RP-HPLC determination of tiger nut and orgeat amino acid contents

The amino acid profile of 11 samples of tiger nuts (Cyperus esculentus L.) grown in the area of L'Horta Nord in Valencia (Spain) and one sample of African origin were determined, along with the amino acid contents of 10 samples of natural orgeat from Valencia. Protein was hydrolysed by hydrochloric acid at 110degreesC for 23 h, and amino acids were derivatised with AQC and determined by RP-HPLC with fluorescence detection. The chromatographic conditions were optimised. The analytical parameters (detection and quantification limits, precision and accuracy) showed the method to be sufficiently sensitive and reproducible for determining amino acids resistant to acid hydrolysis in tiger nuts and orgeat. Arginine was the most abundant amino acid in both tiger nuts and orgeat and the lowest contents corresponding to histidine and tyrosine. The essential amino acid contents of tiger nuts and orgeat protein were greater than those proposed in the protein standard for adults by the FAO/WHO, with the exception of histidine. No significant differences were found among the arginine, lysine and isoleucine amino acid contents in tiger nuts from Valencia, Alboraya and Almassera; nor were they found among amino acids in tiger nuts from Valencia and Almassera, with the exception of tyrosine.