Samples of corn, soybean corn and casein (acid hydrolysate) were submitted to acid hydrolysis in oven (110 ± 5°C, for 22 hours) with 6 N HCl in sealed ampoules under vacuum. Four methods of hydrolysate preparation were used: 1) evaporation to dryness in rotary evaporator under vacuum, 2) evacuated desiccator under vacuum and NaOH, 3) flushing the open vial with argon and 4) neutralisation with standard citrate/NaOH solution. Amino acids were isolated and quantified in specific analyzer Beckman System 6300 with ninhidrin post-column derivatization. The neutralization method presented the best result considering all analysed amino acids. Besides, it was more practical for rapid processing of a large number of samples. With regard to the evaporation methods in the rotary evaporator, significant losses were verified only for threonine and serine in the soybean sample. Under flow of argon, low recoveries of threonine, phenylalanine and lysine where observed, whereas in the evacuated desiccator, significant losses of threonine, serine and tyrosine where verified.
amino acid; amino acid analysis; protein hydrolysis; sample preparation
