Drying of MushroomsFresh mushrooms with a moisture content of 85-90% were air-dried at 40-45°C to a final moisture content of 10%. The dried mushrooms were later used for the extraction of flavour compounds.
Isolation of Volatile CompoundsFresh (300 g) and dried (30 g) mushrooms were cut into small pieces and homogenized in a Waring blender (Braun, Model-MX-32-2, Germany) at low speed with 600 ml distilled water for 2 min. The homogenate was subjected to simultaneous distillation and solvent extraction under reduced pressure in a Likens and Nikersontype apparatus, 8 using diethyl ether as the extraction solvent. The volatiles were collected at 15°C, dried over anhydrous sodium sulphate and concentrated to 0.1 ml at 35°C bath temperature. This experiment was replicated three times.
Gas ChromatographyAnalysis was performed on a Perkin-Elmer Autosystem-XL gas chromatograph fitted with 30 m × 0.25 mm i.d. PE-wax (stationary phase, polyethylene glycol) and PE-1 (stationary phase, polydimethylsiloxane) (Perkin-Elmer, USA) fused silica capillary columns. The operational conditions were: 60°C for 4 min, rising at 5°C/min to 200°C, then held for 5 min; injector and detector (FID) temperatures, 230°C and 260°C, respectively; carrier gas, nitrogen at a flow rate of 1.0 ml/min; split ratio, 1:100; sample size, 0.5 µl. The following standards were chromatographed under identical conditions: 1-octen-3-ol,
The triterpenoids isolated from the leaves ofMomordica charantia Linn (bitter gourd) were found to elicit feeding-deterrent activity against red pumpkin beetles (Aulacophora foveicollis Lucas). The most abundant triterpenoid which deterred feeding was identified as momordicine II, 23-O-β-glucopyranoside of 3,7,23-trihydroxycucurbita-5,24-dien-19-al. A concentration of 3200μg/ml and above of the triterpenoids caused significant reduction of feeding by red pumpkin beetles in in vitro bioassay experiments, which compared favorably with the levels of triterpenoids inM. charantia leaves found in nature.
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