Characterization and detection of adulterated whey protein supplements using stationary and time-resolved fluorescence spectroscopy

The objective of this work was to evaluate the efficacy of time-resolved and stationary fluorescence spectroscopic techniques in the detection of adulterations in Whey Protein Concentrate (WPC) powder, used in nutritional supplements. Adulterations were performed by the individual addition of caffeine, creatine and lactose in WPC in different levels (10%, 20% and 30% w/w). Samples were submitted to 275 nm excitation wavelength. Time-resolved fluorescence revealed that the adulterations changed the lifetimes of the tri-exponential decay curves obtained at 335 nm. The 30% adulterations demonstrated higher values of the mean emission lifetime, with caffeine treatment statistically significant. The fluorescence spectra showed an emission peak at approximately 335 nm with a broadband between 325 and 430 nm in the caffeine treatment. Euclidean distance analysis indicated the creatine and lactose treatments (10, 20 and 30% w/w) as similar to control WPC, while caffeine 20% and 30% treatments not. Hierarchical Cluster Analysis could differentiate all caffeine treatments from the other samples. Principal Component Analysis confirmed the differentiation of all adulterants from the control WPC. In general, the application of time-resolved fluorescence and stationary fluorescence spectroscopy techniques allowed the characterization and observation of differences among the samples, when allied to statistical tools.