Dairy Science & Technology · Dairy Microbiology · also Probiotics and Health, Nutraceuticals and Functional Foods
Probiotic organisms, prebiotics, bioactive components and the evidence and regulation behind health claims for dairy foods.
In the exams: ICAR AICE subject 36 Unit 5 and subject 37 Unit 6; ICAR AIEEA-PG group 16 (application of the probiotic concept)
Functional dairy foods are dairy products marketed for a benefit beyond basic nutrition: fermented milks containing probiotic bacteria, products with added prebiotic fibres, infant formulas with oligosaccharides that imitate those of human milk, fermented milks rich in bioactive peptides, and products whose texture comes from bacterial exopolysaccharides. Dairy is the main vehicle for probiotics worldwide, and the science, the market and the regulation of these products have grown rapidly. This subject covers the definitions agreed by scientific bodies, the organisms used and how they are named and selected, how they are thought to act, how they survive in products and in the gut, prebiotics and other bioactive components, the standards of evidence needed to show a health benefit, and the regulation of health claims in the main markets.
The subject requires two kinds of discipline. The first is microbiological and technological: probiotic effects depend on particular strains delivered alive in adequate numbers, so strain identity, viability and dose must be controlled from production to the end of shelf life. The second is scientific honesty about evidence. Many proposed benefits rest on laboratory or animal studies, small trials or surrogate markers, and regulators in several regions have rejected most health claims submitted for probiotics. A dairy technologist must be able to read a claim, ask which strain, what dose, in whom and with what evidence, and know whether the claim is legally permitted in the market concerned. Throughout this manual, effects are therefore described with the strength of the supporting evidence, and claims are described as permitted only where a regulator has accepted them.
The organisms and their metabolism are covered in Starter Cultures and Lactic Acid Bacteria; the technology of fermented milks, including probiotic products, in Fermented Milks Technology; the chemistry of milk peptides in Milk Proteins and Enzymes; and lactose derivatives such as galacto-oligosaccharides in Lactose, Milk Salts and Vitamins. This manual refers to them. It is examined in Unit 5 of ICAR AICE-JRF/SRF subject 36 (Dairy Microbiology) and Unit 6 of subject 37 (Dairy Technology: functional foods and new product development), and in group 16 of ICAR AIEEA-PG, which names the application of the probiotic concept. Expect questions on definitions, nomenclature, selection criteria, mechanisms, viability and dose calculations, prebiotics, evidence and regulation.
The term probiotic has been used in many ways, so internationally agreed definitions matter. An expert consultation convened by the Food and Agriculture Organization and the World Health Organization in 2001 defined probiotics as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host, and a consensus panel of the International Scientific Association for Probiotics and Prebiotics (ISAPP) reaffirmed this wording in 2014. Three elements of the definition are essential: the microorganisms must be alive when consumed, they must be given in an adequate amount, and a health benefit must have been shown. The definition excludes undefined microbial communities, dead cells and products for which no benefit has been demonstrated. Fermented foods such as yoghurt and cheese contain live microorganisms but are not probiotics unless a specific health benefit of their defined microbes has been shown; ISAPP has separately defined fermented foods as foods made through desired microbial growth and enzymatic conversions of food components. A prebiotic was originally defined by Gibson and Roberfroid in 1995 as a non-digestible food ingredient that selectively stimulates the growth or activity of one or a limited number of beneficial colonic bacteria. The ISAPP consensus of 2017 broadened this to a substrate that is selectively utilised by host microorganisms conferring a health benefit, which allows non-carbohydrate substances and sites other than the colon but keeps the requirements of selectivity and demonstrated benefit.
A synbiotic, as defined by an ISAPP consensus in 2020, is a mixture comprising live microorganisms and substrates selectively utilised by host microorganisms that confers a health benefit on the host. The panel distinguished complementary synbiotics, in which a probiotic and a prebiotic are combined and each meets its own criteria, from synergistic synbiotics, in which the substrate is chosen to be used selectively by the co-administered microorganism and the combination has been shown to give a benefit, without either component necessarily qualifying alone. A postbiotic, as defined by ISAPP in 2021, is a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host. Postbiotics include deliberately inactivated cells, for example heat-killed bacteria, with or without their metabolites and cell components; purified metabolites alone, such as short-chain fatty acids, are not postbiotics under this definition. Related terms such as paraprobiotics (inactivated probiotics) and ghost probiotics have been used but are less standardised. Postbiotics are attractive to manufacturers because they avoid the problem of keeping cells alive during storage, but they must still be characterised and shown to have a benefit. These definitions are scientific; legal definitions differ between countries, and in some, such as the European Union, the word probiotic on a food label is itself treated as a health claim, as described in chapter 10. Understanding the definitions helps distinguish marketing language from what has been shown.
Most probiotic strains used in dairy foods belong to the former genus Lactobacillus or to Bifidobacterium. The 2020 reclassification of Lactobacillus into 25 genera, described in Starter Cultures and Lactic Acid Bacteria, renamed many well-studied probiotic species. Lactobacillus acidophilus, Lactobacillus johnsonii, Lactobacillus gasseri, Lactobacillus crispatus and Lactobacillus helveticus keep the genus name. Lactobacillus rhamnosus became Lacticaseibacillus rhamnosus, so the widely studied strain GG is now Lacticaseibacillus rhamnosus GG; Lactobacillus casei and Lactobacillus paracasei became Lacticaseibacillus casei and Lacticaseibacillus paracasei, so the strain long sold as Lactobacillus casei Shirota is now classified as Lacticaseibacillus paracasei strain Shirota; Lactobacillus plantarum became Lactiplantibacillus plantarum; and Lactobacillus reuteri and Lactobacillus fermentum became Limosilactobacillus reuteri and Limosilactobacillus fermentum. Because effects are strain-specific, a probiotic must be named by genus, species, subspecies where relevant and strain designation, for example Lacticaseibacillus rhamnosus GG, and the strain should be deposited in an international culture collection. Labels and older scientific papers still use the former names, and regulators have accepted a transition period, so both forms should be recognised. Trade names used on products are not scientific names and do not identify the strain unless the strain designation is also given.
Bifidobacteria are Gram-positive, anaerobic, non-motile, often branched rods of the phylum Actinomycetota, which dominate the intestinal microbiota of breast-fed infants. They ferment sugars by a distinctive pathway, the fructose 6-phosphate phosphoketolase pathway or bifid shunt, producing acetate and lactate in a theoretical ratio of 3 to 2. Probiotic species include Bifidobacterium animalis subspecies lactis, the most widely used in dairy products because it is relatively tolerant of oxygen and acid; Bifidobacterium longum, including subspecies longum and infantis, the latter specialised in using human milk oligosaccharides; Bifidobacterium breve; and Bifidobacterium bifidum. Other organisms used as probiotics include the yeast Saccharomyces cerevisiae variety boulardii (sometimes called Saccharomyces boulardii), used mainly in supplements for diarrhoea; Streptococcus thermophilus, as a yoghurt organism with an accepted effect on lactose digestion; spore-forming Bacillus species, such as the organism formerly called Bacillus coagulans, now Heyndrickxia coagulans, valued for survival in processed foods; Escherichia coli strain Nissle 1917, used as a drug in some countries; Enterococcus and Propionibacterium strains; and newer candidates such as Akkermansia muciniphila, a strain of which, in pasteurised form, has been authorised as a novel food in the European Union. Many next-generation candidates are strict anaerobes from the human gut that are hard to grow and keep alive, and they are subject to novel food or drug regulation because they lack a history of safe food use.
The FAO/WHO Guidelines for the Evaluation of Probiotics in Food, published in 2002, set out a sequence for establishing a strain as a probiotic: identification of the strain by current molecular methods and deposit in a culture collection; in vitro tests relevant to the intended effect; assessment of safety; and at least one, preferably more, well-designed human trial showing the benefit, followed by appropriate labelling. Classical in vitro screening tests include tolerance to gastric acid, often tested at about pH 2 to 3, and to bile salts; adhesion to intestinal mucus or to cultured intestinal cell lines; antimicrobial activity against pathogens; bile salt hydrolase activity; and effects on immune cells in culture. These tests help choose candidates, but they do not by themselves prove a health benefit, because conditions in the human gut are far more complex. The human origin of a strain was once regarded as essential but is no longer considered necessary; what matters is the evidence for benefit and safety. Technological criteria are equally important for dairy use: the strain must grow or survive in milk, tolerate the acid and oxygen of the product, remain viable to the end of shelf life at the claimed level, not cause off-flavours or excessive post-acidification, be compatible with the starter culture, and be produced and preserved at industrial scale. Many strains with promising laboratory results fail on these practical grounds.
Probiotics are consumed in very large numbers, sometimes by vulnerable people, so their safety must be established. Species with a long history of safe use in food, such as many lactobacilli and Bifidobacterium animalis, are covered in the European Union by the Qualified Presumption of Safety (QPS) list maintained by the European Food Safety Authority, and in the United States many strains have been notified as generally recognised as safe for specific uses. Even for such species, each strain is checked for transferable antimicrobial resistance genes, which could spread to pathogens in the gut; phenotypic resistance is compared with species cut-off values and whole-genome sequencing is used to look for acquired resistance genes and their location on mobile elements. Strains are also screened for virulence factors, toxin genes and harmful metabolites such as biogenic amines, and for haemolytic activity; some guidance considers D-lactic acid production in products for infants and people with short bowel syndrome. Infections caused by probiotic organisms are rare but have been reported, including Lactobacillus and Lacticaseibacillus bacteraemia and Saccharomyces boulardii fungaemia, mainly in critically ill or immunocompromised patients and those with central venous catheters, in whom fungaemia has resulted from contamination of catheters during preparation. Regulators have warned against giving probiotic products to preterm infants outside approved medical pathways after a fatal infection linked to such a product. Production quality also matters: a probiotic product must contain the strains declared, at the declared count, free of contaminants, which requires the quality systems described in Microbiological Quality Assurance and Rapid Methods.
Probiotics are thought to act through several mechanisms, and the ISAPP consensus of 2014 grouped them by how widely they are shared. Some mechanisms are widespread among probiotic genera, such as colonisation resistance, production of acids and short-chain fatty acids, regulation of intestinal transit and normalisation of a disturbed microbiota. Some are frequent at species level, such as vitamin synthesis, direct antagonism of pathogens, gut barrier reinforcement, bile salt metabolism and enzymatic activity. Others are rare and strain-specific, such as particular immunological or neurological effects and the production of specific bioactive molecules. Most probiotics do not colonise the adult gut permanently; they pass through within days to weeks after consumption stops, so their effects are expected mainly during and shortly after intake. Mechanisms acting on the microbiota include competition for nutrients and adhesion sites (competitive exclusion), production of lactic and acetic acids that lower local pH, production of hydrogen peroxide and bacteriocins, and cross-feeding that supports beneficial resident bacteria. Mechanisms acting on the host barrier include stimulation of mucus production, strengthening of the tight junctions between epithelial cells, and production of metabolites that nourish colonic cells, notably butyrate produced by resident bacteria from substrates provided directly or indirectly.
Probiotic bacteria interact with the gut-associated lymphoid tissue through receptors such as Toll-like receptors on epithelial and dendritic cells, which recognise bacterial cell wall components. Such interactions can influence the balance of inflammatory and regulatory responses, for example the production of interleukin-10 and the development of regulatory T cells, and may modulate responses to vaccines and infections; these effects vary greatly between strains and have been shown in humans only for some. Metabolic mechanisms include the provision of beta-galactosidase by live yoghurt bacteria, which helps people with lactose maldigestion digest the lactose in the product, a mechanism well established and accepted by regulators (chapter 10). Bile salt hydrolase activity deconjugates bile salts and has been proposed as a way to lower blood cholesterol, but human evidence is inconsistent. Effects on the gut-brain axis, on body weight and on conditions outside the gut are active research areas with mostly preliminary human evidence. Understanding mechanism helps explain why benefits are strain-specific and condition-specific: a strain shown to reduce antibiotic-associated diarrhoea cannot be assumed to help allergy or mood. It also explains why some benefits, such as better lactose digestion from yoghurt, are shared widely among cultures, while others require evidence for the particular strain and dose. A dairy technologist should be careful not to present a plausible mechanism as proof of a benefit.
A probiotic product must deliver the declared number of live organisms at the end of its shelf life, not just at manufacture, so survival during storage is a central technological problem. Many factors in fermented milks reduce viability. Acidity is the main one: probiotic lactobacilli and especially bifidobacteria lose viability at low pH, and post-acidification by Lactobacillus delbrueckii subspecies bulgaricus during cold storage lowers the pH further. Oxygen harms bifidobacteria, which are anaerobic, and some lactobacilli; oxygen enters during mixing and through plastic packaging. Hydrogen peroxide produced by some starter lactobacilli is toxic to probiotics. Storage temperature, competition from starter organisms, the presence of salt, flavourings, fruit preparations and preservatives, and freezing in frozen products also matter. Strategies to improve survival include choosing acid- and oxygen-tolerant strains, such as Bifidobacterium animalis subspecies lactis; using mild starter cultures that cause little post-acidification, such as the combination of Lactobacillus acidophilus, bifidobacteria and Streptococcus thermophilus without L. bulgaricus; adding probiotics after fermentation; adding growth factors or prebiotics; using oxygen scavengers such as ascorbate or cysteine; packaging with good oxygen barriers; and strict refrigeration. Cheese, with its higher pH, buffering, fat and solid structure, is often a better vehicle than yoghurt for some strains. Viable counts in products are made on selective media, and flow cytometry can detect cells that are viable but not culturable.
After ingestion, probiotics must survive gastric acid, at pH about 1.5 to 3 in a fasting stomach but higher after a meal, then bile salts and digestive enzymes in the small intestine, to reach the lower gut alive in sufficient numbers. The food matrix can protect them: milk proteins and fat buffer gastric acid and shield cells, which is one argument for dairy vehicles. Losses can be calculated as log reductions: a product with a billion colony-forming units per gram that retains 20 million after simulated gastric digestion has lost about 1.7 log units. Microencapsulation encloses cells in a protective matrix to improve survival in products, during processing and in the stomach. Common methods include extrusion of cells mixed with sodium alginate into calcium chloride solution, forming calcium alginate beads; emulsion methods that produce smaller beads; coating of beads with chitosan or proteins to reduce porosity; and spray drying or freeze drying of cells with protective matrices such as whey proteins, skim milk, resistant starch or prebiotic fibres. Capsules must be small enough not to affect texture, often below about 100 micrometres for dairy products, and must release the cells in the intestine. Encapsulation often improves survival under laboratory conditions; its benefit in real products and in people is less consistently shown. The required dose is usually expressed per serving or per day: for example, a product with 10 million colony-forming units per gram eaten in a 125-gram serving supplies about 1.25 billion. Doses that have shown benefits in trials, commonly in the range of hundreds of millions to tens of billions per day, depend on the strain and the condition.
Because a probiotic claim depends on the number of live organisms, reliable counting methods are essential, and they are harder than they look. Products often contain several species, starter bacteria in much larger numbers than the probiotic, and cells stressed by acid, cold or drying that grow poorly on laboratory media. Selective media and conditions are therefore used for each group. The international standard ISO 29981 (IDF 220) describes counting presumptive bifidobacteria in milk products on transgalactosylated oligosaccharide propionate agar with mupirocin, incubated anaerobically; ISO 20128 (IDF 192) describes counting presumptive Lactobacillus acidophilus on a selective medium containing antibiotics; and media such as MRS agar adjusted in pH or supplemented with antibiotics, and M17 agar for Streptococcus thermophilus, are used for other organisms, each with known limitations in selectivity. Because plate counts miss cells that are alive but unable to form colonies, flow cytometry with fluorescent viability stains, described in ISO 19344 (IDF 232), is used to count viable cells by membrane integrity and enzyme activity, and molecular methods such as quantitative PCR combined with treatments that exclude DNA from dead cells can count specific strains. Strain identity in a finished product is confirmed with strain-specific PCR or genome-based methods. Counts are expressed as colony-forming units, or as active fluorescent units for flow cytometry, per gram or per serving, and specifications are set so that the declared count is still met at the end of shelf life under the stated storage conditions. Laboratories validate their methods for each product matrix, because fruit, fat and other ingredients can affect recovery, and they apply the quality systems described in Microbiological Quality Assurance and Rapid Methods.
Prebiotics are mainly non-digestible carbohydrates that reach the colon intact and are fermented selectively by beneficial bacteria, especially bifidobacteria, producing short-chain fatty acids and lowering colonic pH. Galacto-oligosaccharides (GOS), made from lactose by transgalactosylation with beta-galactosidase as described in Lactose, Milk Salts and Vitamins, are the prebiotic most closely linked to dairy: they are produced from whey lactose and added to infant formula, often in a 9 to 1 mixture with long-chain fructo-oligosaccharides, to promote a bifidobacteria-rich microbiota similar to that of breast-fed infants. Inulin is a fructan, a chain of fructose units linked by beta-2,1 bonds, usually with a terminal glucose, extracted mainly from chicory root; its chains range from a few to about 60 units. Partial hydrolysis gives oligofructose, or fructo-oligosaccharides (FOS), with shorter chains, which can also be synthesised from sucrose. Inulin is used in dairy products both as a prebiotic and as a fat replacer and texture modifier. Lactulose, described in Lactose, Milk Salts and Vitamins, is a prebiotic and laxative. Prebiotics are fermented in the colon, so high intakes cause flatulence and bloating; tolerance varies between people and with chain length. Effects shown in human trials include increased faecal bifidobacteria and, for some prebiotics, improved stool frequency; in the European Union, a health claim that native chicory inulin contributes to normal bowel function by increasing stool frequency has been authorised for a daily intake of 12 grams.
Human milk oligosaccharides (HMOs) are the third most abundant solid component of human milk after lactose and fat, present at several grams per litre in mature milk and more in colostrum, with more than 150 different structures identified. They are built from lactose extended with galactose, N-acetylglucosamine, fucose and sialic acid; the most abundant in many women is 2'-fucosyllactose, whose amount depends on the mother's secretor genotype. HMOs are not digested by the infant; they act as prebiotics, especially for Bifidobacterium longum subspecies infantis, which has genes to use them; as soluble decoy receptors that block the attachment of some pathogens; and possibly as modulators of the immune system. Cow milk contains far smaller amounts and a different, less varied range of oligosaccharides. Since the 2010s, individual HMOs, such as 2'-fucosyllactose and lacto-N-neotetraose, have been produced at industrial scale by fermentation with engineered microorganisms and authorised for use in infant formula and other foods in the European Union, the United States and other countries, after safety assessment. Clinical trials in infants have shown that formulas with these HMOs are safe and support growth, with some evidence of effects on the microbiota and on infections; whether they reproduce the full benefits of human milk is not established. Bovine milk oligosaccharides recovered from whey streams are another research area. Because infant formula is strictly regulated, any added prebiotic must be authorised, its level justified and its safety shown.
Bioactive peptides are protein fragments released by digestion, fermentation or enzymatic hydrolysis that have a physiological activity; their chemistry, sources in the casein and whey protein sequences and the main types are described in Milk Proteins and Enzymes. In functional dairy foods, the most studied are the angiotensin-converting enzyme (ACE) inhibitory lactotripeptides valine-proline-proline (VPP) and isoleucine-proline-proline (IPP), released from beta-casein during fermentation of milk with strongly proteolytic strains of Lactobacillus helveticus, sometimes with yeasts; caseinophosphopeptides (CPP), which bind calcium and have been used in dental products to support remineralisation of enamel; opioid peptides such as beta-casomorphins; lactoferrin and its peptide lactoferricin; and caseinomacropeptide or glycomacropeptide, used as a protein source for people with phenylketonuria. Fermented milks enriched in VPP and IPP were developed and marketed in Japan and Finland as foods to help maintain healthy blood pressure. Enzymatic hydrolysis of caseins and whey proteins with selected proteases, followed by ultrafiltration or chromatography to concentrate active fractions, is the main industrial route; the choice of enzyme, the degree of hydrolysis and the control of bitterness determine the product, as described in Milk Proteins and Enzymes. Whey proteins themselves, rich in leucine and quickly digested, are used in sports and clinical nutrition to support muscle protein synthesis, an effect of the protein rather than of a specific peptide.
For a bioactive peptide to work in the body, it must survive digestion by gastric and pancreatic proteases and brush-border peptidases, be absorbed intact or as an active fragment, and reach its target at an effective concentration. Small peptides, especially di- and tripeptides, can be absorbed by the peptide transporter PepT1, and proline-rich sequences such as VPP and IPP resist digestion relatively well, but many peptides active in the laboratory are degraded before they can act. As a result, the human evidence for most bioactive peptides is limited. For lactotripeptides, randomised trials have given mixed results: meta-analyses have found small reductions in blood pressure, larger in Asian than in European populations, while some well-designed European trials found no effect. The European Food Safety Authority did not accept the proposed health claim for VPP and IPP and blood pressure, concluding that a cause-and-effect relationship had not been established. Casein phosphopeptides are used with calcium phosphate in dental products, where the evidence concerns local effects on enamel. Beta-casomorphins and the A1/A2 beta-casein question are discussed in Milk Proteins and Enzymes, where the evidence is also described as contested. A functional dairy product based on peptides should therefore be developed with attention to the stability of the peptide in the product and in digestion, its measured concentration, a dose supported by human trials, and the legal status of any claim in the target market.
Exopolysaccharides (EPS) are long-chain sugar polymers secreted by many lactic acid bacteria, either as a capsule bound to the cell or as slime released into the medium. Homopolysaccharides contain a single kind of sugar: dextrans, made of glucose, and levans, made of fructose, are synthesised outside the cell from sucrose by glucansucrases and fructansucrases, for example by Leuconostoc species; because milk contains no sucrose unless it is added, they are less important in dairy than in sugar-containing foods. Heteropolysaccharides contain repeating units of two or more sugars, typically glucose, galactose and rhamnose, sometimes with other substituents; they are synthesised inside the cell from sugar nucleotides, assembled on a lipid carrier in the membrane, and exported and polymerised. The genes for heteropolysaccharide synthesis are clustered and, in lactococci, often carried on plasmids, so the ability can be lost. Dairy strains of Streptococcus thermophilus, Lactobacillus delbrueckii subspecies bulgaricus, Lactococcus lactis and Lacticaseibacillus species produce heteropolysaccharides. The amounts produced in milk are small, typically tens to a few hundred milligrams per litre, yet they have marked effects on texture because of their high molecular mass and their interactions with casein. Kefiran, a heteropolysaccharide of glucose and galactose produced by Lactobacillus kefiranofaciens, forms the matrix of kefir grains, as described in Starter Cultures and Lactic Acid Bacteria.
In fermented milks, EPS-producing cultures increase viscosity, give a smooth, creamy mouthfeel and reduce syneresis, allowing manufacturers to reduce or avoid added stabilisers, milk solids or thickeners, which supports clean-label products. Some EPS are ropy, giving long strings when a spoon is lifted, a texture valued in Nordic fermented milks such as viili and långfil but considered a defect in other products, while capsular EPS give viscosity without ropiness. In cheese, EPS-producing cultures increase moisture retention and can improve the texture and yield of low-fat cheeses, though excessive moisture can cause other problems. EPS production is assessed by precipitation with ethanol and measurement of total sugar, by microscopy and staining, and simply by the ropiness of colonies or of cultured milk. Health effects have been proposed for some EPS, including prebiotic effects, immunomodulation, cholesterol lowering and antioxidant activity, mostly from laboratory and animal studies; human evidence is limited, and no health claims for EPS have been accepted by major regulators. The value of EPS in dairy is therefore currently technological, with health effects regarded as possible but unproven. Because EPS production can be unstable and is sensitive to culture conditions, temperature and medium, manufacturers select strains for consistent production under their process conditions and monitor texture as a quality parameter.
Health claims for probiotics and functional foods must rest on evidence from people, and not all evidence is equal. Laboratory studies with cells and studies in animals can suggest mechanisms but cannot show benefit in humans. Observational studies in populations can show associations, for example between yoghurt consumption and lower risk of a disease, but cannot exclude confounding by other features of the diet and lifestyle of yoghurt consumers. The strongest primary evidence comes from randomised controlled trials: participants are randomly allocated to the product or a control, ideally a matched placebo product without the active component; allocation is concealed; participants and investigators are blinded; the trial is large enough to detect a meaningful effect; the outcome is a clinically relevant endpoint or a validated biomarker; and the analysis includes all randomised participants. Trials should be registered in advance with their primary outcome stated, to limit selective reporting. Systematic reviews and meta-analyses combine trials, and frameworks such as GRADE rate the certainty of the evidence as high, moderate, low or very low, taking account of risk of bias, inconsistency, imprecision, indirectness and publication bias. For probiotics, a key principle is that evidence for one strain, dose and population cannot be transferred to another: a meta-analysis that pools different strains may hide the fact that only some are effective.
Graded honestly, the evidence for probiotics varies by condition. Better digestion of lactose from yoghurt containing live cultures, in people with lactose maldigestion, is well established and accepted by regulators. Prevention of antibiotic-associated diarrhoea by certain probiotics, including some strains of Lacticaseibacillus rhamnosus and Saccharomyces boulardii, is supported by systematic reviews with moderate certainty, including reduction of Clostridioides difficile-associated diarrhoea in some settings. Reduction of necrotising enterocolitis and death in preterm infants by certain probiotic combinations is supported by meta-analyses, but concerns about product quality and rare infections have led regulators to caution against use outside controlled medical settings. For treatment of acute infectious diarrhoea in children, earlier reviews suggested a shorter duration, but large, well-designed randomised trials published in 2018 found no benefit of the strains tested, and the most recent systematic reviews regard the evidence as uncertain. For irritable bowel syndrome, some strains show modest benefits in some trials, with low to moderate certainty. Evidence for effects on respiratory infections, allergy prevention, weight, cholesterol, mood and other outcomes ranges from limited to inconsistent and depends on the strain. A dairy professional should therefore describe probiotic benefits by strain and condition, with the level of certainty, and avoid general statements such as probiotics boost immunity. Industry-funded trials are common and acceptable if well designed, registered and fully reported, but independent replication strengthens confidence.
In the European Union, nutrition and health claims on foods are governed by Regulation (EC) No 1924/2006. Health claims are permitted only if authorised after scientific assessment by the European Food Safety Authority and listed in the Union register. General function claims fall under Article 13, and disease risk reduction claims and claims about children's development and health under Article 14. EFSA assessed several hundred claims for probiotic strains and rejected all of them, mainly because the microorganism was insufficiently characterised, the claimed effect was not a beneficial physiological effect, or the human studies did not establish cause and effect. The only authorised claim concerning live cultures states that live cultures in yoghurt or fermented milk improve the digestion of lactose in individuals who have difficulty digesting lactose, for products containing at least 100 million colony-forming units of live starter microorganisms per gram. In most member states, the word probiotic on a food label is itself regarded as an implied health claim and is therefore not permitted, although a few states have allowed it under national guidance. In the United States, probiotics are sold as conventional foods, whose ingredients must be generally recognised as safe or approved, or as dietary supplements under the Dietary Supplement Health and Education Act of 1994. Structure and function claims, such as supports digestive health, can be made without prior approval, with a disclaimer on supplements, but claims to treat or prevent disease make the product a drug. Health claims about disease risk require FDA authorisation or are allowed as qualified health claims with limited evidence; in 2024, FDA allowed a qualified health claim that regular consumption of yoghurt may reduce the risk of type 2 diabetes, with wording indicating limited evidence.
Japan introduced the first regulatory system for functional foods in 1991 with Foods for Specified Health Uses (FOSHU), under which products are individually approved on the basis of evidence of efficacy and safety and may carry an approved claim and logo; many fermented milks with probiotics and products with lactotripeptides have FOSHU approval. Since 2015, Foods with Function Claims allow claims based on evidence notified by the business without individual approval. In India, the Food Safety and Standards Authority's regulations of 2016 on health supplements, nutraceuticals, foods for special dietary use, foods for special medical purposes, functional foods and novel foods include probiotic and prebiotic ingredients and specify conditions for their use and labelling, and earlier guidelines from the Indian Council of Medical Research and the Department of Biotechnology set out how probiotics in food should be evaluated. Canada allows certain non-strain-specific claims for listed probiotic species in foods at a minimum level per serving, and strain-specific claims for natural health products with evidence. China regulates health foods with approved functions through a registration and filing system. Codex Alimentarius has general guidelines for nutrition and health claims but no specific standard for probiotics. Across jurisdictions, common labelling expectations include identifying the strains by genus, species and strain, stating the number of viable organisms at the end of shelf life, giving storage conditions and the recommended intake, and making only claims permitted in that market. Because the rules differ and change, a product launched in several countries may need different labels and evidence packages for each.
A student uses this subject in fermented products and new product development courses. You will count probiotic organisms on selective media, test acid and bile tolerance in the laboratory, follow viability during storage of a probiotic yoghurt, make alginate microcapsules, and calculate doses per serving. Learn the agreed definitions, the current names of probiotic species, the selection and safety criteria, and how to grade evidence and read a health claim, because examiners ask them and because product development depends on them.
Five years into work in product development or quality assurance, you choose strains with suppliers, design formulations and packaging that keep counts above the declared level to the end of shelf life, set up viability testing, check that every label claim is permitted in each market, prepare evidence summaries for regulators and retailers, and explain to marketing colleagues why a claim cannot be made, and keep the evidence file that supports every claim the company does make. You also handle complaints about low counts and investigate their causes.
A senior technical or regulatory director with twenty-five years of experience decides the company's functional food strategy: which strains, prebiotics or bioactive ingredients to invest in, whether to fund human trials and how to design them, how to adapt products and claims to the rules of the EU, the US, Japan, India and other markets, and how to defend claims against challenge. Such a person balances commercial ambition with scientific integrity and consumer trust, and builds the relationships with regulators, clinicians and culture suppliers that long-term programmes need.
A researcher with long experience studies how particular strains, prebiotics and dairy components interact with the host and the microbiota, designs and runs well-powered randomised trials with clinically meaningful outcomes, develops technologies for viability and delivery, investigates human milk oligosaccharides and next-generation probiotics, and contributes to consensus definitions and regulatory guidance. Such a person publishes negative as well as positive results and helps the field separate evidence from enthusiasm, training the next generation to do the same. Such a person also works with regulators on how new evidence should change permitted claims.
This manual gives the agreed definitions, organisms, mechanisms and regulatory frameworks; it does not review the clinical evidence for each strain and condition, which changes as trials are published and should be checked in current systematic reviews. Regulatory details, such as permitted species lists, minimum counts and claim wording in each country, change frequently and are given as examples. Taxonomic names follow the 2020 Lactobacillus reclassification and later changes such as Heyndrickxia coagulans; further changes are likely. Production of probiotic cultures is covered in Starter Cultures and Lactic Acid Bacteria, and fermented milk technology in Fermented Milks Technology. The microbiome science underlying newer concepts is evolving rapidly and is treated only in outline.
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