John F Weeks

Bio: John F Weeks is an academic researcher from Food and Drug Administration. The author has contributed to research in topics: Moisture & Shrimp. The author has an hindex of 2, co-authored 3 publications receiving 7 citations.

Flame photometric and atomic absorption determination of calcium, potassium, and sodium in Ringer's solution and injection and in lactated Ringer's solution.

Abstract: Authentic and commerical counterparts of Ringer's solution and lactated Ringer's solution were analyzed by 14 collaborators. Calcium, potassium, and sodium were to be determined by any flame emission or atomic absorption instrument operated at prescribed performance levels, and basic procedures for comparing samples and standards were also given. Recoveries of the cations from authentic and commercial solutions were as follows: calcium 95.6-102.1 and 95.6-103.6%, respectively; potassium 97.9-101.7 and 98.7-102.4%; sodium 98.2-103.1 and 97.3-103.7%. The results indicate that the method yields acceptable precision for the determination of the 3 cations in fluid and electrolyte replenishers. The method has been adopted as official first action.

Histamine Test Kit Comparison

Abstract: Six commercially available test kits designed to determine histamine in canned and raw fish were selected to compare the performance of each kit. The histamine concentration in seven tuna and eight mahimahi test samples as determined by each test kit was compared to the histamine concentrations as determined by the official AOAC method 977.13. All the kits tested were acceptable for use as screening tests for histamine and were able to distinguish between products that contained less than 50 ppm and those that contained more than 50 ppm.

Potassium and sodium measurements at clinical concentrations using phase-modulation fluorometry

Abstract: We describe the possibility of measuring sodium and potassium at the concentrations present in whole blood using lifetime-based sensing and phase-modulation fluorometry. The probe SBFO was shown to display changes in phase or modulation at sodium concentrations near 100 mM, and to be mostly independent of interfering effects due to potassium. The probe CD222 was found unsuitable for measurements of potassium in blood using intensity-ratio measurements, due to similar spectral changes induced by sodium. However, sodium at blood concentrations near 100 mM causes only a minor change in the lifetime of CD222. Hence, CD222 and lifetime-based sensing can be used to measure blood levels of potassium in the presence of 130 mM sodium. Similarly, sodium causes only a modest change in the lifetime of the potassium probe PBFI, which displays potassium-dependent lifetimes. For both CD222 and PBFI, the presence of blood levels of sodium increases the apparent potassium dissociation constants into the blood physiological range. In total, these results demonstrated the possibility of lifetime-based sensing of sodium and potassium at the extracellular cation concentrations present in blood or blood serum.

Identification and Characterization of the Aroma-Impact Components of Thai Fish Sauce

Abstract: Comprehensive analysis of the potent odorants in Thai premium fish sauce samples was accomplished by use of complementary volatile isolation methods combined with gas chromatography-olfactometry (GC-O) and GC-mass spectrometry. Odorants of intermediate and low volatility were determined by direct solvent extraction/solvent-assisted flavor evaporation (DSE-SAFE) and aroma extract dilution analysis (AEDA). Meanwhile, static headspace dilution analysis (SHDA) and headspace solid-phase microextraction (H-SPME) were used to determine the highly volatile odorants. Results of AEDA indicated the importance (log3FD factor≥6) of five acidic odorants (butanoic acid, 3-methylbutanoic acid, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 4-hydroxy-2-ethyl-5-methyl-3(2H)-furanone, and 2-phenylacetic acid) and four neutral/basic odorants (3-methylbutanal, (Z)-1,5-octadien-3-one, phenylacetaldehyde, and o-aminoacetophone). Results of SHDA indicated the predominant (log3FD factors≥5) headspace odorants were methanethiol, 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, dimethyl trisulfide, 3-(methylthio)propanal, and butanoic acid. Concentrations for 21 odorants were determined by stable isotope dilution analysis (SIDA), and their odor-activity values (OAVs) were calculated. Among these, methanethiol, 2-methylpropanal, 3-methylbutanal, dimethyl trisulfide, 3-(methylthio)propanal, and butanoic acid had the highest OAVs (>500). Results of aroma recombination and omission studies revealed the importance of acids, aldehydes, and sulfur-containing compounds to the overall aroma of the Thai fish sauce.