The Potential of Conductivity, Redox Potential and Dissolved Oxygen in Raw Milk Quality Prediction

Abstract

Changes in milk quality are associated with changes in dissolved oxygen (DO), redox potential (E_h) and conductivity (Co) reflecting the potential of these parameters in quality prediction. However, limited interpretation of those changes/results limits the application of the same in raw milk quality prediction. The aim of this study was therefore to explore the potential of DO, E_h and Co in milk quality assessment. Raw milk, lactoperoxidase system (LP-s) activated raw milk and LP-s activated Ultra High Temperature (UHT) milk inoculated singly with pure strains were used in this study. The performances of DO, E_h and Co in quality prediction were assessed against the objective methods: pH, titratable acidity (TA), alcohol stability test (AST), clot on boiling (COB), dye reduction tests and total viable counts (TVC). The results showed that any negative E_h value, a Co value greater than the initial Co value and DO around zero or below detection limit all indicated spoilage. These corresponded well with increases in microbial numbers indicative of spoilage recorded at about 7 log cycles of bacterial counts.  Co and Eh were in consistent agreement in quality estimate with AST and TA but more sensitive than COB and pH. On the other hand, DO showed similar sensitivity as COB and pH but was more lenient than AST and TA. The results generally confirmed the suitability of DO and E_h for routine analysis in both normal and LP-s activated milk; however, the use of Co requires a prior knowledge of the initial Co value of milk under test which complicates its use in routine analysis.

Key words: Quality prediction, conductivity, redox potential, dissolved oxygen