L-leucine

Grades and forms of L-leucine powder

L-leucine is supplied as the free amino acid, not as a salt. One gram of material therefore delivers one gram of leucine, corrected only by the assay on the certificate of analysis. It is one of the three branched-chain amino acids in the Amino Acids category.

Manufacturers buy L-leucine in two physical forms:

• Crystalline powder: the standard form for capsules, tablets and dry blends where the powder is not dispersed in water by the consumer.
• Instantised powder: L-leucine agglomerated with a small proportion of lecithin so that it wets and disperses in drinks and shakes.

Three points decide the choice: the final format, whether the product is mixed into liquid, and the grade standard the specification must meet (food grade or a pharmacopoeia grade). The production route also matters, because it determines which source declarations the supplier can give. SoleChem sends the specification sheet and certificate of analysis with its quote; state the grade and form you need in the quote form.

EU regulatory status

Annexes I and II of Directive 2002/46/EC list vitamins, minerals and their permitted forms only. Amino acids are not covered by those lists, so the directive does not set an EU-wide positive list for L-leucine.

Use of amino acids in food supplements is governed by national rules. These differ by member state: some apply positive lists or maximum amounts, and many require notification of placing on the market to the competent authority. Check the rules of each target market; the labelling guide covers the notification step.

Regulation (EC) No 1925/2006 allows the Commission to prohibit, restrict or place under scrutiny “other substances” through Annex III. Confirm that the current consolidated Annex III contains no entry for leucine before launch.

Novel-food status under Regulation (EU) 2015/2283 should be confirmed for the specific material and production route. See the novel food guide for how to check.

Instantised grades contain lecithin, a food additive under Regulation (EC) No 1333/2008. If the lecithin is from soy, check the soybean entry in Annex II of Regulation (EU) No 1169/2011: substances listed there must be emphasised in the ingredient list under Article 21.

Formulation notes

Wetting and dispersion. Leucine has a hydrophobic isobutyl side chain. Crystalline L-leucine wets poorly, floats on water and forms lumps in shakes. This is the main reason the instantised form exists. In powders and sports nutrition, add it to the liquid with vigorous mixing or use the instantised grade.

Taste. L-leucine has a bitter taste. Ready-to-mix powders usually need flavour masking and sweetening, tested at the declared amount per serving.

Flow and fill. Fine crystalline amino acid powders can be cohesive and prone to static. A flow aid such as silicon dioxide is common in capsules. Leucine is light and voluminous, which limits the amount per capsule; check bulk density on the specification sheet before choosing a capsule size.

Tablets. L-leucine is used as a water-soluble lubricant in effervescent tablets. It avoids the insoluble film that magnesium stearate can leave on the surface of the solution.

Blends. L-leucine is often combined with isoleucine, valine and L-glutamine in fixed-ratio amino acid blends. Ingredients with different particle sizes can segregate during transfer, so compare the particle size data on each specification and validate blend uniformity.

Stability. Like other amino acids, leucine can take part in Maillard browning with reducing sugars under heat and moisture. Keep blends dry and test colour change in stability studies.

Label-claim arithmetic. Because L-leucine is not a salt, no elemental conversion applies. Input per serving equals the label claim divided by the leucine content on the certificate of analysis, times 100. For instantised grades, use the leucine content of the agglomerate, not of the pure amino acid. Add any overage with the overage calculator.