Determination of the total phenolics in juices and superfruits by a novel chemical method

The total phenols in foods and beverages are currently measured with Folin–Ciocalteu, through its reducing capacity. A novel method was developed to quantify polyphenols or phenolic compounds through direct interactions of polyphenols with Fast Blue BB in an alkaline medium and the absorbance was measured at 420 nm. The gallic acid calibration lines (0–500 μg/mL) had a linear correlation (R) greater than 0.99 in all analysis. The limit of detection was <10 μg/mL and the limit of quantification was 10 μg/mL. The total phenolics in beverage samples had gallic acid equivalents (GAE) of 168–1868 (Fast Blue BB) and 70–1390 (Folin–Ciocalteu) mg GAE/100 mL in juices and juice mixes. The solid samples (fresh fruits and dry fruits) were extracted with 70% ethanol and the resulting Fast Blue BB:Folin-Ciocalteu were 37–1291:21–315 and 337–595:399-1036 GAE (mg/100 g) in fresh and dry fruits, respectively. The Fast Blue BB:Folin–Ciocalteu ratios ranged from <1 to 4.8. The freeze-dried acai powder had 10,000:3000 mg GAE/100 g (Fast Blue BB:Folin–Ciocalteu) while the fresh blueberries had 1291:315 GAE/100 g. The novel method demonstrated that GAE values were higher with Fast Blue BB method than with the Folin–Ciocalteu method.

► Phyto-polyphenols were detected by chemical interaction with Fast Blue BB (FBBB).
► Total phenolics were calibrated against gallic acid and detected at 10–500 μg/ml.
► Linear regression, R = >0.99 with <5% RSD for standards and <10% RSD for samples.
► Juice and fruit samples had higher total phenols with FBBB than Folin-Ciocalteu method.
► Total phenols were highest in fresh blueberries, acai powder and superfruits juice mixtures.