Application of single and dual fluorophore-based pH sensors for determination of milk quality and shelf life using a fibre optic spectrophotometer

Milk is a high nutrient value food substance consumed by the entire population in several forms. Spoilage and degradation of milk and its products during transportation, processing and packaging are some of the major losses by dairy industries. The change in milk pH with time is an indicating factor of milk degradation. This research reports a rapid, sensitive and facile fluorescence-based technique to study the time-based milk degradation at room temperature. Fluorescein isothiocyanate (FITC)/ FITC-dextran (FITC-dex) and Tris (2, 2'-bipyridyl) dichloro ruthenium (II) hexahydrate (Ru-bpy) were used to develop solution phase and immobilized phase pH sensors. Immobilized phase sensors constituted of alginate microspheres (5 +/- 3 mu m) produced using an air driven atomizer. The pH sensor works in a linear range of 3-8 pH units with a quick response time of 30 s. The percentage recovery of the system lay in the range of 89.23%-101.28% for detection of milk pH. Accurate detection was possible during entire shelf life of milk ((similar to)24 h) and Inter-sample and inter-day reproducibility was checked over 10 days duration. The results clearly indicate that both single and dual fluorophore-based assay in solution phase and immobilized phases can predict milk pH with good accuracy.