Quality attributes and anthocyanin content of rice coated by purple-corn cob extract as affected by coating conditions

• Inlet air temperature significantly influenced in final MC and fissure.
• Head rice yield was decreased with longer spraying time.
• Increasing temperature decreased TPC, TFC and TAC.
• Keracyanidin, malvin, dephinidin and cyaniding were found in coated rice.
• Malvin, malvidin acid and pelargonidin were not attached to the rice materials.

We investigated the optimal conditions for coating rice with the water extract of purple-corn cob (PCC) using a top-spray fluidized bed coating method with variations of inlet air temperature of 50, 60 and 70 °C and spraying time of 5, 10 and 15 min. The results showed that increasing the inlet air temperature significantly reduced the final MC. Fissured coated rice increased with increasing temperature and spraying time. The percentage of head rice yield was not affected by inlet temperature, while it tended to decrease with longer spraying time except at 15 min. In addition, longer spraying time resulted in higher values of chroma implying a larger amount of coating solution. We also found that increasing the temperature decreased the total phenolic, total flavonoids and total anthocyanins contents as well as their antioxidant activities as determined by DPPH and FRAP assays. In contrast, those values were increased when the spraying time increased. The same trend was found for anthocyanin composition. Based on the optimization criteria with the highest desirability of 0.702, we recommend an inlet air temperature of 50 °C and spraying time of about 15 min to obtain the minimum fissure and maximum coating material.