Exploring Metallic Flavor Perception: Analysis of Human Salivary Proteins and the Use of the Iron-Binding Protein Lactoferrin in Reducing Metallic Off-Flavors

Metallic flavors are of concern for many industries including food, health, and water. Metallic off-flavor, induced by ferrous sulfate solution (10mg/L), and its remediation using pre- and post-rinse treatments of water (control) or metal chelators, were studied. Metal chelators included lactoferrin (1 ?M), a natural metal-binding protein in milk and saliva, and EDTA (36 ?M), a synthetic chelator. Time-intensity (TI) evaluation (n=6, 4 female; age 40-70) of lingering metallic flavor indicated that metallic flavor decreased with a post-rinse adjuvant treatment of lactoferrin as indicated by a reduced maximum intensity and area under the curve compared to a pre-rinse treatment; EDTA and water post-rinses were equally effective for three of the TI parameters. Alterations in salivary components were studied in saliva collected (n=8; 5 female, age 40-70) after sipping a lactoferrin solution (1?M) followed with a ferrous sulfate sample (10 mg/ml) to stimulate metallic flavor, as compared to unstimulated whole saliva. Protein concentration, oral lipid oxidation as indicated by thiobarbituric acid reactive substances assay, and iron concentration were determined on individual saliva samples, with no significant differences found between treatments (p>0.05). Protein patterns were qualitatively characterized for each pre-rinse and metallic stimuli from four panelists by two-dimensional gel electrophoresis. A consistent pattern of regions containing major salivary components was observed. This research has shown that lactoferrin protein is a potential natural alternative to synthetic EDTA for reducing iron-induced metallic off-flavors. This study provides a foundation of method development to better understand salivary protein interaction with metals and flavor perception.