphur amino acids. At the same time, legumes contain anti-nutritional factors and flatulence-causing sugars, have long cooking times and characteristic beany flavours, and some, such as soybean and peanut, are major allergens. Processing solves or reduces many of these problems.
The subject is named in the ICAR AICE-JRF/SRF 35.a syllabus (pulses, oilseeds, protein concentrates and isolates, dairy analogues) and touches GATE XE-G Section 3 through oil processing. Examiners ask for composition and amino acid complementation, anti-nutritional factors and their removal, dal milling, soybean processing, coagulants for tofu, organisms in fermented legume foods, the steps of isolate manufacture and the functional properties of proteins, extrusion of textured protein, and nut processing. The engineering of pulse dehulling and oil expression is taught in the Agricultural Engineering subject post-harvest-cereals-pulses-oilseeds, protein chemistry and functionality in food-chemistry-major-constituents, oil extraction and refining in fats-oils-technology, and the toxicology of natural toxicants in food-toxicology-contaminants-allergens; this manual refers to them.
A pulse seed has three parts: the seed coat or hull, about 8 to 15 per cent of the seed by weight depending on species; the two cotyledons, about 85 to 90 per cent, which store protein, starch and other reserves; and a small embryonic axis. Dehulled split cotyledons are the dal of South Asian cooking. Pulses typically contain about 20 to 25 per cent protein, 55 to 65 per cent carbohydrate, mainly starch with dietary fibre and oligosaccharides, and only 1 to 6 per cent fat, though chickpea is higher than most. They are good sources of folate, iron, zinc, magnesium and potassium, although phytate and tannins reduce the availability of minerals.
The storage proteins are mainly globulins, chiefly legumin (11S) and vicilin (7S), with albumins. Legume protein is rich in lysine but limited in the sulphur amino acids methionine and cysteine, and in tryptophan in some species, while cereal protein is limited in lysine. Eaten together, as in dal with rice or chapati, they complement each other, giving a mixture of higher protein quality than either alone. The oligosaccharides raffinose, stachyose and verbascose are not digested in the small intestine, because humans lack the enzyme α-galactosidase, and are fermented by colonic bacteria, producing gas and flatulence. Pulses stored at high temperature and humidity can develop the hard-to-cook defect, in which cotyledons fail to soften on cooking because of changes in cell wall pectins, phytate and phenolic compounds.
Oilseeds store energy as oil rather than starch, and their composition decides how they are processed. Approximate oil contents are about 40 to 50 per cent in groundnut kernels and sesame, 35 to 45 per cent in rapeseed-mustard and sunflower, about 18 to 22 per cent in soybean and about 15 to 20 per cent in cottonseed, with large variation between varieties. Soybean is unusual in being both an oilseed and a protein crop, with about 36 to 40 per cent protein, and much of its value lies in the meal. Its main storage proteins are glycinin (11S) and β-conglycinin (7S), whose proportions affect gelation and tofu quality.
Oilseed meals left after oil extraction typically contain about 35 to 50 per cent protein, depending on the seed, hull removal and residual oil. Each seed carries characteristic minor components and anti-nutritional factors that limit food use: trypsin inhibitors and lectins in soybean, gossypol in cottonseed, glucosinolates and erucic acid in traditional rapeseed and mustard, chlorogenic acid in sunflower, and oxalate in sesame hulls. Groundnuts are prone to aflatoxin contamination, as discussed in food-microbiology and food-toxicology-contaminants-allergens. Oil contents and composition of the oils themselves are covered in fats-oils-technology.
Anti-nutritional factors are natural compounds that reduce nutrient availability or cause harm, especially when the seeds are eaten raw or poorly processed. Their toxicology is described in food-toxicology-contaminants-allergens; here the focus is on processing. Protease inhibitors, notably the Kunitz and Bowman-Birk trypsin inhibitors of soybean, reduce protein digestibility and, in rats, cause pancreatic enlargement. Lectins, such as phytohaemagglutinin of red kidney beans, bind to intestinal cells and cause severe gastrointestinal illness if beans are undercooked. Phytic acid binds iron, zinc and calcium. Tannins and other polyphenols, concentrated in coloured seed coats, bind proteins and iron. Saponins have bitter taste and foam-forming properties. Flatulence-causing oligosaccharides were described in chapter 1.
Some species have specific toxicants: β-ODAP in grass pea (Lathyrus sativus, khesari dal), which causes neurolathyrism; vicine and convicine in faba beans, which cause favism in people with glucose-6-phosphate dehydrogenase deficiency; cyanogenic glycosides in some lima beans; gossypol in cottonseed, toxic and binding to lysine; and glucosinolates in rapeseed and mustard meals, which are goitrogenic. Allergens, especially in soybean, peanut and lupin, are a different class of hazard that processing rarely removes.
Many traditional and industrial processes reduce anti-nutritional factors. Dehulling removes tannins concentrated in the seed coat. Soaking leaches water-soluble oligosaccharides, some phytate and tannins, especially if the soaking water is discarded; adding sodium bicarbonate speeds softening. Germination activates enzymes that degrade phytate and oligosaccharides and raises some vitamins. Cooking with moist heat is the most important step: boiling or pressure cooking destroys lectins and most protease inhibitors and gelatinises starch. Dry heat, such as roasting, is less effective against heat-stable factors. Fermentation, as in idli, dosa, tempeh and miso, degrades phytate and oligosaccharides and improves digestibility. Enzyme treatments, such as added phytase or α-galactosidase, and extraction steps in protein isolate manufacture further reduce specific factors.
Plant breeding has removed some problems at source. Canola cultivars of rapeseed, developed in Canada, are 'double-low', with low erucic acid in the oil and low glucosinolates in the meal; glandless cottonseed varieties lack gossypol glands; low-ODAP grass pea and low-vicine faba bean varieties have been bred; and soybean varieties lacking the Kunitz trypsin inhibitor or lipoxygenases have been developed. Processing conditions must also avoid creating new problems: excessive heating lowers protein quality by Maillard reactions and lysine damage, and alkaline treatment at high temperature can form lysinoalanine. Industrial soybean meal for feed is toasted to inactivate trypsin inhibitors, while edible protein products need careful heat treatment to balance inhibitor inactivation and protein functionality.
Dal milling removes the seed coat and splits the seed into its two cotyledons. Dehulling improves appearance, cooking time, texture, digestibility and palatability, and reduces tannins. Its difficulty varies widely between pulses because in some, gums and mucilage bind the husk tightly to the cotyledons: pigeon pea, black gram and green gram are difficult to dehull, while chickpea and peas are easier. The machinery, from traditional chakkis to abrasive roller and under-runner disc mills, and the wet and dry pretreatment methods are described in the Agricultural Engineering subject post-harvest-cereals-pulses-oilseeds.
In brief, the traditional dry method pits or scratches the seed coat, smears the seeds with a small amount of edible oil, then alternately wets and sun-dries them over several days so that the husk loosens before dehulling and splitting. The wet method soaks the seeds before drying. Industrial methods use heat, chemical treatments such as sodium bicarbonate solutions, and enzymes to loosen husks more quickly and independently of weather. Pigeon pea is the most important dal in southern and western India, and its milling has been the focus of many improved methods.
Dal yield is the weight of dal obtained per unit weight of whole seed. The theoretical maximum is the cotyledon fraction, commonly about 85 per cent or more for pigeon pea, but commercial mills obtain substantially less, often around 70 to 75 per cent, because some cotyledon is lost as powder and brokens during abrasion, and some seeds remain undehulled. If 1,000 kg of pigeon pea gives 720 kg of dal, the yield is 72 per cent of seed and about 85 per cent of the theoretical maximum where the cotyledon fraction is 85 per cent. Losses are reduced by good pretreatment, gentle and staged dehulling, and recycling of partly dehulled seeds.
Dal quality is judged by colour, uniformity, freedom from husk and brokens, cooking time and taste. Polishing with oil, water or other materials improves appearance and is controlled by food law, because colouring dal with non-permitted dyes such as metanil yellow and polishing with mineral oil are known adulteration practices. By-products, husk and powder (chuni), are used as cattle feed. Cooking quality depends on variety, storage history (hard-to-cook defect) and the degree of dehulling and splitting.
Soaking hydrates the seed, commonly roughly doubling its weight over several hours depending on temperature and seed type, softens tissues, shortens cooking time and leaches some anti-nutritional factors. Soaking in dilute sodium bicarbonate speeds softening by solubilising pectic substances, but raises pH, which destroys thiamine and can produce a soapy taste. Calcium and magnesium in hard water slow softening because they cross-link pectins in the cell walls.
Germination for one to a few days activates seed enzymes: amylases, proteases, phytases and α-galactosidase. It lowers phytate and flatulence sugars, raises vitamin C and some B vitamins, and improves digestibility. Sprouted pulses such as moong sprouts are widely eaten raw or lightly cooked, but sprouting seeds have caused outbreaks of Salmonella and STEC, because warm, moist sprouting conditions allow pathogens on the seed to multiply, as noted in food-microbiology; seed disinfection and hygienic sprouting are therefore important.
Cooking softens cotyledons by dissolving the pectic middle lamella so that cells separate, and gelatinises starch within intact cells, which slows its digestion and gives pulses a low glycaemic index. Pressure cooking, standard in Indian kitchens, shortens cooking time greatly. Cooking destroys lectins and trypsin inhibitors and improves protein digestibility, while some water-soluble vitamins and minerals are lost to the cooking water.
Dry heat processes make pulses into snacks and flours. Roasting and puffing of chickpea in hot sand or air give roasted chana and puffed products with crisp texture and nutty flavour; the hull is then easily removed. Roasted Bengal gram flour is the basis of sattu, a traditional drink and food in eastern India. Roasting develops Maillard flavour but is less effective than moist heat against heat-stable anti-nutritional factors.
Fermentation of legumes is ancient and widespread. In southern India, idli and dosa batters are made from soaked and ground rice and black gram, fermented overnight by naturally occurring lactic acid bacteria, chiefly Leuconostoc mesenteroides with Enterococcus and other species, which acidify the batter and produce carbon dioxide that leavens it; black gram's mucilaginous proteins and polysaccharides hold the gas. Dhokla is a fermented, steamed chickpea flour product. In East and South-East Asia, soybeans are fermented into tempeh, made by growing the mould Rhizopus oligosporus on cooked, dehulled beans so that its mycelium binds them into a cake; natto, made with Bacillus subtilis (var. natto), which produces a sticky polyglutamate; and miso and soy sauce, made with koji, a culture of Aspergillus oryzae on rice, barley or soybeans, followed by long brine fermentation with lactic acid bacteria and yeasts. Fermentation improves digestibility, degrades phytate and oligosaccharides, and creates flavour. These foods are discussed further in chapter 6 and in the fermentation subject.
Pulses reach the Indian diet in many forms. Whole and split dals are cooked as dal, sambar and curries. Besan, the flour of dehulled chickpea (Bengal gram), is used in batters for pakoras and bhajis, in sweets such as laddus and mysore pak, in dhokla and kadhi, and in fried namkeen such as sev and bhujia, described in bakery-pasta-snacks. Papad (papadum) is made from black gram flour, sometimes blended with other pulses, mixed with salt, spices and an alkaline salt traditionally called papad khar, rolled into thin discs and sun-dried; it is fried or roasted before eating. Vadi (wadi or bari) are sun-dried nuggets of ground, spiced pulse paste, used in curries. Roasted and puffed chana, sattu and fried dal snacks (dalmoth) are popular. Ready-to-cook mixes for idli, dosa, vada and dhokla, made from pulse and cereal flours with or without dried starter cultures, are a growing industrial sector.
Quality and safety concerns in these products include adulteration of besan with cheaper flours such as khesari, colour, rancidity of oil-rich products, moisture and mould growth in dried products, and microbiological hygiene in batters and ready-to-eat mixes.
Outside South Asia, pulses are eaten as whole cooked or canned beans, baked beans in tomato sauce, refried beans in Mexican cuisine, hummus made from cooked chickpeas and sesame paste (tahini), falafel made from soaked, ground chickpeas or faba beans and fried, split pea soup, lentil dishes, and pulse-based noodles such as Chinese mung bean starch noodles. Canned beans are thermally processed as low-acid foods, as described in thermal-processing-canning; soaking and blanching before canning control texture and remove some oligosaccharides.
Pulse flours and fractions are now widely used as ingredients: in gluten-free and high-protein bakery products and pasta, in snacks and breakfast cereals, and as sources of protein, fibre and starch. Dry fractionation by fine milling and air classification separates pulse flours into a protein-rich fine fraction and a starch-rich coarse fraction without water or chemicals, a process discussed in chapter 8. The characteristic beany flavours, partly from lipoxygenase-derived volatiles such as hexanal, limit acceptance in some products and are reduced by heat treatment, variety selection and flavour masking.
Soy milk is a water extract of soybeans. Beans are soaked, then ground with water, and the slurry is filtered to separate soy milk from the insoluble residue, okara, which is used in foods and feed. The milk is heated, commonly by boiling or ultra-high-temperature treatment, to inactivate trypsin inhibitors, destroy microorganisms and improve flavour. The main flavour problem, the beany or grassy taste, comes from lipoxygenase acting on polyunsaturated lipids when beans are ground in the presence of water and oxygen, producing hexanal and other volatiles. It is reduced by grinding beans in hot water or with steam so that lipoxygenase is inactivated immediately, by dehulling and blanching, by grinding under deaeration, and by using lipoxygenase-free varieties. Commercial soy beverages are often formulated with sugar, flavour, salts and stabilisers, homogenised and fortified, as discussed in chapter 11.
Tofu is soy milk curd. Hot soy milk is coagulated with salts or acids: calcium sulphate (gypsum), magnesium chloride (nigari, traditionally from sea water) or glucono-delta-lactone, which hydrolyses slowly to gluconic acid and gives a smooth, silken curd. Calcium and magnesium ions bridge negatively charged protein molecules, and acid lowers pH towards the isoelectric point; heat-denatured glycinin and β-conglycinin then aggregate into a gel that traps lipids and water. For firm tofu the curd is broken and pressed in cloth-lined moulds to remove whey; silken tofu is coagulated in its final package without pressing. Tofu yield and texture depend on soybean variety (especially the ratio of 11S to 7S proteins), soy milk solids, coagulant type and dose, and temperature.
Fermented soy foods were introduced in chapter 4. Soy sauce is made by mixing steamed soybeans with roasted crushed wheat, inoculating with Aspergillus oryzae to make koji, which supplies proteases and amylases, then mixing the koji with brine to form moromi, which ferments for months with salt-tolerant lactic acid bacteria such as Tetragenococcus halophilus and yeasts such as Zygosaccharomyces rouxii, before pressing, pasteurisation and bottling. Chemically hydrolysed soy sauce, made quickly by hydrolysing protein with hydrochloric acid, can contain 3-MCPD, as described in food-toxicology-contaminants-allergens, and labelling distinguishes brewed from hydrolysed products in many countries. Miso is a fermented paste of soybeans with rice or barley koji and salt; natto and tempeh were described earlier.
Industrial soybean processing produces oil and meal (fats-oils-technology), and from the meal a range of food ingredients: full-fat and defatted soy flours, grits, protein concentrates and isolates, textured proteins and soy lecithin. Full-fat soy flour is made from dehulled, heat-treated beans; enzyme-active flour, with lipoxygenase retained, is used in small amounts to bleach and strengthen bread doughs. In India, most soybean is crushed for oil and the meal is used mainly for animal feed and export, with soy nuggets (textured soy chunks), soy flour and soy milk the main food uses.
After oil extraction, oilseeds leave a protein-rich residue: cake from mechanical expression, which retains several per cent oil, or meal from solvent extraction, with residual oil commonly below about 1 per cent. The extraction processes are described in fats-oils-technology and post-harvest-cereals-pulses-oilseeds. Most meal is used as animal feed; using it for food requires that it be clean, low in anti-nutritional factors and toxins, and processed so that its protein retains functional properties.
The suitability of each meal differs. Defatted soybean meal, with about 44 to 48 per cent protein, or more when dehulled, is the main source of food-grade plant protein ingredients. Groundnut meal is high in protein and bland but carries a high risk of aflatoxin, so only meal from carefully sorted kernels, tested for aflatoxin, can be used for food. Cottonseed meal contains gossypol, so food use requires glandless varieties or processes that remove the pigment glands. Rapeseed and mustard meals contain glucosinolates and phenolics, reduced in double-low canola. Sunflower meal is low in anti-nutritional factors but contains chlorogenic acid, which turns green when the meal or its protein is processed at alkaline pH, limiting its use unless the phenolics are removed. Sesame meal is rich in methionine but its hulls contain oxalate and should be removed. Coconut and other meals are mainly used for feed.
The heat history of a meal determines its uses. In the conventional desolventiser-toaster used for feed meal, steam removes solvent and the toasting step denatures protein and inactivates trypsin inhibitors, giving good feed but low protein solubility. For food ingredients, meal is desolventised under gentler conditions, for example in flash desolventising systems that use superheated solvent vapour and vacuum, giving white flakes with high protein solubility. Solubility is measured by the nitrogen solubility index (NSI) or protein dispersibility index (PDI), the percentage of protein that dissolves or disperses in water under standard conditions; high-PDI flakes are used to make isolates and functional ingredients, and lower-PDI, toasted products for flours where cooked flavour is wanted.
Food-grade meals require hygienic handling, since meals can carry Salmonella, and control of solvent residues, mycotoxins and pesticide residues. Defatted flours and grits are used in bakery, meat products, snacks and extruded foods, and as raw material for concentrates, isolates and textured proteins. In India, groundnut protein flour and other edible oilseed flours were developed in earlier decades for nutrition programmes, and the use of oilseed meals for food remains an opportunity limited mainly by quality control, flavour and cost.
Protein ingredients are classified by protein content on a dry basis, using nitrogen multiplied by 6.25. For soy, flours and grits contain about 50 per cent protein, concentrates about 70 per cent and isolates 90 per cent or more. Soy protein concentrates are made from defatted, desolventised white flakes by removing the soluble sugars (sucrose and the flatulence oligosaccharides) and some minerals while keeping the protein insoluble. Three processes are used: leaching with aqueous ethanol, commonly about 60 to 80 per cent, in which protein is insoluble; leaching with dilute acid at the isoelectric point of the protein, about pH 4.5, followed by neutralisation; and moist heat treatment that denatures the protein before water leaching. Alcohol-washed concentrate has low solubility and a bland flavour; acid-leached concentrate, once neutralised, retains more solubility.
For pulses, dry fractionation by fine milling and air classification is an important alternative. Fine milling detaches protein bodies, which are small, from larger starch granules, and an air classifier separates the flour by particle size and density into a fine, protein-rich fraction, often roughly double the protein content of the original flour, and a coarse, starch-rich fraction. It uses no water or chemicals, preserves native protein functionality, and suits pulses such as peas, faba beans and lentils, which have low oil content; the protein fraction is less pure than wet-process isolates.
Protein isolates are made by alkaline extraction and isoelectric precipitation. Defatted flour or meal is dispersed in water and the pH raised, commonly to about 8 to 9, to dissolve the protein; the insoluble fibre and residue are removed by centrifugation; the extract is acidified to the isoelectric point, about pH 4.5 for soy and pea proteins, where the protein has no net charge and precipitates as a curd; the curd is separated, washed to remove soluble sugars and salts, and then either neutralised with alkali, giving a soluble proteinate, or dried in its isoelectric form; it is usually spray dried. Ultrafiltration and diafiltration can replace isoelectric precipitation, concentrating protein while removing sugars and salts, and give isolates with different functionality and lower phytate.
Yields are limited by the fraction of protein extracted and recovered. As a worked example, if 1,000 kg of defatted soy flour containing 50 per cent protein yields isolate in which 60 per cent of the flour protein is recovered, and the isolate contains 92 per cent protein, the isolate mass is 1,000 × 0.50 × 0.60 / 0.92, about 326 kg. The by-products, a fibrous residue and the whey containing sugars and soluble proteins, must be used or treated. Process conditions, such as pH, temperature and heat treatment, decide the solubility, gelling and emulsifying properties of the isolate, discussed in chapter 9. Pea protein isolates, made by similar processes, have grown rapidly as allergen-lower, non-GM alternatives to soy in plant-based foods; isolates are also made from canola, faba bean, chickpea, mung bean, rice and potato.
Functional properties are the physical and chemical properties of proteins that affect their behaviour in foods during processing, storage and eating. They depend on protein structure and on the environment, especially pH, ionic strength and temperature. The general principles are described in food-chemistry-major-constituents; here they are applied to plant proteins.
Solubility is the foundation of most other properties. Plant proteins are least soluble near their isoelectric point, about pH 4 to 5 for most legume proteins, and more soluble at neutral and alkaline pH; salts can increase solubility at low concentration (salting in) and decrease it at high concentration (salting out). Heat treatment during processing usually lowers solubility. Water holding and oil absorption capacities, the amounts of water or oil bound by a protein ingredient, matter in meat products, bakery goods and analogues. Emulsifying properties, measured as the emulsifying activity index and emulsion stability index, reflect how well a protein adsorbs at oil-water interfaces and forms a protective film; soluble, flexible proteins emulsify best, and the globular storage proteins of legumes are less effective than milk caseins unless partially unfolded or hydrolysed. Foaming capacity and stability depend on similar properties at air-water interfaces.
Gelation, the formation of a three-dimensional network that traps water, is one of the most valued properties of soy and other legume proteins. When heated above their denaturation temperatures, the 7S and 11S globulins unfold and aggregate through hydrophobic interactions and disulphide bonds, forming heat-set gels on cooling; salts and acids, as in tofu, promote aggregation. Glycinin forms firmer, more elastic gels than β-conglycinin. Gel strength depends on protein concentration, pH, ionic strength, heating temperature and time. Viscosity and thickening depend on protein swelling and concentration.
Proteins can be modified to improve functionality. Limited enzymatic hydrolysis increases solubility, emulsifying and foaming properties, but extensive hydrolysis destroys gelation and may produce bitter peptides. Deamidation converts glutamine and asparagine to their acids, increasing charge and solubility. Physical treatments, including high-pressure processing, ultrasound and controlled heating, alter structure and aggregation. Chemical modifications such as phosphorylation and glycation are mainly research tools because of regulatory limits. Off-flavours, such as beany, grassy and bitter notes, often bound to the protein, are a functional limitation in themselves and are reduced by careful processing, deodorisation and flavour masking. A protein ingredient's specification therefore states not only protein content but solubility index, gel strength, emulsifying capacity, colour, flavour and microbiological quality.
Textured vegetable protein (TVP) is plant protein processed into a fibrous or chunky structure that resembles meat when rehydrated. The main method is extrusion cooking, introduced for cereals in cereal-science-milling. In low-moisture extrusion, defatted soy flour, concentrate or blends with other proteins, at relatively low moisture, commonly about 20 to 35 per cent, are heated and sheared in the extruder barrel, typically to about 130 to 180 °C, forming a plastic melt in which proteins are denatured and aligned by flow. At the die the melt expands as water flashes to steam, giving porous, spongy pieces that are cut into granules, flakes or chunks and dried. Soy nuggets and chunks sold in India are products of this kind; they are rehydrated in water before cooking, absorbing several times their weight, and used in curries and as minced meat extenders. Rehydration ratio, texture after cooking, colour and flavour are the main quality criteria. Fibrous structure depends on protein content and type, moisture, temperature, screw configuration and die design.
High-moisture extrusion cooking uses much wetter mixtures, commonly above about 40 to 60 per cent moisture, and a long cooling die attached to the extruder outlet. The cooling die prevents expansion and allows the protein melt to set while flowing in layers, producing dense, aligned fibrous structures that closely resemble whole muscle meat such as chicken breast. Such products, made from soy, pea, wheat gluten and other proteins with oils, flavours and binders, are the basis of many current plant-based meat analogues, which are sold chilled or frozen rather than dried.
Other texturisation methods include fibre spinning, an early method in which protein dope is forced through spinnerets into an acid-salt bath, shear cell technology, in which proteins are sheared between rotating cylinders, and wet spinning and 3D printing in research. Plant-based meat analogues combine textured proteins with binders such as methylcellulose, fats designed to mimic animal fat, colours such as beet juice that change on cooking, and flavours; their nutritional profile, salt content and processing degree are debated, and labelling rules on terms such as 'meat', 'burger' or 'sausage' differ between jurisdictions, as discussed in food-law-regulatory-affairs. Mycoprotein, produced by continuous fermentation of the fungus Fusarium venenatum, is a related, non-legume alternative protein texturised by its own hyphae.
Plant-based beverages, often marketed as alternatives to milk, are made from soy, oats, almonds, rice, coconut, peas, cashews and other sources. Soy beverages are made as described in chapter 6. Oat beverages are made by milling oats in water and treating the slurry with enzymes, amylases to hydrolyse starch into sugars, which give sweetness and reduce viscosity, and sometimes β-glucanases; the insoluble fibre is removed, and oil and stabilisers are added. Almond and other nut beverages are made from ground nuts or nut paste, with relatively low nut content in many products. Rice beverages are made by enzymatic hydrolysis of rice starch. Pea protein beverages are formulated from isolates with oil and sugar.
The processing steps are similar across types: extraction or dispersion, enzyme treatment where needed, separation of insolubles, formulation with oil, sugar, salts, flavours and hydrocolloids such as gellan gum to prevent sedimentation of particles and added calcium, homogenisation to give stable emulsions and fine particles, and heat treatment, usually UHT, with aseptic packaging. Fortification with calcium, vitamin D, vitamin B12 and sometimes riboflavin and iodine is common, because these beverages naturally provide little of them compared with cow's milk. Protein content varies widely: soy and pea beverages approach that of milk, while oat, almond and rice beverages contain much less, which matters for children and older people who rely on milk for protein.
Plant-based yoghurt analogues are made by fermenting soy, coconut, oat, almond or pea bases with yoghurt cultures, often with added sugar, starch, pectin or other thickeners because plant proteins form weaker acid gels than milk proteins. Cheese analogues are made either from cultured nut pastes, especially cashew, or from formulated blends of starches, coconut oil and proteins, which melt and stretch differently from dairy cheese and are often low in protein. Butter alternatives are made from vegetable fat blends, as discussed in fats-oils-technology.
Labelling is contested. In the European Union, the Court of Justice ruled in 2017 that terms such as milk, butter and cheese are reserved for products of animal milk, with listed exceptions such as coconut milk, so plant products are sold as 'drinks' or with other names. India's regulations also restrict the use of dairy terms for non-dairy products, and other countries differ; the current rules should be checked, as discussed in food-law-regulatory-affairs. Nutritional comparability, allergen labelling (soy and tree nuts are major allergens), added sugar and the use of terms such as 'alternative' are recurring issues. For the technologist, the main technical challenges are stability against sedimentation and creaming, flavour, protein functionality in fermented and heated products, and achieving nutrient profiles appropriate for consumers who substitute these products for milk.
Groundnut (peanut) is both an oilseed and a food nut. Pods are dried in the field and in storage to safe moisture, then shelled (decorticated) mechanically. Kernels are graded by size and sorted, by hand and increasingly by colour sorters, to remove damaged, mouldy and discoloured kernels, which are the main carriers of aflatoxin; sorting can reduce aflatoxin levels in a lot dramatically, as described in food-microbiology and food-toxicology-contaminants-allergens. Kernels are then blanched to remove the thin red skins (testa), either by dry heat followed by gentle abrasion, or by water or spin blanching.
Roasting at about 160 °C or above develops the characteristic roasted flavour through Maillard reactions and pyrazine formation, and dries the kernels. Peanut butter is made by grinding roasted, blanched kernels with salt and often sugar into a smooth or crunchy paste; because the released oil tends to separate on standing, stabilisers such as fully hydrogenated vegetable fat or other high-melting fats are added at a few per cent to form a crystal network that holds the oil, while 'natural' peanut butters without stabiliser must be stirred. Peanut butter is a low-moisture food that has carried Salmonella in large outbreaks, so roasting must be validated as a kill step and post-roasting contamination prevented. Groundnuts are also used for roasted and salted nuts, coated snacks, chikki (groundnut-jaggery brittle) in India, oil and protein flour.
Tree nuts, such as almonds, cashews, walnuts, pistachios, hazelnuts and pecans, are processed by hulling, shelling, drying, sorting, and often pasteurising, roasting or blanching. Cashew processing is distinctive: the raw nut is enclosed in a shell containing cashew nut shell liquid, rich in anacardic acid and cardol, which is caustic to skin. Nuts are steamed or roasted to make the shell brittle, the shell is cut or cracked, and the kernel is separated, dried and its thin skin (testa) peeled before grading. India and Vietnam are leading processors. Cashew nut shell liquid is recovered as an industrial raw material.
Almonds became the subject of mandatory pasteurisation in the United States in 2007, after outbreaks of salmonellosis linked to raw almonds in 2001 and 2004; validated treatments include steam pasteurisation, propylene oxide fumigation where permitted, and roasting, each required to achieve a defined log reduction. Low-moisture nuts are susceptible to rancidity because of their high unsaturated fat content, so packaging with low oxygen and moisture transmission, nitrogen flushing and cool storage are used. Tree nuts and peanuts are major allergens; nut processing plants need careful allergen management, as described in food-safety-management-systems, and their aflatoxin limits, especially for nuts for direct consumption, are strict in importing markets such as the European Union.
A student uses this subject to understand why legumes are both valuable and difficult: complementary amino acids, but anti-nutrients, flatulence sugars and beany flavour. Learning the steps of soy milk, tofu and isolate manufacture, the coagulants and fermentation organisms, and the pH logic of isoelectric precipitation answers most exam questions. Making tofu with different coagulants or running an alkaline extraction and precipitation in the laboratory makes the principles concrete.
Five years into a dal mill, soy processing plant, protein ingredient company or plant-based food business, a technologist improves dal yield and quality, controls aflatoxin in groundnut lines, sets heat treatments that inactivate trypsin inhibitors without destroying functionality, runs extraction and drying of isolates to specification, adjusts extruder settings for textured protein, formulates stable fortified plant beverages, and manages allergen and labelling compliance.
A senior technical or business leader with twenty-five years' experience chooses which protein sources and processes to invest in, from pulses and soy to pea, canola and mycoprotein, builds supply chains with farmers and processors, manages by-product value such as okara, hulls and whey, and steers product portfolios through changing consumer demand, nutrition debates and labelling regulation in several markets.
A researcher at this level works on protein structure-function relationships, gentle and sustainable fractionation, removal of off-flavours, fibre formation in high-moisture extrusion, digestibility and amino acid scores of plant protein foods, breeding and processing to reduce anti-nutrients and allergens, and life-cycle assessment of alternative proteins. Such work links plant science, chemistry, process engineering and nutrition.
This manual covers principles and typical ranges; it does not give machine designs for dal mills (in post-harvest-cereals-pulses-oilseeds), oil extraction and refining (in fats-oils-technology), or detailed protein chemistry (in food-chemistry-major-constituents). Protein quality scoring methods such as PDCAAS and DIAAS are only mentioned through the FAO source and belong to human nutrition. National standards for dals, soy products and plant-based alternatives and their labelling rules change and must be checked. Mycoprotein, insect and algal proteins are mentioned only briefly.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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