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Effect of Saliva Esterase Activity on Ester

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Effect of Saliva Esterase Activity on Ester 1 EFFECT OF SALIVA ESTERASE ACTIVITY ON ESTER 2 SOLUTIONS AND POSSIBLE CONSEQUENCES FOR THE IN- 3 MOUTH ESTER RELEASE DURING WINE INTAKE 4 5 María-Pérez-Jiménez, Nuria Rocha-Alcubilla, Maria Ángeles Pozo-Bayón* 6 7 Instituto de Investigación en Ciencias de la Alimentación (CIAL) CSIC-UAM, 8 C/Nicolás Cabrera, 20049, Madrid, Spain. 9 *Corresponding author: [email protected] Tel: 34 91 0017961; Fax: 34 910017905 10 11 Short title: Effect of saliva esterase activity on wine esters 12 1 13 Abstract: 14 The aim of the present study was to investigate the role of saliva esterase activity on 15 carboxylic esters typically associated with pleasant and fruity aromas in wine. For this, 16 ex-vivo experiments using the same fresh and inactivated (without enzymatic activity) 17 human saliva with a mixture of carboxylic esters with different aliphatic chain length 18 (ethyl butanoate, ethyl pentanoate, ethyl hexanoate, ethyl octanoate, ethyl decanoate and 19 isoamyl acetate) were prepared. Liquid-liquid extraction with dichloromethane and GC- 20 MS analysis were applied to the saliva systems in order to determine the reduction in 21 ester content and the formation of their corresponding metabolic products (carboxylic 22 acids) in the saliva systems before and after incubation at 37ºC. In addition, to check if 23 there was a relationship between the susceptibility of esters to saliva hydrolysis and the 24 amount of -in mouth ester release during wine intake, the remaining oral amount of each 25 ester was determined by comparing the intraoral amount immediately after spitting out 26 the wine and four minutes later. Ex -vivo experiments showed ester degradation by 27 saliva esterase enzymes mainly acted on long chain esters (ethyl octanoate and ethyl 28 decanoate), which gave rise to the formation of their corresponding carboxylic acids. 29 Nonetheless, in spite of their higher susceptibility to saliva enzymes, -in vivo 30 experiments showed that long chain carboxylic esters remained in the oral cavity long 31 after swallowing. This confirmed that ester hydrophobicity is closely related to the –in 32 mouth temporal release of these odorants and therefore, behind wine aroma persistence. 33 34 Key words: saliva esterase activity, carboxylic esters, wine, in-mouth aroma release, 35 aroma persistence 36 2 37 Practical applications 38 In wines, esters represent a group of aromatic compounds of great interest since they are 39 linked to pleasant fruity aroma nuances. Today wine consumers are demanding fresh 40 and long persistent fruity aromatic wines. The present research contributes to better 41 understanding the relationship between ester content in the wine and oral aroma release 42 experienced during wine tasting, considering the changes in these compounds during 43 oral processing. This is a necessary step when trying to unravel the factors involved in 44 wine aroma perception and in consumer preferences, and it represents a necessary 45 knowledge in promoting winemaking practices (e.g. the use of selected 46 microorganisms) for improving the type and amount of these aroma compounds in the 47 wine. 48 49 50 51 3 52 1. INTRODUCTION 53 Ethyl esters of volatile acids and higher alcohols acetates are typical wine aroma 54 compounds produced during alcoholic fermentation. Different studies have associated 55 these compounds to the pleasant and fruity character of many types of wines (Escudero, 56 Campo, Fariña, Cacho, & Ferreira, 2007; Francis & Newton, 2005; Rapp & Mandery, 57 1986). In addition, through perceptual interactions, these compounds enhance the 58 perception of fruity aroma even at concentrations below their individual olfactory 59 thresholds (Lytra, Tempere, Le Floch, de Revel, & Barbe, 2013) The fact that most 60 esters are present in concentrations around their threshold values, implies that minor 61 concentration changes might have a dramatic effect on wine flavor. Therefore, a better 62 understanding of ester hydrolysis/synthesis of these compounds in the wine matrix is 63 essential to aid the winemaker in achieving the best possible winemaking outcome 64 (Sumby, Grbin, & Jiranek, 2010). 65 Aditionally, besides their changes in the wine itself, it is interesting to know what 66 happens with these compounds during oral processing and what type of chemical or 67 biochemical transformations might occur before reaching, via the retronasal route, the 68 olfactory receptors during wine tasting. Recently, it was shown, that some wine esters 69 can be adsorbed into the oral mucosa in a relatively large amount (23% to 44% for 70 isoamyl acetate and ethyl hexanoate) after 30 seconds of oral exposure to wine 71 (Esteban-Fernández, Rocha-Alcubilla, Muñoz-González, Moreno-Arribas, & Pozo- 72 Bayón, 2016). However, they are quickly released from oral mucosa and they do not 73 remain in the oral cavity for a long time (Esteban-Fernández, et al., 2016), thus, having 74 a moderated contribution to aroma persistence. One possible explanation could be the 75 weak interactions between these compounds and saliva proteins from the saliva pellicle 76 (Ployon, Morzel, & Canon, 2017). Although there are not -in vivo studies confirming 4 77 this, results from -in vitro studies have shown that hydrophobic interactions can be 78 behind these interactions (Pagès-Hélary, Andriot, Guichard, & Canon, 2014). The 79 presence of other wine matrix compounds such as polyphenols, have also been proven 80 to have a role on the adsorption capacity of some esters to oral mucosa (Esteban- 81 Fernández, Muñoz-González, Jiménez-Girón, Pérez-Jiménez, & Pozo-Bayón, 2018; 82 Esteban-Fernández, et al., 2016). Another plausible explanation could be the oral 83 degradation of esters by some saliva enzymes. 84 Salivary aroma converting enzymes might originate from the salivary glands, oral 85 tissues or even microorganisms (Ployon, et al., 2017). The effect of saliva enzymes on 86 the metabolism of different types of aroma compounds such as thiols, aldehydes, 87 ketones and esters has been shown in different works (Buettner, 2002a, 2002b; Muñoz- 88 González, Feron, Brulé, & Canon, 2018; Pagès-Hélary, et al., 2014). In the case of 89 esters, hydrolysis can be seen as the most probable mechanism as many esterolytic 90 enzymes can be found in human saliva (Buettner, 2002b). Apart from carboxylesterases, 91 other enzymes such as acetylcholinesterase, trypsin, chymotrypsin, carbonic anhydrase, 92 and pseudocholinesterase can exhibit esterase activity (Krisch, 1971; Ployon, et al., 93 2017). The esterolytic activity of saliva was investigated in a previous work (Buettner, 94 2002b). In this work, a reduction in the content of some carboxylic esters (ethyl 95 butanoate, ethyl hexanoate, ethyl octanoate) was observed after ten minutes of 96 incubation in the presence of human saliva, which did not happen when saliva was 97 thermally inactivated. Nonetheless, the corresponding degradation products (carboxylic 98 acids) were not found in the saliva, which the authors explained by the low aroma 99 concentration used in the experiments. In another work, using static headspace 100 conditions, Pages-Hèlary and co-workers (Pagès-Hélary, et al., 2014), also investigated 101 the effect of human saliva on the concentration of a series of carboxylic esters (from 5 102 ethyl butanoate to ethyl heptanoate). They observed a decrease in the headspace 103 concentrations of all of them, although it was not clear whether ester reduction was due 104 to interaction with salivary proteins or to saliva esterase activity. Moreover, the 105 consequence of this effect for -in vivo ester release during food consumption remains 106 uncertain. 107 Because of the outstanding role of esters for many fermented beverages such as wine, 108 and the lack of a clear relationship between the role of esterase enzymes and their effect 109 on wine aroma, this work has two main objectives. Firstly, to evaluate the esterolytic 110 capacity of human saliva on wine aromatic esters associated to fruity aromas through - 111 ex vivo experiments, in which five ethyl esters of volatile acids (ethyl butanoate, 112 pentanoate, hexanoate, octanoate and decanoate) and one higher alcohol acetate 113 (isoamyl acetate), were incubated (at 37ºC) or not in enzymatic (without any treatment) 114 and non-enzymatic pooled saliva (after enzymatic inhibition with CaCl2) from ten 115 individuals. The reduction in esters content and the formation of the corresponding 116 metabolic products (carboxylic acids) was followed by liquid-liquid extraction with 117 dichloromethane and GC-MS analysis. The second objective was to check the -in mouth 118 ester release after the exposure of the oral cavity to an aromatized wine with the same 119 six esters previously tested in the ex-vivo experiments. The rationale for this objective, 120 was to probe if the higher or lower susceptibility of some esters to saliva esterase, might 121 also affect in-mouth ester release. In this case, oral aroma release was monitored 122 immediately after rinsing the mouth and spitting off the wine and then, four minutes 123 later, using the same ten volunteers who donated the saliva samples for the -ex vivo 124 experiments. 125 MATERIALS AND METHODS 6 126 1.1.Saliva samples 127 Unstimulated saliva samples were collected from 10 healthy subjects (4 men and 6 128 women), aged between 21 and 36 years old. All subjects were nonsmokers and had not 129 taken any antibiotics or other medical treatments during at least three months prior to 130 the sampling. Participants were asked not to consume any food or drink two hours 131 before the saliva was collected. They let the saliva naturally accumulate in the mouth 132 and then spat it directly into a collection tube. This fresh saliva collected from all the 133 individuals was pooled together and centrifuged at 2600 g for 15 min at 4 ºC. This 134 mixture of saliva had a protein concentration determined using the Bradford protein 135 assay (Pierce Thermo Scientific, Illinois, USA) of 1,04 mg/mL and a pH of 7,13.
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