Optimization of microwave roasting of peanuts and evaluation of its physicochemical and sensory attributes

In this study, the microwave (MW) roasting (MWR) of peanuts (Arachis hypogaea L.) is attempted, optimized and compared with conventional drum roasting. A two factor/three level face centered composite design based MWR experiments was conducted at different roasting time (60, 180 and 300 s) and MW power levels (180, 540 and 900 W). The roasting quality was analyzed by physicochemical and sensory attributes of roasted peanuts and extracted oil viz., moisture loss, hardness, browning index (BI), induction period (IP) based on Rancimat, peroxide value (PV) and overall acceptability (OA), respectively. A roasting time and MW power dependent improvement in the desired quality of roasted peanuts and extracted oil was observed attributable to the formation of antioxidant Maillard reaction compounds. A second order polynomial model adequately described the roasting experimental data (p < 0.0001, R² > 0.90) with an insignificant lack of fit (p > 0.05). Using response surface methodology, the MWR was optimized at roasting time of 201 s and MW power level of 900 W which yielded favorable values of quality attributes (moisture loss, 3.06%; hardness, 4528.34 g; BI, 58.89; IP, 8.12 h; PV, 8.80 milliequivalents O₂/kg; OA, 6.40). Furthermore, the quality assessment of ground peanuts for selected time-power combinations (low, optimum and high roasts) was attempted using scanning electron microscopy, electronic nose and Fourier transform infrared spectroscopy which revealed better quality of optimized MWR peanuts.