Impact of functional spray coatings on smoke volatile phenol compounds and Pinot noir grape growth

Abstract

The frequency and intensity of wildfires have been increasing over the last 50 years and negatively impacted the wine industry. Previous methods of smoke mitigation during grape processing have shown little impact in reducing smoke taint in wines. Therefore, a novel method of using edible spray coatings for vineyard application was developed to help prevent volatile smoke phenol uptake in wine grapes. Four cellulose nanofiber-based coating suspensions incorporated with chitosan and/or β-cyclodextrin were evaluated. Films derived from the coating suspensions were exposed to volatile phenols found in wildfire smoke (guaiacol, 4-methyl guaiacol, m-cresol, o-cresol, p-cresol, syringol, and 4-methyl syringol) and evaluated with ultraviolet-visible spectroscopy where the results indicated that the coatings could uptake smoke phenols in varying degrees. The coatings were also applied in a vineyard at three different application times during grape growth: pea-sized, pre-bunch closure, and both at pea-sized and pre-bunch closure. The results showed that the application time did not have a significant (p < 0.05) effect on berry size, weight, • Brix, pH, or titratable acidity. The type of coating, time of application and washing were found to impact the number of volatile phenols in the grapes after a smoke event. Results from this study indicated that edible coatings could help mitigate smoke uptake in wine grapes without sacrificing the growth and key composition parameters of wine grapes.

Evaluation of Functional Spray Coatings for Mitigating the Uptake of Volatile Phenols by Pinot Noir Wine Grapes via Blocking, Absorption, and/or Adsorption

“…Once homogenized, each suspension was degassed with a water vacuum pump to remove excess air bubbles before casting onto leveled 170 mm × 170 mm Teflon-coated glass plates and dried at 21 ± 1 °C and 40 ± 5% relative humidity (RH) for 3 days to obtain a film. Since obtaining a similar thickness for each derived film is critical for evaluating and comparing their properties, the amount of each poured coating suspension was controlled based on the calculation of TSS (°Brix) i × W i = TSS (°Brix) i × W i = TSS (°Brix) i × W i , where TSS (total soluble solids, °Brix) is the total soluble solids of the film suspension, W is the weight casted onto the Teflon plates, and i was the i th number for the treatment group. , The TSS of each film-forming suspension was measured using a digital refractometer (Brix RA-250 HE, Kyoto Electronics Manufacturing Co., Ltd., Kyoto, Japan).…”

“…This percent weight gain of the films was calculated as WA. WS was calculated as the percent weight loss of the films after suspending in water for 2 h and dried at 40 °C for 24 h. , A cup method following ASTM Standard E96-87 was used to determine WVP . Briefly, a 75 × 75 mm film sample was sealed with vacuum grease between two pieces of Plexiglass that contained a 7.5 mm-diameter opening with 11 mL of deionized water at the bottom.…”

“…After 7 days of storage, the center piece of each film in the box was cut into a 7.5 mm-diameter piece and VPs were extracted using acetone from films for further analysis . Briefly, each piece of the cut film was inserted into a 7 mL amber glass vial with a Thermoset PTFE-lined cap (Sigma-Aldrich, St. Louis, Missouri, USA) containing 4 mL of HPLC-grade acetone.…”

“…Preharvest methods and strategies have also been tested and some have shown promising results. , One preharvest method is the use of spray coatings on wine grapes. In our previous study, spray coatings made of cellulose nanofiber (CNF), chitosan (CH), and beta-cyclodextrin (CD) were evaluated to determine any negative impact on the overall physiochemical properties of Pinot noir wine grapes. In addition, films were prepared from spray coating suspensions, and their ability to prevent the uptake of VPs was evaluated via UV–vis absorption study.…”

“…Second, among the three coating formulations tested, the films derived from coating suspensions containing CH exhibited potential in preventing smoke VP uptake by reducing the amount of guaiacol, m -cresol, and syringol extracted from the films. However, the films were still able to uptake smoke compounds and release the compounds as found in the qualitative UV–vis absorption study . Hence, it was necessary to improve the existing coating formulations to completely block volatile smoke phenols or prevent the release of VPs absorbed by coatings.…”