R.M. Callejón

Determination of amino acids in grape-derived products: a review.

The amino acids present in foods and beverages affect the quality of these products and they play an important role in enology. Amino acids are consumed by yeasts as a source of nitrogen during alcoholic fermentation and are precursors of aroma compounds. In this review various chromatographic methodologies for the determination of amino acids are described, and specific applications for the analysis of amino acid content are discussed. Amino acids usually need to be derivatized to make them more detectable. Several derivatizing reagents have been employed for the determination of amino acids in enological applications, and each has its advantages and disadvantages.

Comprehensive analysis of chromatographic data by using PARAFAC2 and principal components analysis.

The most straightforward method to analyze an obtained GC-MS dataset is to integrate those peaks that can be identified by their MS profile and to perform a Principal Component Analysis (PCA). This procedure has some important drawbacks, like baseline drifts being scarcely considered or the fact that integration boundaries are not always well defined (long tails, co-eluted peaks, etc.). To improve the methodology, and therefore, the chromatographic data analysis, this work proposes the modeling of the raw dataset by using PARAFAC2 algorithm in selected areas of the GC profile and using the obtained well-resolved chromatographic profiles to develop a further PCA model. With this working method, not only the problems arising from instrumental artifacts are overcome, but also the detection of new analytes is achieved as well as better understanding of the studied dataset is obtained. As a positive consequence of using the proposed working method human time and work are saved. To exemplify this methodology the aroma profile of 36 apples being ripened were studied. The benefits of the proposed methodology (PARAFAC2+PCA) are shown in a practitioner perspective, being able to extrapolate the conclusions obtained here to other hyphenated chromatographic datasets.

Volatile and sensory profile of organic red wines produced by different selected autochthonous and commercial Saccharomyces cerevisiae strains.

Organic wines were produced at pilot scale to select the best autochthonous and commercial yeast strains to obtain wines with high organoleptic qualities. We tested the behaviour of five S. cerevisiae yeast strains and determined their volatile composition and organoleptic characteristics by sensory analysis. A total of 51 volatile compounds were quantified in the wines produced. The concentration of most of the volatile compounds was significantly influenced depending on which yeast strain was inoculated. The differences observed in the volatile composition of the wines appear to be quantitative rather than qualitative. In general, acetals were the most abundant group of volatile compounds in all the samples studied, followed by alcohols without ethanol. The highest contents of volatile compounds were found in two of the wines produced by autochthonous yeast strains. The results obtained in the sensory analysis suggest that autochthonous yeast produced wines of higher organoleptic quality because this sample gave the highest value for the general impression attribute.

Optimization and validation of headspace sorptive extraction for the analysis of volatile compounds in wine vinegars

Quantification of aroma compounds in wine vinegars is challenging due to the complexity of the matrix and the low concentrations expected. A method for the determination of volatile compounds in wine vinegars employing headspace sorptive extraction-thermal desorption-gas chromatography-mass spectrometry (HSSE-TD-GC-MS) was developed. A central composite design was used to optimize the sampling condition. The proposed method was successfully validated and low detection and quantification limits was obtained. The application of the proposed methodology allows the determination of 53 compounds in different wine vinegars (red, Sherry). Five of them have been detected in wine vinegars for the first time.

Defining the Typical Aroma of Sherry Vinegar : Sensory and Chemical Approach

The aroma of the three different classes of Sherry vinegar was evaluated by gas chromatography/mass spectrometry (GC-MS) and gas chromatography/olfactometry (GC-O). GC-O was employed to identify substances responsible for aromatic notes associated with the selected descriptors of the typical aroma of Sherry vinegar and odor activity values (OAV) calculated to measure the single impact effect of different compounds selected by GC-O. Diacetyl, isoamyl acetate, ethyl isobutyrate, isovaleric acid, sotolon, and ethyl acetate reached high OAVs, turning out to be characteristic odor active compounds in Sherry vinegars. A total of 58 compounds were quantified, among them, 7 had not been previously reported in Sherry wine vinegars: ethyl 2-methylbutyrate, ethyl heptanoate, ethyl furoate, and ethyl benzoate, acetophenone, nonanoic acid, and sotolon. Linear discriminant analysis (LDA) reveals that using aroma compounds as variables, we can classify Sherry vinegars with 100% correct scores as different from red wine vinegars.

Effect of barrel design and the inoculation of Acetobacter pasteurianus in wine vinegar production

The traditional production of wine vinegar is a lengthy process with little or no microbiological control. The aim of this study was to shorten the acetification process via three different strategies: changes in wood type; barrel shape; and the inoculation of an Acetobacter pasteurianus pure culture. The barrel shape was modified by constructing two prototypes with higher liquid-air interface. We compared the changes in acetic acid bacteria (AAB) population dynamics in these barrels with those of a submerged method. The wood type had no effect on the acetification length, whereas the shape of the barrel resulted in a significant shortening of the acetification length. Although the selected AAB strain did not always take over, it reduced the biodiversity of the AAB. The inoculated strain was predominant in oak barrels, whereas in the highly aerated prototypes Gluconacetobacter species (Ga. intermedius and/or Ga. europaeus) displaced A. pasteurianus, as what occurs in the submerged method.

Analysis for chloroanisoles and chlorophenols in cork by stir bar sorptive extraction and gas chromatography–mass spectrometry

A complete methodology for the determination of chloroanisoles and chlorophenols in cork material is proposed. The determination is accomplished by means of a previous liquid-solid extraction followed by stir bar sorptive extraction (SBSE) coupled to gas chromatography-mass spectrometry (GC-MS). Two different liquid-solid extraction experiments were conducted and eight compounds considered (2,6-dichloroanisole, 2,4-dichloroanisole, 2,4,6-trichloroanisole, 2,4,6-trichlorophenol, 2,3,4,6-tetrachloroanisole, 2,3,4,6-tetrachlorophenol, pentachloroanisole and pentachlorophenol). From the results obtained we can conclude that high volume extraction extending extraction time up to 24h is the best choice if we have to release compounds from the inner surfaces of cork stoppers. Recovery percentages ranged from 51% for pentachloroanisole to 81% for 2,4-dichloroanisole. This method allows the determination of an array of compounds involved in cork taint at very low levels from 1.2ng g(-1) for 2,4,6-tricholoroanisole to 23.03ng g(-1) for 2,3,4,6-tetrachlorophenol.

Glycosidically bound aroma compounds and impact odorants of four strawberry varieties.

This paper reports the determination of glycosidically bound aroma compounds and the olfactometric analysis in four strawberry varieties (Fuentepina, Camarosa, Candonga and Sabrina). Different hydrolytic strategies were also studied. The results showed significant differences between acid and enzymatic hydrolysis. In general terms, the greater the duration of acid hydrolysis, the higher was the content of norisoprenoids, volatile phenols, benzenes, lactones, Furaneol, and mesifurane. A total of 51 aglycones were identified, 38 of them unreported in strawberry. Olfactometric analyses revealed that the odorants with higher modified frequencies were Furaneol, γ-decalactone, ethyl butanoate, ethyl hexanoate, ethyl 3-methylbutanoate, diacetyl, hexanoic acid, and (Z)-1,5-octadien-3-one. This last compound, described as geranium/green/pepper/lettuce (linear retention index = 1378), was identified for the first time. Differences with regard to fruity, sweet, floral, and green aroma characters were observed among varieties. In Candonga and Fuentepina, the green character overpowered the sweet. In the other two strawberry varieties sweet attributes were stronger than the rest.

Targeting key aromatic substances on the typical aroma of sherry vinegar

Two gas chromatography-olfactometry (GC-O) techniques were used to screen targeting compounds with an impact on the perceived quality of Sherry vinegar: detection frequency and aroma extract dilution analysis (AEDA). The GC-O study revealed the presence of 108 aromatic notes, of which 64 were identified. Diacetyl, isoamyl acetate, acetic acid, and sotolon reached the highest frequency and flavor dilution (FD) factors. Ethyl acetate accounted for the maximum frequency but only a FD factor of 4. To test the sensory impact of these odorants, they were added to a 7% (w/v) acetic acid solution. We determined similarity values (SV) between solutions and the Sherry vinegar. The highest value from the similarity test was observed when diacetyl, ethyl acetate, and sotolon were added simultaneously. The profile of this model solution and a representative Sherry vinegar showed good similarity in the general impression descriptor, which emphasizes the important contribution of these three compounds to the global aroma of this vinegar.

Validation of an analytical method for the determination of ethyl carbamate in vinegars

A solid phase extraction method (SPE) using Isolute ENV+ cartridges was validated for the determination of ethyl carbamate (EC) in different kinds of vinegars. The method proved to be quite sensitive, precise and accurate, improving the recovery and LQD of other existing methods for the same purpose. For the optimization of the method, different pH values of the sample were tested, resulting 5.5 the most adequate. Among the 14 samples analysed, only 5 of them had contents of EC above the quantification limits, ranging between 6.73 μg/L and 56.4 μg/L. The highest value was found in red wine vinegar. Taking into account the amount of vinegar consumed in a meal and the limits established for alcoholic beverages in some countries, the levels of ethyl carbamate in the vinegars tested in this work were acceptable.