Front-Face Fluorescence Spectroscopy Allows the Characterization of Mild Heat Treatments Applied to Milk. Relations with the Denaturation of Milk Proteins

Abstract

Emission and excitation spectra of intrinsic fluorophores present in milk were used to evaluate changes in milk following thermal treatments in the 57−72 °C temperature range from 0.5 min up to 30 min. Alternatively, the concentrations of native alkaline phosphatase, lactoferrin, immunoglobulin G, bovine serum albumin, β-lactoglobulin, and α-lactalbumin were determined in the same samples by enzymatic and immunochemical techniques. As principal component analysis applied to the normalized fluorescence spectra successfully discriminated different milk samples according to the temperature and time of thermal treatment, principal component regression was applied to predict the amounts of the native proteins investigated using fluorescence data. The results showed strong correlations between measured and predicted data for alkaline phosphatase and β-lactoglobulin. This study has demonstrated that front-face fluorescence spectroscopy has a promising potential to become a rapid and nondestructive analytical technique for the evaluation of physicochemical changes in milk induced by low thermal treatment. Keywords: Milk; heat treatment; radial immunodiffusion; front-face fluorescence; intrinsic fluorophores; multivariate analysis