L-cysteine
L-cysteine is a sulfur-containing amino acid. Because the free form oxidizes readily to cystine, it is mostly sold as L-cysteine hydrochloride monohydrate. It has long been made by hydrolyzing keratin from feathers or hair and reducing the cystine, and it is now also made by fermentation of sugars. Bakers use it as a dough conditioner, flavor houses use it in process flavors, and supplement brands use it in amino acid blends.
Suppliers sell different products under the same name. Specify the one you need.
The most common commercial form, more stable than the free base; about 30% of its weight is HCl and water, so dose on L-cysteine content.
L-cysteine HCl without the water of crystallization, with a higher cysteine content per kilogram.
L-cysteine itself, used where chloride is unwanted; it oxidizes faster in storage.
L-cysteine made by fermentation of plant sugars, offered with vegan, kosher or halal statements where keratin-derived material is not acceptable.
L-cysteine made from feathers or hair; the supplier's spec should state the source.
Compare each result with your own specification when the lot arrives.
Store L-cysteine in tightly closed, lined containers in a cool, dry place away from light and strong odors, and reseal opened packs promptly. Air and moisture oxidize it to cystine and it has a sulfur odor, so keep packs full and closed and away from flavors. Shelf life or retest date is set by the supplier's specification; assay, loss on drying and micro are the usual retest points for older stock.
Record assay, salt form and source (fermentation or keratin) for each lot, and keep the source statement on file for labeling and certification. Rotate stock FEFO.
Facts from regulators and standards bodies, each linked to its source.
21 CFR 172.320 lists L-cysteine among the amino acids that may be safely used as nutrients added to foods; added plus naturally present L-cystine and L-cysteine may not exceed 2.3 percent by weight of the total protein of the finished food.
Source: ecfr.gov (opens in a new tab)21 CFR 184.1271 affirms L-cysteine as GRAS for supplying up to 0.009 part of total L-cysteine per 100 parts of flour as a dough strengthener in yeast-leavened baked goods and baking mixes.
Source: ecfr.gov (opens in a new tab)21 CFR 184.1272 affirms the same use for L-cysteine monohydrochloride, defined there as the monohydrochloride monohydrate.
Source: ecfr.gov (opens in a new tab)FDA's Substances Added to Food inventory lists L-cysteine with technical effects including dough strengthener, flour treating agent and nutrient supplement.
Source: hfpappexternal.fda.gov (opens in a new tab)This is general information, not regulatory advice. Status differs by country and by how the ingredient is used, so check the rules for your product and market.
Manufacturers and distributors whose own websites say they sell it.
Manufacturer · Raleigh, NC
North American subsidiary of the Ajinomoto Group. It supplies pharmaceutical- and food-grade amino acids made by fermentation, in pack sizes from R&D pails to bulk, plus custom amino acid blends.
Suppliers are in alphabetical order and none pays to appear. Each claim is checked against the supplier’s own website on the date shown. Ask for the specification sheet and a recent COA before you order, and confirm details with the supplier.
Common forms include hydrochloride monohydrate, anhydrous hydrochloride, free base, fermented (non-animal) grade and keratin-derived grade. Ask each supplier for the specification sheet of the exact grade they quote.
Expect identity, assay, related substances, loss on drying and residue on ignition, heavy metals and microbiology and source statement, each with its method, specification and result for that lot.
Store L-cysteine in tightly closed, lined containers in a cool, dry place away from light and strong odors, and reseal opened packs promptly. Air and moisture oxidize it to cystine and it has a sulfur odor, so keep packs full and closed and away from flavors. Shelf life or retest date is set by the supplier's specification; assay, loss on drying and micro are the usual retest points for older stock.
21 CFR 172.320 lists L-cysteine among the amino acids that may be safely used as nutrients added to foods; added plus naturally present L-cystine and L-cysteine may not exceed 2.3 percent by weight of the total protein of the finished food. 21 CFR 184.1271 affirms L-cysteine as GRAS for supplying up to 0.009 part of total L-cysteine per 100 parts of flour as a dough strengthener in yeast-leavened baked goods and baking mixes. 21 CFR 184.1272 affirms the same use for L-cysteine monohydrochloride, defined there as the monohydrochloride monohydrate. FDA's Substances Added to Food inventory lists L-cysteine with technical effects including dough strengthener, flour treating agent and nutrient supplement.
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