Effect of sugar beet root weight on estimation of sucrose using densitometry method versus polarimetry method

Estimation of sucrose content in sugar beet through density determination is notable in terms of its non-destructiveness, inexpensive, speed and lack of destructive environmental effects compared with polarimetric method. The aim of this study was to evaluate the effect of sugar beet root weight on sucrose estimation by densitometry compared with polarimetry method. One hundred fifty healthy sugar beet roots cultivated in the field and harvested in Karaj, Iran were randomly selected. Each root was considered as an experimental sample. Brei was prepared from the root samples after weighing and density determination. Qualitative characteristics included sucrose, dry matter, marc, and soluble solids. Identification of outliers’ data was performed by standardization of residues. Samples were divided up into 13 weight classes in 100 g groups and then a linear relationship between density and sucrose was determined for each class. Statistical comparison between slope and intercept of linear relationships was performed in a stepwise manner from the smallest to the highest weight class and if there was no significant difference (P> 0.05) data were placed in a statistical group. Results showed that average sugar content, dry matter, marc, and purity of the samples were 15.10, 23.46, 4.06, and 73.84%, respectively. The coefficient of determination (R2) obtained from the linear relationship between density and sucrose in weight classes decreased with increasing root weight so that R2 = 0.997 for roots smaller than 350 g and R2 = 0.67 for roots larger than 1450 g was obtained. Statistical comparison of slope and intercept width regression coefficients from the origin of linear relationships between density (x) and sucrose (y) in weight classes resulting in three classes with a weight range of <350-750 g (small) including linear relationship y = 43.38x-32.557 and R2 = 0.92, medium weight class with weight range of 751 to 950 g (average) with linear relationship y = 51.55x-41.38 and R2 = 0.89 and weight class of 951 to roots larger than 1450 g (large) with linear relationship y = 58.05 x-48.014 and R2 = 0.77. Therefore, considering the root weight, the linear relationships obtained by density determination can be used instead of polarimetric method to accelerate the estimation of sucrose content.