Iron is one of the most common trace elements in natural water sources and an important component to living systems. The existence of iron may not only cause metallic flavor, it may also deeply impact health of human and animals by interacting with constituents in the related biological fluids such as saliva and milk. The overall goal of this study is to investigate the taste interaction between iron and sweeteners, and the interaction between iron and proteins in bovine milk and human saliva. Based on pairwise-ranking sensory test, we have found that sweetness of sweeteners was varied with different concentrations of minerals in water and with different types of sweeteners. Sweet-metallic taste interaction between sucrose and ferrous ions significantly (p<0.05) increased the acceptance of very hard water (3 mg Fe/L). The sweet-metallic interaction created a unique selection of the emotional term 'mild'. High iron concentration in bovine drinking water (2 mg Fe/L or higher), causing oxidative stress in dairy cattle, affected expression of both casein and whey proteins in the milk. Direct addition of iron above 5 mg Fe/L in processed whole commercial milk led to lipid oxidation during storage at 4°C. Oxidation level was positively associated with increasing concentration of added iron. Minerals (Mg, P, Na, K, Ca, Zn) in milk were not affected with the added iron in milk. Dietary supplementation with metal-binding protein significantly decreased (p<0.05) taste and smell abnormality score in cancer patients receiving chemotherapy, and this effect lasted at least 30 days after the treatment was ended. Although supplementation did not effectively reduce (p>0.05) the metallic taste intensity stimulated by ferrous sulfate solution (1 mg Fe/L), it significantly (p<0.05) decreased salivary Fe for both healthy subjects and cancer patients. The production of metallic taste perception both induced by chemotherapy and ferrous sulfate solution, might be associated with the decreased expression of low-abundance proteins (pH 5.5-8.5, MW 25-75kDa), which were mainly immune proteins in saliva. Supplementation may improve taste disorder by recovering low-abundance salivary proteins in cancer patients. / Ph. D.

Scientific explorations can lead to life changing discoveries or light the path for new discoveries as scientists continue to carry or pass on the torch of knowledge to current and future generations. This torch of knowledge radiates in many directions, as the path of discovery often demands a multidimensional perspective. This research explored the many aspects of metallic flavor in drinking water through applications of sensory science, medicine, health, and the environment. Humans interact with their environment through the five senses and are often exposed to contaminants through multiple routes; oral intake of trace metal contaminants through drinking water is a likely source. The biochemical mechanism by which humans are able to detect the flavor of strongly metallic agents such as iron has been previously elucidated, but little is known about population variability in the ability to sense metallic flavors. This research evaluated sensory thresholds and biochemical indicators of metallic flavor perception in healthy adults for ferrous iron in drinking water; 61 subjects aged 19 – 84 years, participated. The findings demonstrated an age-dependent sensitivity to iron indicating as people age they are less sensitive to metallic perception; impairment of olfactory functions is a contributing factor. Unlike in healthy adults, where human senses are often protective of overexposure to contaminants, and supportive of sensations of everyday life's pleasures, cancer patients often suffer from chemosensory dysfunctions. Metallic phantom taste is a commonly experienced sensation, yet very little studied aspect of this debilitating disorder. Impact of cancer therapy on chemosensory functions of patients with malignant brain tumors undergoing combined modality treatment (CMT) was explored. The results indicated that chemosensory dysfunctions of the patients can range from minimal to moderate impairment with maximum impairment developing during the 6-week CMT. Study of salivary constituents may provide clues on to the causes of chemosensory dysfunctions. On health aspects, implication of individual sensitivity to metallic flavor on beverage choices and overall water consumption was assessed in 33 healthy adults through self-reported beverage questionnaire. The results indicated that among the elderly reduced intake of drinking water coincided with reduced sensitivity to metallic flavor. The findings have important health implications in terms of hydration status and beverage choices. Finally, with environmental exposure relevance, preliminary findings on sensory properties of zerovalent iron nanoparticles (nZVI) indicated that oral exposure to nZVI may induce sensory properties different from that of ferrous iron, likely predictive of a diminished detection of metallic flavor by humans. Further research is warranted in this area. / Ph. D.

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. / Master of Science in Life Sciences

During 20th century main concern was to have sanitary water flowing through the tap. In 21st century constant supply of safe drinking water is common at any home in USA. Hence consumers pay attention to aesthetic quality of tap water. Odorous algal metabolites in source water and metals introduced to drinking water due to corrosion of pipes in the distribution system cause taste, odor and color problems, and result in complaints and perception of tap water as unhealthy. Millions of dollars are spent each year by water industry to address and prevent these issues. This research focused on some of the taste-and-odor issues associated with drinking water. First aim was to understand when geosmin, 2-MIB, and nonadienal become detectable, employing two-resistance mass transfer theory to determine the concentration of odorants in bathroom air. Results showed that water temperature and odorant concentration in water play an important role. Next focus was to develop an international odor standard to be used for training of sensory analysis panelists. There are many sensory methods to monitor drinking water to detect the off-flavors however an odor standard has been missing. Hexanal was studied with trained flavor profile analysis panels and was proposed as an ideal odor reference standard to be used for training and sensory assessment of water samples. Main focus was to understand metallic flavor of drinking water caused by iron and copper. It was shown that metallic sensation has taste and retronasal components creating the flavor and humans are very sensitive to it. Occurrence of lipid oxidation in the oral cavity was shown when metals were ingested, that produces carbonyls which are responsible for the metallic flavor. Antioxidants and chelators were investigated to study prevention of lipid oxidation and, chelators were determined to be more effective. Oral epithelial cell cultures were developed as a model for oral cavity to further investigate lipid oxidation and effectiveness of the antioxidants and chelators. This dissertation is a result of inter-disciplinary work and possibly a good example for how problems may be solved by incorporating different methods and point of views from several disciplines. / Ph. D.