Damascenones 774 INDEX

Figure G1.1.3 shows a chromatogram of the headspace of Concord grape essence prepared by direct injection. At retention index 1320 is the peak caused by methyl anthranilate, one of the strongest odorants characterizing Concord grapes however, (i-damascenone, the second most potent odorant in Concord grapes, elutes at 1360 but is not visible. This is because P-damascenone is lOOOx more potent (i.e., its odor threshold is lOOOx lower than methyl anthranilate). This is typical result for the direct injection of headspace from natural products. Figure Gl.1.4, on the other hand, shows the injection of an extract of Concord grape essence concentrated 500-fold with the fi-damascenone peak large enough for quantitation.

Figured.1.4 An FID chromatogram of concentrated extract of the same Concord grape essence shown Figure G1.1.3, drawn to display the data on a linear retention index scale. By simply comparing the index of a peak with the data listed in the flavornet, the odorants that have similar retention indices can be determined. Notice how large the methyl anthranilate peak is, but still no convincing peak for p-damascenone, even though both compounds have the same odor activity (intensity).

TLC and HPLC. To determine the best solvents for HPLC, 5pl of the C18 concentrated PVP fraction were separated on analytical TLC plates coated with either C18 reversed phase adsorbant or with silica. One cm sections of the plates were removed, placed in buffer, hydrolyzed, extracted and the p-damascenone charm determined. Standards containing 5 mg each of 1 -O-n-octyl- p-D-glucopyranoside and a-methyl-D-mannoside were run simultaneously on the same plate and visualized by spraying with aniline-diphenylamine-acetone-phosphoric acid 80% (4 mL 4 g 200 mL 30 mL) (10). HPLC separations were performed on a 0.46 mm x 25 cm column packed with 5 im C18, eluted with 60/40 methanol water at a flow of 0.8 mL/min. The refractive index of samples was recorded with a Knauer differential refractometer. Fractions were collected every minute and assayed for p-damascenone charm. 

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