Thresholds for Botrytis bunch rot contamination of Chardonnay grapes based on the measurement of the fungal sterol, ergosterol

Abstract

Background and Aims: The threshold for Botrytis contamination of winegrapes is not fully known. Using a measurement of the fungal sterol, ergosterol, we aimed to understand how much grey mould of grapes can be tolerated before there is a perceivable impact on wine sensory characteristics. Methods and Results: Chardonnay grape bunches hand-harvested in January 2016 from the Hunter Valley, NSW, were divided into one of five groups based on the visual assessment of the severity of grey mould using a scale of 0-4. Ergosterol analysis indicated that the fungal biomass of the five batches of grapes was 0.06, 0.28, 0.87, 1.50 and 4.25 g dry mass of fungus per kg wet mass. Grey mould infection resulted in an elevated concentration of benzaldehyde, 2-pentyl furan, ethyl linoleate, (E)-3-hexenol, 3-octanol, 1,5-dimethyl-naphthalene, 1,5-dimethyl tetralin 1-octen-3-ol, 1-octen-3-one and 3-octanone in the juice. 1-Octen-3-ol, and 3-octanone, ethyl-3-hydroxydodecanoate and isoamyl acetamide were elevated in wine made with Botrytis-affected grapes. Sensory discrimination tests identified a difference between wine made from grapes with ≥0.87 g of dry mass of fungus/kg wet mass of grapes (equivalent to ≥2.57 mg ergosterol/kg grapes) and wine made from asymptomatic grapes. Conclusions: Ergosterol correlated with the degree of grey mould contamination and the threshold in Chardonnay grapes was 0.28-0.87 g dry mass fungus/kg fresh mass of grapes. Significance of the Study: Measurement of ergosterol has been evaluated as a quantitative estimate of the threshold for Botrytis contamination of winegrapes.

Use of auxin to delay ripening: sensory and biochemical evaluation of Cabernet Sauvignon and Shiraz

“…Benzaldehyde was the compound with the greatest difference between Control and NAA wines. Neither compound has previously been associated with the NAA treatment of grapes, but both compounds have recently been linked to bunch rot of Chardonnay grapes (Steel et al 2020). As NAA‐treated grapes were left for an additional 21 (Cabernet Sauvignon) and 24 days (Shiraz) on the vines after harvest of the Control fruit, during which time no further fungicide treatments occurred, it is plausible that a low level of grey mould infection had time to develop before the later harvest.…”

Evolution of Markers Involved in the Fresh Mushroom Off-Flavor in Wine During Alcoholic Fermentation

“…In the literature, 2-octanol has never been identified in its free form in either must or wine matrices. However, 1-octen-3-ol has already been found in free form in musts of different grape varieties contaminated by various fungi. − In the fungi kingdom, the biosynthesis of 1-octen-3-ol is well-known, originating from the degradation of linoleic acid under the action of several enzymes via peroxide intermediates . In our study, the musts originated from certified industrial size presses were obtained using very low overpressure (not exceeding 1.2 bar for the “cuvée”- as required by the specifications of Champagne appellation) with a slow rise, maintaining the integrity of the berry throughout the extraction process.…”

“…The 3-octanol concentrations in healthy and contaminated matrices in HM1/CM1 and HM2/CM2 ranged from 0.005 ± 0.008 to 0.034 ± 0.011 μg/L, lower than those in HM3/CM3, which ranged from 0.07 ± 0.01 to 0.08 ± 0.02 μg/L (Figure C). Recently, Steel et al, identified 3-octanol in Chardonnay musts affected by Botrytis cinerea but did not quantify it. It is therefore difficult to correlate our observations with those of their work.…”

“…Empirically, winemakers in Champagne observed that Pinot noir and Meunier grapes with gray rot symptoms or Chardonnay grapes with symptoms of powdery mildew can produce wines with FMOff, but not systematically. Two decades ago, it was scientifically demonstrated that this defect was commonly associated with grapes affected by Botrytis cinerea or Ascomycetes fungi including Erysiphe necator and some Penicillium sp. ,− More recently, a fungus called Crustomyces subabruptus has been shown to consistently induce FMOff under laboratory conditions, providing a useful laboratory tool to be able to mimic FMOff character of musts and wines and usable to deepen the knowledge on the origin of these compounds.…”

Development of a Methodology for Estimating the Ergosterol in Meat Product-Borne Toxigenic Moulds to Evaluate Antifungal Agents

“…The analytical methods for its detection have been usually based on high-performance liquid chromatography (HPLC), with methanol as eluent [ 23 , 24 , 25 ], or gas chromatography (GC) with mass spectrometry detection [ 26 ]. Concretely, HPLC coupled with a UV detector is the most used method for analysing ergosterol [ 27 , 28 ], since it is easy to handle and has lower maintenance costs and technical requirements than other detectors or chromatographic techniques [ 29 , 30 ]. Whatever the method chosen, it is necessary to consider that the loss of ergosterol due to decomposition and light sensitivity can occur because of the time required for the different steps of the procedure [ 31 ].…”