Hot air drying of red beet: Process and product quality monitoring by digital images and near infrared spectroscopy

The use of nondestructive techniques that can guarantee <i>in situ</i> monitoring of the quality of food products during drying processes can promote improvements in industrial processes. In this context, digital imaging and near infrared spectroscopy can play an important role. Red beet moisture content, betalain content, shrinkage, and color were measured during drying. The digital images showed changes in color, which intensified with increasing temperature and correlated with betalain content through multivariate linear regression (R² of 0.90). In addition, sample shrinkage was identified by digital images. The volumetric shrinkage increased proportionally to the drying air temperature, with a shrinkage of 85.4 ± 0.3% at 70 °C. Spectral data were obtained by a low-cost portable near infrared spectrometer. Partial least square regression was used to predict the product moisture content (RP2=0.89;RMSEP=0.79%) and total betalain content (RP2=0.79;RMSEP=0.30mggd.b.) during drying. These tools can be used for the <i>in situ</i> control of red beet drying.