Potential Mitigation of Smoke Taint in Wines by Post-Harvest Ozone Treatment of Grapes

When bushfires occur near grape growing regions, vineyards can be exposed to smoke, and depending on the timing and duration of grapevine smoke exposure, fruit can become tainted. Smoke-derived volatile compounds, including volatile phenols, can impart unpleasant smoky, ashy characters to wines made from smoke-affected grapes, leading to substantial revenue losses where wines are perceivably tainted. This study investigated the potential for post-harvest ozone treatment of smoke-affected grapes to mitigate the intensity of smoke taint in wine. Merlot grapevines were exposed to smoke at ~7 days post-veraison and at harvest grapes were treated with 1 or 3 ppm of gaseous ozone (for 24 or 12 h, respectively), prior to winemaking. The concentrations of smoke taint marker compounds (i.e., free and glycosylated volatile phenols) were measured in grapes and wines to determine to what extent ozonation could mitigate the effects of grapevine exposure to smoke. The 24 h 1 ppm ozone treatment not only gave significantly lower volatile phenol and volatile phenol glycoside concentrations but also diminished the sensory perception of smoke taint in wine. Post-harvest smoke and ozone treatment of grapes suggests that ozone works more effectively when smoke-derived volatile phenols are in their free (aglycone) form, rather than glycosylated forms. Nevertheless, the collective results demonstrate the efficacy of post-harvest ozone treatment as a strategy for mitigation of smoke taint in wine.

A Simple GC-MS/MS Method for Determination of Smoke Taint-Related Volatile Phenols in Grapes

Volatile phenols (VPs) derived from smoke-exposed grapes are known to confer a smoky flavor to wine. Current methods for determination of VPs in grape berries either involve complex sample purification/derivatization steps or employ two analytical platforms for free and bound VP fractions. We report here a simple gas chromatography-tandem mass spectrometry (GC-MS/MS) method for quantification of both free and bound VPs in grapes, based on optimized (1) GC-MS/MS parameters, (2) an analyte extraction procedure, and (3) phenol glycoside hydrolysis conditions. Requiring neither sample cleanup nor a derivatization step, this method is sensitive (LOD ≤ 1 ng/g berries) and reproducible (RSD < 12% for repeated analyses) and is expected to significantly reduce the sample turnover time for smoke taint detection in vineyards.

A New Phenol Glycoside from Root Exudates of Peperomia pellucida L. HBK. and its Role in Plant Invasion

Peperomia pellucida is an annual, shallow-rooted, succulent, delicate, glabrous herb. It is a native weed species of tropical North and South America, and it is now pantropic in distribution and abundant in India as an invasive aggressive colonizer. Medicinal properties of the plant have been well documented but no work has been done to find out the reason behind its invasive aggressive nature. The objective of our present work was to study the allelopathic activity of allelochemicals released by root exudates of P. pellucida which may play an important role in invasive and aggressive properties of the plant. Root exudates of P. pellucida were collected in root exudates trapping system. Main compound was isolated from methanol fraction of root exudates of P. pellucida, purified by thin layer and column chromatography and finally subjected to mass spectra, infrared, and nuclear magnetic resonance (both 1H and 13C) for complete structural elucidation. In vitro allelopathic activities of the compound were studied by rice, wheat and mustard seed bioassays. A new phenol glycocide [(6-(4-hydroxyphenoxy)-tetrahydro-2H-pyran-2, 3, 4, 5-tetraol); C11H14O7; Mol. Wt. 258] has been isolated and purified from root exudates of P. pellucida. This pure compound exhibited significant allelopathic activities on rice, wheat and mustard seeds in vitro bioassay experiment. This compound showed maximum inhibitory activity on rice, than in wheat and mustard bioassays. Peperomia pellucida released a phenol glycoside through root exudates into rhizophere which may act as a major allelopathic agent and may be responsible for its invasive and aggressive nature.

ALLELOPATHIC POTENTIAL AND PHYTOCHEMICAL SCREENING OF FOUR MEDICINAL PLANTS OF NEPAL

The laboratory tests were conducted to evaluate the allelopathic potential and phytochemical study of the four selected medicinal plants Ageratum conyzoides, Eclipta prostrata, Cannabis sativa and Woodfordia fructicosa. The aqueous extract bioassay of the plants with stem and root were conducted on the two test seeds Triticum aestivum (wheat) and Pisum sativum (pea) by filter paper method. Germination, seedling growth and biomass production were observed under the allelopathic study whereas under phytochemical study qualitative or presence or absence and quantitative or crude amount of the phytochemicals present were also estimated. For the allelopathic studies the germination and seedling growth of wheat and pea test species under the different concentrations 2 %, 4%, 6%, 8% and 10% of the stem and root extracts of the plants under study were carried out. Increased concentration of the aqueous extracts of the plants increased the inhibitory rate or decreased the germination and seedling growth.Species sensitivity varied with the test seeds and alkaloid, flavonoid, saponin, tannin, phenol, glycoside and essential oil were the phytochemicals present in the plant extracts.Scientific World, Vol. 12, No. 12, September 2014, page 56-61