Exploring MBTH as a spectrophotometric probe for the determination of total phenolic compounds in beverage samples

Abstract

In this work, we propose an alternative method using MBTH (3-methyl-2-benzothiazolinone hydrazine) as a spectrophotometric probe for the determination of total phenolic compounds. The method is based on the oxidative coupling reaction of MBTH with phenolic compounds in acidic medium to generate a colored product. Under optimum conditions the oxidizing Fe(III) was prepared in H₂SO₄. The sensitivity of the MBTH method was compared with that of the Folin–Ciocalteu (FC) method for 17 phenolic compounds. Samples of wines (red and white), coffees (instant and brewed), teas and infusions were analyzed by the proposed method and the results were compared with those of FC and 4-AAP (total phenolic compounds) besides ABTS˙⁺ and DPPH˙ (antioxidant capacity) methods. The results were submitted to a linear correlation analysis at a 95% confidence level, between MBTH and FC (r = 0.9665); MBTH and 4-AAP (r = 0.8425); MBTH and DPPH˙ (r = 0.9667) and MBTH and ABTS˙⁺ (r = 0.9670). A more detailed analysis was performed according to the different sample classes and we observed that the results of the MBTH method were more consistent with those of DPPH˙ and ABTS˙⁺ than those of other methods. Thus, the spectrophotometric method developed was characterized as simple and feasible for the samples analyzed and with results comparable to the usual assays.