ABSTRACT
Changes of volatile flavor compounds of watermelon juice by heat treatment were investigated by gas chromatography-olfactometry-mass spectrometry. Although the major volatile compounds in watermelon juice, three aldehydes, three alcohols, and one ketone, did not increase significantly by heat treatment, dimethylsulfide and methional increased in heated juice. These two sulfides were suggested to contribute to the off-flavors in heated watermelon juice.
Subject(s)
Citrullus/chemistry , Food Handling , Fruit and Vegetable Juices/analysis , Hot Temperature , Taste , Volatile Organic Compounds/analysisABSTRACT
Four new compounds, namely, nectriapyrones A (2) and B (3), nectriaquinone B (5), and zythiostromic acid C (8), were isolated from the brown rice culture of Nectria pseudotrichia 120-1NP together with four known compounds (1, 4, 6, and 7). To the best of our knowledge, this is the first report of 4 from a natural source. Their structures were determined on the basis of 1D/2D-NMR spectroscopy and HRESITOFMS data. In addition, the absolute configuration of secondary alcohols in 8 were determined using modified Mosher's ester method. All isolated compounds were evaluated for their antimicrobials activity, phytotoxicity, and cytotoxicity.
Subject(s)
Diterpenes/isolation & purification , Isocoumarins/isolation & purification , Naphthoquinones/isolation & purification , Nectria/chemistry , HL-60 Cells , Humans , Lactuca/drug effects , Microbial Sensitivity Tests , Molecular StructureABSTRACT
Trehalose dimycolate (TDM) is a major surface-exposed mycolyl glycolipid that contributes to the hydrophobic cell wall architecture of mycobacteria. Nevertheless, because of its potent adjuvant functions, pathogenic mycobacteria appear to have evolved an evasive maneuver to down-regulate TDM expression within the host. We have shown previously that Mycobacterium tuberculosis (M.tb) and Mycobacterium avium (M.av), replace TDM with glucose monomycolate (GMM) by borrowing host-derived glucose as an alternative substrate for the FbpA mycolyltransferase. Mycobacterium leprae (M.le), the causative microorganism of human leprosy, is also known to down-regulate TDM expression in infected tissues, but the function of its mycolyltransferases has been poorly analysed. We found that, unlike M.tb and M.av FbpA enzymes, M.av FbpA was unexpectedly inefficient in transferring alpha-branched mycolates, resulting in impaired production of both TDM and GMM. Molecular modelling and mutational analysis indicated that a bulky side chain of leucine at position 130 of M.le FbpA obstructed the intramolecular tunnel that was proposed to accommodate the alpha-branch portion of the substrates. Notably, even after a highly reductive evolution, M.le FbpA remained functional in terms of transferring unbranched acyl chains, suggesting a role that is distinct from that as a mycolyltransferase.