José M. Obón

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.

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.

Fermentation of Opuntia stricta (Haw.) fruits for betalains concentration.

Fermentation of juice and homogenized fruits of Opuntia stricta fruits has been developed and optimized. The aim was to obtain the red food colorant betanin from prickly pear, at high concentration and low viscosity. Among three strains assayed, Saccharomyces cerevisiae var. bayanus AWRI 796 has been the optimum for this process. The optimum temperature value was found to be 35 degrees C for both sugar consumption and pigment preservation. After fermentation, biomass and residual vegetal tissue were discarded by centrifugation. Supernatant was concentrated under vacuum. Therefore, liquid concentrated betanin was obtained, with low viscosity and being sugar free. Besides, bioethanol was obtained as byproduct. Characteristics of the final product obtained were pH 3.41, 5.2 degrees Brix, 9.65 g/L betanin, color strength of 10.8, and viscosity of 52.5 cP. These values are better than obtained by other procedures.

Production of an anthocyanin‐rich food colourant from Thymus moroderi and its application in foods

BACKGROUND Anthocyanins and other polyphenols from flowers and bracts of Thymus sp. are studied. An anthocyanin-rich food colourant with interesting high antioxidant activity from Thymus moroderi has been obtained, and applied to colour foods. RESULTS Anthocyanins and other polyphenols from T. moroderi and another five Thymus sp. were extracted in methanol/hydrochloric acid 0.1 mol L(-1) (50/50, v/v) 2 h stirring at 50 °C. They were identified and quantified by HPLC-PDA-MS and UHPLC-PDA-fluorescence, as total individual polyphenols. Total polyphenols were also determined. Flowers had higher anthocyanins and other polyphenols concentrations than bracts; for example, total polyphenols content of T. moroderi were 131.58 and 61.98 g GAE kg(-1) vegetal tissue, respectively. A liquid concentrated colourant was obtained from T. moroderi using water/citric acid as solvent. It was characterised and compared with other two commercial anthocyanin-rich food colourants from red grape skin and red carrot (colour strength of 1.7 and 3.6 AU, respectively). T. moroderi colourant had 1.2 AU colour strength, and high storage stability (>97.1% remaining colour after 110 days at 4 °C). It showed a higher polyphenols content than commercial colourants. Its antioxidant activity was 0.707 mmol Trolox eq. g(-1) plant dry weight, 69.5 times higher than red carrot. The three colourants were applied to colour yogurts, giving pinky tonalities. The colour did not change evidently (ΔE*(ab)  < 3) when stored under refrigeration during 1 month. CONCLUSIONS T. moroderi can be a source of anthocyanin-rich food colourant (E-163) with both high polyphenols content and high antioxidant activity. This colourant gives a stable colour to a yogurt during 1 month. These results expand the use of natural colourants.