Effect of Steaming Time on the Bioactive Compound Content and Antioxidant Activity of Sprouted Cowpea (Vigna unguiculata) Tempeh Flour

Cowpea (Vigna unguiculata) is a local legume rich in protein, minerals, vitamins, and bioactive compounds such as GABA and antioxidants. One promising innovation is the use of cowpea sprouts as raw material for tempeh production. However, tempeh has a short shelf life, which can be extended by converting it into flour. Tempeh flour often exhibits a beany flavor, that may be reduced through steaming, although this process may also decrease its nutritional and bioactive components. This study contributes to evaluating the effect of steaming time on the proximate composition, GABA, total phenolic content (TPC), and antioxidant activity (IC50) of sprouted cowpea tempeh flour. A completely randomized design with a single factor was employed, consisting of steaming times of 0, 15, 30, 45, and 60 minutes. Data were analyzed using one-way ANOVA, DMRT, correlation analysis, and determination of the optimal treatment using the De Garmo method. Results showed that steaming significantly decreased moisture, fat, and protein contents (p<0.05), while increasing ash and carbohydrate levels. The highest GABA content was observed at 15 minutes (8.95 mg/g), then declined due to thermal degradation. TPC reached its peak at 45 minutes (247.81 mg GAE/100 g). Antioxidant activity (IC50) fluctuated with steaming time, with the highest activity in the control sample (IC50 19.01 mg/mL). Correlation analysis indicated that antioxidant activity was more closely associated with total phenolic content than with GABA. Based on the De Garmo evaluation, considering GABA, TPC, and IC50, 15 minutes was identified as the optimal treatment.