In Shiitake mushroom (Lentinus edodes),5′-nucleotides, especially 5′-GMP, are major umami components.5′-Nucleotides are degraded products by ribonuclease (RNase) from RNA and moreover they degrade into nucleosides by phosphomonoesterase (PMase). In this process, RNase is more stable on heating than PMase and consequently 5′-nucleotides accumulates.
Taking this property into account, we studied on the effect of various heat processing and damaging of tissues on 5′-nucleotide contents of Shiitake mushroom. The following results were obtained.
1. In various heat processing tests, the heating from water to boiling or by a 100W electronic oven accumulated the more amount of 5′-nucleotide than that by putting in boiling water or a 500W electronic oven.
2. Heating from water to boiling after damaging the tissues of Shiitake mushroom, especially damaging by freezing led to the increase of 5′-nucleotides.
3. According to the defrosting methods, the amounts of 5′-nucleotides in frozen Shiitake mushroom, when heated from water to boiling, increased in the order of defrosting in a refrigerator, without defrosting and defrosting in an electronic oven.
4. Though the amounts of 5′-AMP,5′-UMP and 5′-CMP in frozen Shiitake mushroom seemed to decrease slightly when heated after defrosting in a refrigerator or an electronic oven after storage at -40°C, RNA and 5′-GMP were constant in any way.