Luis Almela

Proposal of an index for the objective evaluation of the colour of red table grapes

Abstract A colour index for the objective determination of the colour in red table grapes is described. This index is based on the CIELAB values. A statistical study revealed a high correlation between L ∗ and b ∗ , while a ∗ was not a representative parameter. The usefulness of this index is investigated to classify the red grapes depending on their external colour. The proposed colour index for red grapes (CIRG) is based on the parameters L ∗ (lightness), H (hue angle) and C (chroma) and its expression is “ (180-H) (L ∗ + C ) ” All the colour indexes previously proposed were defined in fruits whose colour varied between yellow and red, and, therefore, were not suitable for red grapes which show a dark violet colour. This new index showed a good linearity with the visual colour of the berries and distinguished between sample groups of different external colour.

Determination of antioxidant constituents in cactus pear fruits.

An analytical study was carried out on the presence of antioxidant constituents and the in vitro antioxidant capacity in the extracts of three species of Spanish red-skinned cactus pear fruits (Opuntia ficus-indica, Opuntia undulata and Opuntia stricta). The cactus pear fruit extracts were analyzed for determined constituents: ascorbic acid, flavonoids (quercetin, isorhamnetin, myricetin, kaempferol and luteolin), betalains, taurine, total carotenoids and total phenolics. The antioxidant capacity was assessed by means of two different methods: the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (Trolox equivalent antioxidant capacity) method and the 2,2-diphenyl-1-picrylhydrazyl radical method. Opuntia ficus-indica fruit extract had the strongest antioxidant capacity and taurine content. O. stricta fruits were the richest in ascorbic acid and total phenolics, whereas O. undulata fruits showed the highest carotenoid content. Quercetin and isorhamnetin were the main flavonoids detected. This study provides basic information on the presence of bioactive compounds and antioxidant capacity in extracts of cactus pear fruits, in order to consider these extracts as ingredient for the production of health-promoting food.

Application of high-performance liquid chromatography to the characterization of the betalain pigments in prickly pear fruits

The qualitative and quantitative betalain pigment content of two cultivars of prickly pear (Opuntia ficus-indica) fruits grown in southeastern Spain was evaluated. After methanolic extraction of crushed fruits, reversed-phase high-performance liquid chromatography and photodiode array detection were applied simultaneously for the separation, identification and quantification of these pigments. Two main pigments were obtained, which were identified as indicaxanthin (lambda(max) 484 nm) and betanin (lambda(max) 535 nm). Spectrophotometric evaluation of both pigments showed a yield of around 20-30 mg per 100 g of fresh pulp. When the influence of temperature (25 to 90 degrees C) on betacyanin pigment stability was investigated, the results revealed a substantial degree of thermodegradation at temperatures higher than 70 degrees C.

Dependence between colour and individual anthocyanin content in ripening grapes

Abstract Three red grape cultivars of different coloration (Flame seedless, Exotic and Monastrell), grown in Murcia (southeast Spain) were analysed during ripening for external colour and individual pigment content. The application of the CIRG colour index, calculated from the coordinates hue angle (h), lightness (L*) and chroma (C*) of the CIELAB colour space, and defined as [(180-h)/(L*+C*)], permitted an objective evaluation of the colour at the different ripening stages. External colour and anthocyanic profile were closely linked. Cyanidin-3-glucoside was the most abundant pigment in Flame seedless (low pigmented cultivar), while malvidin-3-glucoside was the main anthocyanin in the cultivars Monastrell and Exotic (both of them with a high pigment content). Data derived from the study of the ratios between anthocyanins with different degree of hydroxilation and/or methoxylation leads to know information on differences between grapevines linked to the synthesis of these pigments. ©

High-performance liquid chromatographic screening of chlorophyll derivatives produced during fruit storage

Reversed-phase high-performance liquid chromatography with photodiode array and fluorescence detection was applied to the systematic screening of chlorophylls and derivative pigments. The chromatographic procedure proposed made it possible to successfully separate and identify eight chlorophyll derivatives (the a and b forms of chlorophyll, chlorophyllide, pheophytin and pheophorbide) by using a linear gradient of methanol, acetone and ammonium acetate. The method has been routinely applied to study chlorophyll degradation during the postharvest storage of cherimoya (Annona cherimola, Mill.) fruits. The brilliant green colour even at maturity, and its high chlorophyllase and Mg-dechelating activities, indicate that this plant material might be suitable for investigating the as yet not well known chlorophyll breakdown processes.

Comparison between the tristimulus measurements Yxy and L*a*b* to evaluate the colour of young red wines

Abstract The chromatic characteristics of 10 young red wines elaborated in the region of Murcia (Spain) were determined. The colour measurements obtained using the Yxy and CIELAB systems were compared. The calculation of dominant wavelength and its representation in the C.I.E. chromatic diagram revealed almost imperceptible differences in the wines classified, while L ∗ a ∗ b ∗ values achieved a much better differentiation. L ∗ and a ∗ gave an accurate definition of the wines. L ∗ ranged from 37 to 72 while a ∗ varied between 23 and 54. One wine sample was clearly different from the others, showing the highest degree of lightness ( L ∗ ), the lowest redness ( a ∗ ) and the lowest saturation ( C ∗ ). The graphical representation of metric lightness difference (Δ L ∗ ) against metric chroma difference (Δ C ∗ ) showed the difference in colour between the wines analyzed. Wine number 1 showed the deepest colour followed by wines numbered 9 and 5, while wine number 7 was very pale. The data obtained were correlated by means of the corresponding matrix of Spearman correlation coefficients, which revealed that the highest correlations existed between L ∗ and colour intensity and between L ∗ and ionised anthocyanin content.

Varietal classification of young red wines in terms of chemical and colour parameters

Six varietal red wines produced in Murcia (Spain) were analysed for selected enological and colour parameters (31 variables in total). As regards acid content there were no important differences among the vinifications studied. The initial content of glucose and fructose was quite high in all the wines, which resulted in very high ethanol content (between 14.1% in Cinsault Noir wine and 16.4% in Tempranillo wine). The colour of the wines was determined by means of the Yxy coordinates and CIELAB parameters, but not one of them could significantly differentiate among vinifications. Principal component analysis and discriminant analysis were used to identify and to explain differences among samples. Discriminant analysis allowed a clear separation of the 80.7% of the cases analysed by a selection of only three variables (L*, a*, C*). With a selection of 10 variables including x coordinate, colour intensity 1 and 2, pH, ionised anthocyanins, total phenolics, percentage of yellow pigments, total anthocyanins, hue and L* was possible to characterise the 95% of the cases analysed, but 100% in Monastrell-1, Tempranillo Graciano and Cinsault Noir wines.

Separation and identification of chlorophylls and carotenoids from Caulerpa prolifera, Jania rubens and Padina pavonica by reversed-phase high-performance liquid chromatography

Abstract Thirty-one photosynthetic pigments (chlorophylls, carotenoids and degradation products) from the seaweed, Caulerpa prolifera (chlorophyta), Jania rubens (rhodophyta) and Padina pavonica (phaeophyta), were separated in a single-step procedure by reversed-phase high-performance liquid chromatography, using an elution gradient of methanol, acetone and ammonium acetate solution, and a program time of 65 min, to obtain high resolution peaks of the separated photosynthetic pigments. We consider that the program times used make it possible to inject a mixed extract of the different seaweed groups. Eighteen photosynthetic pigments were separated from Caulerpa prolifera, 16 from Jania rubens and 14 from Padina pavonica. Chlorophyll b, micronone, microxanthin, neoxanthin, siphonein and siphonoxanthin were the most typical and characteristic pigments of Caulerpa prolifera, while chlorophyll c1, c2, fucoxanthin, fucoxanthol, flavoxanthin, diatoxanthin were the most typical pigments in Padina pavonica. In Jania rubens, on the other hand, chlorophyll d, α-cryptoxanthin, β-cryptoxanthin and fucoxanthin were the most common pigments.

Separation and determination of individual carotenoids in a Capsicum cultivar by normal-phase high-performance liquid chromatography

Abstract A normal-phase high-performance liquid chromatographic system was developed for the separation of individual carotenoid pigments in a saponified extract of a Capsicum cultivar. Eighteen major components were separated, of which sixteen pigments were identified. The chromatographic system described permits a good separation and quantification of pigments. It can be used in physiological studies for the characterization of different varieties and in the food industry.

Screening and mass-spectral confirmation of betalains in cactus pears

SummaryThe presence of betalain pigments in fruits ofOpuntia stricta, Opuntia undulata andOpuntia ficus-indica has been studied. Cultivars of deep red-purple colour, with high betacyanin content, were choosen for this investigation. The total betacyanin content was estimated spectrophotometrically E1cm1%=1120) and the results obtained indicated a higher betacyanin content inO. stricta (70 mg · 100 g−1 fresh fruit), than inO. undulata andO. ficus-indica (14–19 mg · 100 g−1 fresh fruit). Individual pigment analysis by HPLC with photodiode array detection revealed substantial differences between these species. In cactus pears fromO. stricta only betanin and isobetanin were detected. However, in cactus pears fromO. undulata andO. ficus-indica the predominant pigments were betanin and indicaxanthin, with very low levels of isobetanin. The identity of all these pigments was confirmed by mass-spectral analysis. The presence of neobetanin was not detected in fruits of any of the three species considered.