Colorimetry has practical advantages over spectrophotometry for estimating entomopathogenic fungi spore concentration...

Accurate quantification of spore concentration is essential in producing, analyzing, and applying diverse biotechnological products. Typically, spore concentration is estimated using a Neubauer hemocytometer, which is labor-intensive, time-consuming, and often imprecise. Methods based on spore optical properties can be explored as an alternative to using the Neubauer hemocytometer, improving the practicality and precision of analysis. This study aimed to establish the analysis conditions for quantifying the spore concentration using spectrophotometry and colorimetry (using L*a*b color space). For this study, spores from entomopathogenic fungi Beauveria bassiana, Hirsutella thompsonii, Cordyceps fumosorosea, Cordyceps javanica, Akanthomyces dipterigenus, Metarhizium acridum, Metarhizium anisopliae, and Metarhizium robertsii were produced and analyzed. The results indicate that both spectrophotometry and colorimetry analysis accurately estimate spore concentration. The quantification ranges achieved with both methods directly depend on the spore volume. Spores with a 15 µm³ or less volume exhibit a wider quantification range than those with larger volumes. Moreover, the L*a*b* color space analysis allows quantifying spores in a concentration range from 4.5 × 10⁶ to 3 × 10⁸ spores/mL, which is wider than the range obtainable through spectrophotometry. This extended concentration range provided by colorimetry offers a practical advantage for producing and applying entomopathogenic fungi spores.