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

- The effects of microwave vacuum drying on dried lotus seeds were analyzed.
- Relationships between glass transition temperatures and water state were studied.
- Two kinds of browning reactions were distinguished during microwave vacuum drying.
- The highest power level resulted in the highest rehydration capacity of seeds.
- High amino acid and low starch were achieved at the highest power level.

This study investigated the effects of microwave power density on effective moisture diffusion coefficient (Deff), glass transition temperature (Tg), gelatinization temperature (TP), physical and chemical qualities of lotus seeds during microwave vacuum drying. Deff increased by 42% and 127% at 15 W/g and 20 W/g, respectively, when compared with 10 W/g. TP was negatively correlated with the relaxation times of T21 and T22, while Tg 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 20 W/g exhibited the higher content of amino acid (540.19 mg/100 g d.b.) while lower starch (17.53 g/100 g d.b.).