Antioxidant capacity, phenolic content and total flavonoids of orange juice

Nowadays, the search for healthier dietary food choices has increased the demand for fresh and nutritive products. Several epidemiological studies indicate that fruits, vegetables and less processed food ensure a higher protection against diseases caused by oxidative stress. Citrus juices attract attention as a result of their health-related properties, due to the presence of natural antioxidants. Orange juice, in particular, is one of the most consumed juices worldwide and it is an important source of flavonoids and phenolic compounds. As a result of the development of new technologies and the improvement of traditional industrial processing, there is a wide range of new commercial juices promoted by strong marketing strategies. In fact, it is important to evaluate whether these processed products maintain similar properties to a freshly squeezed juice. The main objective of the present work was to evaluate the antioxidant activity of six samples of orange juice: one nectar, three concentrated juices, and two freshly squeezed juices (filtrated and non-filtrated). The oranges and orange juices were acquired in local supermarkets, and the antioxidant activity was determined comparing three different methods: 2,2-diphenyl-1-picrylhydrazyl (DPPH●), Folin-Ciocalteu method (applied to determine total phenolics, using gallic acid as standard) and total flavonoids assay (using epicatechin as standard). All the analyses were performed at least in duplicate. For DDPH● assay, the EC50 value (inversely proportional to antioxidant activity) was higher for the nectar (13.8 ± 0.33 mg/mL), followed by freshly squeezed juices (12.6 ± 0.59 and 12.3 ± 0.22 mg/mL, filtrated and non-filtrated, respectively) and concentrated juice (9.01 ± 0.03 mg/mL). The highest value for total phenolics was found in concentrated juices (0.208 ± 0.04 mg/mL), whereas the lowest corresponds to the orange nectar (0.134 ± 0.00 mg/mL). With respect to total flavonoids content, the values varied between 0.099 ± 0.00 and 0.158 ± 0.01 mg/mL, for nectar and concentrated juices, respectively. Our results indicated that orange juice can be considered a good source of natural antioxidants, including flavonoids and phenolic compounds. The methods for antioxidant activity evaluation showed that orange nectar had the lowest antioxidant capacity, whereas the concentrated juices presented the highest. There is no evidence that filtration of the freshly squeezed juice produced considerable variations. Although the industrial processing of orange juice may cause losses of vitamin C, it is a common practice of food industry to add L-ascorbic acid at the end of the processing. In fact, commercial concentrated juices revealed higher values of antioxidant activity, flavonoids and phenolic compounds, than the freshly squeezed juices.

This work was funded by National Institute of Health Dr. Ricardo Jorge (INSA), I.P. under project “Compostos bioactivos e os seus benefícios para a saúde” (2012DAN730). Tânia Gonçalves Albuquerque is grateful for the research grant (BRJ/DAN-2012) funded by INSA.