Response surface methodology optimization of microwave and pulsed electric field pretreatments for enhancing bioactive properties of licorice stem powder

Licorice stems are of high potential food and pharmaceutical applications; however, they are still not fully explored. This study optimizes the microwave (MW) and pulsed electric field (PEF) pretreatments for enhancing the bioactive properties and antimicrobial activity of licorice stem powder (LSP). The effects of MW (power and time) and PEF (intensity, time, and number of pulses) process variables on bioactive characteristics (TPC and DPPH), antimicrobial activity ( Escherichia coli and Staphylococcus aureus ), and total color changes (ΔE) of LSP were optimized using response surface methodology (RSM) and a four-level Box–Behnken design (BBD). The optimum conditions for MW and PEF pretreatments were MW power of 480 W, MW time of 8.5 min, PEF intensity of 5 kV/cm, PEF time of 20 μs, and PEF pulses of 50 pulse/s. At the ideal conditions, the levels of 112.06 and 109.93 mg GAE/g TPC, 82.65 and 84.94 % DPPH antiradical activity, 9.00 and 9.86 mm E . coli inhibition zone, 7.00 and 7.72 mm S . aureus inhibition zone, and 2.82 and 1.41 ΔE for MW and PEF pretreatments, respectively were similar to predicted levels. This study identifies the ideal conditions for MW or PEF pretreatments for improving bioactive properties and antimicrobial activity of LSP. • Licorice stem powder (LSP) is underexplored in food application • Response surface methodology (RSM) was used to optimize microwave (MW) and pulsed electric field (PEF) processing conditions. • Improve bioactive properties of LSP at optimal MW and PEF processing conditions. • Optimal condition of MW and PEF demonstrated high antioxidant and antimicrobial activities of LSP.