The technique, which measures the total antioxidant capacity of a product, including insoluble fractions, suggests that the antioxidant levels of common citrus juices may be greater than previously thought.
Writing in Food Chemistry, the Spanish team behind the research noted that using the technique generates values that are ten times higher than those indicated by current analysis methods.
"The problem is that the antioxidant activity of the solid fraction (the fibre) isn't measured, as it's assumed that it isn't beneficial,” explained Professor José Ángel Rufián Henares from the University of Granada. “However, this insoluble fraction arrives at the large intestine and the intestinal microbiota can also ferment it and extract even more antioxidant substances, which we can assess with our new methodology."
As a result, the authors suggest that the antioxidant activity of citrus juices and other foods may be undervalued – adding that the results may also mean that tables of antioxidant capacities of food products that dieticians and health authorities use must be revised.
The new technique, developed by Rufián Henares and colleagues, is technique called 'global antioxidant response' (GAR), which includes an in vitro simulation of the gastrointestinal digestion that occurs in our body, whilst taking into account the 'forgotten' antioxidant capacity of the solid fraction.
The method includes assessments of various physical and chemical parameters, such as colour, fluorescence, and the relationship between the concentrations analysed and compounds indicators such as furfural.
Upon applying the technique to commercial and natural orange, mandarin, lemon and grapefruit juices, the team showed that their antioxidant capacity values were increased greatly.
For example, in the case of orange juice, the value ranges from 2.3 mmol Trolox/L (units for the antioxidant capacity) registered with a traditional technique to 23 mmol Trolox/L with the new GAR method.
"The antioxidant activity is, on average, ten times higher than that which everyone thought up until now, and not just in juices, but also in any other kind of food analysed with this methodology," said Rufián Henares, who noted that the new technique has potential applications in better guiding dietary guidelines.
"This technique and the results derived from it could allow dieticians and health authorities to better establish the values of the antioxidant capacity of foods,” he said.
Source: Food Chemistry
Published online ahead of print, doi: 10.1016/j.foodchem.2014.05.047
“Nutritional and physicochemical characteristic of commercial Spanish citrus juices”
Authors: J. Álvarez, S. Pastoriza, et al