Sub-samples from each freeze-dried nubbin were weighed and digested in a persulfate potassium solution autoclaved at 121 °C [86 (link)]. Samples were then placed in triplicate on a 96-well microplate with a solution of ammonium molybdate and incubated at room temperature for 10 min before the addition of a solution of malachite green. After 30 min, the absorbance was measured at 630 nm using a spectrofluorometer (Xenius®, SAFAS, Monaco) to quantify the orthophosphate content. The standard curve was prepared with known concentrations of potassium phosphate.
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