A sensitive method for determination of allergenic fragrance terpene hydroperoxides using liquid chromatography coupled with tandem mass spectrometry

First time β-farnesene production by the versatile bacterium Cupriavidus necator

Background

Terpenes are remarkably diverse natural structures, which can be formed via two different pathways leading to two common intermediates. Among those, sesquiterpenes represent a variety of industrially relevant products. One important industrially produced product is β-farnesene as a precursor for a jet fuel additive. So far, microbial terpene production has been mostly limited to known production hosts, which are only able to grow on heterotrophic substrates.

Results

In this paper, we for the first time describe β-farnesene production by the versatile bacterial host Cupriavidus necator on fructose, which is known to grow hetero- and autotrophically and even in bioelectrochemical systems. We were able to show a growth-dependent production of β-farnesene by expressing the β-farnesene synthase from Artemisia annua in C. necator H16 PHB^-4. Additionally, we performed a scale-up in a parallel reactor system with production titers of 26.3 ± 1.3 µM β-farnesene with a fed-batch process.

Conclusions

The β-farnesene production titers reported in this paper are not in the same range as titers published with known heterotrophic producers E. coli or S. cerevisiae. However, this proof-of-principle study with C. necator as production host opens new synthesis routes toward a sustainable economy and leaves room for further optimizations, which have been already performed with the known production strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01562-x.

Rapid analysis of fragrance allergens by dielectric barrier discharge ionization mass spectrometry

RATIONALE

Fragrances are organic compounds with pleasant odors that are widely used in every aspect of our daily life; some fragrance ingredients can cause allergic reactions. Hence, the qualitative and quantitative analysis of fragrance allergens can prevent consumers coming into contact with these compounds. In this study, we evaluated the ability of a dielectric barrier discharge ionization (DBDI) source for analyzing allergens that occur in fragrances.

METHODS

A home-built liquid-infusion device was used to evaporate the liquid samples. An active capillary plasma ionization source, which is based on a dielectric barrier discharge, was used to ionize the analytes. Mass spectra were acquired in positive ion mode with an LTQ Orbitrap mass spectrometer.

RESULTS

Seven typical fragrance allergens were analyzed in this study. The limits of detections (LODs) were as low as 0.0001 ppm and a linear dynamic range of 2-3 orders of magnitude was achieved. Allergens in five different perfume products were successfully analyzed and quantified by this method, with analysis times of less than 1 min per sample.

CONCLUSIONS

This work introduces a DBDI-MS-based analytical method for detecting and quantifying fragrance allergens. Since DBDI has the advantages of high sensitivity, simple operation and fast analysis time, it is very suitable for the rapid analysis of trace allergens in fragrances, and could easily be used for quality control of consumer products in the cosmetics market.

Rapid Spectrophotometric Method for Assessing Hydroperoxide Formation from Terpenes in Essential Oils upon Oxidative Conditions

Essential oils are widely used in the food and cosmetics industry as natural flavoring and fragrance substances. For this reason, a thorough quality control applying selected analytical methods is required. Oxidation along with hydroperoxide formation is an important drawback during production and storage of essential oils. Hydroperoxides constitute the main products formed upon photo-oxidation of essential oils. Due to hydroperoxide instability, gas chromatography (GC) and high-performance liquid chromatography (HPLC) analyses are required. According to the European Pharmacopoeia, titration is the official method for oxidation assessment. However, this analysis is time-consuming, and large sample quantities are required. Here, we present a simple and accurate spectrophotometric method for the detection of peroxide trace amounts in essential oils and terpenes. The principle is based on the formation of Wurster's red, which is enforced by the peroxide-driven oxidation of N,N-dimethyl-p-phenylenediamine dihydrochloride (DMPD). The method was validated using dibenzoyl peroxide (DBP) and cumene hydroperoxide (CHP). To demonstrate the suitability of the method for routine analysis, various oxidized terpenes and essential oils were chosen. Moreover, photo- and thermal oxidation experiments were compared and evaluated using gas chromatography/mass spectrometry (GC/MS) and a synthesized limonene-2-hydroperoxide (Lim-2-OOH) reference standard to gather detailed information on the structural changes of the respective terpenes.

Reconsidering Hydrosols as Main Products of Aromatic Plants Manufactory: The Lavandin (Lavandula intermedia) Case Study in Tuscany

: The present work evaluates for the first time two Lavandin (Lavandula × intermedia Emeric ex Loisel.) aromatic waters obtained from different plant organs, the flowers and the stems. Both extracts were analysed by GC-MS, which indicates semi-quantitative differences between the major metabolites including linalool, 1,8-cineole, camphor, linalyl acetate and 4-terpineol. ¹H-NMR and LC-MS investigation confirmed the presence of these compounds. Moreover, behavioural tests with the food insect pest Tribolium confusum (Coleoptera Tenebrionidae) showed a good repellency for both hydrosols extracts with RD₅₀ values of 3.6 and 3.3 µL cm^-2 for the flowers and stems, respectively; at the higher concentrations, however, the hydrosol extract from the flowers is expected to be more effective than the one from the stems. The effect of the flowers and stems aromatic water of Lavandin on seed germination of Raphanus sativus was also evaluated. Results showed that seed germination was completely inhibited by flowers hydrolate, having a possible application as natural herbicide. The overall experience with these Lavandin extracts indicates the potential of improved hydrolates to become the main distillation products, rather than by-products, of the aromatic plants manufacturing; this stimulates further discussions about the potential positive impacts that such a shift could have in the context of ecopharmacognosy.

Anti-inflammatory and anti-cancer activity of citral: Optimization of citral-loaded solid lipid nanoparticles (SLN) using experimental factorial design and LUMiSizer®

Essential oils containing monoterpenes are widely used in pharmaceuticals and cosmetic products on account of their wide range of bioactive properties (including anti-cancer activity). Two monoterpenes (citral and geraniol) were firstly tested for their anti-inflammatory activity in a RAW 264.7 cell line, demonstrating citral to have enhanced capacity to inhibit NO production (ca. 84% for citral and 52% for geraniol at the lowest tested concentration of 5 µg/ml). As citral showed higher NO inhibitory activity than geraniol, to measure the level of cytotoxicity of citral, AlamarBlue reduction assay was run in two cell models (non-tumoral HaCaT and tumoral A431). Citral exhibited a strong cytotoxic effect in both cell lines, i.e. cell viability lower that 10% after 24 h exposure at 100 µg/ml of monoterpene. An optimized solid lipid nanoparticles (SLNs) formulation for citral was further developed by design of experiments (2² factorial design), followed by accelerated stability testing (LUMiSizer®). An optimal SLN composed of 1 wt% of citral, 4 wt% of lipid and 2.5 wt% surfactant were successfully produced by hot high pressure homogenization (hot HPH) showing a mean particle size (Z-Ave) of 97.7 nm and polydispersity index of 0.249. The produced formulations were analyzed in a high-end dispersion analyzer LUMiSizer® to characterize any demixing phenomena, demonstrating to be long-term stable at room temperature (25 °C), exhibiting very low instability indices (0.032 after production and 0.042 after one month of storage).

Fragrance contact allergens in 5588 cosmetic products identified through a novel smartphone application

BACKGROUND

More than 25% of the adult European population suffers from contact allergy, with fragrance substances recognized as one of the main causes. Since 2005, 26 fragrance contact allergens have been mandatory to label in cosmetic products within the EU if present at 10 ppm or above in leave-on and 100 ppm or above in wash-off cosmetics.

OBJECTIVE

To examine exposure, based on ingredient labelling, to the 26 fragrances in a sample of 5588 fragranced cosmetic products.

METHODS

The investigated products were identified through a novel, non-profit smartphone application (app), designed to provide information to consumers about chemical substances in cosmetic products. Products registered through the app between December 2015 and October 2016 were label checked according to International Nomenclature of Cosmetic Ingredients (INCI) for the presence of the 26 fragrance substances or the wording 'fragrance/parfum/aroma'.

RESULTS

The largest product categories investigated were 'cream, lotion and oil' (n = 1192), 'shampoo and conditioner' (n = 968) and 'deodorants' (n = 632). Among cosmetic products labelled to contain at least one of the 26 fragrances, 85.5% and 73.9% contained at least two and at least three of the 26 fragrances, respectively. Linalool (49.5%) and limonene (48.5%) were labelled most often among all investigated products. Hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC/Lyral^® ) was found in 13.5% of deodorants. Six of the 26 fragrance substances were labelled on less than one per cent of all products, including the natural extracts Evernia furfuracea (tree moss) and Evernia prunastri (oak moss). A total of 329 (5.9%) products had one or more of the 26 fragrance substances labelled but did not have 'parfum/fragrance/aroma' listed on the label.

CONCLUSIONS

Consumers are widely exposed to, often multiple, well-established fragrance contact allergens through various cosmetic products intended for daily use. Several fragrance substances that are common causes of contact allergy were rarely labelled in this large sample of cosmetic products.

Oxidized limonene and oxidized linalool - concomitant contact allergy to common fragrance terpenes

BACKGROUND

Limonene and linalool are common fragrance terpenes. Both oxidized R-limonene and oxidized linalool have recently been patch tested in an international setting, showing contact allergy in 5.2% and 6.9% of dermatitis patients, respectively.

OBJECTIVE

To investigate concomitant reactions between oxidized R-limonene and oxidized linalool in consecutive dermatitis patients.

METHODS

Oxidized R-limonene 3.0% (containing limonene hydroperoxides 0.33%) and oxidized linalool 6% (linalool hydroperoxides 1%) in petrolatum were tested in 2900 consecutive dermatitis patients in Australia, Denmark, Singapore, Spain, Sweden, and the United Kingdom.

RESULTS

A total of 281 patients reacted to either oxidized R-limonene or oxidized linalool. Of these, 25% had concomitant reactions to both compounds, whereas 29% reacted only to oxidized R-limonene and 46% only to oxidized linalool. Of the 152 patients reacting to oxidized R-limonene, 46% reacted to oxidized linalool, whereas 35% of the 200 patients reacting to oxidized linalool also reacted to oxidized R-limonene.

CONCLUSIONS

The majority of the patients (75%) reacted to only one of the oxidation mixtures, thus supporting the specificity of the reactions. The concomitant reactions to the two fragrance allergens suggest multiple sensitizations, which most likely reflect the exposure to the different fragrance materials in various types of consumer products. This is in accordance with what is generally seen for patch test reactions to fragrance materials.

Air-oxidized linalool elicits eczema in allergic patients - a repeated open application test study

BACKGROUND

Linalool is a commonly used fragrance terpene that forms potent sensitizers upon oxidation. In a recent multicentre study, we found that 7% of 2900 patients showed positive patch test reactions to oxidized linalool at 6.0%. No elicitation studies have been performed.

OBJECTIVE

To identify threshold concentrations for elicitation of allergic contact dermatitis caused by oxidized linalool in allergic individuals with repeated exposures.

METHODS

Repeated open application tests were performed in 6 participants previously diagnosed with contact allergy to oxidized linalool. Creams containing 3.0%, 1.0% and 0.30% oxidized linalool (corresponding to 0.56%, 0.19% and 0.056% linalool hydroperoxides, respectively) and 'fine fragrance' containing 1.0%, 0.30% and 0.10% oxidized linalool (corresponding to 0.19%, 0.056% and 0.019% linalool hydroperoxides, respectively) were used twice daily for up to 3 weeks. Patch testing with a dilution series of oxidized linalool was performed.

RESULTS

Five of 6 participants reacted to the cream containing 3% oxidized linalool. With 1% oxidized linalool, a reaction was seen in 3 (cream) and 4 (fine fragrance) participants, respectively. With 0.3% oxidized linalool, 2 (cream) and 1 (fine fragrance) participants reacted.

CONCLUSION

Repeated exposure to low concentrations of oxidized linalool can elicit allergic contact dermatitis in previously sensitized individuals.