水分活性對洋菇菌種性質之影響

Abstract

為改善洋姑菌種之品質並延長其保存期限，將菌種脫濕使水分活性下降誠屬必須。菌種之生長特性深受水分活性所影響，特別是ATP、呼吸、生長速率及灰分含量。本實驗即以此來探討菌種於貯藏期間之生長活力變化之情形。 從最大保水力及脫濕曲線來看，麥粒具較高之保水能力；顆粒則脫濕易，速度也快。 洋菇（Agaricus bisporus）品系547,F3,111及高溫菇（Agaricus bitorquis）品系G；經一個月的培養，然後置於22℃，相對濕度60-70%，貯藏五個月。菌f種之總重量漸減，但水分活性高達0.98以上。以水分含量而言，麥粒菌種逐月增加，範圍由13%(111）至64％(547)；顆粒菌種逐漸下降，範圍由6%（111）至15%（547)，此水分之來源可推論係由於菌體量的增加，呼吸旺盛及生長強勢所產生之代謝水所致。此亦與灰分百分比的增加相關，表示基質中有機成分為增殖的菌體所消耗。菌落生長速率及過氧化酵素活性以年輕菌種較高，呼吸速率及細胞ATP含量，洋菇品系F3及111者以貯藏第二個月為最高，而品系547及高溫菇品系G，則繼續升高至第五個月，表示有較強的生長趟勢。故以洋菇菌種之三品系而言，其生長活力的高低次序為547，次為F3，再次為111，高溫菇品系G則與547較近似。另由實驗顯示顆粒菌種之菌體量比麥粒菌種為少。 以七種控制水分活性的鹽類，範圍為0.33至0.98Aw，將菌種脫濕達90天。結果顯示較適合洋菇生長之水分活性約在0.96左右。 另之脫濕法，乃以無菌空氣將菌種風乾，其結果水分活性由0.98降至O.83，但呼吸速率及細胞ATP含量則顯著降低，表示此種處理會減低菌種生長活力。

To improve the quality and prolong the storage time of mushroom spawn, dehydration of the spawn in order to curtail water activity is considered to be a necessary step. The effect of water activity upon properties of mushroom spawn, parti-culary ATP contents, respiration, growth rate and ash contents, etc. during various periods of storage were investigated. The wheat grain had a higher water holding capacity than the granule which dehydrated rather faster. After one month of cultivation, wheat grain spawn and granular spawn of Agaricus bisporus strains 547,F3,111, and A. bitorquis, strain G, were incubated at 22℃, RH. 60-70％ for five months. In general, though the total weight of spawn were gradually decrcesed, but their water activity were shown higher than O.98, however. The moisture content of grain. spawn was increasing from 13℅ (111) to 64℅ (547). While the granular spawn was decreasing from 6% (111) to 15 % (547). This increase of moisture in grain spawns is probably related to the accumulation of metabolic water in grains by increasing biomass of mycelia, their active respiration and high growth vigor. The increase of metabolic water is also correlated to the increase of ash content of spawns. The result indicated that the organic compounds of the substrate was consumpted by mycelia in spawns during the in-croasing period. The growth rate of colonies and polyphenol oxidase activity were high in young spawn. Resparation rate and cell ATP of wheat grain incubated with strain F, and 111 of A. bispo-rus were highest in the 2nd month of storage. While the Strain 547 and G were still increasing even at the end of 5th month of storage. The order of growth vigor of A. bisporus was strain 547> P,>111. and the strain G of A. bitorquis was compatible with strian 547. It is evident that biomass of granular spawns is much less than these of grain spawns. The seven level of water activity ranged from 0.33 to 0.98 by salt method on desicator were designed to controll water activity of stored grain spawns up to 90 days. The results indicated that the optium water activity for mycelial growth was about 0.96. In another set of dehydration experiment, the grain spawn were exposed in front of Laminar flow for 48 hours. The resulted change of water activity of grains was from 0.98 to 0.83, accompanied with a sharp decrease on respiration rate and cell ATP content. The viability of exposed spawns evidently decrease and mycelia were hurt under this treatment.