What this work is about, in plain words
The spectrum of a spirulina culture is distorted by light scattering. The authors showed how to obtain the "true" absorption spectrum and traced how it changes as the culture grows.
The optical spectrum of a culture shows how much light its pigments absorb. But the cells and the pigments themselves also scatter light, so the instrument shows not pure absorption but the total attenuation of the beam. The authors studied how to obtain a spectrum without the contribution of scattering and traced how it changes as a culture of the cyanobacterium Arthrospira (Spirulina) platensis grows.
A spectrophotometer with an integrating sphere, which also collects scattered light, was used. The sample was measured in two positions: right against the sphere and at a distance of 1 cm. The absorption spectrum corrected for scattering was calculated from the difference.
According to the authors, with the usual cuvette position the instrument shows a non-zero optical density even in the 750–800 nm range, where pigments hardly absorb — this is the contribution of scattering. A correction factor of 1.61 was found. The corrected spectra show that, with sufficient nutrients, the ratios between chlorophyll, carotenoids and the blue pigment phycocyanin do not change as the culture grows.
The work helps to assess the pigment composition of cultures more accurately by optical methods.
Limitations. The correction was determined for one species and one instrument under laboratory conditions.