Photometric measurement of high cell density by continuous dilution of broth with a circulating system

A photometric system for the measurement of cell density in a culture broth using continuous dilution was developed. The system was comprised of a photometer with a flow cell, two tubing pumps and a magnetic circulating pump. The culture broth was introduced from a fermentor to the measurement system by a tubing pump, and diluted with water fed continuously by another tubing pump. The diluted broth was circulated through the flow cell of the photometer by the circulating pump. The cell density of the culture broth was calculated with the optical density, a sampled volume of the culture broth, the water flow rate for dilution, and the dilution time, and then converted to dry cell mass concentration by a predetermined calibration curve. The effects of the operating conditions on the calculation of the cell density were studied to select the optimum conditions. The cell density values measured by this method were in good agreement with the values obtained by the drying method over a wide range of cell densities, from 10 to 100 g dry cells/ l of Candida brassicae .