A gene encoding glutathione synthetase from Candida utilis is provided and food containing .gamma.-glutamylcysteine cysteine or cystenylglycine is produced by cultivating Candida utilis modified by means of a gene encoding glutathione synthetase under a suitable condition and mixing the obtained culture or a fraction thereof or the culture or a fraction thereof subjected to heat treatment with a raw material of food or drink to process food or drink.