Permeability of cork for water and ethanol

Cork cellular and chemical features underlying bark environmental protection in the miombo species Parinari curatellifolia

Parinari curatellifolia is an important evergreen tree from the Miombo woodland of south-central and eastern Africa. The bark is corky, suggesting an increased protection against the ecosystem high temperatures and drought conditions as well as against wild fires. The cork in the bark rhytidome of P. curatellifolia was analyzed here for the first time with a focus on chemical and cellular features. P. curatellifolia cork has the cellular characteristics of cork tissues, with typical honeycomb structure in the tangential section and a brick-wall layer in the transverse and radial sections, without intercellular voids. Chemically P. curatellifolia cork has 8.4 % extractives, 33.9 % suberin, 31.9 % lignin and 25.2 % polysaccharides of the cork. The hemicelluloses are mostly xylans, with a substantial proportion of arabinose and galactose. Suberin showed a proportion of long chain lipids to glycerol (LCLip:Gly, mass ratio) of 8.5, and the long chain monomeric composition included a similar proportion of α,ω-diacids and ω-hydroxy acids (35.4 % and 31.5 % of long chain monomers) with a substantial proportion of monoacids (19.4 % of long chain monomers). Lignin is a guaiacyl-syringyl lignin with S/G of 0.32 and H:G:S of 1:14.1:4.5. The rhytidome composition and the cellular and chemical features of its cork are in line with environment-targeted protective features namely as a transpiration and insulation barrier, and as an increased fire protection.

Conditioning of pretreated birch by liquid-liquid organic extractions to improve yeast fermentability and enzymatic digestibility

By-products from hydrothermal pretreatment of lignocellulosic biomass inhibit enzymatic saccharification and microbial fermentation. Three long-chain organic extractants (Alamine 336, Aliquat 336 and Cyanex 921) were compared to two conventional organic solvents (ethyl acetate and xylene) with regard to conditioning of birch wood pretreatment liquid (BWPL) for improved fermentation and saccharification. In the fermentation experiments, extraction with Cyanex 921 resulted in the best ethanol yield, 0.34 ± 0.02 g g^-1 on initial fermentable sugars. Extraction with xylene also resulted in a relatively high yield, 0.29 ± 0.02 g g^-1, while cultures consisting of untreated BWPL and BWPL treated with the other extractants exhibited no ethanol formation. Aliquat 336 was most efficient with regard to removing by-products, but the residual Aliquat after the extraction was toxic to yeast cells. Enzymatic digestibility increased by 19-33% after extraction with the long-chain organic extractants. The investigation demonstrates that conditioning with long-chain organic extractants has the potential to relieve inhibition of both enzymes and microbes.

Development of Cork Biocomposites Enriched with Chitosan Targeting Antibacterial and Antifouling Properties

The demand for bio-based and safer composite materials is increasing due to the growth of the industry, human population, and environmental concerns. In this framework, sustainable and safer cork-polymer composites (CPC), based on green low-density polyethylene (LDPE) were developed using melt-based technologies. Chitosan and polyethylene-graft-maleic anhydride (PE-g-MA) were employed to enhance the CPC's properties. The morphology, wettability, mechanical, thermal, and antibacterial properties of the CPC against Pseudomonas putida (P. putida) and Staphylococcus aureus (S. aureus) were examined. The CPC showed improved stiffness when compared with that of the LDPE matrix, preferably when combined with chitosan and PE-g-MA (5 wt. %), reinforcing the stiffness (58.8%) and the strength (66.7%). Chitosan also increased the composite stiffness and strength, as well as reduced the surface hydrophilicity. The CPCs' antibacterial activity revealed that cork significantly reduces the biofilm on the polymer matrix. The highest biofilm reduction was found with CPC containing cork and 5 wt. % chitosan for both P. putida (54% reduction) and S. aureus (36% reduction), confirming their potential to extend the lifespan of products for packaging and healthcare, among other applications. This work leads to the understanding of the factors that influence biofilm formation in cork composites and provides a strategy to reinforce their behavior using chitosan.

Wine Closure Performance of Three Common Closure Types: Chemical and Sensory Impact on a Sauvignon Blanc Wine

A Napa Valley Sauvignon blanc wine was bottled with 200 each of a natural cork, a screw cap, and a synthetic cork. As browning is an index for wine oxidation, we assessed the brown color of each bottle with a spectrophotometer over 30 months. A random-effects regression model for longitudinal data on all bottles and closure groups found a browning growth trajectory for each closure group. Changes in the wine’s browning behavior at 18 months and 30 months showed that the browning of the wine bottles appeared to slow down later in the storage period, especially for natural corks. The between-bottle variation was the highest for the natural cork. At 30 months, we separated the bottles by the extent of browning and samples were pulled from the high, mid, and low levels of browning levels for each closure. The degree of browning is inversely correlated with free SO₂ levels ranging from 5 to 12 mg/L. However, a Quantitative Descriptive Analysis (QDA™) sensory panel could not detect any difference in their aroma and flavor profile between closure types regardless of browning level. Even low levels of free SO₂ retain protection against strong oxidation aromas, and visual browning detected by spectrophotometer seemed to precede oxidative aroma and flavor changes of the aging Sauvignon blanc.

Cross Contamination of 2,4,6-Trichloroanisole in Cork Stoppers

Cork stoppers are the preferred choice for sealing bottled wines around the world. However, the quality of cork stoppers is also defined by the presence of 2,4,6-trichloroanisole (TCA), which gives the wine an unpleasant moldy/musty taste. It is a matter of concern for both cork stopper manufacturers and wine producers whether TCA can be transported between stoppers. As little is known about cross contamination between stoppers, this work provides enough experimental data to discuss the extent of TCA transfer in naturally contaminated stoppers in the liquid and gas phase that can be useful to the cork industry and the wine industry. We found that when a clean stopper is soaked together with a contaminated one in hydro-alcoholic solution, 12% of the TCA can be transferred. In gas-phase contamination, only stoppers with 12 ng/L, or more, contaminate clean stoppers when enclosed together for several days. In a second experiment, where clean corks were exposed to a controlled contaminated environment, it was found that TCA contamination was not confined to the outermost layer of the stoppers. Based on these findings, some recommendations are given to prevent TCA cross contamination between stoppers during the cork stopper manufacturing, storage, wine making, and bottling.

The Compressive Behavior and Crashworthiness of Cork: A Review

Cork, a natural material from renewable resources, is currently attracting increasing interest in different industrial fields because of its cellular structure and the presence of the flexible suberin as its main chemical component. In an agglomerated form, it proved to be a compelling product not only as a thermal and acoustic insulator, but also as core material in sandwich structures and as a liner or padding in energy absorbing equipment. From this perspective, the assessment of its compressive response is fundamental to ensure the right out-of-plane stiffness required to a core material and the proper crashworthiness in the safety devices. Considering the complex nature of cork and the resulting peculiar compressive response, the present review article provides an overview of this paramount property, assessing the main parameters (anisotropy, temperature, strain rate, etc.) and the peculiar features (near-zero Poisson’s ratio and unique dimensional recovery) that characterize it in its natural state. Furthermore, considering its massive exploitation in the agglomerated form, the design parameters that allow its compressive behavior to be tailored and the operating parameters that can affect its crashworthiness were assessed, reporting some potential industrial applications.

Bottle Aging and Storage of Wines: A Review

Wine is perhaps the most ancient and popular alcoholic beverage worldwide. Winemaking practices involve careful vineyard management alongside controlled alcoholic fermentation and potential aging of the wine in barrels. Afterwards, the wine is placed in bottles and stored or distributed in retail. Yet, it is considered that wine achieves its optimum properties after a certain storage time in the bottle. The main outcome of bottle storage is a decrease of astringency and bitterness, improvement of aroma and a lighter and more stable color. This is due to a series of complex chemical changes of its components revolving around the minimized and controlled passage of oxygen into the bottle. For this matter, antioxidants like sulfur oxide are added to avoid excessive oxidation and consequent degradation of the wine. In the same sense, bottles must be closed with appropriate stoppers and stored in adequate, stable conditions, as the wine may develop unappealing color, aromas and flavors otherwise. In this review, features of bottle aging, relevance of stoppers, involved chemical reactions and storage conditions affecting wine quality will be addressed.

Cork powder as a new natural and sustainable fining agent to reduce negative volatile phenols in red wine

In red winemaking, especially those aged in wood barrels, the contamination and growth of Dekkera/Brettanomyces yeasts results in the formation of 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG). These volatile phenols (VPs) are responsible for negative aromatic notes like horsy, barnyard, smoky and medicine, decreasing significantly red quality and its commercial value. In this work, cork powder waste was especially prepared and used to remove these negative volatile phenols (4-EP and 4-EG) from spiked red wine. The optimisation of cork powder performance by removal of dichloromethane and ethanol cork extractives, air removal and ethanol impregnation, allowed to obtain 41 to 62% of 4-ethylphenol and 50 to 53% of 4-ethylguaiacol removal from VPs spiked red wine applied at 250 g/hL. There was no significant impact on phenolic acids and monomeric anthocyanins, although being observed a decrease in the headspace aroma abundance (40%). This optimised cork powder allowed to decrease significantly the wine negative phenolic character, bitterness and astringency, recovering the positive fruity and floral sensory attributes. Results show that optimised cork powder can be a good solution for VPs removal, presenting a great potential to be a new oenological fining agent, contributing to the wine industry sustainability.

Modified method combining in situ detoxification with simultaneous saccharification and cofermentation (SSCF) as a single step for converting exploded rice straw into ethanol

This paper reports an improved fermentation process that includes simultaneous saccharification, detoxification, and cofermentation as steps for producing bioethanol. Rice straw was first steam exploded (SE) or butanone solution exploded (BSE) and then cofermented with Saccharomyces cerevisiae and Candida shehatae. To overcome the inhibitors, the exploded rice straw was continuously and slowly introduced into a 10 L ventilated fermenter. When the fermentation conditions were set to 1.0% initial dry matter, 10% total dry matter, addition rate of 120 mg/min, total fermentation time of 234 h, and dose of 0.1% (NH4)2SO4, yields of 25.8 g/100 g of dry matter ethanol and 88% total sugar use were obtained for BSE rice straw. The ethanol yields were not significantly different between detoxified materials and non-detoxified materials. Most of the furfural, hydroxymethylfurfural (5-HMF), acetic acid, and butanone were removed during the fermentation of non-detoxified materials, and the sugar concentrations were very low. The in situ detoxification and fermentation was effective and inexpensive when the pre-detoxification of exploded materials and the pre-adaptation of strains steps were omitted.