A microorganism associated with disease in man. A measure of the acidity or alkalinity of a solution, defined as the - log10 of the hydrogen ion concentration. Such damage must be repaired before normal growth can recommence. The vegetative cell state is the form in which an organism is able to grow and divide continuously, given favourable conditions. Unlike endospores, vegetative cells are relatively poor at surviving environmental stresses such as high temperature and drying.
Water activity is a measure of the amount of free unassociated water molecules in a system.
It runs on a scale of 0 to 1.0, where pure water equals 1.0. This parameter can also be expressed as a percentage referred to as the relative humidity. It is influenced by dissolved solutes and insoluble food components which act to bind water, thus reducing the available free water and hence aW value.