Optimisation of phenolic compounds and antioxidant activity extraction conditions of a roasted mix of Tetrapleura tetraptera (Schumach & Thonn.) and Aframomum citratum (C. Pereira) fruits using response surface methodology (RSM)

The therapeutic abilities of Tetrapleura tetraptera and Aframomum citratum fruits used as spices are attributed to their bioactive molecules, including polyphenols. Sometimes used together and heated, they can undergo denaturation. The aim of the current study is to optimize the extraction of phenolic compounds and antioxidant potential of a roasted mix of Tetrapleura tetraptera and Aframomum citratum (95/5: w/w) fruits using RSM in a home food consumption context. The mix of spices was chosen according to the highest content of TPP and preliminary studies were performed to select the influencing variables. Roasting temperatures (130-170 °C), roasting times (10-15 min) and brewing times (8-15 min) were investigated with a rotatable central composite design. Experimental results were fitted to the second-order polynomial model where multiple regressions and ANOVA were used to determine the coefficients of the model and the optimal conditions for the considered responses. The two spices are good sources of phenolic compounds, and they also show significant (p < 0.05) dose-dependent radical scavenging activities (DPPH assay and inhibition of β-carotene discoloration) and reductive activities (FRAP assay and Phosphomolybdenum method). They significantly inhibit bovine serum albumin and 5-LOX denaturation. Brewing time and roasting time significantly (p < 0.05) influence the responses and there is a strong (R² = 0.93) correlation between the TPP and TAC of the beverage. The quadratic model fit well and the different factors used to test its accuracy and fitness were in satisfactory ranges. For TPP extraction (38.90 mgGAE/g dw) and TAC (50.75 mg TE/g dw) expression, the optimal conditions were reached at a roasting temperature of 150 °C, roasting time of 12.62 min, brewing time of 11.91 min and a desirability of 0.95. The novel information on the optimisation of the process can be further used by scientists, consumers and herbalists for effective handling of fruits during the extraction process.

Keywords: Aframomum citratum; Optimization; Polyphenols; Roasting; Tetrapleura tetraptera.