The potential risk of heavy metals and residual pesticides in imported sawdust media inoculated with oak mushroom cultures is a concern for safe mushroom production in Korea. To obtain preliminary data for a sound analysis of this risk, this study was undertaken to analyze the presence of heavy metals and residual pesticides in the oak mushroom media imported from six different regions in China, between 2013 and 2015. Lead, arsenic, chrome, mercury, and cadmium were analyzed; arsenic, chrome, and mercury were not detected. Lead was detected in the imported oak mushroom media from Jinlin, Shandong, Liaoning, and Tianjin. The detection level of lead ranged from 1.7 to 3.2 mg/kg. Cadmium was detected at a level of 0.028 to 0.037 mg/kg in the media from Shandong and Liaoning. No residual pesticides were detected in any of the samples.

For centuries, Lentinula edodes called “Pyogo” in Korea has been cultivated as a high-grade edible mushroom in Asia. This is known as medicinal mushroom for cold prevention in oriental medicine. In the world market, this mushroom of Lentinula edodes is introduced as representative edible and medicinal mushroom in Asia. As consumer interest increases, Asian Lentinula edodes market is also growing. There is a record that Korea has already been used as a gourmet food on the royal meal table for the king in the 15th century Joseon Dynasty. In Korea's famous oriental book, it is cooked with many traditional foods because of the pharmaceutical efficacy of this mushroom. For long time ago, difference in cultivation as well as in mushroom growth of Lentinula edodes has studied in Korea. Recent advances in cultivation of selected high quality mushroom studied from substrate optimization using log and sawdust of oak tree. Cultivation of Lentinula edodes strain research controlled the production of large quantity of various substrate conditions. This mushroom mycelia and fruit-body were cultivated in log of oak tree and sawdust substrate cultivation in types of bioreactors. According to compared cultivation method, it presented the optimistic condition for the amount production of various Lentinula edodes strain in Korea.

표고 재배에 이용되는 참나무 톱밥의 발효과정에서 물리화학적 특성변화를 알기 위하여 참나무 톱밥 33 ton을 적재하고, 46일 동안 기간별로 깊이별로 변화를 조사하였다. 톱밥의 물리화학적 특성은 발효기간과 적재 깊이에 따라 변화정도가 달랐다. 대부분의 물리-화학적 성질은 발효 동안 점진적으로 변화하였지만, 온도는 기간과 깊이에 따라 다르게 변하였다. 톱밥의 온도는 표면 20 cm 깊이는 환경에 따라 민감하게 변하는데 비하여, 40~100 cm 깊이에서는 점진적으로 변하여 적재 12일 만에 3˚C에서 최고온도 58.9˚C에 도달하였고, 150 cm 깊이에서는 24일 만에 최고온도에 도달하였다. 수분함량은 발효 24일 만에 초기 31%에서 26.5~28.0%로 점진적으로 감소하였다. 발효기간 중 톱밥의 화학성을 보면, pH는 대체로 5.2에서 5.6으로 점진적으로 상승하였으나, 150 cm 깊이에서만은 16일만에 4.4~4.7로 낮아졌다. 톱밥의 탄소함량은 68~70%로 변화가 적은데 비하여, 질소함량은 0.22%에서 0.25%로 점진적으로 상승하여 C/N비는 320에서 280으로 낮아졌다. 톱밥의 P함량은 0.005%에서 46일째 0.022%로 점진적으로 증가하였다. 톱밥의 열수추출액 삼투압 농도는 41.5~44.2 mmol/kg로 적재 깊이에 따른 차이는 없었다. 초기 톱밥의 방사유세포에는 전분 입자가 존재하고 도관에는 균사가 없었으나, 발효 35일 후에는 세포 내 전분입자는 소수 남았고, 톱밥입자의 표면과 목질부 도관 내에는 균사가 생장하였다. 톱밥발효가 표고재배에 미치는 영향은 차후 계속적인 연구가 필요하다.

The effect of sterilization and incubation temperatures of fermented oak sawdust on Lentinula edodes hyphal growth was investigated. The pile of 33 tonnes of oak sawdust fermented in a plastic shed for 24 days. During the fermentation the acidity of the sawdust within the pile was lowered to pH 4.2 and temperatures increased to 58℃ in over 20cm depth. The sawdust samples collected at 20, 60, 80 and 100㎝ depth each and moistened to 65% water content were sterilized at 65, 100 and 121℃ each for an hour. The sterilized sawdust contained in 50㎖ test tubes was inoculated with L. edodes hyphae cultured on potato dextrose agar medium and then was incubated at 15, 20, 25℃ for four weeks. L. edodes hyphae grew faster, 94.6mm, on the sawdust collected from 60cm depth than other depths, and did at 25 incubation temperature after sterilization at 121℃. The hypahe grew only 9.9cm on the sawdust from 100cm depth. When the sawdust from 60cm depth was sterilized at 100℃, the hyphae grew best by 22.1cm at 15℃. However, on the sawdust sterilized at 65℃ the hyphae did not grow at all. Thus, we conclude that sawdust fermentation under 60㎝ depth and autoclaving it can improve L. edodes hyphal growth, but the sterilization of sawdust at 65℃ is not sufficient for the hyphal growth.

The microscopic characteristics of brown layers in oak sawdust cultivation bed of Lentinula edodes was investigated with scanning electron microscope. Parenchymatous cells became thinner and the middle layers of the cells degraded in the oak sawdust bed at a plastic cultivation shed in four months. L. edodes hyphae penetrated into the pit and profusely branched within the bassal tube cells. Pit pores of ray parenchymatous cell in the decomposed sawdust became larger than in the uncolonized cells and were circular or irregular. The brown layer producing fruit body was 0.34㎜ thick and 0.67㎏/㎠ in hardness with especially 0.20㎜ thick layer of highly dense hypahe. On the other hand the brown layer without fruit body was 1.17㎜ thick, 0.94㎏/㎠ in hardness, and 0.80㎜ thick with smooth surface of highly compact dense hypae. This nonfruiting brown surface was heavily colonized with contaminating fungal hyphae and bacterial cells. We conclude that physical and biological characteristics of brown layer can affect fruiting of L. edodes.