Application of native fluorescence tracers for quick evaluation of thermal damage in milk
- Autores: Olga Noemi Ayala Zarate
- Directores de la Tesis: J. Saldo (dir. tes.), Anna Zamora Viladomiu (dir. tes.), Manuel Castillo Zambudio (tut. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Francesc Sepulcre Sánchez (presid.), José Juan Rodríguez Jerez (secret.), Colette Fagan (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia de los Alimentos por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Resumen
Different heat treatments are applied in milk during industrial processing in order to extend its shelf-life. However, organoleptic, functional and nutritional properties of milk can be altered by those treatments. The changes produced can be monitored analyzing the intrinsic fluorophores of milk using front-face fluorescence, which is a cheap, rapid and non-invasive technique. Since front-face fluorescence is suitable for turbid samples, this technique could be easily implemented inline. The main objective of this thesis was to study the changes produced in milk, by thermal processing, on the concentration of chemical markers and the response of intrinsic fluorescent markers for quick characterization of heat treatments.
Lactulose and furosine concentrations were chemically quantified in milk treated at different heat loads. Kinetics of both chemical markers, which followed a pseudo-zero reaction order, allowed estimating the activation energy and kinetic rate constant of the corresponding formation reactions. In parallel, fluorescent markers, such as tryptophan, Maillard compounds, riboflavin and dityrosine, were analyzed with front-face fluorescence. Changes induced by heat treatments on the fluorescent spectra of the different markers allowed to discriminate the different milk samples using Principal Component Analysis. Specifically, the response of tryptophan fluorescence was characterized. An increase in the intensity of the heat-treatment load induced both a decrease in tryptophan fluorescence intensity and a red shift. Consequently, tryptophan showed a remarkable potential as heat damage marker.
In addition, correlations between the concentration of both lactulose and furosine and the emission intensity of selected fluorescent compounds were evaluated. Prediction models for these two chemical markers were successfully obtained and validated using fluorescent markers as predictors. Commercial milk samples from different brands were purchased and analyzed in order to classify them according to their fat composition and heat treatment intensity. Particularly, pasteurized samples were allocated in a separated group on tryptophan Principal Component Analysis score-plot while UHT milk formed a different group partially overlapped with other categories.
The results obtained in this PhD dissertation contribute to establish the bases for further development of front-face florescence methodology as a quick characterization tool for the evaluation of heat damage in milk at industrial level.
