Abstract: Continuous process for the cultivation of yeast cells under aerobic conditions in an aqueous growth medium, to which an aqueous nutrient medium comprising a source of assimilable nitrogen and methanol of a source of assimilable carbon is continuously added. The yeast belongs to the species Candida boidinii and the nutrient medium comprises a primary source of assimilable nitrogen consisting of urea and a secondary source of assimilable nitrogen chosen from ammonia, ammonium hydroxide and ammonium salts, the ratio between nitrogen in the primary source and that in the secondary source being from 2:1 to 1:20.

Abstract: The commercial process of preparing citric acid by submerged fermentation of hydrolized carbohydrates under aerobic conditions with yeasts of the genus Candida, while maintaining the pH value at 5-7 by addition of calcium hydroxide, is improved by submitting the broth obtained from a first fermentation operation to a first centrifuging to separate calcium citrate and then to a second centrifuging to separate the yeast cells. The cells thus recovered are recycled for use in a further fermentation operation. The use of said recycle cells permits higher yields and outputs of citric acid to be obtained in the further fermentation operation.

Abstract: Process for the production of microorganism lysates, comprising subjecting the said microorganisms suspended in water to thermal shock produced by a spray-drying treatment and then subjecting the product resulting from spray drying to autolysis.