Search

This study investigated the effect of storage time on biochemical characteristics of hawk tea (Litsea coreana) and explored the correlation between the content of flavonoids and polyphenols and antioxidant activity. The antioxidant activity and the content of inclusions, amino acid, and mineral elements in hawk tea processed by boiling water fixation and packed in airtight polypropylene bags and stored in 0°C refrigerator under different storage time (one year, three years, and six years) were analyzed. Results indicated that the biochemical characteristics of hawk tea changed less within 12 months. The total content and types of amino acids in hawk tea reached the maximum in the third year, as well as the content of total trace elements. The water extracts, tea polyphenol, caffeine, lysine, valine, isoleucine, glycine, proline, Ca, and Zn decreased continuously in the storage period of 6 years, but the total flavonoids, Mg, and Ni changed just the opposite. Total polyphenol is the main antioxidant material in hawk tea. Results of the present study provided useful information for people to systematically understand the changes of tea in the storage process and to reasonably develop hawk tea product.

A fully calibrated strategy has been investigated for the first time for the accurate determination of absolute isotopic composition and atomic weight of molybdenum using multiple-collector inductively coupled plasma mass spectrometry. The correction for instrumental mass bias was performed using synthetic isotope mixtures, which were gravimetrically prepared with all of the seven high-purity and isotopically enriched molybdenum isotope materials together. Six natural molybdenum materials, including molybdenum standard solution NIST SRM 3134, were accurately measured and yielded the absolute isotopic composition (in atom %, k = 1) of 92Mo-14.690(18), 94Mo-9.173(6), 95Mo-15.865(5), 96Mo-16.666(3), 97Mo-9.588(4), 98Mo-24.307(16), and 100Mo-9.711(13). These isotopic data enable an atomic weight Ar(Mo) of 95.9466(34) (k = 2) to be calculated, which is slightly lower than the current standard atomic weight 95.95(1) and with a much improved uncertainty. The associated uncertainties were evaluated according to t...