Influence of microwave vacuum drying on glass transition temperature, gelatinization temperature, physical and chemical qualities of lotus seeds

Abstract

This study investigated the effects of microwave power density on effective moisture diffusion coefficient (D_eff), glass transition temperature (T_g), gelatinization temperature (T_P), physical and chemical qualities of lotus seeds during microwave vacuum drying. D_eff increased by 42% and 127% at 15W/g and 20W/g, respectively, when compared with 10W/g. T_P was negatively correlated with the relaxation times of T₂₁ and T₂₂, while T_g was negatively correlated with the relative areas A₂₂. The rates of change of color were observed to be divided roughly into two periods, consisting of a rapid change caused by enzymatic browning and a slow change caused by non-enzymatic browning. An equation is provided to illustrate the relationship of k₁ and k₂ of Peleg's model depending on power density during rehydration kinetics. The samples at 20W/g exhibited the higher content of amino acid (540.19mg/100gd.b.) while lower starch (17.53g/100gd.b.).

Keywords: Amino acid; Color; DSC; Microwave vacuum drying; Rehydration capacity; Starch; Water state.