IngredientsKluyveromyces lactis (van der Walt) is a non-pathogenic, single-celled ascomycetous yeast belonging to the kingdom Fungi. The genus Kluyveromyces is classified within the Saccharomycotina subphylum, Saccharomycetes class, Saccharomycetales order, and Saccharomycetaceae family. It is commonly known in food and biotechnology contexts as "milk yeast" or "dairy yeast," and its principal commercial product, the enzyme β-galactosidase (lactase), has given the organism its broad recognition in the dietary supplement and food-processing industries.
Synonyms and nomenclatural history: The organism was initially named Zygosaccharomyces lactis (also referred to as Saccharomyces lactis) by Hugo Dombrowski in 1910, based on samples from milk sources where it demonstrated the ability to ferment lactose. This name is now considered a synonym, with the valid basionym Torulaspora lactis described by Stelling-Dekker in 1931. This initial classification highlighted its role in dairy environments, distinguishing it from other non-lactose-fermenting yeasts commonly studied at the time. The U.S. Food and Drug Administration (FDA) regulatory listing formally acknowledges it as having been previously named Saccharomyces lactis.
Intraspecific varieties: The species includes two varieties: K. lactis var. lactis, which is dairy-adapted and lactose-positive, and var. drosophilarum, which is associated with insects and lacks lactose fermentation capability.
Taxonomic consolidation: During the 1970s and 1980s, further taxonomic refinements by van der Walt and collaborators consolidated the genus Kluyveromyces from over 20 species to six core species, including K. lactis, through detailed morphological, physiological, and DNA reassociation studies. Van der Walt's 1970 monograph emended the genus definition, emphasizing ascospore morphology and growth patterns. By the 1984 third edition of The Yeasts edited by Kreger-van Rij, these revisions solidified K. lactis as a distinct species.
Natural occurrence: The yeasts included in the genus Kluyveromyces have been isolated from diverse environments including soil, plants, fruits, beer, wine, insects, seawater, food, animals, and humans. Two members — K. marxianus and its anamorph Candida kefyr, and K. lactis and its anamorph C. sphaerica — are frequently found in dairy products because they metabolize lactose.
Common forms and preparations: In commercial and dietary supplement contexts, K. lactis is encountered in several forms:
K. lactis itself does not have a documented traditional or folk-medicine history as a deliberately administered remedy. Its association with human health is derived from its ancient and ubiquitous presence in fermented dairy foods rather than from a tradition of purposeful therapeutic use. There is no significant traditional or folk use of the yeast itself for lactose intolerance; its application is entirely based on scientific discovery and biotechnological advances.
That said, the broader context of yeast use in food is ancient. Species most important for the dairy industry are K. lactis and K. marxianus, whose strains contribute to the ripening process of different cheeses and to the production of kefir. The organism has thus been a constituent of fermented dairy foods — including certain traditional cheeses, kefir, and fermented milk products — consumed across many cultures for centuries, even if its presence was not identified until the early 20th century.
The domestication of dairy strains of K. lactis was not a conscious human act but rather the result of selection pressures imposed by dairying. The ability to ferment lactose was acquired very recently (in evolutionary terms) by K. lactis var. lactis by introgression of LAC12 and LAC4 on a 15-kb subtelomeric region from a dairy strain of K. marxianus. The genomic history of the LAC genes shows that strong selective pressures were imposed on yeasts by early dairy farmers.
Though not as widely documented as Saccharomyces cerevisiae in folk medicine, related yeasts have been used for centuries as natural remedies to promote digestive health, support immune function, and enhance nutritional intake. The consumption of yeast-rich foods was often recommended as a remedy for vitamin and mineral deficiencies, particularly B-vitamins and trace elements, which are abundant in K. lactis.
K. lactis is a prominent producer of native enzymes for industrial applications, particularly β-galactosidase (also known as lactase, encoded by the LAC4 gene). β-Galactosidase catalyzes the hydrolysis of lactose into glucose and galactose, enabling its use in dairy processing to produce lactose-free products that alleviate lactose intolerance.
β-Galactosidases (EC 3.2.1.23) constitute a large family of proteins known to catalyze both hydrolytic and transgalactosylation reactions. The hydrolytic activity has been applied in the food industry for decades for reducing the lactose content in milk, while the transgalactosylation activity has been used to synthesize galacto-oligosaccharides and galactose-containing chemicals.
The enzyme's catalytic characteristics have been well defined. The enzyme has a pH optimum of 6.5–7.0 with Kms of 1.25 and 28 mM for the substrates O-nitrophenylgalactopyranoside and lactose, respectively. This near-neutral pH optimum distinguishes it from fungal lactases (e.g., from Aspergillus species), which function optimally at lower pH, and gives it particular utility in supplemental forms taken at or near a meal, when the gastric pH is buffered by food.
The β-galactosidase from Kluyveromyces lactis is a protein of outstanding biotechnological interest in the food industry and milk whey reutilization. However, due to its intracellular nature, its industrial production is limited by the high cost associated with extraction and downstream processing.
Beyond simple hydrolysis of lactose, the β-galactosidase of K. lactis also conducts transgalactosylation reactions, producing prebiotic galacto-oligosaccharides (GOS). β-Galactosidases from Kluyveromyces lactis and Aspergillus oryzae mainly produce β-1,6-linked GOS. Using 400 g/L lactose, the maximum GOS yield measured by HPAEC-PAD analysis was 177 g/L (44% w/w of total carbohydrates). The major products synthesized were the disaccharides 6-galactobiose [Gal-β(1→6)-Gal] and allolactose [Gal-β(1→6)-Glc], as well as the trisaccharide 6-galactosyl-lactose [Gal-β(1→6)-Gal-β(1→4)-Glc].
In many ascomycetous yeasts, the cell wall is composed of two main types of macromolecules: (a) polysaccharides, with a high content of beta-1,6- and beta-1,3-linked glucan chains and minor amounts of chitin; and (b) cell wall proteins of different types. These beta-glucan components are shared with other well-studied yeasts and are recognized in the broader yeast supplement literature for their immunomodulatory potential, though research on K. lactis-specific cell wall glucans is less developed than for Saccharomyces cerevisiae.
K. lactis is a rich source of bioavailable B vitamins (such as riboflavin and vitamin B12), proteins, and β-galactosidase (lactase) enzymes, which can aid lactose digestion. As with other yeasts, the whole-cell organism and yeast extracts contain a complement of amino acids, nucleotides, and trace minerals; however, the specific quantitative nutritional composition of K. lactis preparations is not as thoroughly documented in the peer-reviewed literature as that of S. cerevisiae-derived nutritional yeast.
The ability of K. lactis var. lactis to transport and metabolize lactose depends on the LAC12-encoded lactose permease in addition to the LAC4-encoded β-galactosidase. The most interesting population is constituted by the dairy yeast pertaining to the variety K. lactis var. lactis, characterized by the presence of the lactose regulon in their genome.
Lactase in the small intestinal villi breaks down lactose into glucose and galactose. In the absence of lactase due to mucosal injury or, more commonly, due to reduced genetic expression of the enzyme lactase-phlorizin hydrolase, undigested lactose reaches the colon, where bacteria ferment it, generating Hâ‚‚, COâ‚‚, lactic acid, and acetic acid, drawing water into the colon by osmosis. This results in clinical symptoms like diarrhea, abdominal pain, bloating, borborygmi, nausea, and flatulence after ingestion of milk or dairy products. Orally administered K. lactis-derived lactase supplements this deficient enzymatic activity during digestion, acting within the intestinal lumen to hydrolyze lactose before it reaches the colon.
Galacto-oligosaccharides (GOS) have been established as prebiotic ingredients after in vitro and animal and human in vivo studies. Currently, GOS are produced by glycoside hydrolases using lactose as substrate. GOS produced by K. lactis β-galactosidase selectively stimulate the growth of beneficial colonic bacteria, particularly bifidobacteria and lactobacilli, representing an indirect mechanism by which K. lactis-derived preparations may benefit gut health.
A complete characterization of five strains with a long history of safe use in food, including Kluyveromyces lactis, was performed with a focus on their capacity to protect against gut inflammation using an in vivo dextran sodium sulfate-induced colitis model in mice. K. lactis living cells showed a clear reduction in mouse sensitivity to colitis in vivo. Interestingly, K. lactis did not survive transit in the gut, suggesting that its anti-inflammatory effect in this model may be mediated by immunomodulatory signals from the yeast cell surface rather than colonization.
In a high-fat diet mouse model, the probiotic strain K. lactis JSA 18 was found to exert effects on lipid metabolic pathways. Lipid metabolism was enhanced by the downregulation of ACC1, PPAR-γ, SREBP-1, and Fasn — genes involved in fatty acid synthesis and adipogenesis. This represents a mechanistic hypothesis for its anti-obesity effects in the animal model, though no human studies have confirmed this pathway.
This is by far the best-documented area of application for K. lactis-derived products, with a substantial body of clinical evidence.
Regulatory recognition: The U.S. Food and Drug Administration (FDA) affirmed lactase preparations produced by Kluyveromyces lactis (formerly known as Saccharomyces lactis) as generally recognized as safe (GRAS) in 1984. The enzyme preparation is derived from the nonpathogenic, nontoxicogenic yeast Kluyveromyces lactis. It contains the enzyme β-galactoside galactohydrase (CAS Reg. No. CBS 683), which converts lactose to glucose and galactose. It is prepared from yeast that has been grown in a pure culture fermentation and by using materials that are generally recognized as safe.
Clinical trial evidence — lactase supplementation: A crossover, placebo-controlled study conducted at the Department of Gastroenterology, Pushpawati Singhania Research Institute for Liver, Renal & Digestive Diseases, New Delhi, registered at Clinical Trials Registry India (CTRI/2018/03/012295), evaluated orally supplemented lactase in confirmed lactose-intolerant patients. Reduction in cumulative hydrogen breath level over 180 minutes was 55% when patients received lactase compared to placebo. Orally supplemented lactase enzyme significantly reduced the clinical symptoms and hydrogen breath excretion in patients with lactose intolerance.
Pediatric and adult population study: In vitro studies of lactose hydrolysis in milk with 20–125 neutral lactase units (NLUs) carried out at 38.0°C for 15 minutes with a β-galactosidase derived from Kluyveromyces lactis resulted in 85–95% of the hydrolysis observed with standard incubation conditions. Thirty-three lactose-maldigesting Guatemalan subjects — 16 children and 17 adults — were challenged with oral doses of lactose in milk preincubated with 50–125 NLU lactase. Under these conditions, the subjects consumed milk without presenting any signs of intolerance. Furthermore, their breath-hydrogen excretion showed a 91–93% reduction compared with a similar load of milk containing non-hydrolyzed lactose.
In vitro milk-treatment evidence: When reconstituted skim milk containing 20% total solids was treated with the lactase preparation (60,000 lactase units/L of milk) at 18°C, 82% of the milk lactose was hydrolyzed within 24 hours.
Comparative efficacy: Evidence suggests that lactase from K. lactis may be more efficacious than lactase derived from Aspergillus species. This comparison relates to the near-neutral pH optimum of the K. lactis enzyme being more compatible with intestinal conditions at the time of food consumption. It is important to note that digestive proteases and gastrointestinal pH can affect enzyme activity during transit through the gastrointestinal tract.
Evidence strength assessment: The evidence for K. lactis-derived lactase in reducing lactose maldigestion symptoms is well-established and supported by multiple clinical and in vitro trials. Regulatory bodies in the United States and Europe have evaluated and acknowledged this evidence. The evidence is strongest for the enzyme preparation used as a dairy treatment or taken orally with lactose-containing foods.
A complete characterization of five food-grade fungal strains including Kluyveromyces lactis examined their capacity to protect against gut inflammation using an in vivo dextran sodium sulfate-induced colitis model in mice. K. lactis living cells showed a clear reduction in mouse sensitivity to colitis in vivo. However, K. lactis did not survive transit in the gut, suggesting that the immunomodulatory effect, if any, occurs through transient host-yeast interactions rather than colonization and persistent residence.
Research aimed at assessing the probiotic potential of different Kluyveromyces lactis strains isolated from Canastra cheese tested their resistance to the passage through the simulated gastrointestinal tract, adhesion properties, and functional effects such as inhibition of enteric pathogens, short-chain fatty acids (SCFA) production, and β-galactosidase activity.
Evidence strength assessment: Evidence for K. lactis as a probiotic agent in gut inflammation is preliminary and limited to animal models and in vitro systems. No human clinical trials have yet specifically investigated K. lactis as a live probiotic for inflammatory bowel conditions. This area requires substantially more research before clinical conclusions can be drawn.
A novel probiotic fungal strain, Kluyveromyces lactis JSA 18, was isolated from yak milk and was found to possess anti-obesity properties. In the animal study: K. lactis caused a notable reduction in weight gain, liver and fat indexes, and hyperlipidemia in mice fed a high-fat diet. Administering K. lactis to mice on a high-fat diet resulted in a reduction of serum triglyceride levels. Furthermore, the supplements reduced ALT and AST activity and inhibited the production of inflammatory cytokines such as TNF-α and IL-1β.
The study found that K. lactis and Lactobacillus plantarum have little effect on gut bacteria. K. lactis partially influenced intestinal fungi, while L. plantarum had a minor influence on gut mycobiota.
Evidence strength assessment: All evidence for anti-obesity and hypolipidemic effects of K. lactis is from animal (mouse) models. No human clinical data exist on this application. Findings should be interpreted as exploratory and hypothesis-generating only.
GOS have been established as prebiotic ingredients after in vitro and animal and human in vivo studies. The β-galactosidase of K. lactis is one of the principal enzymatic sources used industrially to produce GOS from lactose. Previous studies have shown the synthesis, structural characterization, and prebiotic effect of GOS produced by β-galactosidase from Aspergillus species and Kluyveromyces lactis.
A double-blind intervention trial in healthy women assessed the impact of GOS supplements on gut microbiota, finding beneficial impacts on bifidobacterium abundance. The impact of GOS supplements on study outcomes was assessed using a within-subject design, comparing the intervention period with the control period. This design was chosen because of the large inter-individual variation in gut microbiota composition. Fecal samples were collected to determine the abundance of Bifidobacterium and gut microbiota composition, and questionnaires were completed on sleep, mental wellbeing, and gastrointestinal comfort.
Evidence strength assessment: The prebiotic status of GOS produced by K. lactis β-galactosidase is supported by clinical human trials, though the specific prebiotic credentials relate to the GOS product rather than to the intact yeast organism itself. This distinction is important: the clinical evidence supports GOS as a category, while K. lactis is the enzymatic source of those GOS in industrial production.
Beyond direct nutritional supplementation, K. lactis has served as the host organism for producing food-relevant enzymes, including chymosin (rennet substitute) used in cheese-making. The food enzyme chymosin (EC 3.4.23.4) is produced with the genetically modified Kluyveromyces lactis strain CIN by DSM Food Specialties B.V. The genetic modifications do not give rise to safety concerns. The food enzyme is free from viable cells of the production organism and its recombinant DNA. It is intended to be used in milk processing for cheese production and for the production of fermented milk products.
Dosages for K. lactis-derived products in the scientific literature are reported in terms of enzyme activity units (NLU — Neutral Lactase Units — or IU/FCC units) rather than in milligrams of the organism itself.
The FDA-regulated use in food processing specifies that the ingredient is used in food at levels not to exceed current good manufacturing practice.
Since K. lactis is present in many dairy products consumed by humans, it is considered to be GRAS, and the yeast can be utilized for production of food ingredients and as a dietary supplement. The FDA affirmed lactase preparations produced by Kluyveromyces lactis as generally recognized as safe (GRAS) in 1984.
The enzyme preparation was examined for subacute oral toxicity and mutagenic potential. No evidence of oral toxicity, mutagenicity, or clastogenicity was found. Administration of the lactase enzyme preparation at doses of 500, 3,000, and 10,000 mg/kg body weight/day for 28 days did not induce noticeable signs of toxicity. The no-observed-adverse-effect level (NOAEL) of the enzyme preparation in the acute toxicity study was 10,000 mg/kg body weight/day (equivalent to 114,000 NL units/kg body weight/day).
No safety concerns were identified in the studies conducted with this lactase enzyme preparation derived from Kluyveromyces lactis under controlled fermentation conditions.
The European Food Safety Authority (EFSA) has conducted safety evaluations of K. lactis-derived food enzymes. Dietary exposure to the chymosin enzyme preparation was estimated to be up to 0.73 mg total organic solids (TOS)/kg body weight per day in European populations. Genotoxicity tests did not raise a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 1,000 mg TOS/kg bw per day, the highest dose tested, which when compared with the estimated dietary exposure, results in a margin of exposure of at least 1,300.
The food enzyme β-galactosidase (β-d-galactoside galactohydrolase; EC 3.2.1.23) is produced with the genetically modified Kluyveromyces lactis strain KLA by DSM Food Specialties B.V. The genetic modifications did not give rise to safety concerns.
With the exception of the potential skin and eye irritating effects of some proteases, and the well-documented potential for respiratory sensitization in case of workplace exposure, enzymes in general do not produce acute toxicity, dermal sensitization, genotoxicity, or repeated dose oral toxicity. Acute inhalation, reproduction, chronic toxicity, and carcinogenicity are not relevant for enzymes. Several hundred mutagenicity studies have been conducted on bacterial and mammalian cells using a variety of enzymes. No positive findings were observed.
More than 225 90-day studies have been performed and submitted to EFSA with no adverse findings, including in the bone marrow. The data showing no adverse effects for enzyme preparations also confirms that microbial metabolites and fermentation materials lack toxicity as well.
A notable, source-backed safety consideration pertains to occupational rather than consumer exposure. The well-documented potential for respiratory sensitization exists in case of workplace exposure to enzyme powders, including those derived from K. lactis. This is an inhalation risk relevant to manufacturing workers handling bulk enzyme powders, not to consumers ingesting formulated supplements or treated foods.
For the EFSA-evaluated chymosin produced by a genetically modified K. lactis strain: The allergenicity assessment considers only the food enzyme and not any carrier or other excipient that may be used in the final formulation. The potential allergenicity of the chymosin was assessed by comparing its amino acid sequence with those of known allergens. Using higher than 35% identity in a sliding window of 80 amino acids as the criterion, four matches were found — to pepsin A from wild boar, an aspartic protease-like protein from German cockroach, and proteins from Aspergillus fumigatus. The EFSA panel nonetheless concluded no safety concern was raised by these findings in context of the overall weight of evidence.
Individuals with documented hypersensitivity to yeasts or yeast-derived products may potentially react to preparations derived from K. lactis, in parallel with reactions to other food yeasts (S. cerevisiae, etc.). However, peer-reviewed literature specifically documenting hypersensitivity reactions to K. lactis-derived dietary supplement preparations in consumers is limited, and this consideration is drawn by analogy with the broader yeast allergy literature.
K. lactis forms the killer toxin zymocin that is active against certain ascomycetous yeasts. This property has been studied in the context of yeast ecology and biotechnology. Zymocin is active against select competing yeast species and is not documented as posing a health risk to human consumers of K. lactis-derived food-grade preparations.
Health conditions that Kluyveromyces lactis may help support.
Body systems that Kluyveromyces lactis may help support.
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