José A. Fernández-López

Thiobarbituric acid test for monitoring lipid oxidation in meat

Lipid oxidation is a significant problem relative to off-flavour and off-odour, and warmed-over flavour appears to be related to lipid oxidation in meat. In this review article the thiobarbituric acid (TBA) test for lipid oxidation measurements is described. Works on other techniques to measure lipid oxidation, as determination of malondialdehyde content by high performance liquid chromatography or gas chromatography are reviewed. A detailed description of the different TBA test procedures, possible interferences and limitations of this technique are also given.

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. ©

Thermal stability of selected natural red extracts used as food colorants.

The color degradation of aqueous solutions of six natural red pigment extracts (elderberry, red cabbage, hibiscus, red beet, Opuntia fruits and red cochineal) used commercially as food colorants was investigated at temperatures between 50 and 90xa0°C. Color degradation was studied in respect to both spectral properties and visual color. The remaining absorbance at 535xa0nm as a function of the incubation time and temperature was used to quantify the degradation process. Red cochineal was the most thermoresistant extract with a remaining absorbance of 95xa0% after 6xa0h at 90xa0°C. Anthocyanin extracts (elderberry, red cabbage, hibiscus) showed remaining absorbance percentages of 63.8, 46.1 and 26.7, respectively. Betacyanin extracts (red beet, Opuntia fruits) were the most thermosensitive maintaining only 12.5 and 1.7xa0%, respectively, of the initial absorbance at 535xa0nm. Applying a first-order kinetic model to the degradation processes, reaction rate constants (k) and half-life periods (t1/2) were calculated. The temperature dependence of the degradation rate constant obeyed the Arrhenius relationship, with activation energies (Ea) ranging between 3.02 and 53.37xa0kJu2009mol−1. The higher activation energy values indicated greater temperature sensitivity. Changes in visual color attributes corroborated the high thermal stability of the red cochineal extract.

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.

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.

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.

Effect of electron beam irradiation on color and microbial bioburden of red paprika.

The effect of irradiation with electron beams on the microbiological quality and color properties of red paprika was examined. The irradiation doses ranged from 0 to 12.5 kGy. The counts performed were total mesophilic aerobic microorganisms, Enterobacteriaceae, coliforms, sulfite-reducing clostridia, molds, and yeasts. It was concluded that molds, yeasts, and sulfite-reducing clostridia were the most resistant species, although a 10-kGy dose of irradiation leads to optimum sanitation. Extractable color and apparent color were analyzed to appraise the incidence of the irradiation treatments in the color properties of red paprika. Extractable color was determined according to the American Spice Trade Association method, and apparent color was analyzed by reflectance using the CIELab color space. Data showed no significant differences between the color properties of irradiated and nonirradiated samples. Irradiation was a suitable procedure to minimize the bioburden of red paprika with small modifications of its color properties.