An approach for estimating the maximum specific growth rate of Gluconobacter japonicus in strawberry purée without cell concentration data

• Non-readily culturable bacteria hinder obtaining reliable cell concentrations.
• Complex media containing suspended solids make worse the previous problem.
• Estimation of specific growth rates (μmax) without using cell concentration data.
• μmax could be estimated using substrate concentrations from the exponential phase.
• Selective biotransformation of glucose into gluconic acid is considered as example.

The estimation of the maximum specific growth rate (μmax) for non-readily culturable bacteria, growing on complex media containing suspended solids, is a difficult task considering the important problems in obtaining reliable measures of cell concentration. An example of this situation can be a culture of Gluconobacter japonicus growing in strawberry purée for producing gluconic acid. Based on the dependency between energy requirements of the genus Gluconobacter and substrate uptake as well as its constant relationship between gluconic acid production and total substrate uptake, the total substrate concentration profile during the exponential growth phase could be used for estimating μmax without cell concentration measures. In this case, the high selectivity of the strain for glucose in comparison to fructose resulted in no fructose consumption during the batch; so, just using the glucose concentrations data during the exponential phase allow us to obtain an estimation of μmax. Additionally, a rough estimation of the apparent and stoichiometric yields of cell on glucose is also possible.