M. Lourdes Morales

Ion-exclusion chromatographic determination of organic acids in vinegars

A new ion-exclusion HPLC procedure for the determination of organic acids in vinegars under isocratic elution was developed. Optimum experimental conditions for pH of the eluent, column temperature and mobile phase flow-rate were estimated from a factorial design. The method was successfully validated and enables the reliable separation of major organic acids in wine vinegars (i.e. tartaric, citric, malic, lactic and acetic acid) in about 25 min. It was applied to the analysis of different vinegar samples.

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.

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.

Fluorescence excitation-emission matrix spectroscopy as a tool for determining quality of sparkling wines.

Browning in sparkling wines was assessed by the use of excitation-emission fluorescence spectroscopy combined with PARAllel FACtor analysis (PARAFAC). Four different cava sparkling wines were monitored during an accelerated browning process and subsequently storage. Fluorescence changes observed during the accelerated browning process were monitored and compared with other conventional parameters: absorbance at 420nm (A420) and the content of 5-hydroxymethyl-2-furfural (5-HMF). A high similarity of the spectral profiles for all sparkling wines analyzed was observed, being explained by a four component PARAFAC model. A high correlation between the third PARAFAC factor (465/530nm) and the commonly used non-enzymatic browning indicators was observed. The fourth PARAFAC factor (280/380nm) gives us also information about the browning process following a first order kinetic reaction. Hence, excitation-emission fluorescence spectroscopy, together with PARAFAC, provides a faster alternative for browning monitoring to conventional methods, as well as useful key indicators for quality control.

A comparative study on aromatic profiles of strawberry vinegars obtained using different conditions in the production process.

Impact odorants in strawberry vinegars produced in different containers (glass, oak and cherry barrels) were determined by gas chromatography-olfactometry using modified frequency (MF) technique, and dynamic headspace gas chromatography-mass spectrometry. Aromatic profile of vinegar from strawberry cooked must was also studied. All strawberry vinegars retained certain impact odorants from strawberries: 3-nonen-2-one, (E,E)-2,4-decadienal, guaiacol, nerolidol, pantolactone+furaneol, eugenol, γ-dodecalactone and phenylacetic acid. Isovaleric acid, pantolactone+furaneol, p-vinylguaiacol, phenylacetic acid and vanillin were the most important aroma-active compounds in all vinegars. The strawberry cooked must vinegar accounted for the highest number of impact odorants. Wood barrels provided more aroma complexity than glass containers. Impact odorants with grassy characteristics were predominant in vinegar from glass containers, and those with sweet and fruity characteristics in vinegars from wood barrels. Principal component analysis indicated that the production process led to differences in the impact odorants.