Betaxanthin-Rich Extract from Cactus Pear Fruits as Yellow Water-Soluble Colorant with Potential Application in Foods.

Cactus pear (Opuntia ficus-indica) fruit juice is a source of betaxanthin pigments which can be used as a natural yellow food colorant. The HPLC chromatographic pigment pattern corresponding to the betaxanthin-rich extract revealed the presence of four betaxanthins, of which indicaxanthin (proline-betaxanthin) accounts for around 85%. A betaxanthin-rich water-soluble food colorant from cactus pears fruits was produced by spray-drying microencapsulation using maltodextrin as a wall material. The resulting powder was characterized by scanning electron microscopy, and its apparent color was analyzed by spectrometry. The stability of the microcapsules was examined at +20, +4 and -20 °C in the dark during six months of storage. The degradation of betaxanthins was delayed by microencapsulation and their colorant stability increased at lower temperatures. The potential application of the colorant microcapsules was successfully assessed in two food model systems: a yogurt and a soft-drink. Both foods presented an attractive pale yellow color. Pigment retention and color parameters were investigated during storage under controlled conditions. Slight changes in the pigment retention, in both model systems, pointed to excellent preservation in the dark, even after 28 days at 4 °C. However, the presence of light contributed to betaxanthin deterioration. Spray-drying microencapsulation succeeds in reducing volumen of the pigment extract and can be easy in storage and delivery of the powders. It is proved to be a suitable process that can be recommended for stabilizing betaxanthins from cactus pears to be used as water-soluble natural colorants in foods.

Comparative Thermal Degradation Patterns of Natural Yellow Colorants Used in Foods.

There is a great interest in natural yellow colorants due to warnings issued about certain yellow food colorings of synthetic origin. However, no comparative studies have been reported of their thermal stability. For this reason, the thermal stabilities of six natural yellow colorants used in foods--lutein, riboflavin, curcumin, ß-carotene, gardenia yellow and Opuntia betaxanthins--were studied in simple solutions over a temperature range 30-90 °C. Spectral properties and visual color were investigated during 6 h of heat treatment. Visual color was monitored from the CIEL*a*b* parameters. The remaining absorbance at maximum wavelength and the total color difference were used to quantify color degradation. The rate of color degradation increased as the temperature rose. The results showed that the thermal degradation of the colorants followed a first-order reaction kinetics. The reaction rate constants and half-life periods were determined as being central to understanding the color degradation kinetics. The temperature-dependent degradation was adequately modeled on the Arrhenius equation. Activation energies ranged from 3.2 kJmol(-1) (lutein) to 43.7 kJmol(-1) (Opuntia betaxanthins). ß-carotene and lutein exhibited high thermal stability, while betaxanthins and riboflavin degraded rapidly as temperature increased. Gardenia yellow and curcumin were in an intermediate position.

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.

Monitoring by liquid chromatography coupled to mass spectrometry the impact of pH and temperature on the pigment pattern of cactus pear fruit extracts.

The influence of pH and moderate heating (50 degrees C) on the color and individual betacyanin content of pigment extracts from cactus pear fruits (Opuntia stricta) is studied in the course of this paper. The study is carried out by using a high-performance liquid chromatograph equipped with a photodiode array detector and coupled to a mass spectrometer. The results point to a pH-dependent degradation mechanism, which is reflected in the chromatographic patterns obtained at different exposure times (0-28 h). At pH 3, 15-descarboxy-betanin is the most resistant betacyanin derivative. At pH 5, seven peaks are detected after 8 h, the most prominent being betanin, cyclo-dopa-5-O-beta-glucoside, and betalamic. In the assay conducted at pH 7, rapid color loss affects all the pigments, except for betanin.

Color properties and stability of betacyanins from Opuntia fruits.

The colorant properties of pigments from Opuntia stricta, Opuntia undulata, and Opuntia ficus-indicafruits were studied. The pigments were extracted with different solvents and identified by high-performance liquid chromatography. On the basis of their visible light spectra, the pigments were identified as betalains. In O. undulata and O. ficus-indica fruits, both betacyanins and betaxantins were identified, while in O. stricta fruits only betacyanins (betanin and isobetanin) were detected. O. stricta fruits showed the highest betacyanin content (80 mg/100 g fresh fruit). The thermal stability of the pigment extracts was dependent on the pH, with the maximum stability being at pH 5, as expected for betacyanins. At this value and a storage temperature of 4 degrees C, a deactivation half-life time of more than 1 year, with no added stabilizers, was determined. According to these studies, cactus pears from O. stricta may well be considered as a potential source of natural red colorants.