Elsevier

Food Chemistry

Volume 187, 15 November 2015, Pages 112-119
Food Chemistry

Ability of human oral microbiota to produce wine odorant aglycones from odourless grape glycosidic aroma precursors

https://doi.org/10.1016/j.foodchem.2015.04.068Get rights and content

Highlights

  • Human oral microbiota can hydrolyse grape glycosidic precursors releasing odorant compounds.

  • This ability is bacteria-dependent.

  • The generated odorant profile was different among individuals.

Abstract

Grape aroma precursors are odourless glycosides that represent a natural reservoir of potential active odorant molecules in wines. Since the first step of wine consumption starts in the oral cavity, the processing of these compounds in the mouth could be an important factor in influencing aroma perception. Therefore, the objective of this work has been to evaluate the ability of human oral microbiota to produce wine odorant aglycones from odourless grape glycosidic aroma precursors previously isolated from white grapes. To do so, two methodological approaches involving the use of typical oral bacteria or the whole oral microbiota isolated from human saliva were followed. Odorant aglycones released in the culture mediums were isolated and analysed by HS–SPME–GC/MS. Results showed the ability of oral bacteria to hydrolyse grape aroma precursors, releasing different types of odorant molecules (terpenes, benzenic compounds and lipid derivatives). The hydrolytic activity seemed to be bacteria-dependent and was subject to large inter-individual variability.

Introduction

The aromatic profile of many wines depends on the varietal compounds of the grapes that have been employed in their production. These varietal compounds can be present in grapes as free volatile compounds and, in much higher concentrations, as aroma precursors (Baumes, 2009). Among them, non-volatile sugar-bound conjugates are odourless molecules which represent a natural reservoir of odorant compounds in wines, which can be naturally and slowly released during wine ageing, or intentionally released by using oenological enzymes during winemaking. The volatile compounds that could be released from glycosidic aroma precursors are mainly terpenes, C13 norisoprenoids, benzenic derivatives, volatile phenols and C6 compounds (Baumes, 2009). These compounds are generally potent flavour compounds characterised by low odour thresholds and interesting sensory properties (Maicas & Mateo, 2005). For example, terpenes could provide floral notes that are characteristic of some grape varieties such as Muscat (Etievant, 1991).

Although the composition of wine aroma (both, free and conjugate forms) and its impact on orthonasal aroma has been extensively studied (Escudero et al., 2007, Ferreira et al., 2000, Grosch, 1997, Guth, 1997, Rapp, 1998, Sarry and Gunata, 2004), the mechanisms involved in retronasal aroma released during wine consumption and its impact on aroma perception have received very little attention. Besides the wine matrix composition or the physicochemical characteristics of the aroma compounds, other factors that can affect retronasal aroma might be dependent on human physiological parameters (oral microbiota, saliva composition, oral mucosa, temperature, in-mouth air cavity volume changes, etc.). Among these physiological factors, the influence of saliva on aroma release from wine has been recently evaluated (Genovese et al., 2009, Muñoz-González et al., 2014). Moreover, some in vitro studies with human saliva have demonstrated the role of salivary enzymes (β-glycosidases, esterases, etc.) in the degradation of free aroma volatiles (Buettner, 2002a, Buettner, 2002b, Lasekan, 2013). In addition, oral microbiota could be an important parameter influencing retronasal aroma. In fact, the ability of some oral anaerobic bacteria to hydrolyse odourless cysteine-S-conjugates from onion, bell pepper and grapes into their corresponding odorant thiols has previously been reported (Starkenmann et al., 2008), which might be related to a delay in aroma perception, as was already observed by Peynaud (1996) after the consumption of Golden Sauvignon grapes. The microbiota composition of two types of saliva from obese and normal individual was characterised, although its role on aroma was only indirectly assessed (Piombino et al., 2014). More recently, the ability of human salivary enzymes to release free volatile phenols from the corresponding glycosylated phenols has been shown (Mayr et al., 2014), although exactly what role the oral microbiota play in this remains uncertain.

Oral microbiota is one of the most complex bacterial communities associated with the human body and it is formed by more than 700 bacterial species (Tian et al., 2010). These micro-organisms can be present in the saliva or they can adhere to oral surfaces and form an organised multispecies communities known as biofilms (Kuramitsu, He, Lux, Anderson, & Shi, 2007). The main sources of nutrients for oral microbiota include saliva, crevicular fluid, and host diet. Although saliva is the main nutrient source, due to its chemical composition and continuous production, food is rich in a wide variety of components, which could be used by the microbiota to generate secondary products. The relatively short residence time of wine within the oral cavity might suggest a limited effect of oral microbiota on wine aroma perception. However, results from recent research (Muñoz-González, Martín-Álvarez, Moreno-Arribas, & Pozo-Bayon, 2014), suggest a possible interaction of some wine matrix non-volatile compounds with oral and pharyngeal mucosa, which might increase the residence time of aroma precursors and free aroma compounds in the oral/pharyngeal cavities, thus, increasing their susceptibility to oral parameters (saliva, oral microbiota, etc.). Moreover, the fact that during an in vivo consumption situation, wine is continuously replenished in the oral cavity makes viable the idea that oral microbiota might have an influence on wine aroma perception.

To our knowledge, the transformation of wine odourless glycosidic aroma precursors into odorant aglycones by human microbiota is unstudied. To check this hypothesis, a glycosidic precursor extract isolated from white grapes was incubated with representative oral bacteria species and with human oral microbiota isolated from human saliva, thereby considering the complexity of the whole oral microbiota. Odorant aglycones were isolated from the cultures and analysed by HS–SPME–GC/MS, and chemometric tools were applied, in order to gain insight into the effect of different experimental factors (bacteria type, growing requirements, incubation time, saliva treatment, intra/inter-individual differences) on the ability of oral bacteria to hydrolyse wine glycosidic aroma precursors.

Section snippets

Reagents and solvents

Solvents (ethanol, dicloromethane, pentane, ethyl acetate and methanol) were obtained from Merck (Darmstadt, Germany) and LabScan (Gliwice, Poland). Pure water was obtained from a Milli-Q purification system (Millipore, Bedford, MA, USA). Sodium chloride, sodium phosphate dibasic, sodium phosphate monobasic monohydrate and Octyl-β-d-glucopyranoside were provided by Panreac (Barcelona, Spain) and Sigma–Aldrich (Steinheim, Germany).

Preparation of white grape precursor extract

Methodologies based on the protocol already published by

Results and discussion

The ability of human oral microbiota to hydrolyse odourless glycosidic aroma precursors was studied using two different approaches. In the first one, in vitro experiments with representative bacteria isolated from the oral cavity were performed (experiment 1), while the second approach consisted of ex vivo experiments using the whole oral microbiota isolated from the saliva of three individuals (experiment 2). The main results are explained in the following sections.

Conclusions

In summary, in this study the ability of oral microbiota to release varietal aroma compounds from odourless grape glycosides has been proven. This capacity is bacteria-dependent and related to their growth requirements. Another important finding of this work was the fact that odorant aglycones were only produced during the incubation of the aroma precursor extract with oral microbiota isolated from fresh saliva samples, but odorant release was not produced when the incubation was performed with

Acknowledgements

We sincerely thank the volunteers for their participation in this study. This work was funded by the MINECO (Spanish National Project AGL2012-40172-C02-01) and the Comunidad de Madrid – Spain (ALIBIRD-CM S2013/ABI-2728) Project. C. Muñoz-González and C. Cueva would like to thank the European Social Fund and JAE-pre Programme (CSIC) and the ‘Técnicos de Apoyo’ MINECO Programme and the CSIC Intramural Project 201270E065, for their research contracts, respectively.

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