Francisco J. Heredia

Chromatic characterization of anthocyanins from red grapes-I. pH effect

Abstract Five anthocyanins (the 3-monoglucoside of delphinidin, cyanidin, petunidin, peonidin and malvidin), isolated from red grape skins, were subjected to a spectroscopic study to characterize their chromatic properties in a model solution imitating wine in the pH range 1.5–7.0. Tristimulus colorimetry (CIEXYZ, CIELUV and CIELAB colour spaces) proved to be a useful tool for the chromatic characterization of these anthocyanins. Significant colour differences were found among them, related to the number and type of substituents in their B rings. Two-substituted compounds were located in the area of orange hue, while three-substituted compounds were in the area of red–purple. As the methoxylation degree increased, a shift was observed toward purple. Also, a relationship was found between saturation and chroma and the number of hydroxy groups in the B ring. In all the anthocyanins studied, the increase in pH provoked a curve displacement in chromaticity, approaching that of the illuminant..

Characterisation of Moroccan unifloral honeys by their physicochemical characteristics

Physicochemical parameters of 98 samples of Moroccan honeys were analysed; nine parameters were measured, including water content, pH, acidity (free, lactonic, total and lactonic acidity/free acidity ratio), hydroxymethylfurfural, diastase activity and proline. In addition, characterisation of the five unifloral honeys (Eucalyptus sp., Citrus sp., Lythrum sp., Apiaceae and honeydew) by principal component analysis (PCA) and stepwise discriminant analysis (SDA) was carried out. PCA showed that the cumulative variance was approximately 62%, and about 82% of the samples were correctly classified by using the stepwise discriminant analysis, with the best results being obtained for the eucalyptus and honeydew honeys (100% correct).

Effects of Salinity Stress on Carotenoids, Anthocyanins, and Color of Diverse Tomato Genotypes

One nonanthocyanin-accumulating (Ailsa Craig) and three anthocyanin-accumulating tomato genotypes (Anthocyanin fruit type, Atroviolaceum, and Sun Black) were analyzed to assess differences in their carotenoid and anthocyanin levels and color and to evaluate the effects of nutrient solutions with different salt concentrations on these parameters. The carotenoid content of control Atroviolaceum tomatoes was ca. 2-2.5-fold higher relative to the other two types, and the color of its puree could be visually distinguished from those of other genotypes. Salinity stress led in some cases to a 2-3-fold increase in the lycopene content. Saline treatment increased the accumulation of total anthocyanins in fruits of Sun Black (2-fold increase), while it reduced it in fruits of Anthocyanin (10-fold decrease). In general, the treatment increased the differences in color of different purees. These results indicate that salinity stress can lead to similar or higher increases in tomato carotenoids than those achieved by genetic engineering. In addition, these changes were accompanied by visually discernible color differences in tomato products. Our findings show the considerable potential of exploiting saline soils to obtain tomatoes with higher levels of secondary metabolites like carotenoids and anthocyanins.

Determination of technological maturity of grapes and total phenolic compounds of grape skins in red and white cultivars during ripening by near infrared hyperspectral image: A preliminary approach

Hyperspectral images of intact grapes during ripening were recorded using a near infrared hyperspectral imaging system (900-1700 nm). Spectral data have been correlated with grape skin total phenolic concentration, sugar concentration, titratable acidity and pH by modified partial least squares regression (MPLS) using a number of spectral pre-treatments and different sets of calibration. The obtained results (RSQ and SEP, respectively) for the global model of red and white grape samples were: 0.89 and 1.23 mg g(-1) of grape skin for total phenolic concentration, 0.99 and 1.37 °Brix for sugar concentration, 0.98 and 3.88 g L(-1) for titratable acidity and for pH 0.94 and 0.12. Moreover, separate calibration models for red and white grape samples were also developed. The obtained results present a good potential for a fast and reasonably inexpensive screening of these parameters in intact grapes and therefore, for a fast control of technological and phenolic maturity.

Effect of orange juice's processing on the color, particle size, and bioaccessibility of carotenoids.

This study was aimed at assessing the differences between industrially processed and hand-squeezed orange juices (OJs) in relation to their color, particle size, carotenoid content, and carotenoid bioaccessibility. Specifically, industrial samples of fresh squeezed OJs after the finishing steps (FISO) and the same OJs after pasteurization (PISO), as well as hand-squeezed OJs (HSO) were studied. The results showed that the HSO and PISO were different (p < 0.05) in terms of color (darker and more reddish vs brighter, more yellowish and colorful), particle size (volume and surface area mean diameter), and total carotenoid content (29 ± 5 and 22 ± 3 mg/L, respectively). On the other hand, the industrial extraction of OJs reduced the particle size distribution, and accordingly, the relative bioaccessibility of bioactive carotenoids increased (p < 0.01). Independently of the type of OJ, the bioaccessibility of carotenoids in decreasing order was the following: α-carotene > β-cryptoxanthin > β-carotene > zeaxanthin > lutein.

Influence of prefermentative cold maceration on the color and anthocyanic copigmentation of organic Tempranillo wines elaborated in a warm climate.

The stabilization of red wine color by the copigmentation phenomenon is a crucial process that does not always proceed favorably under natural conditions during the first stages of vinification. The impact of the prefermentative cold maceration technique on the phenolic composition and magnitude of the copigmentation level of organic Tempranillo wines elaborated in a warm climate have been studied as an enological alternative to the traditional maceration for obtaining highly colored wines. Tristimulus colorimetry was applied to study the color of wines during vinification, and a high-performance liquid chromatography (HPLC) procedure was used for the analysis of phenolic compounds. Spectrophotometric and colorimetric analyses were also performed to evaluate the copigmentation level of the wines. Significant chemical and color differences were found depending on the maceration technique applied. Prefermentative cold macerated wines were richer in those compounds accounting directly for the color of red wine (anthocyanins) and those involved in anthocyanin stabilization through copigmentation reactions (phenols), which was in accordance with the higher copigmentation degree and darker, more saturated and vivid bluish colors. The evaluation of the copigmentation based on colorimetric parameters in the CIELAB color space showed that prefermentative cold maceration caused greater effectiveness of copigmentation than traditional maceration since it induces more important and hence more easily perceptible color changes.

Comprehensive Colorimetric Study of Anthocyanic Copigmentation in Model Solutions. Effects of pH and Molar Ratio

New colorimetric variables have been defined in the uniform CIELAB color space to assess the quantitative and qualitative color changes induced by copigmentation and their incidence on visual perception. The copigmentation process was assayed in model solutions between malvidin 3-glucoside and three phenolic compounds (catechin, epicatechin, and caffeic acid) as a function of the pH and the pigment/copigment molar ratio. Along the pH variation, the greatest magnitude of copigmentation was obtained at pH 3.0, being significantly higher with epicatechin and caffeic acid. At high acidic pH, the main contribution of copigmentation to the total color was qualitative, whereas between pH 2.0 and 4.0, the main colorimetric contribution was quantitative. The contribution of epicatechin and caffeic acid to the color changes was more marked for the quantitative characteristics. On contrast, particularly at higher pH values, the qualitative contribution was more important in catechin copigmented solutions. Increasing copigment concentration induced perceptible color changes at molar ratios higher than 1:2, consisting in a bluish and darkening effect of the anthocyanin solutions. Among the different CIELAB attributes, hue difference was the best correlated parameter with the increase of copigment concentration, proving the relevance of this physicochemical phenomenon on the qualitative changes of anthocyanin color.

Assessment of white grape pomace from winemaking as source of bioactive compounds, and its antiproliferative activity

The antiproliferative effects of a purified white grape pomace extract (PWGPE), as well as of some phenolic standards on colon cancer cells were examined. The phenolic composition of the PWGPE was determined by rapid resolution liquid chromatography/mass spectrometry (RRLC/MS). The PWGPE had 92.6, 43.3 and 6.01mg/g of flavanols, flavonols and phenolic acids, respectively and, along with pure catechin, epicatechin, quercetin and gallic acid, they were all found capable of inhibiting cellular proliferation. PWGPE (100μg/ml) inhibited the proliferation of cells by 52.1% at 48h, whilst catechin, epicatechin, quercetin and gallic acid (60μg/ml) inhibited growth by 65.2%, 62.2%, 81.0% and 71.0%, respectively, at 72h. The PWGPE is an interesting source of phenolic compounds with antiproliferative properties, that could be of interest in the food and pharmaceutical industries.

Feasibility Study on the Use of Near-Infrared Hyperspectral Imaging for the Screening of Anthocyanins in Intact Grapes during Ripening

The potential of near-infrared hyperspectral imaging to determine anthocyanins in intact grape has been evaluated. The hyperspectral images of intact grapes during ripening were recorded using a near-infrared hyperspectral imaging covering the spectral range between 900 and 1700 nm. Reference values of anthocyanins were obtained by HPLC-DAD. A number of spectral pretreatments and different mask development strategies were studied. Calibrations were performed by modified partial least-squares regression (MPLS) and present a good potential (RSQ of 0.86 and SEP values of 2.62 and 3.05 mg g(-1) of grape skin for nonacylated and total anthocyanins, respectively) for a fast and reasonably inexpensive screening of these compounds in intact grapes.

A novel method for evaluating flavanols in grape seeds by near infrared hyperspectral imaging.

Chemical composition of seeds changes during grape ripening and this affects the sensory properties of wine. In order to control the features of wines, the condition of seeds is becoming an important factor for deciding the moment of harvesting by winemakers. Sensory analysis is not easy to carry out and chemical analysis needs lengthy procedures, reagents, and it is destructive and time-consuming. In the present work, near infrared hyperspectral imaging has been used to determine flavanols in seeds of red (cv. Tempranillo) and white (cv. Zalema) grapes (Vitis vinifera L.). As reference measurements, the flavanol content was estimated using the p-dimethylaminocinnamaldehyde (DMACA) method. Not only total flavanol content was evaluated but also the quantity of flavanols that would be extracted into the wine during winemaking. A like-wine model solution was used for this purpose. Calibrations were performed by partial least squares regression and they provide coefficients of determination R(2)=0.73 for total flavanol content and R(2)=0.85 for predicting flavanols extracted with model solution. Values up to R(2)=0.88 were reached when cultivars were considered individually.