Theoretical Investigation of Linalool Oxidation

Characterization of Key Odorants in Chardonnay Seeds

Chardonnay marc, a co-product of the winemaking industry, is a combination of skins, seeds, and stems remaining after the juice is pressed from the grapes. This co-product amounts to over half a million tons per year. Recently, Chardonnay marc has been emerging as a healthy and flavorful food ingredient. The aroma contribution of the seeds to the overall aroma of Chardonnay marc remains unknown. In the present study, 43 odorants were identified in Chardonnay seeds employing aroma extract dilution analysis (AEDA) performed on a distillate prepared by solvent extraction and solvent-assisted flavor evaporation (SAFE) distillation. Of those, 6 odorants with a flavor dilution (FD) factor ≥64 were quantitated using stable isotope dilution assays (SIDAs). The odorants included (2E,4E)-deca-2,4-dienal (fatty, OAV 8028), 3-methylnonane-2,4-dione (hay, OAV 4772), (2E,4E)-nona-2,4-dienal (fatty, OAV 1750), hexanal (green, OAV 1481), linalool (floral, citrus, OAV 28), and 2-phenylethanol (floral, rose, OAV 2). An aroma simulation model was prepared based on the quantitative data, and its aroma was a close match to the Chardonnay seed powder. Omission studies applied to the aroma simulation model showed that hexanal and 3-methylnonane-2,4-dione were the key odorants driving the aroma profile. This research established a foundation for future studies aimed at optimizing the flavor of Chardonnay marc powder.

One hundred years of allergic contact dermatitis due to oxidized terpenes: What we can learn from old research on turpentine allergy

Although in recent years the focus on sensitizing terpene oxidation products has been on oxidized limonene and linalool, the autoxidation of terpenes in relation to allergic contact dermatitis is not new and dates back to the early part of the 20th century with the use of turpentine causing occupational contact dermatitis in painters. This review is written in a way as to allow us to get closer to the work of the scientists in earlier days, to participate in the successes, and also to observe the weak points. The researchers concluded that the main culprit in Scandinavian turpentine was Δ³ -carene hydroperoxides. This explains its high sensitizing effect compared with French turpentine which is of the Iberian type with no or only traces of Δ³ -carene. Historical exposure to turpentine showed that ending the industrial exposure stopped the occupational skin sensitization. Patch test studies demonstrated that monoterpene hydroperoxides, far from being an obsolete source of contact allergy solely related to turpentine, is a common cause of contact allergy in the population. A hundred years of extensive chemical and clinical studies worldwide should be sufficient to meet the evidence requirement regarding allergic contact dermatitis caused by terpenes. HIGHLIGHTS: The autoxidation of terpenes in relation to allergic contact dermatitis is not new and dates back to the early part of the 20th century with the use of turpentine. The main culprit in Scandinavian turpentine was Δ³ -carene hydroperoxides. This explains its high sensitizing effect compared with French turpentine with no or only traces of Δ³ -carene. Recent patch test studies demonstrated that monoterpene hydroperoxides, far from being an obsolete source of contact allergy solely related to turpentine, is a common cause of contact allergy in the population.

Influence of Different Dehydration Levels on Volatile Profiles, Phenolic Contents and Skin Hardness of Alkaline Pre-Treated Grapes cv Muscat of Alexandria (Vitis vinifera L.)

A dehydration experiment was carried out on Vitis vinifera L. cv Muscat of Alexandria (synonym Zibibbo) following the process for the production of renowned special dessert wines produced on Pantelleria island (Sicily, Italy). Harvested berries were pre-treated in a sodium hydroxide dipping solution (45 g/L, dipped for 185 s, 25 °C) to accelerate the drying process, rinsed, and dehydrated in simulated conditions (relative humidity 30%, 30 °C temperature, air speed 0.9 m/s). Three dehydration levels were achieved, corresponding to “Passolata”, “Bionda”, and “Malaga” stages (35%, 50%, and 65% of weight loss, respectively) of the Pantelleria denomination of origin (DOC). Grape skin mechanical properties, technological parameters, phenolics, and aroma profile varied considerably during dehydration. The most important aroma compounds for their olfactory impact, such as linalool, geraniol, nerol, and citronellol, especially in glycosylated forms, significantly increased in dried grapes compared to fresh ones, even if aroma profile modification occurred. A decrease in break skin force could have induced higher release of flavonoids. The findings showed relevant changes, allowing winemakers to better select the ratio of fresh and dehydrated grapes in the function of the final desired wine.

Large scale preparation, stress analysis, and storage of headspace volatile condensates from Jasminum sambac flowers

In this study, a large-scale preparation of jasmine floral volatile condensate (FVC) was conducted using fresh flowers without any extraction solvent involvement. Condensate volatile profiles were compared to those of fresh flowers for their scent characteristics and ability to withstand manufacturing and storage. The FVC possessed a typical jasmine flower scent, a similar odor polygon shape and greatly enhanced odor intensity and character odorants linalool, indole, and methyl anthranilate. In late August and September in Fuzhou, China, the ratio of odor activity values for indole/linalool in FVCs was close to that of fresh flowers, indicating that these were suitable local harvest times for FVC preparation. Room temperature storage for 30 months dramatically reduced the abundance of potent odorants and FVC scent intensity, while cold temperature (4 °C) storage was able to maintain FVC clarity and scent intensity. Our findings should be helpful at improving FVC quantity, quality, and storage.

Plant Secondary Metabolite-Derived Polymers: A Potential Approach to Develop Antimicrobial Films

The persistent issue of bacterial and fungal colonization of artificial implantable materials and the decreasing efficacy of conventional systemic antibiotics used to treat implant-associated infections has led to the development of a wide range of antifouling and antibacterial strategies. This article reviews one such strategy where inherently biologically active renewable resources, i.e., plant secondary metabolites (PSMs) and their naturally occurring combinations (i.e., essential oils) are used for surface functionalization and synthesis of polymer thin films. With a distinct mode of antibacterial activity, broad spectrum of action, and diversity of available chemistries, plant secondary metabolites present an attractive alternative to conventional antibiotics. However, their conversion from liquid to solid phase without a significant loss of activity is not trivial. Using selected examples, this article shows how plasma techniques provide a sufficiently flexible and chemically reactive environment to enable the synthesis of biologically-active polymer coatings from volatile renewable resources.

Essential Oil from Sweet Potato Vines, a Potential New Natural Preservative, and an Antioxidant on Sweet Potato Tubers: Assessment of the Activity and the Constitution

Pathogenic fungi and oxidation are the major factors that cause the deterioration of sweet potatoes and also cause the loss of quality that makes consumption unsafe. In the present study, the in vitro results demonstrate that the essential oil from sweet potato vines exhibits significantly enhanced activity compared to that of the control. Furthermore, the essential oil can actively inhibit the growth of some common microorganisms inducing pathogenic bacteria and fungi (inhibition rates above 50% at low concentrations). A total of 31 constituents were identified using GC-MS and confirmed that linalool and p-hydroxybenzoic acid are the major active ingredients. The experiment involving actual tubers showed that the essential oil could retains its quality and effectiveness again the fungus disease. This suggests that it could be used in the food industry to increase the shelf life of stored produce (tubers) to ensure food safety without the use of additives or preservatives.

Preparation, characterization and pharmacokinetic studies of linalool-loaded nanostructured lipid carriers

Context Linalool (LL) is associated with numerous pharmacological activities. However, its poor solubility usually results in poor bioavailability, and further limited its applications. Objective To reduce volatilization and improve bioavailability of LL, linalool-loaded nanostructured lipid carriers (LL-NLCs) were prepared. Materials and methods LL-NLCs were prepared using high-pressure homogenization method and optimized via response surface methodology-central composite design, followed by characterization, including particle size (PS), zeta potential (ZP), transmission electron microscope (TEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and in vitro release study. Rats were administered 300 mg × kg (-) (1) LL with each preparation (LL-NLCs or LL) via oral gavage. Results LL-NLCs had a PS of 52.72 nm with polydispersity index of 0.172, and ZP of -16.0 mV. The encapsulation efficiency and drug loading gave 79.563 and 7.555%, respectively. The cumulative release of LL from free LL reached 51.414% at 180 min, while LL from LL-NLCs was 15.564%. All the pharmacokinetics parameters of LL-NLCs were better than those of LL, including Cmax (from 1915.45 to 2182.45 ng × mL (-) (1)), AUC0-t (from 76003.40 to 298948.46 ng × min × mL (-) (1)) and relative bioavailability (393.34%). The t1/2, MRT and tmax of LL-NLCs (110.50, 146.66 and 60 min) were also longer than that of LL (44.72, 45.66 and 40 min). Discussion and conclusion LL-NLCs were for the first time prepared and its oral administration in rats thoroughly investigated. LL-NLCs exhibited sustained release effect and increased absorption of LL. Therefore, these findings might provide a potential possibility for clinical application of LL.

Kinetic study on the linalool ozonolysis reaction in the atmosphere

In the atmosphere, linalool ozonolysis will generate a series of oxidation products and then form particles through nucleation. In this study, the linalool ozonolysis mechanisms were studied and some of the main products detected from experiment are verified. The Rice–Ramsperger–Kassel–Marcus (RRKM) theory and the canonical variational transition state theory (CVT) with small curvature tunneling effect (SCT) are used to calculate rate constants over the temperature range of 200∼800 K. The total rate constant for the reaction of ozone with linalool is 4.50 × 10−16 cm3 molecule–l s–l, and the addition of ozone to (CH3)2C=CH– is the main ozone addition position. Furthermore, the Arrhenius formulas are fitted and the lifetimes of reaction species in the troposphere are discussed for the first time. The total atmospheric lifetime of linalool relative to O3 is 2.30 h. The O3-initiated atmospheric lifetimes of P1, P3, and P6 are 2.64 months, 16.67 days, and 15.5 h, respectively.

Synthesis of allylic hydroperoxides and EPR spin-trapping studies on the formation of radicals in iron systems as potential initiators of the sensitizing pathway

Many terpenes used as fragrance compounds autoxidize when exposed to air, forming allylic hydroperoxides that have the potential to be skin contact allergens. To trigger the immunotoxicity process that characterizes contact allergy, these hydroperoxides are supposed to bind covalently to proteins in the skin via radical pathways. We investigated the formation of reactive radical intermediates from 7-hydroperoxy-3,7-dimethylocta-1,5-dien-3-ol and 2-hydroperoxylimonene, responsible for the sensitizing potential acquired by autoxidized linalool and limonene. Both compounds were synthesized through new short and reproducible synthetic pathways. The hydroperoxide decomposition catalyzed by Fe(II)/Fe(III) redox systems, playing a key role in degradating peroxides in vivo, was examined by spin-trapping-EPR spectroscopy. Alkoxyl and carbon-centered free radicals derived from the hydroperoxides were successfully trapped by the spin-trap 5,5-dimethyl-1-pyrroline N-oxide, whereas peroxyl radicals were characterized by spin-trapping studies with 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide. Using liquid chromatography combined with mass spectrometry, we demonstrated the formation of adducts, via radical mechanisms induced by Fe(II)/Fe(III), between the hydroperoxides and N-acetylhistidine methyl ester, a model amino acid that is prone to radical reactions. Free radicals derived from these hydroperoxides can thus induce amino acid chemical modifications via radical mechanisms. The study of these mechanisms will help to understand the sensitizing potential of hydroperoxides.

Secondary organic aerosol from ozonolysis of biogenic volatile organic compounds: chamber studies of particle and reactive oxygen species formation

The formation of secondary organic aerosol (SOA) produced from α-pinene, linalool, and limonene by ozonolysis was examined using a dynamic chamber system that allowed the simulation of ventilated indoor environments. Experiments were conducted at typical room temperatures and air exchange rates. Limonene ozonolysis produced the highest SOA mass concentrations and linalool the lowest with α-pinene being intermediate. Simplified empirical modeling simulations were conducted to provide insights into reaction chemistry. Assessment of variability of particle-bound reactive oxygen species (ROS) may be important in the understanding of health effects associated with particulate matter. The ROS intensities defined as ROS/SOA mass were found to be moderately correlated with the SOA densities. Greater ROS intensities were observed for the cases where ozone was in excess. ROS intensities approached a relatively constant value in the region where ozone was in deficit. The estimated initial ROS half-life time was approximately 6.5 h at room temperature suggesting the time sensitivity of ROS measurements. The ROS formed from terpenoid ozonolysis could be separated into three categories: short-lived/high reactive/volatile, semivolatile/relatively stable and nonvolatile/low reactive species based on ROS measurements under various conditions. Such physical characterization of the ROS in terms of reactivity and volatility provides some insights into the nature of ROS.

The Schenck Rearrangement of Allylic Hydroperoxides

It is 50 years since Schenck's discovery of the ubiquitous rearrangement of allylic hydroperoxides, and its unique homolytic mechanism has now been clarified by a combination of experimental and computational methods. The recognised examples of the reaction are surveyed and the way in which the present mechanistic picture has emerged is reviewed. A brief account is given of the closely related Smith epimerisation of allylic hydroperoxides.

Allergic contact dermatitis--formation, structural requirements, and reactivity of skin sensitizers

Contact allergy is caused by a wide range of chemicals after skin contact. Its clinical manifestation, allergic contact dermatitis (ACD), is developed upon repeated contact with the allergen. This perspective focuses on two areas that have yielded new useful information during the last 20 years: (i) structure-activity relationship (SAR) studies of contact allergy based on the concept of hapten-protein binding and (ii) mechanistic investigations regarding activation of nonsensitizing compounds to contact allergens by air oxidation or skin metabolism. The second area is more thoroughly reviewed since the full picture has previously not been published. Prediction of the sensitizing capacity of a chemical is important to avoid outbreaks of ACD in the population. Much research has been devoted to the development of in vitro and in silico predictive testing methods. Today, no method exists that is sensitive enough to detect weak allergens and that is robust enough to be used for routine screening. To cause sensitization, a chemical must bind to macromolecules (proteins) in the skin. Expert systems containing information about the relationship between the chemical structure and the ability of chemicals to haptenate proteins are available. However, few designed SAR studies based on mechanistic investigations of prohaptens have been published. Many compounds are not allergenic themselves but are activated in the skin (e.g., metabolically) or before skin contact (e.g., via air oxidation) to form skin sensitizers. Thus, more basic research is needed on the chemical reactions involved in the antigen formation and the immunological mechanisms. The clinical importance of air oxidation to activate nonallergenic compounds has been demonstrated. Oxidized fragrance terpenes, in contrast to the pure terpenes, gave positive patch test reactions in consecutive dermatitis patients as frequently as the most common standard allergens. This shows the importance of using compounds to which people are exposed when screening for ACD in dermatology clinics.