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

本研究旨在阐明香菇在烹调过程中5‘-GMP积累的控制机制。(1)研究了香菇生长过程中RNA、核酸酶和磷酸酶的分布及其变化。在生长过程中，花冠部分比花柄部分更丰富的RNA含量呈下降趋势。在生长后期，盖部的浓度大小顺序为：鳃&GT>上表面&GT>中层。在生长过程中，帽部的核酸酶和磷酸酶活性逐渐降低。核酸酶定位于鳃，磷酸酶定位于上表面。(2)研究了香菇在蒸煮过程中RNA及相关物质的变化。香菇匀浆在60ﾟC孵育时，5‘-核苷酸含量在5min左右迅速增加，达到最大值，然后下降。香菇组织中5‘-核苷酸的含量在60ﾟC的水中浸泡后变化规律与香菇匀浆中相同，但浸泡水中的5’-核苷酸含量迅速增加，在15min时达到最大值，之后几乎没有下降。整个香菇在60~70ﾟ℃恒温蒸煮时，5‘-核苷酸的含量在60-70ﾟ℃时迅速增加，在80ﾟC时达到恒定水平。这些观察结果表明，香菇组织中5’-核苷酸的扩散可能在香菇组织中5‘-核苷酸的积累中起关键作用。(3)香菇的干燥条件和蒸煮条件对香菇组织中形成的5’-核苷酸的扩散起关键作用。香菇在蒸煮过程中的升温速度和pH对5‘-核苷酸的积累有直接影响，在4ﾟC/m in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.