Dairy Science & Technology · Dairy Processing & Product Technology · also Novel Processing Technologies, Advances in Dairy Processing
Alternatives and additions to heat: high pressure, pulsed electric fields, ultrasound, ohmic and microwave heating, irradiation, carbonation and hurdle technology.
In the exams: ICAR AICE subject 37 Unit 3 and subject 35a Unit 1; ICAR AICE subject 36 Unit 4
Heat has been the backbone of dairy processing for more than a century. Pasteurisation made milk safe, sterilisation made it storable, and evaporation and drying made it tradeable. Heat also has costs: cooked flavours, loss of some vitamins and bioactive proteins, Maillard browning, fouling of equipment and large energy use. Emerging and non-thermal processes aim to keep or improve safety and shelf life while reducing these costs, or to create textures and products that heat cannot. Some are already used commercially in dairy and related foods; others remain at pilot or research scale.
This manual treats each family on the same pattern: the principle, what it does to microorganisms and to milk components, equipment and practical limits, and current applications in dairy. It starts with hurdle technology, the framework for combining mild treatments, then covers high pressure processing, pulsed electric fields, ultrasound, the electro-heating methods (ohmic, microwave, radio-frequency and infrared heating), irradiation and ultraviolet treatment, cold plasma, carbonation and carbon dioxide, supercritical fluid extraction, microencapsulation and nanotechnology, and three-dimensional printing and other new formats. It closes with the regulatory approval of novel processes, which decides whether a technology can leave the pilot plant.
Doctoral fellowship examinations in dairy technology, food processing and dairy microbiology include advances in processing as named units, and ask about the principles, mechanisms of microbial inactivation, effects on milk constituents, typical process conditions and calculations such as field strength, adiabatic heating and treatment dose. The same knowledge is needed by product developers and engineers evaluating whether a new technology will pay its way and pass regulators.
Hurdle technology preserves food by combining several moderate preservative factors instead of relying on one intense treatment. The usual hurdles are heat, chilling, low water activity, low pH, low redox potential, preservatives, competitive microflora and packaging; emerging processes such as high pressure, pulsed electric fields and ultrasound add new hurdles. Each factor alone would be too weak or would damage quality if applied strongly enough to work alone, but together they stop microbial growth or kill microorganisms.
The approach works because microorganisms must spend energy to maintain their internal environment, their homeostasis, against each stress. Several stresses at once exhaust their energy reserves, so stressed cells die during storage instead of growing, a principle called metabolic exhaustion. Hurdles that act on different targets in the cell, such as the membrane, enzymes, internal pH and DNA, act synergistically, the multitarget principle. Sublethally injured cells may also become more sensitive to the next hurdle, which is why sequences of treatments matter.
The approach has limits. Hurdles must be measured and controlled; if one drifts, such as pH rising during storage, the product can fail. Stress can also induce cross-protection, where cells exposed to one mild stress become more resistant to another, so combinations must be validated against the target organisms rather than assumed.
Many dairy products are hurdle products. Cheese combines low pH, salt, reduced water activity, competitive lactic acid bacteria and their bacteriocins, low redox potential inside the block and often packaging; hard cheeses add long ripening, during which pathogens die out. Fermented milks rely on low pH, organic acids, competitive flora and refrigeration. Concentrated sweetened milk products, from sweetened condensed milk to the cooked milk confections of South Asia, Latin America and elsewhere, rely mainly on high sugar and low water activity combined with heat, sometimes with packaging that excludes oxygen. Processed cheese combines heat, emulsifying salts, low water activity and, where permitted, nisin against spore-formers. Butter relies on finely dispersed water droplets, salt and cold.
Hurdle thinking also guides modern processes for liquid milk. Extended shelf life milk combines microfiltration or bactofugation, which physically remove bacteria and spores, with pasteurisation at a higher temperature, very clean filling and strict refrigeration. Thermosonication combines ultrasound with mild heat; high pressure processing is combined with mild heat or with natural antimicrobials such as lactoperoxidase or lysozyme; carbon dioxide is added to raw milk to slow psychrotrophs during storage.
Designing a hurdle product follows a sequence: identify the target organisms and the required log reductions or growth limits, choose hurdles that act on different targets, set limits for each, validate with challenge testing, and monitor each hurdle in production. Predictive microbiology models help estimate the combined effect, but challenge tests in the real product remain the final proof.
High pressure processing, also called high hydrostatic pressure processing, subjects food, usually packed in flexible containers, to pressures of about 100 to 600 MPa, commercially most often 400 to 600 MPa, for a few minutes, typically one to five, using water as the pressure medium. For comparison, 600 MPa is about 6,000 bar or 87,000 psi. Two principles govern it. Pressure is transmitted uniformly and instantly throughout the product (the isostatic principle), so treatment does not depend on the size or shape of the food, unlike heating. And by Le Chatelier's principle, pressure favours reactions and structural changes that reduce volume, which breaks hydrophobic and electrostatic interactions but leaves covalent bonds largely intact; small molecules such as vitamins, pigments and flavour compounds are therefore little affected.
Compression heats the product adiabatically, by about 3 °C per 100 MPa for water and more for fats, so a product starting at 10 °C reaches roughly 28 °C at 600 MPa and cools again on decompression. Most commercial systems are batch vessels into which packed products are loaded in baskets; bulk systems process pumpable liquids before aseptic filling. Packages must be flexible and withstand compression, and air spaces must be small.
Pressure inactivates vegetative bacteria, yeasts and moulds by damaging membranes, denaturing proteins and disrupting ribosomes. Gram-positive bacteria are generally more resistant than Gram-negative ones, and resistance varies widely between strains. Bacterial spores are highly resistant to pressure alone at ambient temperature; pressure combined with high temperature, pressure-assisted thermal sterilisation, can inactivate them, and has been accepted by at least one national regulator for a low-acid product.
Pressure changes milk in ways quite unlike heat. Casein micelles dissociate into smaller particles above about 200 to 300 MPa, because colloidal calcium phosphate solubilises and hydrophobic bonds weaken; milk becomes less white and more translucent and its viscosity rises. β-Lactoglobulin denatures progressively above about 100 to 200 MPa, while α-lactalbumin is much more resistant. Many indigenous enzymes are pressure resistant: alkaline phosphatase survives treatments that inactivate pathogens, so it cannot be used to verify pressure treatment as it is for pasteurisation, and plasmin is also largely resistant. Pressure can induce crystallisation of milk fat.
These changes have useful consequences. Pressure-treated milk forms firmer rennet gels with better curd yield and acid gels with higher viscosity and less syneresis, so pressure has been studied as a pretreatment for cheese and yoghurt milk. Pressure applied to cheese can accelerate ripening and inactivate pathogens or spoilage organisms after manufacture. High pressure processing is used commercially for some dairy-based dips, sauces, fresh cheeses and smoothie-type drinks, and for donor human milk in some milk banks, where it retains more immunoglobulin A, lactoferrin and lipase activity than the standard thermal treatment at 62.5 °C for 30 minutes.
Pressure processing has costs: high capital investment, batch operation with limited throughput, need for refrigerated distribution because spores and some enzymes survive, and regulatory questions, because in many jurisdictions 'pasteurised milk' is defined by thermal processes, so pressure-treated milk needs a different name or a specific approval. Validation is per product, by challenge studies against the most resistant relevant pathogens.
Pulsed electric field processing applies very short pulses, typically microseconds long, of high voltage across a pumpable food flowing between two electrodes. The electric field strength is the voltage divided by the gap: 30 kV across a 0.5 cm gap gives 60 kV/cm. For microbial inactivation, fields of about 20 to 80 kV/cm are used; lower fields, about 0.5 to 3 kV/cm, are used to permeabilise plant and animal tissues for extraction, drying or cutting, as in the commercial treatment of potatoes before cutting into chips.
The field causes electroporation: it induces a transmembrane potential in cells, and when this exceeds a critical value of about 1 V, pores form in the membrane. At high field strength and energy, pores become irreversible and the cell dies; at lower intensities they reseal. Inactivation increases with field strength, number of pulses, treatment time and temperature, and is greater for larger cells, so yeasts are more sensitive than bacteria. Bacterial spores are resistant, and many enzymes are only partly inactivated.
Equipment consists of a high-voltage pulse generator and treatment chambers, usually co-field or coaxial, through which the liquid flows. The specific energy delivered is the product of voltage, current and pulse duration per pulse, multiplied by the pulse frequency, divided by mass flow. For example, pulses of 20 kV and 100 A lasting 2 µs carry 4 J each; at 1,000 pulses per second this is 4 kW, and for a flow of 100 kg/h the specific energy is 4 kW ÷ 0.0278 kg/s ≈ 144 kJ/kg. Part of this energy appears as temperature rise, so PEF is often combined with mild preheating and followed by cooling.
In fruit juices PEF is used commercially as an alternative to thermal pasteurisation for fresh-tasting products with chilled shelf lives. In milk, research has shown useful reductions of vegetative bacteria such as Escherichia coli, Listeria and Pseudomonas, and better results when PEF is combined with temperatures of 50 to 65 °C, but milk's high electrical conductivity, fat globules and proteins, and the need to meet established pasteurisation performance standards, have limited commercial use. PEF has also been studied for treating whey and colostrum, extending the shelf life of skim milk and producing products with intact heat-sensitive proteins.
Practical limits include: only pumpable liquids without large air bubbles can be treated, because bubbles cause dielectric breakdown and arcing; conductivity must be controlled, as high conductivity raises current and heating; electrode materials must resist corrosion and electrochemical reactions that could release metals; and uniform treatment across the chamber is hard to guarantee. Spores and many enzymes survive, so products still need refrigeration.
PEF also has non-preservative uses relevant to dairy: improving extraction of compounds from plant material used in dairy desserts, assisting drying, and modifying protein structure. As with other new processes, validation by challenge tests with the relevant pathogens, and regulatory acceptance that the process gives equivalent safety to pasteurisation, are required before PEF-treated milk could be sold as such.
Ultrasound is sound above the range of human hearing, above about 20 kHz. Two kinds are used in food. Low-intensity, high-frequency ultrasound, usually above about 1 MHz and well below 1 W/cm², is used for non-destructive measurement: the velocity and attenuation of sound reveal composition, fat content, particle size, gelation and crystallisation, for example to monitor milk coagulation in a cheese vat. High-intensity or power ultrasound, at about 20 to 100 kHz and intensities above about 1 W/cm², changes the material. A probe delivering 100 W through a 10 cm² tip gives 10 W/cm².
Power ultrasound acts mainly by acoustic cavitation. Pressure waves create, grow and collapse tiny gas or vapour bubbles in the liquid. Collapse is violent and very fast, producing local hot spots of thousands of kelvin and pressures of hundreds of atmospheres, shock waves, intense shear, liquid microjets near surfaces and free radicals from water. These effects disrupt cells and particles, emulsify, clean surfaces and drive chemical reactions.
Ultrasound alone inactivates microorganisms only slowly, and large-scale liquid treatment is energy intensive, so for preservation it is combined with heat (thermosonication), pressure (manosonication) or both (manothermosonication), which increases the lethality of each. Spores are resistant. Long treatment of milk can create off-flavours, described as rubbery or burnt, from radical-driven oxidation of lipids and sulphur-containing amino acids, which limits intensity and time.
Ultrasound has many dairy applications beyond preservation. It homogenises milk and creates fine emulsions; it reduces the viscosity of concentrated whey and milk protein solutions by breaking protein aggregates, which helps evaporation and spray drying; it modifies the functional properties of whey proteins, improving solubility and gelation; and it accelerates crystallisation. Sonocrystallisation of lactose from concentrated whey gives faster nucleation, smaller and more uniform crystals and higher yield, and ultrasound can control fat crystallisation in butter and anhydrous milk fat. Ultrasound assists the extraction of compounds, defoaming of fermentation and processing lines, and the cutting of cheese and frozen desserts with ultrasonic knives that give clean cuts without smearing.
Cleaning is one of the most established uses. Ultrasonic baths clean small parts, filters, nozzles and membranes, where cavitation and microjets dislodge deposits from crevices that circulating detergents do not reach. Ultrasound applied to membrane modules during filtration reduces fouling and concentration polarisation and can restore flux. Applying ultrasound to fouled heat exchanger surfaces and pipework has been studied as a way to cut cleaning time and chemical use.
Practical limits include the attenuation of ultrasound with distance, which makes uniform treatment of large volumes difficult, erosion of probe tips, which can shed metal particles and must be monitored, noise and the energy cost of high-power systems. Continuous flow cells with multiple transducers are used to scale up.
Ohmic heating, also called Joule or electrical resistance heating, passes an alternating electric current directly through the food, which heats because of its own electrical resistance. Heat is generated throughout the volume rather than transferred from a hot surface, so heating can be fast and uniform, and there is no hot surface to cause fouling or burn-on in the same way as in heat exchangers. The power generated per unit volume equals the electrical conductivity multiplied by the square of the field strength, P = σE². A food with σ = 0.5 S/m in a field of 1,000 V/m generates 500 kW/m³; with density 1,030 kg/m³ and specific heat 3.9 kJ/kg K, it heats at about 0.12 K/s.
Electrical conductivity is therefore the key property. It rises with temperature, typically by about 2% per kelvin, and with salt content, and it falls with fat content. In foods with particles, such as fruit pieces in yoghurt preparations or particulate dairy desserts, ohmic heating can heat particles as fast as or faster than the liquid if their conductivity is matched, which conventional heating cannot do because heat must be conducted into each particle. Mismatched conductivity leads to under- or over-heating and must be designed out.
Challenges include electrochemical reactions at the electrodes, which can corrode them and release metal ions; these are reduced by using high-frequency alternating current and inert electrode materials. In milk, deposits can still form on electrodes at high temperature, and uniformity depends on flow. Ohmic heating is used commercially for some fruit and particulate products and has been studied for milk, cheese making, whey processing and sterilisation of dairy desserts.
Microwave and radio-frequency heating are dielectric heating methods: an oscillating electromagnetic field makes polar molecules, chiefly water, rotate and ions move, generating heat by friction and resistance. The heating depends on the dielectric loss factor of the food and on the frequency and field strength. Industrial microwave frequencies are 915 MHz and 2,450 MHz, allocated for industrial, scientific and medical use; their wavelengths in air are about 33 cm and 12 cm. Microwaves penetrate only a few centimetres into moist food, less at 2,450 MHz than at 915 MHz, and heating is often uneven, with hot and cold spots from standing waves, edges and corners, and runaway heating as thawed regions absorb more energy. Applications include tempering frozen blocks of butter and meat at 915 MHz, rapid thawing, microwave-vacuum drying, which can puff cheese into crunchy snacks, and microwave-assisted pasteurisation and sterilisation of packaged foods, which has been accepted for some products in at least one jurisdiction.
Radio-frequency heating uses lower frequencies, 13.56, 27.12 and 40.68 MHz, with much longer wavelengths and deeper penetration, so it heats large blocks and powders more uniformly. It is used for post-baking drying, tempering, and pasteurisation and disinfestation of powders and low-moisture ingredients, including dairy powders.
Infrared heating transfers energy as electromagnetic radiation of wavelengths about 0.78 to 1,000 µm from heated emitters to the food surface. Penetration is shallow, so it heats surfaces quickly, which suits drying, roasting, browning, surface pasteurisation and melting cheese toppings. All electro-heating methods share the advantages of rapid, energy-efficient heating and the need for careful control of uniformity and validation of the coldest point.
Food irradiation uses gamma rays from cobalt-60 or caesium-137, X-rays, or electron beams to kill microorganisms and insects. The absorbed dose is measured in grays (1 Gy = 1 J/kg). Codex permits irradiation within the General Standard for Irradiated Foods, with a maximum absorbed dose that should not exceed 10 kGy unless a higher dose is necessary for a legitimate technological purpose, and requires labelling. Permitted foods and doses differ greatly between countries.
Liquid milk and most dairy products are poor candidates for irradiation. Even low doses produce off-flavours in milk, often described as burnt, oxidised or 'irradiated', from radiolysis of water and oxidation of lipids and sulphur-containing amino acids, and dairy fat is particularly sensitive. Irradiation has been studied for cheese, milk powders and ice cream ingredients, and for sterile diets for immunocompromised patients, where low temperature during treatment reduces flavour damage. Dairy ingredients such as spices or dried fruits added to cheese or desserts may themselves have been irradiated where permitted, which can affect labelling requirements.
Electron beam and X-ray systems avoid radioactive sources and are increasingly used for packaging sterilisation, including aseptic packaging materials, which is an important indirect dairy application. Detection methods such as thermoluminescence and electron spin resonance allow authorities to check whether foods have been irradiated.
Ultraviolet light in the UV-C range, 200 to 280 nm, is germicidal. Low-pressure mercury lamps emit mainly at 253.7 nm, close to the absorption maximum of DNA; UV-C causes thymine dimers and other DNA damage that prevent replication. Pulsed light and UV light-emitting diodes are newer sources. The dose, or fluence, is intensity multiplied by time: 10 W/m² for 3 s gives 30 J/m², which is 3 mJ/cm² (1 mJ/cm² = 10 J/m²).
UV-C penetrates opaque liquids very poorly: milk absorbs and scatters it within a fraction of a millimetre. Treating milk therefore requires thin films or turbulent flow that continually brings fresh liquid to the irradiated surface, as in coiled-tube reactors with Dean vortices or thin-film annular reactors. Even then, achieving pasteurisation-equivalent reductions throughout the milk is difficult, and riboflavin-sensitised photo-oxidation can cause off-flavours. UV-C is widely used to disinfect water, air and surfaces in dairy plants, conveyor belts, packaging and the surfaces of cheeses.
UV light has another dairy use: increasing vitamin D. Short exposure of milk to UV light converts 7-dehydrocholesterol to vitamin D3. Pasteurised milk treated with UV light to raise vitamin D was authorised as a novel food in the European Union in 2016, with conditions on the treatment and the vitamin D content. This shows how a process can be approved for a specific purpose and product rather than in general.
Plasma, the fourth state of matter, is a partially or fully ionised gas containing electrons, ions, free radicals, excited molecules and photons. In cold or non-thermal plasma, generated at or near atmospheric pressure, the electrons are very energetic but the heavy particles stay near room temperature, so the gas can treat heat-sensitive foods. Plasmas are generated by applying high voltage to a gas such as air, oxygen, nitrogen, argon or helium, in devices including dielectric barrier discharges, in which an insulating barrier between electrodes prevents arcing, atmospheric pressure plasma jets, corona discharges and gliding arcs.
The active agents are reactive oxygen species such as atomic oxygen, ozone, hydroxyl radicals and singlet oxygen; reactive nitrogen species such as nitric oxide and nitrite; ultraviolet photons; and charged particles. Together they etch and oxidise cell surfaces, damage membranes and proteins, and break DNA, inactivating bacteria, yeasts, moulds, viruses and, with longer treatment, spores. Because the species are short-lived and act mainly at surfaces, cold plasma is best suited to surface decontamination.
In-package plasma treatment generates the plasma inside a sealed package by applying a field through it, so reactive species act on the product and then revert largely to the original gas, reducing recontamination. Plasma can also be used to activate water, producing plasma-activated water containing reactive species, used as a sanitiser.
In dairy, cold plasma has been studied for decontaminating the surfaces of cheese slices and blocks, milk powders, packaging materials and equipment surfaces; for reducing Listeria, Escherichia coli and moulds; for degrading pesticide residues and mycotoxins; and for modifying the functional properties of milk proteins, for example improving emulsifying or foaming properties by partial oxidation and unfolding. Treating liquid milk has been explored, but uniform treatment of a liquid with a surface-acting process is difficult.
The main concern is oxidation. Reactive oxygen species oxidise lipids, and dairy fat, rich in unsaturated fatty acids and sensitive to light and oxidation, can develop rancid and oxidised flavours; colour and vitamin losses can also occur. Protein oxidation may change digestibility. Ozone and nitrogen oxides must not remain at harmful levels, and nitrate or nitrite may form in treated products, which matters for regulatory compliance. The effect depends strongly on gas composition, power, exposure time, distance and the product surface, so results from one system are hard to transfer to another.
Cold plasma for foods is still largely at research and early industrial scale. Its advantages are low temperature, no chemical residues of the usual sanitiser kind, short treatment times and low water use. Before wider use, standardised equipment and dosimetry, safety data on treated foods and regulatory approval will be needed, and in many jurisdictions plasma-treated foods would be assessed as products of a novel process.
Carbon dioxide inhibits many microorganisms, especially aerobic Gram-negative bacteria such as Pseudomonas, the main spoilage organisms of refrigerated raw milk, while lactic acid bacteria are more tolerant. Its effects come from several mechanisms: it displaces oxygen; it dissolves in the aqueous phase and forms carbonic acid, lowering pH slightly; it diffuses into cells and acidifies the cytoplasm; and it inhibits enzymes and alters membranes. Its solubility, and so its effect, is greater at low temperature, following Henry's law, which is why CO2 works best in chilled products.
Adding carbon dioxide to raw milk, typically to a few tens of millimoles per litre, can substantially slow the growth of psychrotrophs during refrigerated storage and so extend the time raw milk can be held before processing without loss of quality. Most of the gas is removed during heating and vacuum degassing in processing. The same principle has been applied to pasteurised milk and to cottage cheese, where dissolved CO2 extends shelf life.
Dense-phase carbon dioxide, applied under pressure of several to tens of megapascals at moderate temperature, increases the antimicrobial effect strongly and has been studied as a non-thermal pasteurisation method for liquids, including milk and juices.
Modified atmosphere packaging replaces the air in a package with a gas mixture chosen for the product. For hard and semi-hard cheeses, mixtures of carbon dioxide and nitrogen are common: carbon dioxide inhibits moulds and aerobic bacteria, while nitrogen, which is inert and poorly soluble, fills space and prevents the package from collapsing as carbon dioxide dissolves into the cheese. Grated and sliced cheeses, with large exposed surfaces, especially benefit. Too much carbon dioxide in moist fresh cheeses can cause sour or tangy flavours and pack collapse. Mould-ripened and some fresh cheeses need care because the desired cultures are also affected.
Carbonated dairy beverages, including sparkling milk drinks, carbonated fermented milks and carbonated whey drinks, are made by dissolving carbon dioxide under pressure. Traditional products such as some fermented milks of West and Central Asia and the Middle East have a natural fizz from yeast fermentation. Carbonation adds sensory appeal and some preservation, but casein can destabilise at the lower pH and in combination with heat, so stabilisers and pH control are needed, and packaging must hold pressure.
Carbon dioxide must be food grade and its use declared where required. For MAP, gas mixture, headspace volume, film permeability and storage temperature are chosen together and validated by shelf-life studies with the target spoilage organisms and pathogens; MAP is not a substitute for hygiene and refrigeration.
A supercritical fluid is a substance held above its critical temperature and critical pressure, where it is neither a true liquid nor a gas: it has a density approaching that of a liquid, giving good solvent power, and a viscosity and diffusivity closer to a gas, giving rapid penetration and mass transfer. Carbon dioxide is by far the most used supercritical solvent in food, because its critical point is mild, 31.1 °C and 7.38 MPa, and it is non-toxic, non-flammable, inexpensive, available in high purity and easily removed by depressurisation, leaving no solvent residue. Water, propane and dimethyl ether are used in some processes.
The solvent power of supercritical CO2 depends on its density, which can be tuned by adjusting pressure and temperature: higher pressure at constant temperature increases density and dissolves more solute. This allows selective extraction and fractionation, by extracting at one density and then reducing pressure stepwise to precipitate different fractions in separators. Supercritical CO2 is non-polar and dissolves lipids, essential oils and other non-polar compounds well; for more polar compounds such as phospholipids, a co-solvent such as ethanol is added.
Familiar food applications include decaffeination of coffee and tea, extraction of hop resins for brewing, and extraction of spice oleoresins and essential oils. The process runs in high-pressure vessels, often in batch extraction with continuous solvent recycling, and capital costs are high, so it suits high-value products.
The main dairy application studied is reducing cholesterol in milk fat. Supercritical CO2 extracts cholesterol from anhydrous milk fat or butter oil, and with adsorbents or fractionation, large reductions in cholesterol, of the order of 90% in some studies, have been achieved; because triglycerides are also soluble, selectivity and fat losses must be managed. Other routes to low-cholesterol dairy fat, such as complexation with β-cyclodextrin, compete with it on cost.
Supercritical CO2 fractionates milk fat by chain length and melting behaviour, producing fractions with lower or higher melting points for specific uses, such as spreadable butters or bakery fats; dry fractionation by crystallisation is the more common commercial route. It is used to extract flavour compounds, to remove off-flavours, and with ethanol co-solvent or with dimethyl ether to recover phospholipid-rich lipids from buttermilk and whey protein concentrates, valuable as milk fat globule membrane ingredients.
Supercritical CO2 has also been studied for producing powders by expansion, for drying and for inactivating microorganisms (overlapping with dense-phase CO2), and as a solvent for removing residues. The main barriers to wider dairy use are high capital and operating costs, batch processing of solids, and competition from simpler technologies. Products extracted with CO2 are generally regarded as acceptable without special approval in many jurisdictions, because CO2 is a permitted extraction solvent, but the resulting ingredient must still meet compositional and safety requirements.
Microencapsulation surrounds small particles or droplets of an active ingredient, the core, with a wall material to protect it, mask its taste or smell, control its release, or turn a liquid into a free-flowing powder. Dairy proteins are among the best wall materials: whey proteins and caseins emulsify, form films, gel and protect against oxidation, and they are often combined with carbohydrates such as maltodextrin, gum arabic or modified starch.
Main methods include spray drying of an emulsion, the most widely used and cheapest; spray chilling or spray cooling, in which the core is dispersed in molten fat that solidifies in cold air; extrusion and dripping into a gelling bath, as for alginate beads hardened with calcium; complex coacervation, in which oppositely charged polymers such as gelatin and gum arabic separate around droplets; fluidised-bed coating; liposomes; inclusion complexes with cyclodextrins; and freeze drying. Each gives different particle sizes, loading, protection and cost.
Dairy uses include encapsulated fish oil for omega-3 fortification of milk and yoghurt without fishy flavour or oxidation; encapsulated probiotics, protected against stomach acid and bile and against oxygen in storage; encapsulated vitamins and minerals, including iron that would otherwise catalyse oxidation or discolour products; encapsulated flavours and enzymes for accelerated cheese ripening; and spray-dried milk fat and cream powders. Encapsulation efficiency is the fraction of core enclosed: if a powder contains 30 g of oil per 100 g of which 3 g is extractable surface oil, efficiency is (30 − 3)/30 × 100 = 90%. Surface oil oxidises fastest, so high efficiency matters.
Nanotechnology deals with structures of roughly 1 to 100 nm, where properties can differ from those of larger particles because of large surface area and quantum or interfacial effects. Milk is naturally rich in nanostructures: casein micelles, whey protein molecules and their aggregates, and fat globule membrane fragments. Casein micelles can bind hydrophobic nutraceuticals such as vitamin D, curcumin and omega-3 fatty acids and protect them; re-assembled casein micelles and β-lactoglobulin nanoparticles have been developed as nano-vehicles for fortifying clear drinks. Nanoemulsions and nanoliposomes deliver fat-soluble bioactives with improved bioavailability.
In packaging, nanoclays dispersed in polymers improve barrier properties against oxygen and water vapour; nano-silver and nano-zinc oxide have antimicrobial effects; and nanosensors and indicators can signal temperature abuse or spoilage. These raise questions of migration of nanoparticles into food.
Regulation treats engineered nanomaterials cautiously. Some jurisdictions require specific safety assessment and labelling for engineered nanomaterials in food, and scientific authorities have issued guidance on risk assessment that addresses characterisation, digestion, absorption, distribution and toxicity at the nanoscale. Natural dairy nanostructures used in conventional ways are not treated as engineered nanomaterials, but deliberately engineered nanoparticles usually are. Companies must characterise particle size distributions and demonstrate safety before using them.
Three-dimensional printing builds an object layer by layer from a digital design. For foods, extrusion-based printing is the most common: a paste or melt is pushed through a nozzle by a piston, screw or air pressure and deposited along a path controlled by the printer. Other techniques include selective sintering or binder jetting of powders, used for sugar and some powders, and inkjet printing of liquids onto surfaces for decoration.
The key requirement is printability. The material must flow easily through the nozzle under pressure, which needs shear-thinning behaviour, and then hold its shape immediately after deposition, which needs a yield stress, rapid recovery of structure and often gelation by cooling, heating or a chemical trigger. Processed cheese, which melts on heating and sets on cooling, has been printed successfully, with printing temperature affecting texture, fat distribution and meltability. Yoghurt and cream-based pastes, chocolate, protein gels and purées have also been printed, often with added hydrocolloids or proteins to adjust rheology.
Applications include personalised nutrition, with energy, protein and texture adjusted for an individual, for example soft, shaped, protein-enriched foods for older people with chewing or swallowing difficulties; novelty shapes for food service and confectionery; and rapid prototyping in product development. Four-dimensional printing extends the idea to printed foods that change shape, colour or flavour after printing in response to stimuli such as heat or moisture.
3D printing of foods is slow compared with conventional moulding or extrusion, costly per unit and limited in the range of materials that print well. Food safety needs attention: printers must be cleanable, materials held at warm temperatures for long periods risk microbial growth, and products are often high in moisture and perishable. Standards for food printers and for validation of printed products are still developing. For these reasons, printing is likely to remain a niche in food service, health care and product development rather than replacing mass production.
Other new dairy formats come from established processes applied in new ways. Microwave-vacuum drying turns cheese pieces into crunchy, shelf-stable snacks that puff as moisture evaporates under reduced pressure. Freeze-dried yoghurt drops and melts are made for infants and as snack ingredients. High-protein crisps are made by extrusion of milk protein concentrates with starch. Cheese powders and dairy flavour concentrates are made by enzyme-modified cheese technology and spray drying. Shelf-stable cheese-based snacks, dairy-based ready-to-drink protein beverages made by ultra-high-temperature treatment, and hybrid products combining dairy and plant proteins all reflect consumer demand for convenience, protein and new textures.
Developing any new format involves the same steps: defining the target product and its stability, choosing a process, understanding how the process changes structure, testing safety and shelf life, and checking regulatory status and labelling in each market.
A new process can change the composition, structure, safety or nutritional value of a food, so regulators assess it, but jurisdictions do so in different ways. In the European Union, novel food rules cover foods not consumed to a significant degree before May 1997 and also foods produced by a production process not used before that date, if the process gives significant changes in composition or structure that affect nutritional value, metabolism or the level of undesirable substances. Such foods need authorisation after a scientific safety assessment; UV-treated milk with increased vitamin D and some high-pressure-processed products went through this route. Other jurisdictions, including Australia and New Zealand, Canada, China and several Asian countries, have their own novel food or new process provisions.
Elsewhere, processes may not need pre-market approval as such, but the resulting product must meet safety and labelling law, and certain processes are regulated specifically. In the United States, for example, irradiation is legally treated as a food additive requiring approval for each use, and processes for low-acid canned and aseptically packaged foods must be filed with the regulator, which has accepted filings for processes such as pressure-assisted and microwave-assisted thermal sterilisation. Many dairy standards define products by process: rules for Grade A milk, for example, list specified thermal pasteurisation conditions, so milk treated by a different process cannot simply be called pasteurised milk without specific recognition.
Approval of a non-thermal or emerging process for safety purposes rests on validation: evidence that the process, as operated, reliably achieves the required control of hazards. Codex guidance on validation of food safety control measures (CXG 69-2008) describes how. For milk, the Codex hygiene code (CXC 57-2004) sets the performance of pasteurisation as at least a 6-log reduction of Coxiella burnetii, the most heat-resistant non-spore-forming pathogen of concern in milk; an alternative process claiming equivalence must achieve the same, and must be shown to do so for the most resistant relevant organisms in the actual product. Juice regulations in some jurisdictions use a similar performance standard of a 5-log reduction of the pertinent pathogen. If the D value of the target organism under a pressure treatment is 0.8 minutes, a 6-log reduction needs at least 4.8 minutes, plus a safety margin, and the treatment must reach every part of the product.
Validation also needs process control and monitoring: critical parameters such as pressure, holding time and temperature for high pressure processing, or field strength, pulse number and temperature for pulsed electric fields, must be measured and recorded, with deviations handled as in any hazard analysis plan. Beyond microbial safety, regulators consider chemical changes, formation of undesirable substances, nutritional effects, allergenicity, packaging migration and, for nanomaterials, particle-specific risks.
Labelling and consumer acceptance complete the picture. Some processes must be declared, irradiation everywhere and some others in certain jurisdictions; others may be advertised voluntarily as 'cold pressed' or 'high pressure processed', subject to rules against misleading claims. Clear communication about why a process is used and what it does helps acceptance, while poorly explained technologies can meet consumer resistance whatever their scientific merit.
A student uses this subject to understand what each emerging technology does at the level of cells and molecules, and why each has found, or not found, a place in the dairy industry. In examinations they answer questions on operating ranges, mechanisms, effects on casein, whey proteins and fat, and calculations of field strength, adiabatic heating, UV dose and encapsulation efficiency. In projects they learn to design experiments that compare a new process fairly with conventional heat treatment. They learn to report energy use, cost and sensory results alongside microbial reductions, because industry judges a process on all of them.
A process or product development technologist with five years' experience evaluates whether a new technology fits a product: running trials with equipment suppliers or toll processors, measuring microbial reductions, shelf life, sensory quality and cost, and identifying the critical parameters to monitor. They write the validation protocol, work with quality and regulatory colleagues to confirm labelling and approval needs, and present a business case that compares capital, operating cost and market benefit with conventional processing. After installation they train operators, set alarm limits and review records so that the validated conditions are actually delivered every day.
A senior technical or operations director decides which emerging technologies deserve investment, often on uncertain evidence. They balance capital cost, throughput, energy use, regulatory risk and consumer acceptance, and judge whether a technology is mature enough for production or should stay in pilot plants. They negotiate with regulators on equivalence of new processes, oversee scale-up and protect the company against overselling technologies whose benefits have not been proved in the factory. They also decide when to share equipment or toll processing with other companies rather than buy, and how to explain new processes to customers and consumers.
A senior researcher works on the mechanisms and modelling of non-thermal inactivation and structural change, develops dosimetry and process-control methods that regulators can accept, and studies combined processes and their effects on milk constituents and bioactives. They lead collaborative projects with industry, publish validation data that others can build on, advise standard-setting bodies, and keep a critical eye on claims that run ahead of evidence. They train students to report negative results and full process conditions, so that others can reproduce studies, and they help regulators judge when a technology has enough independent evidence behind it to be approved.
This manual gives representative operating ranges and mechanisms; actual conditions, log reductions and effects vary with equipment, product and strain and must be established by validation. Many emerging processes are at research or pilot stage for dairy, and published results from small studies may not transfer to industrial scale. Regulatory positions differ by jurisdiction and change; the examples given illustrate approaches rather than listing current approvals. Detailed engineering design of equipment, energy balances and costs are not covered.
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.
These notes are free to read here, with no account.
What the Laisha app adds:
Free for ten days, then a subscription. We would rather write that here than have you find it later.