Determination of Brix, fructose, glucose, and sucrose with NIRS

Importance of the Topic

Accurate determination of Brix and individual sugars such as glucose, fructose and sucrose is essential for quality control in the food and beverage industry. These parameters influence product taste, nutritional value and regulatory compliance. Rapid, reliable analysis methods help manufacturers maintain consistency, reduce waste and improve process efficiency.

Objectives and Study Overview

The study aimed to develop a cost-effective near-infrared spectroscopy (NIRS) method for simultaneous quantification of Brix, glucose, fructose and sucrose in aqueous solutions. By constructing a robust calibration model, the goal was to achieve high accuracy and precision within one minute per measurement, minimizing sample preparation and consumable costs.

Methodology

• Preparation of 50 aqueous samples with varying concentrations of glucose, fructose and sucrose
• Transmission measurement of each sample using Vis-NIR range (400–2500 nm)
• Development of predictive calibration models using multivariate regression
• Evaluation of model performance via calibration, cross-validation and external validation metrics

Used Instrumentation

The analysis employed the Metrohm NIRS DS2500 Liquid Analyzer configured in transmission mode with a 1 mm pathlength flow cell. Vision Air Complete software facilitated data acquisition, spectral pretreatment and model building. The analyzer covers 400–2500 nm and supports automated temperature control up to 80 °C.

Main Results and Discussion

The predictive models yielded excellent correlation between NIRS predictions and reference values:

• Fructose: R2 = 0.9882; SEC = 0.04 %; SECV = 0.06 %; SEP = 0.05 %
• Glucose: R2 = 0.9877; SEC = 0.11 %; SECV = 0.12 %; SEP = 0.10 %
• Sucrose: R2 = 0.9886; SEC = 0.16 %; SECV = 0.16 %; SEP = 0.13 %
• Brix: R2 = 0.9988; SEC = 0.13 °Brix; SECV = 0.15 °Brix; SEP = 0.09 °Brix

The high coefficients of determination and low error values demonstrate the method’s reliability for routine sugar analysis.

Practical Benefits and Applications

The NIRS approach offers multiple advantages over traditional chromatography:

• Analysis time under one minute without chemical reagents or complex sample prep
• Reduced operating costs and environmental impact
• Ability to measure multiple analytes simultaneously
• Potential for at-line or in-line process monitoring

Future Trends and Potential Uses

• Extension to complex matrices such as fruit juices, syrups and dairy products
• Integration with process control systems for real-time quality assurance
• Enhanced chemometric models using advanced machine learning algorithms
• Development of portable NIR units for field analysis and smaller laboratories

Conclusion

This application note demonstrates that NIR spectroscopy on the DS2500 Liquid Analyzer provides a fast, accurate and cost-effective solution for simultaneous quantification of Brix and major sugars in aqueous samples. The method supports quality control workflows with minimal consumables and rapid data turnaround.