Volatile composition and sensory properties of Vanilla × tahitensis bring new insights for vanilla quality control

Molecular Aroma Composition of Vanilla Beans from Different Origins

The demand for natural Vanilla has increased rapidly, creating the need for more potential sources of high-quality Vanilla essence. Understanding the geographical influences on the aroma profile of Vanilla is essential. This study demonstrates the first comparative analysis of odorant compositions in the three most important Vanilla varieties: Vanilla planifolia, Vanilla pompona, and Vanilla tahitensis from different origins. Following the screening for odor-active molecules through gas chromatography-olfactometry and aroma extract dilution analysis (GC-O and AEDA), selected compounds were quantified using stable isotope dilution assays (SIDA) and their dose over threshold values (DoTs) were calculated. Vanillin was confirmed as the most important odor-active compound due to its highest DoT value, especially in the V. planifolia sample. Meanwhile, 4-methoxybenzyl alcohol and 4-methoxybenzaldehyde showed higher DoT factors than vanillin in V. pompona and partially in V. tahitensis samples. This indicates their role as discriminative odorants for these varieties. The heightened DoT values of 3-hydroxy-4,5-dimethyl-2(5H)-furanone in Uganda Vanilla samples unveil geographical influences on the odorant profile within V. planifolia species. Additionally, 2-methyl-3-(methyldithio)furan was identified for the first time in Vanilla samples with diverse DoT values from different species and origins.

Comprehensive metabolome characterization of leaves, internodes, and aerial roots of Vanilla planifolia by untargeted LC-MS and GC × GC-MS

INTRODUCTION

Untargeted metabolomics is a powerful tool that provides strategies for gaining a systematic understanding of quantitative changes in the levels of metabolites, especially when combining different metabolomic platforms. Vanilla is one of the world's most popular flavors originating from cured pods of the orchid Vanilla planifolia. However, only a few studies have investigated the metabolome of V. planifolia, and no LC-MS or GC-MS metabolomics studies with respect to leaves have been performed.

OBJECTIVE

The aim of the study was to comprehensively characterize the metabolome of different organs (leaves, internodes, and aerial roots) of V. planifolia.

MATERIAL AND METHODS

Characterization of the metabolome was achieved using two complementary platforms (GC × GC-MS, LC-QToF-MS), and metabolite identification was based on a comparison with in-house databases or curated external spectral libraries.

RESULTS

In total, 127 metabolites could be identified with high certainty (confidence level 1 or 2) including sugars, amino acids, fatty acids, organic acids, and amines/amides but also secondary metabolites such as vanillin-related metabolites, flavonoids, and terpenoids. Ninty-eight metabolites showed significantly different intensities between the plant organs. Most strikingly, aglycons of flavonoids and vanillin-related metabolites were elevated in aerial roots, whereas its O-glycoside forms tended to be higher in leaves and/or internodes. This suggests that the more bioactive aglycones may accumulate where preferably needed, e.g. for defense against pathogens.

CONCLUSION

The results derived from the study substantially expand the knowledge regarding the vanilla metabolome forming a valuable basis for more targeted investigations in future studies, e.g. towards an optimization of vanilla plant cultivation.

The isolation and identification of Bacillus velezensis ZN-S10 from vanilla (V. planifolia), and the microbial distribution after the curing process

The market value of vanilla beans (Vanilla planifolia) is constantly increasing due to their natural aroma and flavor properties that improve after a curing process, where bacteria colonization plays a critical role. However, a few publications suggest that bacteria play a role in the curing process. Hence, this study aimed to isolate Bacillus sp. that could be used for fermenting V. planifolia while analyzing their role in the curing process. Bacillus velezensis ZN-S10 identified with 16S rRNA sequencing was isolated from conventionally cured V. planifolia beans. A bacteria culture solution of B. velezensis ZN-S10 (1 mL of 1 × 107 CFU mL-1) was then coated on 1 kg of non-cured vanilla pods that was found to ferment and colonize vanilla. PCA results revealed distinguished bacterial communities of fermented vanilla and the control group, suggesting colonization of vanilla. Phylogenetic analysis showed that ZN-S10 was the dominant Bacillus genus member and narrowly correlated to B. velezensis EM-1 and B. velezensis PMC206-1, with 78% and 73% similarity, respectively. The bacterial taxonomic profiling of cured V. planifolia had a significant relative abundance of Firmicutes, Proteobacteria, Cyanobacteria, Planctomycetes, and Bacteroidetes phyla according to the predominance. Firmicutes accounted for 55% of the total bacterial sequences, suggesting their colonization and effective fermentation roles in curing vanilla.

The multi-faceted food odorant 4-methylphenol selectively activates evolutionary conserved receptor OR9Q2

4-Methylphenol is a food-related odor-active volatile with a high recognition factor, due to its horse stable-like, fecal odor quality. Its ambivalent hedonic impact as key aroma compound, malodor, and semiochemical has spurred the search for its cognate, chemosensory odorant receptors across species. A human odorant receptor for the highly characteristic 4-methylphenol has been elusive. Here, we identified and characterized human receptor OR9Q2 to be tuned to purified 4-methylphenol, but not to its contaminant isomer 3-methylphenol. This highly selective function of OR9Q2 complements an exclusive phenol detection gap in the ancient, most broadly tuned human odorant receptor OR2W1. Moreover, a 4-methylphenol function is evolutionary conserved in phylogenetically related OR9Q2 orthologs from chimpanzee, mouse, and cow. Notably, the cow receptor outperformed human OR9Q2 10-fold in signal strength, consonant with previous reports of 4-methylphenol as a bovine pheromone. Our results suggest OR9Q2 as best sensor for the key food odorant, malodor, and semiochemical 4-methylphenol.

Effects of Different Extraction Methods on Vanilla Aroma

To establish the analytic conditions for examining the aroma quality of vanilla pods, we compared different extraction methods and identified a suitable option. We utilized headspace solid-phase microextraction (HS-SPME), steam distillation (SD), simultaneous steam distillation (SDE) and alcoholic extraction combined with gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS) to identify volatile components of vanilla pods. A total of 84 volatile compounds were identified in this experiment, of which SDE could identify the most volatile compounds, with a total of 51 species, followed by HS-SPME, with a total of 28 species. Ten volatile compounds were identified by extraction with a minimum of 35% alcohol. HS-SPME extraction provided the highest total aroma peak areas, and the peak areas of aldehydes, furans, alcohols, monoterpenes and phenols compounds were several times higher than those of the other extraction methods. The results showed that the two technologies, SDE and HS-SPME, could be used together to facilitate analysis of vanilla pod aroma.

Agonistic/antagonistic properties of lactones in food flavors on the sensory ion channels TRPV1 and TRPA1

Flavor compounds provide aroma and sensations in the oral cavity. They are not present alone in the oral cavity, but rather in combination with several other food ingredients. This study aimed to clarify the relationship between the mixing of pungent flavor compounds and the response of pungent receptors, TRPV1 and TRPA1 channels. We focused on lactones that activate TRPV1 despite their presence in bland foods, such as dairy products and fruits, and analyzed their interaction with receptors using TRPV1- and TRPA1-expressing HEK293 cells. We found that γ-octalactone, γ-nonalactone, and δ-nonalactone activated TRPA1. When mixed with pungent components, some γ- and δ-lactones inhibited capsaicin-mediated TRPV1 responses, and δ-dodecalactone inhibited allyl isothiocyanate-mediated TRPA1 responses. Furthermore, the dose-response relationship of capsaicin and γ-nonalactone to TRPV1 suggests that γ-nonalactone acts as an agonist or antagonist of TRPV1, depending on its concentration. Conversely, γ-nonalactone and δ-dodecalactone were found to act only as agonists and antagonists, respectively, against TRPA1. These results suggest that lactones in foods may not only endow food with aroma, but also play a role in modulating food pungency by acting on TRPV1 and TRPA1. The dose-response relationships of a mixture of flavor compounds with TRPV1 and TRPA1 provide insights into the molecular physiological basis of pungency that may be the cornerstone for developing new spice mix recipes.

Olfactory impact of guaiacol, ortho-vanillin, 5-methyl, and 5-formyl-vanillin as byproducts in synthetic vanillin

To better control the quality of synthetic vanillin obtained by using the guaiacol synthesis method, the olfactory impacts of byproducts on the aroma of the synthetic vanillin samples were evaluated and their optimum concentration ranges were determined. Four byproducts (guaiacol, ortho-vanillin, 5-methyl-vanillin, and 5-formyl-vanillin) were identified by gas chromatography-mass spectrometry (GC-MS) and quantified by gas chromatography-flame ionization detection (GC-FID) in the synthetic vanillin samples with different degrees of purity. The aroma intensities (AIs) of the four byproducts obtained by gas chromatography-olfactometry (GC-O) were: guaiacol (AI: 3.5-4.0, smoke), ortho-vanillin (AI: 1.6-2.5, almond), 5-methyl-vanillin (AI: 2.5-3.3, aldehyde), and 5-formyl-vanillin (AI: 3.2-3.8, green). The aroma perceptual interactions of the four byproducts and the vanillin in the synthetic vanillin samples were determined by S-curve analysis. Guaiacol and 5-methyl-vanillin showed synergistic effects by Feller's additive model. Combined with the results of an addition experiment, when the contents of guaiacol, ortho-vanillin, 5-methyl-vanillin, and 5-formyl-vanillin were within 50, 10, 400, and 1,000 mg/kg respectively, the byproducts had no effects on the aroma quality of the synthetic vanillin samples. PRACTICAL APPLICATION: Synthetic vanillin is one of the most commonly used food additives. Currently, the purity of synthetic vanillin can reach 99.9%, but trace byproducts are still present. Continuing to improve the purity of synthetic vanillin will significantly increase its production costs. Therefore, it is necessary to determine whether the presence of these byproducts affects the aroma quality of the synthetic vanillin samples or not. If they have a negative effect on its aroma, it will be important to reduce their content. If they have no influence or positive role, there is no need to control the content of these byproducts to very low levels. This study determined the content of the byproducts produced during the synthesis of vanillin by guaiacol glyoxylic acid method, judged the perceptual interaction between the byproducts and the vanillin in the synthetic vanillin samples, and determined the optimum range within which the byproducts had no effects on the aroma quality. This study provides a theoretical basis for improving the aroma quality of synthetic vanillin while controlling the production costs.

New Insights on Volatile Components of Vanilla planifolia Cultivated in Taiwan

Vanilla (Vanilla planifolia) is a precious natural flavoring that is commonly used throughout the world. In the past, all vanilla used in Taiwan was imported; however, recent breakthroughs in cultivation and processing technology have allowed Taiwan to produce its own supply of vanilla. In this study, headspace solid-phase microextraction (HS-SPME) combined with GC-FID and GC-MS was used to analyze the volatile components of vanilla from different origins produced in Taiwan under different cultivation and processing conditions. The results of our study revealed that when comparing different harvest maturities, the composition diversity and total volatile content were both higher when the pods were matured for more than 38 weeks. When comparing different killing conditions, we observed that the highest vanillin percentage was present after vanilla pods were killed three times in 65 °C treatments for 1 min each. From the experiment examining the addition of different strains, the PCA results revealed that the volatiles of vanilla that was processed with Dekkera bruxellensis and Bacillus subtilis was clearly distinguished from which obtained by processing with the other strains. Vanilla processed with B. subtilis contained 2-ethyl-1-hexanol, and this was not detected in other vanillas. Finally, when comparing the vanillin percentage from seven different regions in Taiwan, vanilla percentage from Taitung and Taoyuan Longtan were the highest.

Impact of vanilla origins on sensory characteristics of chocolate

The sensory characteristics of white and milk chocolate with three origins of vanilla (Madagascar, Indonesia, Papua New Guinea) were investigated using a multi-analytical approach. The sensory tests included profiling using Quantitative Descriptive Analysis with a trained panel; Temporal Dominance of Sensations test with untrained respondents from various countries currently residing in Belgium, and the consumers sensory preference test with consumers in Belgium, France, Sweden and Canada. The vanilla extracts were also analyzed by gas chromatography-mass spectrometry (GC-MS) in combination with olfactometry (GC-MS-O) to identify the key aroma compounds in the different vanilla origins. This research shows that sensory profile of Papua New Guinea (PNG) samples is different from Madagascan and Indonesian extracts. The flavor signature was correlated with almondy and anisic descriptors. The perceived difference between Madagascan and Indonesian origins was reduced when assessed within complex matrices such as chocolate. In sugared water, Madagascan vanilla has balsamic, phenolic notes while Indonesian has woodier notes. In a chocolate base, the Indonesian sample lost its woody characteristic for a dairy enhanced characteristic. The botanical variety has more impact on difference in sensory profile of a chocolate than the vanilla origin itself. The sensory data correlates with volatile components identified in this study. Guaiacol and vanillin were identified as the main key aroma compounds in all three vanilla origins using GC-MS-O. Additional key aroma compounds were responsible for the differences in sensory characteristics between the three vanilla origins: anisaldehyde for anisic note in the PNG samples and ethyl 2-methylbutanoate and 3/2-methylbutanoic acid in the Indonesian sample. Sensory profiles of vanillas from various origins were more visible and pronounced in white chocolate compared to milk chocolate. This study gives novel insights to the chocolate, as well as the vanilla sectors, indicating possibilities of vanilla replacement and consumer preferences across Europe and Canada. The consumer study shows that, on average, people do not indicate which chocolate is significantly more liked.

2,4-Decadienal does not induce genotoxic effects in in vivo micronucleus studies

2,4-Decadienal (E,E-) occurs naturally in foods and is also used as a flavoring ingredient. In vivo micronucleus studies were used to evaluate the potential for 2,4-decadienal to cause genotoxic effects. Male Han Wistar rats were dosed either by intraperitoneal injection or by gavage in two independent studies. The animals (12/group) received 25, 50, or 100 mg/kg bw of 2,4-decadienal via intraperitoneal injection, or 350, 700, or 1400 mg/kg bw via gavage. Dose-dependent decreases in the percentages of peripheral blood reticulocytes were observed in both studies, indicating that the target tissue was exposed to toxic levels of 2,4-decadienal. No induction of micronuclei in the bone marrow polychromatic erythrocytes or the peripheral blood reticulocytes was observed in either study. These results, coupled with previous mutagenicity studies, support the overall conclusion that 2,4-decadienal does not present a concern for genotoxicity.

Phenolic Profiling for Traceability of Vanilla ×tahitensis

Vanilla is a flavoring recovered from the cured beans of the orchid genus Vanilla. Vanilla ×tahitensis is traditionally cultivated on the islands of French Polynesia, where vanilla vines were first introduced during the nineteenth century and, since the 1960s, have been introduced to other Pacific countries such as Papua New Guinea (PNG), cultivated and sold as "Tahitian vanilla," although both sensory properties and aspect are different. From an economic point of view, it is important to ensure V. ×tahitensis traceability and to guarantee that the marketed product is part of the future protected designation of the origin "Tahitian vanilla" (PDO), currently in progress in French Polynesia. The application of metabolomics, allowing the detection and simultaneous analysis of hundreds or thousands of metabolites from different matrices, has recently gained high interest in food traceability. Here, metabolomics analysis of phenolic compounds profiles was successfully applied for the first time to V. ×tahitensis to deepen our knowledge of vanilla metabolome, focusing on phenolics compounds, for traceability purposes. Phenolics were screened through a quadrupole-time-of-flight mass spectrometer coupled to a UHPLC liquid chromatography system, and 260 different compounds were clearly evidenced and subjected to different statistical analysis in order to enable the discrimination of the samples based on their origin. Eighty-eight and twenty three compounds, with a prevalence of flavonoids, resulted to be highly discriminant through ANOVA and Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) respectively. Volcano plot analysis and pairwise comparisons were carried out to determine those compounds, mainly responsible for the differences among samples as a consequence of either origin or cultivar. The samples from PNG were clearly different from the Tahitian samples that were further divided in two different groups based on the different phenolic patterns. Among the 260 compounds, metabolomics analysis enabled the detection of previously unreported phenolics in vanilla (such as flavonoids, lignans, stilbenes and other polyphenols).