Spectrofluorometric determination of L-tryptophan in canary (Canarium indicum L.) seed protein hydrolysate

Canary (Canarium indicum L.) is an indigenous plant of Indonesia, which mainly grows in the eastern part of Indonesia, especially in the Maluku, North Sulawesi, and Seram islands. We believe that no scientific reports have been conducted about L-tryptophan content in Canarium indicum. Therefore, this study was conducted to determine the presence and quantitate the aromatic amino acid (L-tryptophan) in the canary protein hydrolysate by the spectrofluorometric method. The protein hydrolysate was prepared by two hydrolysis methods, enzymatic and alkaline hydrolysis. L-tryptophan can be differentiated from tyrosine directly without using any reagent by excitation of the sample at 295 nm in order to avoid tyrosine emission. The equation of calibration curve correlation using standard in the range 0.5-5 ppm was y = 6632.3x - 845.42 and correlation coefficient of 0.9997, while the coefficient of variance in linear regression was 1.29%. The detection limit and quantification limit obtained were 0.116 ppm and 0.35 ppm respectively. The recoveries of the accuracy test were obtained in the range of 95-96%. The relative standard deviation of intra-assay precision tests were obtained in the range of 0.5-1.8%, while the intermediate precision in the range of 2.18-3.74%. L-tryptophan was detected in all samples (papain, pepsin, and alkaline hydrolysate), with concentrations 5.6, 5 and 1.53 mg/100mg of protein respectively. The used fluorometric method complied with the validation requirements and can be used to analyze L-tryptophan in samples containing tyrosine without overlapping of spectra and without the use of any specific reagent.

Spectrofluorometric determination of L-tryptophan after preconcentration using multi-walled carbon nanotubes

A solid-phase extraction method based on multi-walled carbon nanotubes (MWCNTs) was applied for the preconcentration of L-tryptophan prior to its spectrofluorometric determination. Due to the high surface area of MWCNTs, satisfactory concentration factor and extraction recovery can be achieved with only 10 mg MWCNTs in 5 min. The effects of pH, sorbent amount, eluent type and time on the recovery of the analyte were investigated. Under the optimum conditions, the detection limit for L-tryptophan was 8.9 ng mL−1. The precision of the method, evaluated as the relative standard deviation obtained by analyzing of 10 replicates, was 2.6%. The practical applicability of the developed method was examined using wheat and barley samples.