Drying Behavior of Lotus Seeds, and Adhesive Properties of the Flour Processed in a Rotary Dryer
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Abstract:
To determine the characteristic behaviors of lotus seeds during drying and assess the quality of the flour produced from dried lotus seeds using a rotary dryer, lotus seeds with an initial moisture content of ≈63% to 10% wet basis (w.b.) were dried at controlled temperatures of 60, 70, 80, and 90 ℃ with rotational speeds of 0.5, 1, and 1.5 r/min. The adhesive properties of the lotus seed flour were investigated using a rapid visco-analyzer (RVA). The results indicate that the drying process is prolonged by rotary drying. No constant-rate drying phase was found. Strong influences of temperature on the drying process were evident (p≤0.05). By contrast, rotational speed did not significantly affect the drying process (p>0.05). Estimates predicted using the Cavalcanti-Mata model were in good agreement with the experimental results (R2>0.999, E%<5.00%, RMSE<0.01). The effective moisture diffusivity of lotus seeds was between 3.94×10-10 and 1.00×10-9 m2/s. This increases as drying temperature increased from 60 to 90 ℃. The drying process considerably affects the adhesive properties of the flour obtained. Peak and final viscosities were significantly lower when the lotus seeds were dried at higher drying temperatures. The corresponding values at 60 ℃ were 1676.33 cP and 2228.00 cP, respectively. Those at 90 ℃ were 1268.00 cP and 1909.33 cP, respectively. The results suggest that lotus seed microstructures change with drying temperature due to starch gelatinization during rotary drying. The surfaces of lotus seeds dried at 60 ℃ are more porous, while more densely packed structures are noted in lotus seeds dried at 90 ℃. Lotus seed surfaces are denser if they are dried at higher temperatures because of changes in their microstructures. Compared to oven drying, rotary drying produces lotus seeds with more uniform moisture content, and a maximum variability in moisture content of only 4.59%. This study may aid in development of high-efficiency and high-quality lotus seed drying techniques and applications of lotus seed flour within the food industry.
