The rapid determination of chemically reactive lysine in the presence of carbohydrates by a modified trinitrobenzenesulphonic acid procedure

Abstract

The trinitrobenzene sulphonic acid (TNBS) method has been shown by previous workers to give low results for chemically reactive lysine if carbohydrates are present in the sample. The major factor responsible has now been identified as loss of E-trinitrophenyl (E-TNP) lysine during the hydrolysis stage, while adsorption of E-TNP lysine by humins formed from carbohydrates during hydrolysis has been shown to be insignificant. The loss can be minimised by a reduction of the hydrolysis time without affecting the necessary degree of protein hydrolysis. A modified procedure is suggested which is shown to give very similar results to Carpenter's method (incorporating the Booth modification) for pure proteins and to the Silcock method in the presence of carbohydrates. E-TNP lysine hydrolysed for 90 min or D,L-lysine taken through the trinitrophenylation procedure followed by hydrolysis for 120 min are the most suitable standards. The procedure can be completed in under 6 h and does not require the use of expensive equipment or hazardous chemicals.

Eliminación de ácido clorogénico durante el procesado acuoso de las almendras de girasol

“…Se mide entonces la absorbancia a 330 nm en la mezcla de los sobrenadantes obtenidos, frente a un blanco del disolvente empleado para la extracción. La Usina disponible se determinó por el método del TNBS (James y Ryley, 1986). Los análisis de digestibilidad de la harina se llevaron a cabo con el ensayo in vitro propuesto por Hsu et al, (1977).…”

Determination of vitamin B6, available lysine and .epsilon.-pyridoxyllysine in a new instant baby food product

“…The available lysine content of baby food samples was determined by using a trinitrobenzenesulfonic acid (TNBS) method, adapted from Hall et al (1973). The method was modified according to James and Ryley (1986), Hall and Henderson (1979), Posati et al (1972), and Hall et al (1975) to be applicable to carbohydrate-rich foods. The method is based on the reaction of the free e-amino group with trinitrobenzenesulfonic acid (Sigma), forming trinitrophenyllysine.…”

“…Sample blanks were needed to subtract the absorbance of the food and reactants at 415 nm that is not due to TNP-L-lysine formation. All tubes were subjected to acid hydrolysis in a vigorously boiling water bath for 1 h (James and Ryley, 1986). After filtering (Posati et al, 1972), 3-mL aliquots from each test tube were pipetted in duplicate into separate test tubes.…”

Degradation Kinetics of Protein Digestibility and Available Lysine During Thermal Processing of Tuna

“…Available lysine (g lys/l6g N) was determined using the method of James and Riley (1986) with slight modifications. This method, an improved version of that of Hall et al (1973), is based on the reaction of trinitrobenzenosulphonic acid (TNBS) with chemically reactive lysine followed by spectrophotometric measurement (at 415 nm) of the resulting compound.…”