What Are Human Milk Oligosaccharides (HMOs)?

Human milk oligosaccharides (HMOs) are complex carbohydrates that occur naturally in human milk. Most HMOs pass through the small intestine without being digested. They then reach the colon, where particular gut bacteria can use them.

Researchers have identified more than 200 HMO structures in human milk, but most occur in small amounts. About 10 to 15 HMO types make up most of the total amount. The amount of each HMO also changes during lactation and varies between mothers, as shown in this review of HMO concentrations in human milk.

HMOs are a family of ingredients, not one single ingredient. Our commercial portfolio includes six separate molecules with exact chemical identities: 2'-FL, 3-FL, LNnT, LNT, 3'-SL Sodium Salt, and 6'-SL Sodium Salt. We produce these HMOs through controlled fermentation, purification, and drying. They are not extracted from human milk.

An HMO is a carbohydrate molecule made from several simple sugar units. Most HMO structures begin with lactose, which contains glucose and galactose. Enzymes then attach other sugar units to create different HMO structures.

What HMOs Are Made Of

HMOs are made by joining five types of simple sugar in different combinations. A particular HMO may contain only some of these five:

Glucose
Galactose
N-acetylglucosamine
Fucose
N-acetylneuraminic acid, commonly called sialic acid

How these sugar units connect matters. Two HMOs may contain the same building blocks but connect them at different positions. Laboratories must identify them separately, gut bacteria may use them differently, and regulations list them as separate ingredients.

For nutrition product development, always begin with the complete HMO name, CAS number, molecular form, and specification. The word "HMO" alone does not identify the ingredient.

In 2'-fucosyllactose, fucose attaches to the galactose unit through an alpha-1,2 linkage. In 3-fucosyllactose, fucose attaches to the glucose unit through an alpha-1,3 linkage. A linkage describes where two sugar units connect. The two HMOs have the same molecular formula and molecular weight, but their different connections make them structural isomers.

Structural isomers contain the same atoms but arrange them differently. Differences in how the sugar units connect also separate LNT from LNnT and 3'-SL from 6'-SL. Nutrition companies therefore need identity tests and isomer limits, not only a molecular formula or a total-carbohydrate result.

HMO Profiles Vary in Human Milk

Human milk does not contain one fixed HMO recipe. Total HMO concentration and the amount of each structure vary between mothers and change during lactation. Colostrum, the first milk produced after birth, generally contains more HMOs in total than milk produced later. The amount of each individual HMO may decrease, increase, or remain relatively stable over time.

Maternal genetics also affect the profile. A functioning FUT2 gene provides instructions for an enzyme that helps produce alpha-1,2-fucosylated HMOs such as 2'-FL. Mothers with this enzyme activity are commonly called secretors and usually have much higher 2'-FL concentrations in their milk. Other genes and enzymes affect additional fucosylated structures.

A nutrition product containing one or several fermentation-derived HMOs does not copy the complete HMO mixture in human milk. The product adds selected HMO structures in measured amounts for a specific purpose.

Product Identity

Three HMO Families and Six Commercial Products

Our portfolio covers fucosylated, neutral core, and sialylated HMOs. Each family name describes a structural feature. The family name alone does not mean that every HMO in that group behaves in the same way or produces the same effects.

Product identity and structural differences across our six HMOs
HMO	Full Name	CAS Number	Structural Family	Key Structural Difference
2'-FL	2'-Fucosyllactose	41263-94-9	Fucosylated HMO	Fucose connects to galactose through an alpha-1,2 linkage
3-FL	3-Fucosyllactose	41312-47-4	Fucosylated HMO	Fucose connects to glucose through an alpha-1,3 linkage
LNnT	Lacto-N-neotetraose	13007-32-4	Neutral Core HMO	Type 2 core with a beta-1,4 galactose-to-N-acetylglucosamine linkage
LNT	Lacto-N-tetraose	14116-68-8	Neutral Core HMO	Type 1 core with a beta-1,3 galactose-to-N-acetylglucosamine linkage
3'-SL Sodium Salt	3'-Sialyllactose Sodium Salt	128596-80-5	Sialylated HMO	Sialic acid connects to galactose through an alpha-2,3 linkage
6'-SL Sodium Salt	6'-Sialyllactose Sodium Salt	157574-76-0	Sialylated HMO	Sialic acid connects to galactose through an alpha-2,6 linkage

Fucosylated HMOs

2'-FL and 3-FL contain fucose. They share the molecular formula C18H32O15 and have the same molecular weight. However, the fucose unit connects to a different sugar and at a different position in each HMO.

The alpha-1,2 and alpha-1,3 linkages affect laboratory testing and which bacteria can use each HMO. In one laboratory system designed to imitate an infant colon, 2'-FL and 3-FL changed the types of bacteria and the compounds those bacteria produced. The bacterial changes differed between stool samples from different infants. This 2'-FL and 3-FL laboratory study supports treating the two HMOs as separate formulation ingredients. The study does not prove that 2'-FL and 3-FL produce the same effects in people.

Neutral Core HMOs

LNT and LNnT are called neutral core HMOs because they do not contain fucose or sialic acid. Each contains four sugar units, and both share the molecular formula C26H45NO21. The final galactose unit connects at a different position: LNT uses a beta-1,3 connection, while LNnT uses a beta-1,4 connection.

Some bacterial enzymes can break one connection more easily than another. Laboratory work with one specific bacterial strain, Bifidobacterium longum subsp. infantis ATCC 15697, identified enzymes that help this strain break down LNT and LNnT. The LNT and LNnT enzyme study does not show that every bifidobacterial strain uses these HMOs in the same way.

Sialylated HMOs

3'-SL and 6'-SL contain sialic acid and are commonly supplied as sodium salts. In 3'-SL, sialic acid connects to the 3-position of the galactose unit in lactose. In 6'-SL, sialic acid connects to the 6-position of that galactose unit.

This small structural change creates two separate molecules. The specification should identify the sodium salt and state the amount of the target HMO. It should also list the sodium level and other sugars. A 3'-SL specification should limit 6'-SL, while a 6'-SL specification should limit 3'-SL.

Research Overview

What Do HMOs Do?

What an HMO does depends on its structure, the bacterial strain, the consumer group, and the complete nutrition product. Evidence for one HMO does not automatically apply to another HMO or a different blend.

Most HMOs Reach the Colon

Most HMOs pass through the small intestine without being digested. In a small study of breastfed infants, much of the measured HMO amount reached the large intestine in seven of eight infants. Gut bacteria then fermented the HMOs. The infant HMO digestion study supports the conclusion that many HMOs reach the colon, but the study was too small to provide a percentage that applies to every infant.

Selected Gut Bacteria Use Particular HMOs

Some bifidobacterial strains have proteins that bring particular HMOs into the cell and enzymes that break them down. Other microorganisms cannot use the same HMO directly. The result depends on both the HMO and the microbial strain.

For example, B. infantisBi-26 used 2'-FL and produced acetate, lactate, formate, and 1,2-propanediol under laboratory conditions. The Bi-26 metabolism study applies to that strain and test system. The study does not show that every B. infantisstrain uses 2'-FL in the same way.

Some HMO Structures Can Affect Microbial Attachment

Certain HMOs resemble carbohydrate structures on the intestinal surface. A study using laboratory tests, mice, and human intestinal tissue outside the body found that alpha-1,2-fucosylated milk oligosaccharides reduced the attachment of Campylobacter jejuni. The Campylobacter attachment study shows one possible interaction between a particular HMO structure and a microorganism. The study does not support an infection-prevention claim for a commercial food or supplement.

Researchers also study how HMOs interact with intestinal cells and affect communication within the immune system. Any statement about these effects requires evidence for the exact HMO and finished product. Laboratory findings can guide research and formulation decisions, but they do not automatically support wording on a finished-product label.

Product Development

HMOs Are Not Probiotics, Lactose, GOS, or FOS

HMOs, probiotics, lactose, GOS, and FOS can appear in the same nutrition formula, but they are not interchangeable.

How HMOs differ from other common nutrition ingredients
Term	What It Is	Main Difference from an HMO
Probiotic	A live microorganism used in an adequate amount for a defined benefit	An HMO is a carbohydrate, not a living bacterium
Lactose	A sugar made from two simple sugar units: glucose and galactose	Human enzymes normally digest lactose and use it as an energy source
GOS	A mixture of galacto-oligosaccharides	GOS has a different composition and does not have the identity of a named HMO
FOS	A mixture of fructose-based oligosaccharides	FOS uses fructose-based structures that are not HMOs
HMO	A defined carbohydrate within the human milk oligosaccharide family	Each commercial HMO needs its own identity, specification, evidence, and market review

HMOs and probiotics may appear in the same synbiotic product. A synbiotic combines a live microorganism with an ingredient that selected microorganisms can use. Product developers still need evidence for the exact probiotic strain because a species name alone does not prove that the strain can use a particular HMO.

Where Nutrition Companies Use HMOs

Nutrition companies evaluate HMOs for early-life nutrition, dietary supplements, functional foods, beverages, nutrition drinks, and tube-feeding formulas. However, not every HMO is allowed in every product category. Before starting a commercial formula, the company must check the exact HMO, the amount used, the consumer age, the finished-product category, and the sales market.

Infant and Young-Child Nutrition

Published infant formula trials have evaluated both individual HMOs and defined blends. One randomized trial tested formula containing 2'-FL and LNnT, while another tested a five-HMO blend containing 2'-FL, 3-FL, LNT, 3'-SL, and 6'-SL.

The 2'-FL and LNnT trial and the five-HMO trial reported growth and tolerance results for the formulas and HMO amounts used in those studies. The results do not approve a different formula, amount, consumer group, or marketing claim.

Dietary Supplements and Functional Foods

Product developers also consider HMOs for microbiome-focused supplements, powders, sachets, capsules, drinks, and selected foods. Before formulation, the company must confirm that a current market rule or U.S. Generally Recognized as Safe (GRAS) conclusion covers the exact HMO, intended amount, consumer age group, and finished-product category.

Adult nutrition should not reuse infant-formula evidence or infant-health language without separate support. The evidence, serving amount, safety review, and claim wording must fit the adult product and destination market.

Medical and Specialized Nutrition

Some FDA GRAS notices and EU novel food entries include nutrition drinks or formulas used for tube feeding. Each record covers only the HMO ingredient, uses, and amounts stated in that record. A record for one HMO does not permit every HMO in every medical nutrition formula.

Multi-HMO Formulas

A multi-HMO formula can combine fucosylated, neutral core, and sialylated structures. The formulation objective and supporting evidence should determine the blend. A larger number of HMOs does not automatically make a better product.

The product review must cover every HMO and the combined intake. For example, a formula containing 2'-FL and LNnT needs a separate identity and specification check for each HMO. The company must also review the amount of each HMO and their combined amount in the finished product.

Actual Production Flow

How We Manufacture 2'-FL

The following sequence comes from our actual 2'-FL production flow chart. This sequence applies to 2'-FL only. The other five HMOs may use different production and purification steps.

Culture Media Preparation: Prepare the controlled nutrient medium used for strain growth and fermentation.
Strain Cultivation: Cultivate the production strain under controlled conditions.
Seed Preparation: Prepare a larger starter culture that will begin the main production fermentation.
Fermentation: Run the controlled fermentation stage that produces 2'-FL.
Inactivation and Microfiltration: Inactivate the culture and use microfiltration to remove cells and suspended material.
Purification 1 - Ultrafiltration, Decolorization, and Desalination: Use membrane filtration and other purification steps to reduce color, salts, larger molecules, and materials left from fermentation. Our production flow chart identifies this stage as CCP1.
First Concentration: Concentrate the purified 2'-FL liquid before the next separation stage.
Purification 2 - Chromatographic Separation: Pass the liquid through a separation system that isolates 2'-FL from related carbohydrates and remaining process materials. Our production flow chart identifies this stage as CCP2.
Second Concentration: Concentrate the purified 2'-FL liquid again before drying.
Drying: Convert the concentrated 2'-FL liquid into powder.
Sampling and Packaging: Take a quality-control sample, run metal detection, and pack the powder in a Class 100,000 cleanroom.
Quality Control and Finished Product Release: Test the batch against the finished-product specification before release.

CCP means Critical Control Point. At each CCP, we monitor defined limits to control a food-safety hazard. Our 2'-FL flow chart marks the first and second purification stages as CCP1 and CCP2.

This sequence explains how we make 2'-FL powder. We release a batch only after its test results meet the finished-product specification.

Technical Review

How to Compare HMO Specifications

A useful HMO specification does more than state purity. It confirms which HMO the powder contains. The specification also sets limits for other sugars, moisture, heavy metals, microorganisms, and materials that may remain after production.

Identity and Assay

Assay means the measured amount of the target HMO in the powder. Confirm the full chemical name, abbreviation, CAS number, molecular formula, molecular weight, salt form, identity test, and test method. An as-is result includes the water in the supplied powder. A dry or water-free result removes the measured water from the purity calculation.

For example, "2'-FL water free, at least 94.0%" means the purity calculation removes the measured water. Do not compare a water-free result directly with an as-is result until both specifications use the same calculation method.

Related Carbohydrates and Isomers

Small amounts of lactose, glucose, galactose, fucose, sialic acid, related oligosaccharides, and structural isomers may remain in the powder. Their limits affect the purity and overall composition of the ingredient. The relevant limits differ by HMO and manufacturing process.

For isomer pairs such as 2'-FL and 3-FL or 3'-SL and 6'-SL, the test method must separate the target HMO from the closely related isomer. A total-carbohydrate test cannot replace an assay that measures the exact HMO.

Safety and Process Limits

Review moisture or water, ash (total inorganic material), remaining protein, heavy metals, and materials left from production. Also check the limits for total bacteria, yeast, mold, and specific pathogens. Some HMO specifications also set an endotoxin limit. Endotoxins come from the outer membrane of Gram-negative bacteria and require close attention in sensitive nutrition products.

The finished-product category determines the required limits. Infant and specialized nutrition projects may require different tests or tighter limits than general food products.

Stability and Finished-Product Processing

Powder stability does not answer every formulation question. Review how the HMO dissolves and how it responds to pH, heat, storage, packaging, and other ingredients. Also check water activity. Water activity shows how much water is available for chemical reactions or microbial growth. Water activity is different from the total water in the product.

A pilot batch followed by analytical testing can show whether the HMO remains within the target specification after mixing, pasteurization, spray drying, and storage. The required processing trial should match the actual finished product.

Market Requirements

U.S. and EU Market Review

The United States and European Union regulate each HMO product and intended use separately. A nutrition company must find the rule or safety conclusion that matches its proposed ingredient and finished product.

United States: GRAS Notices Are Not FDA Approvals

GRAS means Generally Recognized as Safe for stated uses and amounts. A company may send FDA its own GRAS safety conclusion. FDA may reply that it has no questions about the information submitted. The reply applies only to the ingredient, manufacturing information, uses, and amounts described in that notice. An FDA no-questions letter is not an approval for every product sold under the same HMO name. The FDA explanation of the GRAS notification program explains the process.

Each linked FDA record describes one defined ingredient, how it is made, its intended uses, and its use levels.

European Union: Check the Applicable Novel Food Entry

An HMO sold in the EU must match an entry in the Union List of authorized novel foods. The entry identifies the ingredient and lists its specification, permitted food categories, maximum amounts, and labeling rules. In most cases, a company may rely on the authorization when its ingredient meets all conditions in the entry. However, a temporary data-protection period may reserve a new authorization for the original applicant.

Later amendments may add or change the authorized manufacturing source, specification, uses, or data-protection conditions.

Our HMO use-level and regulatory database organizes representative FDA and EU records for all six HMO types. Use the database to find the relevant record. Then verify the current official text before formulation or commercial launch.

Formulation Checklist

A Practical HMO Selection Process

Nutrition companies can narrow the product choice by answering these questions:

Which consumer group will use the finished product?
In which country or region will the product be sold?
What is the finished-product category: infant formula, supplement, beverage, food, nutrition drink, or tube-feeding formula?
Does the concept require one HMO, a defined pair, or a broader blend?
Which GRAS conclusion, EU novel food entry, or other market rule covers the exact HMO and intended use?
Does the formula require purity on an as-is or water-free basis? What limits must apply to related sugars, microorganisms, and materials left from production?
Will heat, pH, moisture, or storage conditions affect the HMO in the finished product?

Answer the application and market questions before choosing the ingredient. Do not select an HMO from a research headline and wait until later to check whether it fits the formula and sales market.

What HMOs Mean for Product Development

Fermentation makes selected HMOs available as commercial ingredients with defined specifications. Start with the exact HMO identity. Then check whether it fits the consumer group, finished-product format, sales market, supporting evidence, and technical requirements.

We manufacture six HMO ingredients across the fucosylated, neutral core, and sialylated families. We provide HMO type recommendations, application guidance, samples, specifications, and product information for formulation review.

Review our six HMO products or contact us about an HMO formulation.

What Are Human Milk Oligosaccharides (HMOs)? A Practical Guide for Nutrition Products