Water Retention Value: A Study Model-based by Asperglillus awamori and Aspergillus oryzae Embrace Three Models of Solid Substrate

The goal of this study was to evaluate the water retention value (WRV) of a test solid substrate and a fungal cell in solid state fermentation (SSF). WRV is the ratio of the weight of water retained after centrifugation under specific conditions by a wet sample to the oven dry weight of the same sample. SSF refers to the microbial fermentation, which takes place in the absence or near absence of free water, thus being close to the natural environment. Many factors are involved in a successful SSF process. In addition to biological parameters, the SSF process is also dependent on physical factors such as WRV. A centrifugal technique has been modified and applied to the evaluation of WRV. Wheat bran, soybean hulls and rapeseed meal were used as model substrate. Aspergillus awamori and Aspergillus oryzae were used as model microorganism. Results revealed that the ability of wheat bran to retain water in the solid substrate is 56% higher than that of soybean hulls and rapeseed meal. In the term of fungal cell, the ability of A. oryzae to retain water in the cells was higher (73% higher) than that of A. awamori. In addition, through oven method moisture content loss from A. awamori is 46% higher than that from A. oryzae during drying process. Nevertheless, it can be seen that A. oryzae is able to retain water content about 5 times higher than A. awamori. Through this results, we found that WRV varies depending on solid substrates and microorganisms. This initial information can be beneficial in the SSF process to be carried out.