Effect of peeling and point of spectral recording on sucrose determination in sugar beet root using near infrared spectroscopy

Abstract

Determination of sucrose content in sugar beet root by Near-Infrared Spectroscopy (NIR) is a rapid, environment friendly and accurate which has been widely used by researchers in recent years. The present study aimed to evaluate the effect of root size, peeling and points of spectral recording on sucrose content determination in sugar beet. Therefore, study was conducted in a factorial (3 × 2 × 4) based on completely randomized design with 22 replications. Sixty-six sugar beet roots were weighted based on three different size criteria including small (<615 g), medium (655–990 g) and large (≥1000 g), and sliced longitudinally into two parts. One half of the root was used for sucrose determination by polarimetric method and the other half by spectra record (942–1576 nm). Spectra recording was performed on two sides: peel and root flesh tissue. Spectral recording samples were taken from four points including, North West (NW), South West (SW), North East (NE), and the South East (SE), approximately one centimeter above and below the root neck where the root diameter is high. Totally, 528 spectra records were taken, 264 from each side, and thirty-three spectra mean from each side were selected for calibration and validation. Determination of the specific wavelength for sucrose content measurement was done by Partial Least Squares regression (PLS) considering minimum Root Mean Square Error of Calibration (RMSEC), Root Mean Square Error of Prediction (RMSEP), and the maximum correlations of calibration (rc) and correlations of Prediction (rp). Results showed that 1393 nm wavelength with a maximum of rc = 0.9999 and rp = 0.9998 and a minimum of RMSEC = 1.045 as well as RMSEP = 1.215 were appropriate for sucrose content determination. Results of ANOVA showed no significant difference between root size and four points of spectral recording samples at 1393 nm wavelength however a significant (P < 0.01) difference was found between the root flesh tissue spectrum and peel spectrum. Based on the results, spectrum recording from the root flesh tissue with RMSEC = 1.04 and rc = 0.9999 is recommended.