Huang Yang, Chapman Belinda, Wilson Mark, Hocking Ailsa D
Food Science Australia, Riverside Corporate Park, North Ryde, NSW, Australia.
Int J Food Microbiol. 2009 Jul 31;133(1-2):179-85. doi: 10.1016/j.ijfoodmicro.2009.05.024. Epub 2009 May 30.
The concept of water activity (a(w)) does not differentiate between water status resulting from the interaction of water with solutes, and that from interaction of water with matrices, which is termed matric potential (psi(m)). This study reports the effect of agar concentration (1.5, 3.0, 4.5, 6.0, and 7.5%, w/w) on matric potential of glycerol agar media (GA) and the germination and growth of xerophilic fungi (Eurotium herbariorum and E. rubrum) and non-xerophilic fungi (Aspergillus niger, A. flavus, and Penicillium roqueforti) on GA with or without sorbic acid (0.1-0.4%, w/w) at 0.90 a(w) and 0.95 a(w). The matric potential of GA decreased when the agar concentration increased from 1.5 to 7.5%. When the agar concentration increased at each a(w), the radial growth rate of the xerophilic fungi generally increased but the biomass density (biomass per unit area) decreased, whereas the radial growth rate of the non-xerophilic fungi generally decreased but the biomass density was unchanged. In the absence of sorbic acid, the time to germination of each species was similar for all agar concentrations. In the presence of sorbic acid, the time to germination of some species was significantly longer at higher agar concentrations (4.5%-7.5%) than 1.5% agar. This study demonstrated the inhibition effect on germination and growth of non-xerophilic fungi and xerophilic fungi by decreased matric potential resulting from increased agar concentrations, and the different responses of non-xerophilic fungi and xerophilic fungi to water stress from solutes and matrices. The concept of matric potential may be useful in food microbiology to provide a better understanding of fungal growth in complex food matrices.
水分活度（a(w)）的概念并未区分水与溶质相互作用所导致的水状态，以及水与基质相互作用所导致的水状态，后者被称为基质势（ψ(m)）。本研究报告了琼脂浓度（1.5%、3.0%、4.5%、6.0%和7.5%，w/w）对甘油琼脂培养基（GA）基质势的影响，以及嗜干性真菌（灰绿曲霉和红曲霉）和非嗜干性真菌（黑曲霉、黄曲霉和罗克福青霉）在含或不含山梨酸（0.1%-0.4%，w/w）的GA上，于0.90 a(w)和0.95 a(w)条件下的萌发和生长情况。当琼脂浓度从1.5%增加到7.5%时，GA的基质势降低。在每个a(w)下，随着琼脂浓度的增加，嗜干性真菌的径向生长速率总体上增加，但生物量密度（单位面积生物量）降低，而非嗜干性真菌的径向生长速率总体上降低，但生物量密度不变。在没有山梨酸的情况下，所有琼脂浓度下各物种的萌发时间相似。在有山梨酸的情况下，一些物种在较高琼脂浓度（4.5%-7.5%）下的萌发时间比1.5%琼脂时显著更长。本研究证明了琼脂浓度增加导致基质势降低对非嗜干性真菌和嗜干性真菌的萌发和生长具有抑制作用，以及非嗜干性真菌和嗜干性真菌对来自溶质和基质的水分胁迫的不同反应。基质势的概念在食品微生物学中可能有助于更好地理解真菌在复杂食品基质中的生长情况。
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