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

Significance of the topic

Rapid and accurate quantification of dissolved sugars—Brix, glucose, fructose and sucrose—is critical for quality control in the food and beverage industry. Traditional techniques such as HPLC, IC and TLC require lengthy sample preparation, use of reagents and high running costs. Near-infrared spectroscopy (NIRS) offers a non-destructive, reagent-free alternative capable of delivering multi-parameter results in under one minute, enabling real-time monitoring and cost savings.

Objectives and study overview

This study aimed to develop and validate a NIRS-based calibration model for simultaneous determination of Brix (°Bx), glucose, fructose and sucrose in aqueous solutions. A set of 50 standard mixtures covering relevant concentration ranges was used to build and evaluate the prediction models.

Methodology and instrumentation

Samples: 50 aqueous solutions prepared with varying levels of glucose, fructose and sucrose.
Spectrometer: Metrohm NIRS DS2500 Liquid Analyzer operating in transmission mode over 400–2500 nm.
Sample presentation: 1 mm pathlength flow cell in a flow-through holder.
Software: Vision Air Complete for data acquisition, preprocessing and multivariate model development.

Main results and discussion

Calibration models exhibited excellent fit to reference data with high correlation coefficients (R²) and low prediction errors:

• 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 %
• Total sugars (°Brix): R² = 0.9988; SEC = 0.13 °Brix; SECV = 0.15 °Brix; SEP = 0.09 °Brix

These figures of merit indicate that NIRS can reliably predict individual sugar concentrations and total dissolved solids with precision comparable to reference methods.

Benefits and practical applications

• Analysis time under one minute per sample
• No chemical reagents or consumables required
• Simultaneous multi-analyte quantification
• Minimal sample preparation and maintenance effort
• Robust design suitable for laboratory and production environments

Future trends and possibilities

Integration of NIRS into inline or at-line process control will further enhance production efficiency. Advances in chemometric algorithms and miniaturized NIR sensors may extend the technique to field applications and other complex matrices such as fermentations, juices and dairy products. Cloud-based model sharing and automated calibration updating will streamline method deployment across multiple sites.

Conclusion

The Metrohm DS2500 Liquid Analyzer coupled with robust chemometric models enables fast, accurate and cost-effective determination of Brix, glucose, fructose and sucrose in aqueous media. NIRS represents a viable alternative to conventional chromatographic methods for routine quality control in the food industry.

Reference

• Internal reference: AW NIR CH-0072-042023