Fit-for-Purpose MIP OES Method to Meet the Requirements of the Brazilian Regulations for K and Na in Coconut Water, and Nutritional Assessment

The Brazilian regulations for processed coconut water establish the range concentrations of Na and K, being necessary high-throughput analytical methods, as microwave-induced plasma optical emission spectrometry (MIP OES) for quality control. Samples of natural (green and mature) and processed coconut water were treated by acid decomposition assisted by microwave radiation before their MIP OES analysis. Recoveries for Na and K were 103 and 95%, whereas the relative standard deviation (RSDs) were 7.6 and 1.3%, respectively. The limit of detection (LOD) was 1.77 mg kg-1 for K and 2.31 mg kg-1 for Na. Na and K were determined in the ranges of, respectively, 27-490 and 1,600-3,500 mg L-1 in natural samples, whereas in processed samples the ranges were 26-168 and 814-2,054 mg L-1. K-means cluster analysis identified a group of processed samples with compositions similar to green coconut water. All the processed samples were in accordance with the established regulation, except one dehydrated sample for which K content was below the accepted range. Natural coconut water is an excellent source of K in the diet as its daily consumption can supply more than 20% of the recommended daily ingestion of K for adults and 30% for children.