Application of native fluorescence tracers for quick quantification of milk changes caused by novel processing technologies

Resumen

This PhD dissertation is focused on using native milk fluorescence indicators to establish models for rapid evaluation and prediction of the effects of thermal (70-90 °C, 0-30 min) and ultra-high pressure homogenization (UHPH) processing (100-300 MPa, inlet temperature 22-83 °C) on bovine milk by means of front-face fluorescence spectroscopy (FFFS). Rapid quantification of retinol concentration, in both thermally and UHPH processed milk, was well modeled with an R2 of 0.92 and 0.90, and standard error of prediction of 0.025 mg/L and 0.016 mg/L, respectively. Retinol degradation originated by thermal treatments followed a first-order kinetic and the activation energy was estimated to be 52.26 kJ/mol. In both skim milk and whole milk, the tryptophan, dityrosine and Maillard intermediate compounds fluorescence could be modeled as functions of UHPH processing parameters. In skim milk, the dityrosine and Maillard compounds fluorescence intensities were only significantly affected by inlet temperature, while all the fluorescence indicators were significantly influenced by both pressure and temperature in UHPH treated whole milk. The changes in fluorescence revealed the milk protein modifications induced by UHPH, including whey protein denaturation, casein disintegration and protein aggregation. Particle size distribution showed that UHPH treatments could effectively reduce the particle size in whole milk. With pressure under 200 MPa, UHPH would not lead to significant protein aggregation in either skim or whole milk. On the contrary, a clear effect of UHPH treatment on milk protein structure modification could be observed above 200 MPa. These findings support and complement the conclusions from the fluorescence indicators about milk protein aggregation.