Determination of free sulphydryl groups in wheat gluten under the influence of different time and temperature of incubation: Method validation

The aim of the present study was to determine the characteristics of an analytical method for determination of free sulphydryl (SH) groups of wheat gluten performed with previous gluten incubation for variable times (45, 90 and 135 min) at variable temperatures (30 and 37 °C), in order to determine its fitness-for-purpose. It was observed that the increase in temperature and gluten incubation time caused the increase in the amount of free SH groups, with more dynamic changes at 37 °C. The method characteristics identified as relevant were: linearity, limit of detection, limit of quantification, precision (repeatability and reproducibility) and measurement uncertainty, which were checked within the validation protocol, while the method performance was monitored by X- and R-control charts. Identified method characteristics demonstrated its acceptable fitness-for-purpose, when assay included previous gluten incubation at 30 °C. Although the method repeatability at 37 °C was acceptable, the corresponding reproducibility did not meet the performance criterion on the basis of HORRAT value (HORRAT < 2).