Curve fitting and linearization of UV-Vis spectrophotometric measurements to estimate yeast in inoculum preparation.

The counting of microorganisms is essential in the area of microbiology, especially in the preparation of inoculum. The main methods for obtaining inoculum are McFarland standard, Neubauer chamber, and plate count. However, the visual comparison is subjective while the counting in the chamber and the plating are technically time-consuming. For this reason, our article aims to correlate the absorbance of the spectrophotometer in the visible ultraviolet region (UV-Vis) with the cell counting in the Neubauer chamber. This study used suspensions of Candida spp. measured at three wavelengths (530, 600, and 700 nm) and counting in a Neubauer chamber. In the next step, curves were adjusted with different polynomials using absorbances and counts. The two best polynomial curve fittings were the Saturation Growth Rate (SGR) and Morgan-Mercer-Flodin (MMF). Therefore, the polynomials were linearized and a direct correlation between absorbance and the number of cells was made. The proposed method proved to be more accurate (5 ± 0.5 × 10) than the comparison with the McFarland turbidity (1-5 x 10) and more practical than plate counting. Predicting the number of cells by UV-Vis is an alternative that reduces the uncertainty of the cell count interval for inoculum preparation.