An Alternative UV–Vis Spectrophotometric Method for Accurate Quantification of Total Selenium in Se-Enriched Microbial Biomass

This study validated a UV-visible spectrophotometric method for quantifying total selenium (Se) in Se-enriched microbial biomass using the selenium-iodine reaction with starch. The protocol employs microwave-assisted acid digestion to ensure complete mineralization of organic Se and was tested in two models: selenized <i>Lactiplantibacillus plantarum</i> and spent brewer's yeast (<i>Saccharomyces</i> spp.). Key validation parameters, including linearity, detection and quantification limits, precision, and accuracy, were assessed and compared with inductively coupled plasma-mass spectrometry (ICP-MS) and a certified reference material (SELM-1). Reagent combinations and ultrasonic pretreatment durations (0-30 min) were evaluated; ultrasound caused overestimation due to interference with the starch-iodine complex. Temperature effects (5-30 °C) showed optimal results at 20 °C. Recoveries were in the ranges of 97-111% (bacteria) and 99-101% (yeast), confirming the method's reliability and robustness. This simple, rapid, and cost-effective protocol enables accurate Se quantification in enriched microbial matrices, making it ideal for quality control in food and biotech industries and for research settings without access to advanced tools like ICP-MS.