Quality control of sugars in fruit juice

Importance of Topic

Fruit juices are widely consumed for their refreshing taste, nutritional benefits, and quick energy supply. Ensuring accurate determination of individual sugars—fructose, glucose, and sucrose—is critical for product consistency, regulatory compliance, and consumer satisfaction. Traditional laboratory techniques such as liquid chromatography, polarimetry, and refractometry require lengthy sample preparation, use of reagents, and multiple instruments.

Objectives and Study Overview

This study aimed to develop and validate a rapid near-infrared spectroscopy (NIRS) method to simultaneously quantify glucose, fructose, sucrose, and total sugars in fruit juices. The goal was to reduce analysis time and complexity while maintaining accuracy comparable to reference techniques.

Methodology and Instrumentation

A calibration set of 27 aqueous solutions containing 0–8 g/100 mL of glucose, fructose, and sucrose was prepared. Spectra were acquired in transmission mode across 400–2500 nm using a Metrohm NIRS DS2500 Liquid Analyzer equipped with disposable 2 mm vials. Ten commercial fruit juice samples were then measured without any sample preparation. Prediction models were built and validated in Vision Air Complete software. Ion chromatography served as the reference for individual sugars, and refractometry was used for total sugar determination.

Main Results and Discussion

High correlation was achieved between NIRS predictions and reference values for all analytes:

• Glucose: R² = 0.9913, SEP ≈ 0.26 g/100 mL
• Fructose: R² = 0.9967, SEP ≈ 0.19 g/100 mL
• Sucrose: R² = 0.9902, SEP ≈ 0.24 g/100 mL
• Total sugars: R² = 0.9985, SEP ≈ 0.28 g/100 mL

The low standard errors and strong linear relationships confirm the method’s precision and reliability for routine quality control.

Benefits and Practical Applications

• Rapid analysis in less than one minute
• No chemical reagents or elaborate sample preparation required
• Single instrument for multiple sugar determinations
• Robust design suitable for laboratory and production environments

This approach streamlines sugar profiling in juice manufacturing, enabling faster decision-making in QA/QC processes.

Future Trends and Applications

Advances in process analytical technology may lead to inline NIRS integration for real-time monitoring during juice production. Portable spectrometers and automated sampling robots can further enhance throughput and measurement consistency. Expanding this methodology to other beverage matrices and incorporating advanced chemometric algorithms will broaden its industrial utility.

Conclusion

The Metrohm NIRS DS2500 Liquid Analyzer offers a fast, accurate, and reagent-free alternative for quantifying glucose, fructose, sucrose, and total sugars in fruit juices. Its high correlation with established reference methods and minimal operational requirements make it ideal for routine quality control in both laboratory and production settings.

Reference

• Metrohm Application Note AN-NIR-108: Fast multiparameter determination of sugars with NIRS
• Internal reference: AW NIR CH-0071-042023