Atividade antioxidante e antimicrobiana de extrato aquoso de couve e potencial suplementar em bebida láctea fermentada

Abstract

Due to the characteristics of the kale and the consumer's awareness of beneficial health products, the objective was to evaluate the antioxidant and antimicrobial potential of aqueous kale extract and verify the viability of its addition in fermented dairy beverages. The leaves were submitted to four treatments: fresh crushed in a blender, fresh pulverized with liquid nitrogen, oven drying for 72 h (45°C) and freezing (-20°C). The aqueous extracts were prepared in a concentration of 0.1 g mL-1. The antioxidant activity with DPPH radical was evaluated and EC 50 of the treatments were determined. To the concentration of total phenolic compounds and flavonoids of all treatments. he antimicrobial activity was analyzed by the method of plate diffusion in paper discs against the bacteria: Staphylococcus aureus ATCC 43300, Escherichia coli ATCC 8759 e Salmonella choleraesuis ATCC 10708. For the addition in the beverage the treatment was chosen that presented satisfactory results in the analyzes of antioxidant activity, determination of phenolics and flavonoids as a function of the extract. The fermented lactic drink was prepared adding concentrations of 5%, 10%, 15%, 15% with sorbate and control (potassium sorbate) of dried kale leaf extract. The antioxidant activity of the beverage was also made using the method of DPPH radical. The number of lactic bacteria in all beverages were calculated. The statistical design of the experiment was completely randomized and the averages were compared by Tukey test at 5% significance. The fresh leaves crushed in a blender (63.16%) and fresh pulverized (62.04%) The fresh leaves crushed in a blender (63.16%) and fresh pulverized (62.04%) were not statistically different. Dry leaves (78.75%) and frozen (71.20%) had the highest values of antioxidant activity. The dry and frozen leaves had EC50 values, respectively, 10 and 43.8 mg mL-1, and the fresh and crushed fresh leaves had higher values of EC50 (61.77 and 76.15 mg mL-1), therefore the lower the EC50 the higher the antioxidant activity. The dried, frozen and fresh leaves pulverized did not differ statistically as for the phenolic compounds presenting average values of 43.53; 42.94; 40.22 mg EAG / g dry weight, respectively. The fresh crushed leaves had a lower phenolic content, with a mean of 29.89 mg EAG / g dry weight, but did not differ from fresh ones. Dry, frozen and fresh crushed leaves were not statistically different from flavonoids, with a mean value of 14.59; 11.53; 9.22 mg EQ / g dry weight, respectively. And the fresh leaves pulverized had the highest content of flavonoids (26.83 mg EQ / g dry weight). The aqueous extracts of kale leaves did not present antibacterial activity against the microorganisms studied. The fermented lactic drink with 15% of extract and the one with 15% with sorbate did not differ statistically and presented greater antioxidant activity. The fermented lactic beverage already possesses the antioxidant potential and a 15% addition of aqueous extract of dried kale leaf increased in three times more this potential. Regarding lactic acid counts, all prepared beverages complied with current legislation with values greater than 106 UFC mL-1. Therefore, the aqueous extract of kale leaf showed promising benefits to be added in fermented lactic beverages, because it increases its antioxidant activity, phenolic compounds and flavonoids. Besides being an easy extract .