L-glutamine

Grades and forms

L-glutamine is a single amino acid declared as itself, so the label claim equals the weight of active material, with no elemental-content conversion. It is bought almost entirely as a dry, white crystalline L-glutamine powder. This page covers how grades differ, how the EU regulates amino acids in food supplements, and where L-glutamine causes problems in formulation.

Three points decide which bulk L-glutamine grade suits a product:

• Quality standard. Material is sold as food grade or tested against a pharmacopoeia monograph. Choose the standard your customers and your own specifications reference.
• Particle size. Fine powders suit capsule filling and dry blends. Coarser, granulated or agglomerated grades flow better and disperse more easily in drink powders.
• Production route. L-glutamine is generally produced by fermentation. Ask for the route if your product makes dietary or origin declarations, and confirm any certificate for the specific lot.

Assay, particle size distribution, loss on drying and contaminant limits are stated on the specification sheet and certificate of analysis. SoleChem supplies these with the quote. Ask for the grade you need in the quote form.

EU regulatory status

Directive 2002/46/EC defines food supplements as concentrated sources of nutrients or other substances with a nutritional or physiological effect. Its harmonised lists in Annexes I and II cover vitamins and minerals only. Amino acids such as L-glutamine are not on those lists.

The use of L-glutamine in food supplements is therefore governed by national rules. Some member states keep lists of permitted substances or set maximum amounts per daily portion. Member states may also require notification of the placing on the market, with a model of the label, under Article 10 of the Directive. Check each target market before launch, and do not assume a rule in one country applies in another.

Regulation (EC) No 1925/2006 contains, in Article 8, a procedure for prohibiting or restricting other substances at EU level. Check whether any measure under that procedure affects L-glutamine. Novel-food status for your intended use should be confirmed against Regulation (EU) 2015/2283; see our guide to novel food status of supplement ingredients.

On the label, Article 8 of Directive 2002/46/EC requires the amount of each substance with a nutritional or physiological effect per recommended daily portion. Ingredient listing follows Regulation (EU) No 1169/2011. Our guide to labelling a food supplement in the EU covers the full set of mandatory particulars.

Formulation notes

Stability in water. Dry L-glutamine is stable under normal storage. In aqueous solution it slowly cyclises to pyroglutamic acid and ammonia. Heat and pH extremes accelerate the reaction. Ready-to-drink liquids and processes with a hot aqueous step, such as cooked gummies, need stability testing on the finished product. Dry powders for reconstitution just before use avoid the issue.

Drink powders. L-glutamine has a mild taste and blends into flavoured or unflavoured mixes. Test dissolution at your serving concentration with the actual grade, since particle size affects it. Combinations with other free-form amino acids, such as L-leucine or glycine, are common in powders and sports nutrition.

Maillard browning. Like other amino acids, L-glutamine can react with reducing sugars such as dextrose under heat and moisture. Control humidity in storage and check colour during stability studies.

Capsules and tablets. Label claims in the gram range need several capsules per serving. Fine grades may need a flow aid such as silicon dioxide. Tablets with a high L-glutamine load usually need a binder or granulation to compress well.

Label-claim arithmetic. To declare 1,000 mg of L-glutamine per serving, divide 1,000 mg by the assay fraction on the certificate of analysis. Then add any overage your stability data supports. The overage calculator handles the second step.