Smartphone Application for Total Phenols Content and Antioxidant Determination in Tomato, Strawberry, and Coffee Employing Digital Imaging

A low-cost, simple method for in situ determination of total phenols and antioxidants in tomato, strawberry, and coffee through digital imaging was developed and validated. The determination of total phenolic was based on the chelation reaction between quercetin and ferric chloride forming a yellow complex. The antioxidants were quantified by the reaction between 2,6-di-tert-butyl-4-methylphenol, potassium ferricyanide, and ferric chloride, forming a bluish-green complex. After optimization, analytical curves were built to monitor the green color channel within the concentration range of 0 to 31.8 mg L−1 (r = 0.9969) and of 0 to 5 mg L−1 (r = 0.9995) for quercetin and 2,6-di-tert-butyl-4-methylphenol, respectively. The recovery of quercetin and 2,6-di-tert-butyl-4-methylphenol ranged from 96.48 to 101.11% and from 99.00 to 106.00%, respectively. Limits of detection and quantification were 0.03 and 0.11 for quercetin and 0.26 and 0.88 mg L−1 for 2,6-di-tert-butyl-4-methylphenol. The proposed method affords simple manipulation, fast response and environmental safety.