Enzymatic degradation of nucleic acid and the related compounds in Shiitake mushroom during the processing and the cooking, and the control.

本研究旨在探讨香菇蒸煮过程中5 '-GMP积累的控制机理。(1)研究了香菇中RNA、核酸酶和磷酸酶的分布及其在生长过程中的变化。RNA含量在生长过程中呈下降趋势，冠部RNA含量高于茎部。在生长后期，冠部的浓度大小顺序为鳃部>上表面>中层。在生长过程中，冠部的核酸酶和磷酸酶活性逐渐下降。核酸酶主要分布在鳃部，磷酸酶主要分布在上表面。(2)研究了香菇在蒸煮过程中RNA及其相关物质的变化。当香菇匀浆在60 ℃孵育时，5 '-核苷酸的含量迅速增加，在5 min左右达到最大值，然后下降。另一方面，当整个香菇浸泡在60 ℃的水中时，香菇组织中的5 ′-核苷酸量以与匀浆中相同的方式变化，但浸泡水中的5 ′-核苷酸量迅速增加，在15分钟内达到最大值，然后几乎没有下降。当整个香菇浸泡在水中，以恒定的加热速率烹调时，5 '-核苷酸的量在60-70 ℃迅速增加，并在80 ℃达到恒定水平。从这些观察结果可以看出，除了磷酸酶比核酸酶更快的热失活外，5'-核苷酸的扩散在香菇组织的有限部分形成，香菇组织中磷酸酶活性较低的部位，可能对香菇蒸煮过程中5 '-核苷酸的积累起关键作用。(3)在香菇的干燥条件和蒸煮条件中，蒸煮过程中的升温速率和pH值对5 ′-核苷酸的积累有直接影响，在4 ℃/min和pH 6.5时最高，此时磷酸酶比核酸酶更不耐热。

This study was undertaken to elucidate the mechanism controlling the accumulation of 5'-GMP in Shiitake mushroom during the cooking.(1) The distribution of RNA, nuclease and phosphatase in Shiitake and these changes during the growth were examined. The concentration on RNA, which is richer in cap part than in stalk part, decreased during the growth. At the second half of growth period, the concentration in cap part was in the following order: gill > upper surface > middle layer. Nuclease and phosphatase activities in cap part gradually decreased during the growth. The distribution of nuclease was localized to gill and that of phosphatase to upper surface.(2) Changes of RNA and the related compounds in Shiitake during the cooking were examined. When Shiitake homogenate was incubated at 60ﾟC, the amount of 5'-nucleotides rapidly increase passed through a maximum within about 5min, and then fell off. On the other hand, when whole Shiitake was soaked in water at 60ﾟC, the amount of 5'-nucleotides in Shiitake tissue changed in the same manner as in the homogenate, but that in soaking water rapidly increased, reached a maximum in 15min, and then scarcely decreased. When whole Shiitake soaked in water was cooked at a constant heating rate, the amount of 5'-nucleotides increased rapidly at 60-70ﾟC, and reached a constant level at 80ﾟC.From these observations, it is suggested that, as well as faster heat inactivation of phosphatase than nuclease, the diffusion of 5'-nucleotides formed at a restricted part of Shiitake tissue, to soaking water or to some parts of Shiitake tissue where is poor in phosphatase activity, may play a key role in the accumulation of 5'-nucleotides during the cooking of Shiitake.(3) Of drying conditions and cooking conditions of Shiitake, heating rate and pH of Shiitake during the cooking had a direct effect upon the accumulation of 5'-nucleotides, being highest at 4ﾟC/min and pH 6.5, where phosphatase became more thermolabile than nuclease.