Ethanol and citric acid were determined by an HPLC apparatus (Ultimate 3000, Dionex, Germering, Germany) equipped with an HPX-87H column. Aliquots of the culture were filtered through 0.2 μm pore size bacteriological filter (Whatman). Ethanol was detected by a R.I. detector while citric acid was detected by a U.V. detector at λ=481 nm.