Yeast extracts with increased RNA content.
Peter Dekker, Carlos Ribeiro
R&D, DSM Food-Specialties, PO Box 1, Delft, 2600 MA, The Netherlands
Two types of yeast extracts can be recognized. Autolytic yeast extracts are concentrates of the soluble materials obtained from autolysis of yeast where degradation is effected by the native yeast enzymes. This type of yeast extract, which is rich in amino acids, is used in the food industry as basic taste building block. Hydrolytic yeast extracts are concentrates of the soluble materials obtained from hydrolysis of yeast; a process by which degradation is effected by exogenous proteases and especially nucleases capable of degrading RNA into 5'-ribonucleotides. Generally the native yeast enzymes are inactivated prior to the lysis. When deaminase is added to the hydrolytic yeast extract, 5'-AMP is converted into 5'-IMP, and the extract is therefore rich in the purines 5'-GMP and 5'-IMP. Often yeast extracts are also rich in monosodium glutamate (MSG). 5'-IMP, 5'-GMP and MSG are known for their flavor enhancing properties. They are capable of enhancing the savory and delicious taste in certain types of food, like soups, sauces, marinades, and flavor seasonings. This phenomenon is described as 'mouthfeel' or umami. For the food industry it would therefore be an advantage to have a yeast strain with a higher content of RNA as precursor for purines. We will present data on the isolation of such a yeast strain using classical mutagenesis and selection, and analysis of the extract of this strain from shake-flask up to 200,000 liter industrial scale fermentations.