Luminescense Probes of Food Quality

Non-Technical Summary: The overall quality and safety of processed foods is a perennial concern of the public and the food industry in America; at the same time, both the public and the food industry are concerned with delivering such food quickly and inexpensively. Consequently, much effort and research is involved with developing rapid and inexpensive instrumental methods to evaluate the quality and safety of foods, food ingredients, and food raw materials. Given the large number of fluorescent molecules that either occur naturally in or are added to foods (colors, flavors, vitamins, etc.), and given the demonstrated versatility of fluorescence and phosphorescence to report on the molecular structure, dynamics, and properties of the local environment, it should be possible to develop novel luminescence techniques to monitor food quality and safety. This project will pursue such a research program. The long term goal of this project is to develop luminescence, that is fluorescence and phosphorescence, spectroscopy as a versatile and useful analytical technique to enhance our molecular understanding of food behavior and to develop novel techniques to assay the quality and safety of foods and food ingredients. This improved understanding will then be used to develop novel luminescence sensors, optical devices with sensitivities to specific chemical or physical properties, that are taylored to monitor specific properties, states, or analytes in foods related to overall quality and safety. <P> Approach: This project will systematically evaluate how various aspects of the fluorescence and phosphorescence emission from aromatic chromophores either naturally present in foods (tryptophan, natural colors and flavors) or added to foods (artificial colors and flavors, other) can be used to monitor the physical and chemical properties of foods that are related to overall quality. The project has three main objectives. In objective 1, we continue our on-going studies of how phosphorescence from aromatic probes can be used to monitor molecular mobility and oxygen permeability in amorphous sold carbohydrates, proteins, and their mixtures. This aspect of the project will use phosphorescence signals from the molecular probes erythrosin B, tryptophan, and vanillin embedded into amorphous thin films. Phosphorescence emission spectra and lifetime, which are found to monitor dipolar relaxation and collisional quenching, respectively, are monitored in different matrixes as a function of temperature and used to determine how matrix mobility varies with temperature over the range from -20 to ~120C. Comparison of emission and lifetime in the presence and absence of oxygen (air versus nitrogen) are used to evaluate how oxygen permeability varies with temperature and molecular mobility. In objective 2, we will survey the literature on chromophores found in foods and generate a database of molecules with luminescence properties that might be exploited as monitors of food quality. Selected molecules from this database will then be further studied experimentally to determine how their luminescence can be used to monitor specific properties related to food quality (pH, oxygen permeability, viscosity, water activity, etc.). In objective 3, we will develop a novel class of edible luminous nanoparticles made from gelatin, chitosan, and starch and labeled with the food-grade luminescence probes identified in objective 2. We will investigate how to make nanoparticle sensors that can monitor pH, temperature, water activity, oxygen, and the presence of specific foodborne pathogens. These novel sensors will be evaluated in model foods to determine their potential use in actual foods and food ingredients.