Abstract：
In feed, propionic acid is the weak organic acid of choice to prevent growth of spoilage fungi. For safe and easy industrial handling this antifungal agent is applied in the presence of neutralizing ammonium, which however has the disadvantage to negatively affect the efficacy of fungus-inhibiting properties of the formulation. In the present study we investigated the impact of medium chain fatty acids (MCFA) on the antifungal efficacy of an ammonium propionate formulation on dormant- and germinating conidia as well as germ tubes and hyphae of Aspergillus chevalieri, a xerophilic fungus predominant on moulded feed. Dormant conidia were not affected by 32 mM of ammonium propionate after a 28 h-treatment in demi water. Similar results were obtained with solely 0.52 mM MCFA. However, the combination of both components nearly eradicated formation of colonies from these conidia and was accompanied by distortion of the cellular structure as was visible with light- and transmission electron microscopy. Germination of conidia, characterised by swelling and germ tube formation, was significantly decreased in the presence of 16 mM ammonium propionate and 0.26 mM MCFA, while the latter component itself did not significantly decrease germination. We conclude that a combination of ammonium propionate and MCFA had a synergistic antifungal effect on dormant and germinating conidia. When the combination of ammonium propionate and MCFA was tested on hyphae for 30 min, we observed that cell death was significantly increased in comparison to components alone. Treatment of the hyphae with 16 mM of ammonium propionate caused aberrant mitochondria, as evidenced by irregularly shaped and enlarged mitochondria that contained electron-dense inclusions as observed by transmission electron microscopy. When the combination of ammonium propionate and MCFA was applied against the hyphae, more severe cell damage was observed, with signs of autophagy. Summarised, our results demonstrate synergistic antifungal effects of ammonium propionate and medium chain fatty acids on fungal survival structures, during their germination and after a short (sudden) treatment of growing cells. This is of potential importance for several areas of feed and food storage and shelf-life.
摘要：
在饲料中，丙酸是弱有机酸的选择，以防止腐败真菌的生长。为了安全和容易的工业处理，这种抗真菌剂在中和铵的存在下应用，然而,其具有不利地影响制剂的真菌抑制性质的效力的缺点。在本研究中，我们研究了中链脂肪酸（MCFA）对丙酸铵制剂对休眠和发芽分生孢子以及切氏曲霉的胚管和菌丝的抗真菌功效的影响，一种在模制饲料中占优势的嗜酸性真菌。在半水中处理28小时后，休眠分生孢子不受32mM丙酸铵的影响。用单独的0.52mMCFA获得类似的结果。然而,两种成分的组合几乎根除了这些分生孢子中菌落的形成，并伴随着细胞结构的扭曲，如在光镜和透射电子显微镜下可见。分生孢子萌发,以膨胀和胚芽管形成为特征，在16mM丙酸铵和0.26mMMCFA的存在下显著降低，而后者本身并没有显着降低发芽。我们得出的结论是，丙酸铵和MCFA的组合对休眠和发芽的分生孢子具有协同抗真菌作用。当丙酸铵和MCFA的组合在菌丝上测试30分钟时，我们观察到,与单独的组分相比,细胞死亡显著增加.用16mM的丙酸铵处理菌丝引起异常线粒体，通过透射电子显微镜观察到的不规则形状和扩大的线粒体包含电子致密的夹杂物。当丙酸铵和MCFA的组合应用于菌丝时，观察到更严重的细胞损伤，有自噬的迹象.总结,我们的结果表明，丙酸铵和中链脂肪酸对真菌存活结构的协同抗真菌作用，在它们的发芽和生长细胞的短暂（突然）处理后。这对于饲料和食品储存和保质期的几个领域具有潜在的重要性。
