E-numbers / Flavour enhancers / E642
also: L-lysine hydrochloride · lysine HCl
The hydrochloride salt of lysine, an essential amino acid. Added to enhance savoury flavour and to fortify protein in processed foods.
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This is not on the UK list of approved food additives, so you will not normally see this E number on a UK label.
Why it’s worth knowing. This is not on the UK list of approved food additives, so you will not normally see this E number on a UK label.
Lysine hydrochloride is the hydrochloride salt form of L-lysine, one of the nine essential amino acids that the human body cannot make on its own. It is produced commercially by bacterial fermentation of glucose or molasses, usually using Corynebacterium glutamicum, then converted to the stable salt form. The pure compound is a white crystalline powder.
As a flavour enhancer, it intensifies savoury and umami taste notes in a similar manner to monosodium glutamate, though it is less potent. It also raises the lysine content of foods that are naturally low in this amino acid, such as cereals and grain-based products, supporting protein quality. In bakery and processed-meat applications it can improve dough handling and water-binding.
Used in fortified breads and cereals, instant noodles, canned and processed meats, savoury snack seasonings, protein-enriched diet foods, and some sports nutrition products. On a UK label it appears as 'lysine hydrochloride', 'L-lysine hydrochloride', or 'E642'.
L-lysine is an essential amino acid required for protein synthesis, collagen formation, and calcium absorption. The hydrochloride salt delivers the same lysine that occurs naturally in meat, fish, dairy and legumes. No additional pharmacological effect arises from the salt form at food-additive use levels.
L-lysine is classified as an essential amino acid for humans; the human body cannot synthesise it and must obtain it from diet. The WHO/FAO/UNU (2007) report on protein and amino acid requirements lists the adult average requirement for lysine at around 30mg per kg body weight per day.
Regulatory bodies in the EU and UK have evaluated lysine hydrochloride as a food additive. Because lysine is an ordinary dietary constituent and the hydrochloride counterion is also ubiquitous in food, no special toxicological concern has been identified at the low concentrations used as a flavour enhancer or fortifier.
The Scientific Committee on Food (SCF) and subsequently EFSA have not identified a need to set a numerical acceptable daily intake for lysine hydrochloride when used as a food additive, reflecting its status as a normal dietary amino acid at the levels of use intended.
E642 does not appear in Annex II of the assimilated Regulation (EC) No 1333/2008, and the FSA's food additive authorisations register holds no entry for it, so no food category or maximum level is set for it in Great Britain.
Studies using lysine as a dietary supplement at doses far higher than food-additive use levels have investigated effects on cold sore (herpes simplex) recurrence and anxiety. These doses (typically 1,000mg to 3,000mg per day as supplements) are orders of magnitude above what E642 contributes in food, so findings from supplement research do not translate directly to the additive context.
A clinical trial found that supplemental L-lysine at 1,248mg per day reduced the frequency of herpes simplex recurrence compared to placebo, but this is a therapeutic supplementation dose, not a food-additive exposure level.
People with the rare inherited metabolic disorder hyperlysinaemia (a defect in lysine degradation) are advised by their metabolic dietitian to limit lysine intake from all sources; label term to look for is 'lysine hydrochloride' or 'E642'. No other population group has a specific reason to single out this additive beyond general food-label reading.
Lysine hydrochloride is one of the more straightforward additives on the approved list. It is the salt form of an amino acid that appears naturally in protein-rich foods every day. The science on L-lysine as a nutrient is well-established, and the regulatory community has not identified a safety question specific to its use as a food additive at the levels used. The supplement literature at therapeutic doses is a separate field and does not apply to trace additive use in food. There is no active scientific controversy or outstanding safety review for E642.
E642 is not authorised as a food additive in Great Britain. It does not appear in Annex II of the assimilated Regulation (EC) No 1333/2008, and the FSA's food additive authorisations register holds no entry for it. Lysine itself is an amino acid present in protein foods; it is the E642 additive designation that is not used on GB labels.
Chemically yes. L-lysine is an essential amino acid found in meat, fish, dairy, eggs and legumes. The hydrochloride form (E642) is the same amino acid combined with hydrochloric acid to make a stable powder. The body absorbs it the same way as dietary lysine from protein.
Fortified breads and breakfast cereals, instant noodles, processed meats, savoury snack powders, and protein-enriched diet products are the most common sources. Check the ingredients list for 'lysine hydrochloride', 'L-lysine hydrochloride', or 'E642'.
Yes, in almost all commercial food applications. Lysine hydrochloride is produced by bacterial fermentation of plant-derived glucose or molasses, not from animal sources. Products certified vegan will have confirmed their specific source.
Last reviewed: 20 June 2026
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