The present invention concerns a novel yeast extract comprising 25% to 55% by weight of 5'-ribonucleotides, including 5% to 20% by weight of adenosine 5'-monophosphate (5'-AMP) and 5% to 20% by weight of guanosine 5'-monophosphate (5'-GMP) in a 5'-AMP/5'GMP ratio ranging from 0.85 to 1.25. The weight percentages are expressed relative to the weight of dry matter of the yeast extract. The invention also concerns the use of such an extract for masking bitter and acid flavours and undesirable notes of sweeteners and proteins and undesirable metallic notes in a product, and a method for masking these flavours and notes.