Effects of different drying temperatures on physicochemical and microstructural properties of foam mat dried red beetroot (Beta vulgaris L. var. Detroit) pulp powder

Red beetroot has high levels of betalain pigments and other phytochemical compounds whichis used as natural food colorant and antioxidant in food industry. Foam-mat drying is a relativelysimple method which facilitates the removal of water from fruit juices and vegetable puree. Themain advantages of this method are rapid drying rates at lower temperatures and shorter dryingtime which helps to maintain nutrients in vegetables. In this study, the effect of hot airtemperature (50, 60 and 70℃) with the foam thickness of 5mm and ovalbumin concentrationof 3% was investigated on foam mat drying of red beetroot. An increase in drying temperaturereduced the carr index and hausner ratio by 12.85 and 1.67 % respectively. Also, the dryingtemperature did not significantly affect the solubility. The effective moisture diffusioncoefficient increased with increasing the temperature. This, in turn, increased the drying rate by27.58%. This difference was statistically significant (α=0.05). Furthermore, increasingtemperature from 50 to 70℃ resulted in the reduction of the total color difference and browningindex by 0.69 and 16.35%, respectively. The images of fiel emission scanning electronmicroscope showed that with increasing temperature, cracking and roughness of the powderparticles were reduced. Moreover, computer simulation was performed to evaluate the effect ofhot air temperature on heat and moisture distributions. Model validation showed a correlationcoefficient of 0.916 which indicated a good agreement between the experimental and predicteddata.

کلیدواژه ها:

Heat and mass transfer ، Computer simulation ، Drying rate ، Solubility