Drying characteristics and quality attributes of thunbergia laurifolia leaves using microwave drying

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Traiphop Phahom
Singhanat Phoungchandang

Abstract

Fresh blanched Thunbergia laurifolia (T. laurifolia) leaves were dried in a microwave dryer (MWD) at 450, 720 and 900 W. The drying data obtained were fitted to four single-layer drying models namely, the Henderson and Pabis, Modified Page, Modified Zero and Three-parameter models. This was done to describe drying behaviors of the leaves. Quality aspects of dried leaves including color, microstructure, total phenolics content and bioactive compound content (caffeic acid and quercetin) were determined. The results showed that the Three‑parameter model was the best model to explain the drying data as evidenced by its  highest coefficient of determination (R2) along with its lowest standard error of estimate (SEE) and root mean square error (RMSE). Increasing microwave power from 450 W to 900 W led to reduction of drying times by 42.82% and 36.51% for fresh and blanched leaves, respectively. The blanched leaves provided better color values in terms of hue angle, browning index and total color difference than dried leaves without blanching. Fresh leaves dried in a MWD at 900 W showed a more porous and uniform structure than with other drying conditions. Drying blanched T. laurifolia leaves in a MWD at 900 W was the best treatment to yield the highest total phenolics content, as well as the most caffeic acid and quercetin retention.

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