Progress 01/01/07 to 12/31/09
Outputs
OUTPUTS: Food sensors, sensitive to food properties, including temperature, oxygen, moisture content and pH, are used in food processing and other food related fields. Recently, applying sensor technology in the food industry has been further emphasized and even connected with nanoparticles. Nanoparticles were prepared from edible starch using a microemulsion method. These particles had diameters of ~100 nm. Quinine was non-covalently and irreversibly bound to these nanoparticles and the spectral response monitored in buffers over the pH range from 3 to 5.5. The ratio of emission intensity at two different emission wavelengths was found to vary systematically with pH using excitation wavelengths ranging from 295 to 325 nm. Studies of these nanoparticles in foods demonstrated that the measured ratio did not accurately indicate the pH of the food. Nanoparticles were prepared from food grade gelatin using a two step desolvation protocol. These particles had diameters of 20-50 nm. Nanoparticles were covalently labeled with fluorescein isothiocyanate (FITC). Fluorescence from the labeled gelatin nanoparticles in buffer solutions of varying pH's showed a repeatable correlation between pH and emission spectra (intensity ratios). The ratio of peak intensity or peak area (using two different excitation wavelengths) decreased as pH increased in the range of pH 2.5-7.5. Studies were done of these nanoparticles in different real food products. Comparing actual food pH with calculated sensor pH based on a calibration curve indicated that these fluorescein-labeled nanoparticles could reproducibly and accurately detect food pH with ~1-5% error. Nanopaticles prepared from food grade gelatin were also covalently labeled with erythrosin-isothiocyanate. Delayed emission spectra from these nanoparticles showed a clear and reproducible trend as a function of temperature. The ratio of the intensity of delayed fluorescence (Idf) to phosphorescence (Ip) was found to track with temperature over the range from 0-60C. Phosphorescence intensity from these particles was also found to be sensitive to the presence of oxygen in solution, varying inversely with oxygen concentration. Gelatin nanoparticles were also double labeled with fluorescein and tetra-methyl rhodamine to investigate whether they could be used to detect the presence of proteolytic enzymes indicative of the presence of specific bacteria. PARTICIPANTS: Richard D. Ludescher, project director; Xiang Zhang, graduate assistant, prepared nanoparticles with sensitivity to pH ; Sanaz Jalalian, graduate assistant, prepared nanoparticles with sensitivity to temperature, oxygen. TARGET AUDIENCES: Results of this research were presented at a meeting of the Institute of Food Technologists and at meetings of the program directors of nanoscale science and technology grants. A manuscript describing the pH sensitive nanoparticles is in draft and will be submitted for publication shortly. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
This study has demonstrated that nanoparticles prepared from food grade hydrocolloids (starch or gelatin) can be labeled with luminescence probes and that these labeled-nanoparticles can be used as sensors for temperature (range 0-60C), ph (range 2.5-7.5), and oxygen (0-saturation).
Publications
- Zhang, Xiang & Ludescher, Richard D. (2009) Novel Panoparticle Sensors of Food pH. IFT Annual Meeting, Anaheim, CA, June, 2009.
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Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: This project has developed luminous edible nanoparticles made from gelatin, chitosan, and starch to measure temperature, oxygen, and pH. We have prepared gelatin nanoparticles containing erythrosin B (Ery B; FD&C red #3) that act as temperature and oxygen sensors. Pigskin gelatin (300 Bloom) was labeled with the isothiocyanate derivative of Ery B. Nanoparticles were prepared by adding excess acetone slowly to aqueous solution of labeled gelatin; nanoparticles were then crosslinked with glutaraldehyde and exess excess acetone was removed by evaporation. Both labeled and unlabeled nanoparticles had an effective diameter of ~135 nm as measured by dynamic light scattering. Erythrosin-labeled nanoparticles exhibited delayed luminescence spectra that varied characteristically with temperature over the range from 3 to 60C: the intensity of the phosphorescence band decreases and intensity of the delayed fluorescence band increases with increasing temperature. Analysis of these
emission bands provides the peak intensity for phosphorescence (IP) and delayed fluorescence (IDF); this ratio varies characteristically and distinctively with temperature. The erythrosin probe is exquisitely sensitive to oxygen with the phosphorescence lifetime varying directly with the concentration of oxygen in the medium. Ery-labeled nanoparticles will thus also provide a sensitive indicator of oxygen concentration. We have prepared starch nanoparticles containing quinine that act as pH sensors. Starch nanoparticles were made using a microemulsion method, followed by crosslinking with phosphorous tricloride. The nanoemulsion was washed three times with acetone and then ethanol to obtain a precipitate of white solid starch nanoparticles; the solid was freeze-dried to obtain the dry powder. Nanoparticles have a mean diameter of 101 nm and an effective diameter of 235 nm as evaluated by dynamic light scattering; since the size distribution was multi-modal, a population of particles
with diameters in excess of ~200 nm diameter was removed by filtration through a 0.2 micron filter. Starch nanoparticles were labeled with quinine by soaking dry starch nanoparticles in solution of quinine. Unbound quinine was then removed by extensive dialysis against distilled water until the dialysis solution exhibited no detectable quinine fluorescence. Quinine-labeled nanoparticles were freeze-dried and stored as dry powder in the dark. Although we have not yet measured the amount of quinine per dry weight of nanoparticles, solutions of nanoparticles at 1 mg/mL gave strong fluorescence signals. The emission spectra were analyzed for peak intensity or integrated and the ratios of the peak intensity or area with excitation at 295 and 345 nm were calculated as a function of solution pH (that is, I345/I295 or A345/A345). The values for quinine standard solutions and for quinine-labeled nanoparticles indicate that both intensity ratios and area ratios are essentially the same in
standard solution and nanoparticles, indicating that labeled nanoparticles provide a sensitive indicator of pH over the range from pH 3-5.
PARTICIPANTS: Richard D. Ludescher, Prinicipal Investigator; Melinda Ligneres, graduate assistant; Sanaz Jalalian, graduate assistant; Xiang Zhang, graduate assistant
TARGET AUDIENCES: The target audience of this research is food technologists, food scientists, and the larger food industry. Upon successful generation of various classes of nanoparticles, that is, nanoparticles sensitive to specific food properties, this audience will be informed of sensor properties and utility by means of scientific publications, reports at meetings, and presentations to target audiences.
Impacts
We have successfully prepared nanoparticles that are sensitive to temperature, oxygen, and pH from food-grade ingredients (porcine pigskin gelatin, starch, FD&C red #3, quinine). Studies in vitro indicate that these nanoparticles provide sensitive indicators of these solution properties over useful ranges (temperature from 0-60C, pH 3-5). We have thus demonstrated proof of principle of this novel class of edible luminous nanoparticles and developed prototype sensors for three food properties. Future studies will establish the feasibility of using these novel sensors in real food systems.
Publications
- No publications reported this period
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