水土保持科学研究的基本思路

该文依据作者２０多年对水土保持科研工作的实践，提出了进行水土保持科研的基本思路是：一定强度的降雨降至无覆盖的坡地地表土壤上，引起水土流失，通过建造植被、水土保持耕作、水土保持工程措施，或通过上述措施的复合组装，或通过复合措施的优化配置，使降雨不能直接达到坡地地表土壤上，或使降雨降至平地，不足引起水土流失，达到保持水土的目的。同时依据这一基本思路，提出了进行水土保持科学研究应采取的主要措施，主要内容     

Taste-active components in a Vietnamese fish sauce

Taste-active components were determined for a typical first-grade Vietnamese fish sauce Nuoc mam , of which total content of extractive compounds reached as high as 20 g/ 100 mL. A complete synthetic extract prepared from 35 compounds according to the analytical data reproduced almost satisfactorily the taste of the original fish sauce. From the synthetic extract, 11 compounds were identified to be the taste-active components by a series of omission and addition tests. The components consisted of glutamic and aspartic acids, threonine, alanine, valine, histidine, proline, tyrosine, cystine, methionine, and pyroglutamic acid. The most effective compound for recreating the characteristic flavor of fish sauce was glutamic acid, followed by pyroglutamic acid and alanine. Many of these components contribute to umami, sweetness, and overall taste of fish sauce. Even though the simplified 11-component extract reproduced the taste of fish sauce, the taste strength was weaker than that of the complete synthetic extract or fish sauce itself.     

Taste effects of oligopeptides in a Vietnamese fish sauce

ABSTRACT: A Vietnamese fish sauce Nuoc mam used in the present study was rich in oligopeptides of which nitrogen content accounted for 20% of total nitrogen. The high-molecular-weight peptide fractions fractionated by ion-exchange chromatographies and ultrafiltration enhanced sweetness and umami as well as sourness and bitterness of the fish sauce, and increased several flavor characteristics including continuity, first taste and aftertaste. Thus, it is apparent that large amounts of peptides produced during the long-term fermentation of fish sauce are responsible for the complicated taste of the sauce. From each fraction, 17 peptides in total were isolated and determined for their amino acid sequences. These di-, tri- and tetra-peptides synthesized by solid- or liquid-phase method gave any one of bitter, sour, umami taste, or practically no taste in the absence of salt. In the presence of 0.3% NaCl, however, almost all peptides showed sweet and umami tastes. Other than these 17 peptides, there existed many other kinds of peptides in the fish sauce. Thus, these peptides are thought to contribute to the overall taste of the fish sauce.