Scientific Opinion on the safety and efficacy of L-cysteine hydrochloride monohydrate as a flavouring additive for pets

L-Cysteine is a non-essential amino acid produced by hydrolysis of natural keratin (typically from duck feathers). In the absence of information on bacterial fermentation, the FEEDAP Panel cannot conclude on this way of manufacturing. The addition of L-cysteine to the food of cats and dogs is safe if the balance between cysteine and methionine in the complete diet is maintained. Owing to the unknown total content of free L-cysteine in the final diet, it cannot be assessed whether or not the addition of L-cysteine as a feed flavouring would disrupt this balance. In the absence of data, the FEEDAP Panel considers it prudent to assume that exposure of the skin, eyes and mucous membranes poses a risk to users. As L-cysteine is intended for use in pets, assessment of the safety for the environment is not needed. It is not clear if the use of L-cysteine, applied as described by the applicant, is the same as that for human food and, therefore, efficacy cannot be assumed and has not been demonstrated. The FEEDAP Panel made a recommendation regarding the specification of the additive.