Determination of sugar beet sucrose content using an infrared-spectrometer-equipped polarimeter compared to the conventional polarimetric method

Extended Abstract
Introduction
The sugar content of sugar beet in the sugar industry is commonly measured by polarimetric method. The advantages of this method include its speed and, when the sample purity is high, its acceptable accuracy and repeatability. However, one limitation of the polarimetric method is the requirement for sample transparency to allow the passage of polarized light. To clarify the sample solution, compounds such as lead acetate or aluminum sulfate are used, with lead acetate being particularly problematic due to its environmental toxicity. Recently, a polarimeter equipped with an infrared source and an auto-filtration extraction device has been introduced to the market, aiming to eliminate the need for the toxic lead acetate clarifying compound. This study aimed to compare the results of analyzing sugar beet brei samples grown under different climatic conditions in the beet-growing regions of the country with those of beets stored in factory silos, using two methods: polarimetry with visible light and polarimetry with near-infrared (NIR) light.
Materials and methods
Frozen beet brei samples from various sugar beet research trials and the Jovein Sugar Factory were analyzed. These included 29 samples from Miandoab, 29 from Isfahan, 27 from Kerman, 28 from Shiraz, and 45 from Jovein Sugar Factory, totaling 158 samples. Each sample was analyzed using both the conventional and Autofilt methods. Each sample consisted of 200 grams of sugar beet brei, prepared from 40 to 50 sugar beet roots that were washed, had their crowns and aerial parts removed, then pulped, homogenized, and frozen at -20°C. Prior to analysis, the samples were thawed at 25°C and re-homogenized. One portion of each sample was analyzed using the conventional method, and the other using the Autofilt system with a polarimeter equipped with an infrared spectrometer. For the conventional method, juice extraction was performed via cold digestion by mixing 26 grams of brei with 177 mL of 0.01 mol/L alkaline lead acetate solution. In the Autofilt method, juice extraction was carried out using a pressurized filtration system at 5 bar (0.5 MPa) by mixing 26 grams of brei with 177 ml of distilled water and diatomaceous earth. The standard extraction and filtration system used was the Venma model, equipped with Dr. Kernschen's automatic Saccharomat device. The Autofilt system and Saccharomat with infrared light by Schmidt and Haensch were used for the alternative method. Sucrose content (pol) for each region and for the combined dataset was statistically compared using a paired t-test.
Result
The results showed that the average sugar content measured in some regions showed statistically significant differences between the two methods. However, for th e total sample set, there was no significant difference between the mean values obtained by the conventional method (17.06%) and the Autofilt method (16.68%) (P <0.094). A linear regression analysis was conducted to evaluate the relationship between the two methods. The resulting equation was: y = 0.963x + 1.0043, with a coefficient of determination of R² = 0.98, where y represents the sucrose content measured by the conventional polarimetric method, and x represents the content measured by the Autofilt method. Given the advantages of the Autofilt method, it is recommended to implement this system alongside the conventional method, especially for high-throughput analysis of fresh beet pulp samples. Adoption in at least one sugar factory is suggested to validate performance under industrial conditions, enabling broader national application with increased confidence.
Conclusion
The results of this study showed that while there were statistically significant differences between the two methods in some regions, the overall mean sugar content measured by the conventional and Autofilt methods did not differ significantly. A strong correlation between the two methods (R² = 0.98) confirms the reliability of the Autofilt system. Given its environmental and operational advantages, particularly the elimination of toxic clarifying agents, the Autofilt method is recommended as a complementary tool to the conventional approach, especially for high-throughput analysis of fresh beet pulp. Pilot implementation in at least one sugar factory is suggested to validate its performance under industrial conditions and support broader adoption.
References
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