Production of tannins from Acacia nilotica pods for the leather manufacturing industry – extractions, characterization, and optimization using design of experiment

Abstract

The pods of Acacia nilotica were successfully utilized for the extraction of tannins using a methanol/water extraction medium. The experimental design employed for the extraction was a central composite design that enabled the evaluation of the effects of time, temperature, and methanol concentration on the dependent variables of extraction yield, total phenolic contents (TPC, as gallic acid equivalents (GAE)), and antioxidant activity (AA, as millimoles of ascorbic acid equivalents (AAE)). Response surface models were developed for the three responses, and statistical analysis of variance was performed to determine the optimum values of the independent variables and the coefficients of determination. The maximum extraction yield of 46.2 wt% (pod extract) was achieved at 200 min, 85 °C, and 40% methanol concentration. Similar conditions also led to the attainment of 50.7 wt% TPC and 51.3 mmol AAE/100 g pod. The coefficients of determinations were 0.9750 for extraction yield, 0.9626 for TPC, and 0.9774 for AA, which indicated that the model equations obtained fitted the experimental data. The result of the retanning of the leather using the extracted A. nilotica tannins also showed that the tear and tensile strength, as well as the elongation at break, of the leather samples were within the range obtained when chestnut extract and chrome tannin were used.