Resíduo da indústria de polpa congelada de uva (cultivar Isabel) como fonte de antocianinas

Abstract

The agribusiness processing of tropical fruits have generated waste that may have great potential, as well as having nutritional constituents, still have significant levels of bioactive compounds. Thus, this research aimed to use frozen pulp residue of grape extract and purify anthocyanins, evaluate its antioxidant capacity as well as its stability to light and heat.The residue was transferred by a processing unit (Recife - PE), whose grapes cultivar Isabel (Vitis labrusca L.) came from the city of São Vincente Ferrer - PE. The anthocyanin content was determined by differential pH method and its purification using C18 cartridges promoted the removal of sugars, acids and not anthocyanin phenolic compounds.The antioxidant activity of purified anthocyanins was evaluated by the ability to scavenge the radicals DPPH• (1,1-diphenyl-2-picrylhydrazyl) and ABTS•+ (2,2’-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid), with gallic acid as reference compound.To evaluate light fastness, anthocyanins were diluted in 95% ethanol solution: 1.5N HCl; 85:15 v/v (pH 1.0) and exposed to light and no light.To assess the effect of heat, anthocyanins were diluted in water, acidified with HCl (pH = 1.0) and subjected to temperatures of 50°C, 70°C and 90°C in thermostated bath. Absorbance readings were taken after 1, 3, 5 and 7 hours of heating. The data obtained from reading the absorbance of diluted anthocyanins were used for the calculation of the rate constant (k) and half-life (t1/2) using 1st order kinetics equations.The total anthocyanin content in grape residue was 15.56 ± 0.33 mg. 100g-1 residue. Anthocyanins purified showed good efficiency against the radical DPPH• (EC50 of 0.14 ± 0.01 g. g DPPH-1 and TEC50 < 5 minutes) and strong ability to sequester (> 80%). Against the radical ABTS•+ anthocyanins showed sequestration capacity of 241.36 ± 3.74 μmol TEAC.g-1 sample. The results showed that in the presence of light, time of half-life (t1/2) of the anthocyanin pigments was 656.87h and in the absence of light was 6.525.42h, demonstrating that the absence of light contributed significantly to the increase the stability of anthocyanins. Anthocyanins subjected to heat at temperatures of 50°C, 70°C and 90°C showed a half-life (t1/2) 159.31h; 8.77h and 3.05h, respectively, demonstrating that these pigments are degraded with increasing temperature. The results show the agroindustrial residue grape frozen pulp is a promising source of anthocyanins, which showed significant antioxidant properties, being efficient at capturing the DPPH• and ABTS•+ and can be used in foods that have acidic pH, put in opaque packaging, and are not subjected to severe heat treatment during processing.